US20140332733A1 - Pure metal and ceramic nanofibers - Google Patents

Pure metal and ceramic nanofibers Download PDF

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Publication number
US20140332733A1
US20140332733A1 US14/342,012 US201214342012A US2014332733A1 US 20140332733 A1 US20140332733 A1 US 20140332733A1 US 201214342012 A US201214342012 A US 201214342012A US 2014332733 A1 US2014332733 A1 US 2014332733A1
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Prior art keywords
metal
precursor
nanofibers
polymer
nanofiber
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Yong Lak Joo
Nathaniel S. Hansen
Daehwan Cho
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Cornell University
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Cornell University
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Priority to US14/342,012 priority Critical patent/US20140332733A1/en
Assigned to CORNELL UNIVERSITY reassignment CORNELL UNIVERSITY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHO, DAEHWAN, HANSEN, NATHANIEL S., JOO, YONG LAK
Publication of US20140332733A1 publication Critical patent/US20140332733A1/en
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    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
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    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
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    • A61K31/185—Acids; Anhydrides, halides or salts thereof, e.g. sulfur acids, imidic, hydrazonic or hydroximic acids
    • A61K31/19—Carboxylic acids, e.g. valproic acid
    • A61K31/20—Carboxylic acids, e.g. valproic acid having a carboxyl group bound to a chain of seven or more carbon atoms, e.g. stearic, palmitic, arachidic acids
    • A61K31/202—Carboxylic acids, e.g. valproic acid having a carboxyl group bound to a chain of seven or more carbon atoms, e.g. stearic, palmitic, arachidic acids having three or more double bonds, e.g. linolenic
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    • A61K31/23—Esters, e.g. nitroglycerine, selenocyanates of carboxylic acids of acyclic acids, e.g. pravastatin of acids having a carboxyl group bound to a chain of seven or more carbon atoms
    • A61K31/232—Esters, e.g. nitroglycerine, selenocyanates of carboxylic acids of acyclic acids, e.g. pravastatin of acids having a carboxyl group bound to a chain of seven or more carbon atoms having three or more double bonds, e.g. etretinate
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Definitions

  • Ceramic and metallic nanofibers have potential for applications in a wide variety of fields, including high performance filtration, chemical sensing, biomedical engineering and renewable energy.
  • Previous methods for producing ceramic or metallic nanofibers include the electrospinning of sol-gel precursors with or without a polymer binder.
  • the nanofibers produced by the sol-gel method have many disadvantages, such as low performance and poor coherence, which makes them unsuitable for many applications.
  • the nanofibers are metal, metal oxide, and/or ceramic nanofibers.
  • the nanofibers are high quality nanofibers, high performance nanofibers, highly coherent nanofibers, highly continuous nanofibers, or the like.
  • the nanofibers are coherent, are long, have few voids and/or defects, and/or have other advantageous characteristics such as flexible control of metal and/or ceramic crystal sizes.
  • the nanofibers are produced by electrospinning a fluid stock comprising a high concentration of ceramic or metal precursor in the fluid feed stock.
  • the fluid stock further comprises well mixed or substantially uniformly distributed precursor in the fluid stock.
  • the fluid stock is converted to a nanofiber comprising few voids, few defects, long or tunable lengths, and the like.
  • a process for producing one or more nanofiber comprising electrospinning a fluid stock, the fluid stock comprising metal precursor(s) and polymer, and
  • the fluid stock is (1) a solution; (2) a substantially uniform dispersion (e.g., of the precursor(s)); or (3) a substantially homogenous dispersion (e.g., homogeneous dispersion of the precursor(s)).
  • the weight-to-weight ratio of the precursor(s) to polymer in the fluid stock is at least 1:2 (e.g., over 1:2) and the fluid stock is aqueous.
  • the weight-to-weight ratio of the precursor(s) to polymer is at least 1:1.
  • the fluid stock is prepared by combining reagent precursor(s), reagent polymer(s) and water to form the fluid stock comprising the precursor(s) and the polymer, and wherein the reagent precursor(s) and reagent polymer(s) are combined in a weight to weight ratio of over 1:2.
  • the reagent precursor(s) and reagent polymer(s) are combined the in a weight-to-weight ratio of at least 1:1.
  • one or more of the precursor(s) are present in the fluid stock in a polymer-precursor association.
  • at least 50% of the polymer is saturated with precursor molecules.
  • at least 50% of the precursor molecules are associated with polymer.
  • the precursor(s) is present in the fluid stock in a concentration of at least 200 mM (e.g., over 200 mM, at least 250 mM, or the like). In specific embodiments, the precursor(s) concentration in the fluid stock is at least 250 mM. In more specific embodiments, the precursor(s) concentration in the fluid stock is at least 300 mM. In further or alternative embodiments, the metal precursor(s) comprises one or more metal-ligand complex. In specific embodiments, the metal-ligand complex is in association with the polymer.
  • the metal precursor comprises metal selected from the group consisting of: Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, Al, Zr, Li, Mn, Cr, Be, Cd, Si, Ti, V, Hf, Sr, Ba, Ge, and combinations thereof.
  • the metal precursor comprises a transition metal, or metalloid.
  • the metal precursor is a metal-ligand complex comprising one or more ligand selected from the group consisting of: a carboxylate, a nitrate, a halide, a diketone, an alkoxide, and combinations thereof.
  • the reagent precursor, the precursor of the fluid stock, or both comprise one or more metal acetate, metal nitrate, metal chloride, metal methoxide, or a combination thereof.
  • the polymer is polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyvinyl ether, polyvinyl pyrrolidone, polyglycolic acid, hydroxyethylcellulose (HEC), ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate, or a combination thereof.
  • the polymer is (i) hydrophilic, and (ii) water soluble or water swellable.
  • the polymer is thermally and/or chemically degradable. In further or alternative embodiments, the polymer is a polymer comprising a plurality of nucleophilic moieties and the reagent precursor is electrophilic. In other embodiments, the polymer is a polymer comprising a plurality of electrophilic moieties and the reagent precursor is nucleophilic. In some embodiments, electrospinning the fluid stock results in the formation of electrospun nanofiber material comprising metal precursor and polymer. In further or alternative embodiments, the process further comprises treating (calcining) the electrospun material to prepare a calcinated nanofiber.
  • the treatment (calcining) of the electrospun material comprises thermally treating the electrospun material, chemically treating the electrospun material, or both.
  • the process further comprises removing (e.g., by calcination) polymer from the electrospun material.
  • calcining the electrospun material e.g., under inert or reducing conditions
  • metal precursor to metal
  • calcining the electrospun material e.g., under oxidative conditions
  • calcining the electrospun material converts a first metal precursor to ceramic and a second metal precursor to metal.
  • the process comprises calcining the electrospun material under oxidative conditions, thereby converting metal precursor to metal oxide (e.g., ceramic metal oxide).
  • the process comprises calcining electrospun material the nanofiber under inert or reducing conditions, thereby converting metal precursor to metal.
  • calcining the electrospun material comprises heating the electrospun material to a temperature of at least 400° C. (e.g., at least 500° C. or at least 600° C.).
  • the fluid stock is co-axially electrospun with a second fluid.
  • the second fluid is a gas (e.g., air).
  • the second fluid is a second fluid stock comprising a second metal precursor and a second polymer, wherein the metal precursor and second metal precursor are the same or different and the polymer and second polymer are the same or different, and wherein the process produces a layered nanofiber (optionally comprising coaxially electrospinning with a third fluid that is a gas, e.g., air).
  • the metal precursor and polymer being present (in the fluid stock or precursor nanofiber) in a weight-to-weight ratio of at least 1:2 (e.g., at least 1:1).
  • a nanofiber prepared according to any process described herein is provided herein.
  • a nanofiber prepared by or preparable by any process described herein is a precursor or electrospun nanofiber prepared or preparable prior to calcination.
  • the nanofiber is a metal, metal oxide, or ceramic containing nanofiber prepared or preparable following calcination.
  • a precursor nanofiber comprising polymer (e.g., organic polymer and metal precursor.
  • the precursor nanofiber has high metal precursor loading (e.g., at least 1:2, metal precursor:polymer; over 1:2; at least 1:1.75; at least 1:1.5; at least 1:1; or the like).
  • the precursor (i.e., electrospun) nanofiber e.g., as prepared according to any process described herein, comprises at least 90% by weight of organic polymer and metal precursor.
  • the precursor (i.e., electrospun) nanofiber comprises at least 5 elemental wt. % metal (e.g., at least 10 elemental wt. %, or at least 15 elemental wt. % metal).
  • nanofiber or plurality of nanofibers comprising metal, metal oxide, ceramic, or a combination thereof, and:
  • the nanofibers have feature (a). In further or alternative embodiments, the nanofibers have feature (b). In further or alternative embodiments, the nanofibers have feature (c). In further or alternative embodiments, the nanofibers have feature (d). In specific embodiments, the nanofibers have features (a) and (b). In other specific embodiments, the nanofibers have features (b) and (c). In still other embodiments, the nanofibers have features (a), (b) and (c). In some embodiments, the nanofibers comprise at least 33% (w/w) (e.g., on average) of a metal, a metal oxide, a ceramic, or, taken together, a combination thereof.
  • the nanofibers are metal nanofibers comprising at least 90 elemental wt. % of metal (e.g., on average).
  • the nanofibers are metal oxide nanofibers comprising at least 90% metal oxide (e.g., on average) and at least 30 elemental wt. % of metal (e.g., on average).
  • the nanofibers are ceramic nanofibers comprising at least 90% ceramic (e.g., on average) and at least 30 elemental wt. % of metal (e.g., on average).
  • the nanofibers are metal alloy nanofibers comprising at least 90% metal alloy (e.g., on average) and at least 30 elemental wt. % of metal (e.g., on average).
  • the nanofibers are composite nanofibers comprising a first material and a second material, the first material being a continuous matrix material, and one or both of the first material or second material comprising metal, metal oxide, ceramic, or a combination thereof.
  • the second material is a second continuous matrix material (e.g., the first and second continuous matrix materials are coaxial layers). In other embodiments, the second material comprises isolated domains of the nanofibers.
  • one or both of the first or second materials comprises metal and the nanofibers comprising an average of at least 5 elemental wt. % of metal (e.g., at least 20 elemental wt. % of metal) (e.g., on average).
  • the first material is ceramic and the second material is metal.
  • the first material is metal and the second material is metal.
  • the first material is ceramic and the second material is ceramic.
  • the nanofiber comprises at least 30 elemental wt. % of metal (e.g., on average).
  • the nanofibers comprises at least 50 elemental wt. % of metal (e.g., on average).
  • the metal is selected from the group consisting of Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, Al, and combinations thereof.
  • the metal component comprises a ceramic or metal oxide selected from the group consisting of Al 2 O 3 , ZrO 2 , Fe 2 O 3 , CuO, NiO, ZnO, CdO, C, Ge, Si, SiO 2 , TiO 2 , V 2 O 5 , VO 2 , Fe 3 O 4 , SnO, SnO 2 , CoO, CoO 2 , Co 3 O 4 , HfO 2 , BaTiO 3 , SrTiO 3 , and BaSrTiO 3 .
  • the nanofibers comprise a metal-non-metal alloy. In further or alternative embodiments, the nanofibers comprise a conductive material, wherein the nanofibers have a conductivity of at least about 10% (e.g., on average) when compared with the conductivity of the conductive material when formed into a sheet.
  • the nanofibers comprise a continuous matrix of amorphous ceramic and comprise an ultimate strength-to-diameter ratio of at least 0.075 MPa/nm (e.g., on average); a Young's modulus-to-diameter ratio of at least 0.15 GPa/nm (e.g., on average); and a fracture toughness of at least 0.6 MPA MPa ⁇ m 1/2 (e.g., on average).
  • the nanofibers comprise a continuous matrix of amorphous ceramic and comprise an ultimate strength-to-diameter ratio of at least 0.15 MPa/nm (e.g., on average); an Young's modulus-to-diameter ratio of at least 0.3 GPa/nm (e.g., on average); and a fracture toughness of at least 0.7 MPa ⁇ m 1/2 (e.g., on average).
  • the nanofibers comprise a continuous matrix of crystalline ceramic and comprise an ultimate strength-to-diameter ratio of at least 5 MPa/nm (e.g., on average); and a Young's modulus-to-diameter ratio of at least 1.5 GPa/nm (e.g., on average).
  • the nanofibers comprise a continuous matrix of crystalline ceramic and comprise an ultimate strength-to-diameter ratio of at least 12.5 MPa/nm (e.g., on average) and a Young's modulus-to-diameter ratio of at least 4 GPa/nm (e.g., on average).
  • the nanofibers have a fracture toughness of at least 1.8 MPa ⁇ m 1/2 (e.g., on average).
  • the nanofibers comprise a continuous matrix of metal and have an ultimate strength-to-diameter ratio of at least 0.35 MPa/nm (e.g., on average) and a Young's modulus-to-diameter ratio of at least 1.1 GPa/nm (e.g., on average).
  • the nanofibers comprise a continuous matrix of metal and have an ultimate strength-to-diameter ratio of at least 0.9 MPa/nm (e.g., on average) and a Young's modulus-to-diameter ratio of at least 2.9 GPa/nm (e.g., on average).
  • the nanofibers have an fracture toughness of at least 3.5 MPa ⁇ m 1/2 (e.g., on average).
  • the nanofibers have a log(S/m) to log(S/m) ratio with an identical bulk material of at least 0.8 (e.g., at least 0.9) (e.g., on average).
  • the nanofibers have a length of at least 50 microns (e.g., on average). In further or alternative embodiments, the nanofibers have a diameter of 500 nm or less (e.g., on average). In further or alternative embodiments, the nanofibers have an aspect ratio of at least 1000 (e.g., on average). In further or alternative embodiments, the nanofibers comprise less than 5% (e.g., less than 3%, or less than 1%) carbon by elemental mass (e.g., on average). In further or alternative embodiments, the nanofibers have (e.g., on average) less than 100 defects (e.g., less than 50, less than 10, or less than 5) per linear mm of nanofiber.
  • the nanofibers described herein are used in a sensor, a battery, a fuel cell, a solar cell, ultracapacitor, catalyst, membrane, or electrode.
  • hybrid nanofibers including hollow nanofibers and multi-axial nanofibers comprising more than one material.
  • high quality nanofibers and processes of preparing high quality nanofibers that are suitable for applications such as electrochemical devices (e.g., batteries and solar cells), advanced filtration, catalysis, and the like.
  • the nanofibers provided and/or prepared according the processes described herein are prepared at costs low enough to be commercially viable.
  • the present disclosure includes hybrid and hollow nanofibers, use of nanofibers in many types of applications, devices incorporating nanofibers, the use of devices incorporating nanofibers, and the like.
  • the process includes electrospinning a fluid stock.
  • the fluid stock comprises metal and/or ceramic precursor and polymer.
  • the weight to weight ratio of the precursor to polymer is at least 1:2.
  • the polymer is water soluble.
  • the process comprising electrospinning a fluid stock, the fluid stock comprising metal precursor(s) and polymer.
  • the fluid stock is (1) a solution; (2) a substantially uniform dispersion (e.g., of the precursor(s)); or (3) a substantially homogenous dispersion (e.g., of the precursor(s)).
  • a method for producing a nanofiber comprising electrospinning a first fluid with a second fluid, at least one of the first or second fluids being an aqueous fluid.
  • the first and second fluids are electrospun about the same or similar axis.
  • the first fluid is an aqueous fluid comprising water, a water soluble polymer, and metal precursor.
  • the second fluid is a second aqueous fluid, comprising water, a water soluble polymer, and a second metal and/or ceramic precursor, wherein the water soluble polymer of the second fluid is the same or different than the water soluble polymer of the first fluid.
  • a method for producing a nanofiber comprising multi-axially electrospinning an aqueous fluid stock and a second fluid.
  • the aqueous fluid stock comprises water, a water soluble polymer, and metal and/or ceramic precursor.
  • the second fluid is a second aqueous fluid stock.
  • the second fluid is a gas.
  • the second fluid at least partially surrounds the aqueous fluid stock.
  • the aqueous fluid stock at least partially surrounds the second fluid.
  • a process for producing a nanofiber comprising electrospinning a fluid stock comprising metal precursor, ceramic precursor, or combination thereof wherein: (a) the fluid stock is aqueous; (b) the concentration of the precursor in the fluid stock is at least 200 mM; or both (a) and (b).
  • the fluid stock further comprises a water-soluble polymer. In some embodiments, the precursor binds to the water-soluble polymer. In some embodiments, the electrospinning step comprises multi-axially electrospinning the fluid stock with a gas or a second fluid stock. In some embodiments, the fluid stock comprises a non-aqueous solvent. In some embodiments, the fluid stock comprises tetrahydrofuran (THF) and polystyrene (PS).
  • THF tetrahydrofuran
  • PS polystyrene
  • a process of producing a nanofiber comprising electrospinning a fluid stock into an electrospun material, the fluid stock comprising polymer and precursor, the precursor comprising (i) metal precursor, (ii) ceramic precursor, or (iii) a combination thereof, and: (a) the weight to weight ratio of the precursor to polymer being at least 1:2; (b) the fluid stock is (1) a solution; (2) a substantially uniform dispersion; or (3) a substantially homogenous dispersion; (c) the concentration of the precursor in the fluid stock is at least 200 mM; or (d) a combination thereof.
  • the fluid stock is an aqueous fluid stock.
  • the process further comprises removing the polymer from the electrospun material.
  • the process further comprises calcination of the precursor to metal, metal oxide, metal alloy, ceramic, or a combination thereof.
  • calcination of the metal and/or ceramic precursor(s) is performed under inert, oxidative, or reductive conditions.
  • the metal is selected from the group consisting of Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, and Al.
  • the ceramic or metal oxide is selected from the group consisting of Al 2 O 3 , ZrO 2 , Fe 2 O 3 , CuO, NiO, ZnO, CdO, C, Ge, Si, SiO 2 , TiO 2 , V 2 O 5 , VO 2 , Fe 3 O 4 , SnO, SnO 2 , CoO, CoO 2 , Co 3 O 4 , HfO 2 , BaTiO 3 , SrTiO 3 , and BaSrTiO 3 .
  • the fluid stock comprises the precursor associated with the polymer by covalent or non-covalent interactions.
  • the association of the precursor with the polymer provides a fluid stock comprising precursor uniformly dispersed therein.
  • the polymer and precursor taken together comprise about 1 weight % to about 20 weight % of the fluid stock.
  • the metal precursor comprises a metal-ligand complex.
  • the metal-ligand complex is a metal acetate, metal nitrate, metal chloride, or metal alko-oxide.
  • the polymer is a thermally degradable or chemically degradable polymer.
  • the polymer is polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, polyvinyl pyrrolidone, polyglycolic acid, polyethylene oxide, hydroxyethylcellulose (HEC), ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate, or any combination thereof.
  • the process of electrospinning the fluid stock comprises electrospinning the fluid stock with a second fluid stock about the same or similar axis to produce a layered nanofiber.
  • a nanofiber comprising a metal, a metal oxide, a metal alloy, a ceramic, a metal precursor, a ceramic precursor or a combination thereof, and: (a) the nanofiber is at least 1 ⁇ m (e.g., at least 50 ⁇ m) long on average; (b) the nanofiber has an aspect ratio of at least about 5 (e.g., at least 10, at least 100, at least 1000, or the like); (c) the nanofiber comprises a segment comprising a continuous matrix of a metal, a metal oxide, a metal alloy, a ceramic, or a combination thereof; (d) the nanofiber has a specific surface area between 1 m 2 /g and about 1000 m 2 /g; or (e) a combination thereof. In some embodiments, the nanofiber comprises at least 33% (w/w) of a metal, a metal oxide, a metal alloy, a ceramic, a metal precursor, a ceramic precursor or a combination thereof.
  • the metal is selected from the group consisting of Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, and Al.
  • the ceramic or metal oxide is selected from the group consisting of Al 2 O 3 , ZrO 2 , Fe 2 O 3 , CuO, NiO, ZnO, CdO, C, Ge, Si, SiO 2 , TiO 2 , V 2 O 5 , VO 2 , Fe 3 O 4 , SnO, SnO 2 , CoO, CoO 2 , Co 3 O 4 , HfO 2 , BaTiO 3 , SrTiO 3 , and BaSrTiO 3 .
  • the nanofiber comprises a conductive material, wherein the nanofiber has an conductivity of at least about 10% when compared with the conductivity of the conductive material when formed into a sheet.
  • a process for producing a nanofiber comprising electrospinning about the same or similar axis a first fluid stock with a second fluid stock, the first fluid stock being aqueous and comprising a first polymer.
  • the first polymer is water soluble.
  • the second fluid is aqueous.
  • the second fluid stock comprises a second polymer, and the first and second polymers are optionally the same.
  • FIG. 1 illustrates a schematic of the process and system of the disclosure.
  • FIG. 2A illustrates an exemplary mechanism of precursor-polymer bonding.
  • FIG. 2B illustrates an FTIR study of the effect of Ni precursor loading on the saturation of —OH bonds in PVA.
  • FIG. 3 illustrates micrographs and an x-ray diffraction plot of Ni nanofibers from electrospinning of Ni—Ac/PVA (2:1) feed.
  • FIG. 4 illustrates micrographs and an x-ray diffraction plot of NiO nanofibers from electrospinning of Ni—Ac/PVA (2:1) feed.
  • FIG. 5 illustrates micrographs and an x-ray diffraction plot of Cu nanofibers from electrospinning of Cu—Ac/PVA (2:1) solution.
  • FIG. 6 illustrates micrographs and an x-ray diffraction plot of CuO nanofibers from electrospinning of Cu—Ac/PVA (2:1) solution.
  • FIG. 7 illustrates micrographs and an x-ray diffraction plot of Ag nanofibers from electrospinning of Ag—Ac/PVA (2:1) solution.
  • FIG. 8 illustrates micrographs and an x-ray diffraction plot of Fe nanofibers from electrospinning of Fe—Ac/PVA (2:1) solution.
  • FIG. 9 illustrates micrographs and an x-ray diffraction plot of ZnO nanofibers from electrospinning of Zn—Ac/PVA (2:1) solution.
  • FIG. 10 illustrates micrographs and an x-ray diffraction plot of CdO nanofibers from electrospinning of Cd—Ac/PVA (2:1) solution.
  • FIG. 11 illustrates micrographs and an x-ray diffraction plot of ZrO 2 nanofibers from electrospinning of Zr—Ac/PVA (2:1) solution.
  • FIG. 12 illustrates micrographs and an x-ray diffraction plot of Pb nanofibers from electrospinning of Pb—Ac/PVA (2:1) solution.
  • FIG. 15 illustrates elemental analysis of pure Ni nanofibers.
  • FIG. 16 illustrates micrographs and an x-ray diffraction plot of ZnO/ZrO 2 hybrid nanofibers.
  • FIG. 17 illustrates micrographs and an x-ray diffraction plot of Ag/ZrO 2 hybrid nanofibers.
  • FIG. 18 illustrates micrographs and an x-ray diffraction plot of Ni/ZrO 2 hybrid nanofibers.
  • FIG. 19 illustrates micrographs and an x-ray diffraction plot of Fe/ZrO 2 hybrid nanofibers.
  • FIG. 20 illustrates TEM micrographs of ZrO 2 hybrid (nanocomposite) nanofibers containing various metal and metal oxides (ZnO, Ni, Ag, and Fe).
  • FIG. 21 illustrates micrographs and an x-ray diffraction plot of Ni/Al 2 O 3 hybrid nanofibers.
  • FIG. 22 illustrates micrographs and an x-ray diffraction plot of CdSe alloy nanofibers.
  • FIG. 23 illustrates micrographs and an x-ray diffraction plot of PbSe alloy nanofibers.
  • FIG. 24 illustrates TEM micrographs of CdSe and PbSe alloy nanofibers.
  • FIG. 25 illustrates elemental analysis of PbSe alloy nanofibers.
  • FIG. 26 illustrates micrographs and an x-ray diffraction plot of CdTe alloy nanofibers.
  • FIG. 27 illustrates micrographs and an x-ray diffraction plot of PbTe alloy nanofibers.
  • FIG. 28 illustrates micrographs and an x-ray diffraction plot of Fe 3 O 4 /FeNi alloy nanofibers.
  • FIG. 29 illustrates TEM micrographs of Fe 3 O 4 /FeNi alloy nanofibers.
  • FIG. 30 illustrates a graphic comparing the electrical conductivity of metal nanofibers from various thermal treatment conditions to the conductivity of a metallic film.
  • FIG. 31 illustrates micrographs and an x-ray diffraction plot of Ni/ZrO 2 hybrid nanofibers.
  • FIG. 32 illustrates TEM micrographs of Ni/ZrO 2 hybrid nanofibers.
  • FIG. 33 illustrates elemental analysis of Ni/ZrO 2 hybrid nanofibers.
  • FIG. 34 illustrates a schematic of the process and system for producing Fe/Pt nanofibers suitable for use in fuel cells.
  • FIG. 35 illustrates a schematic of the process and system for producing hollow Si or Ge nanofibers suitable for use in lithium ion batteries and a micrograph of hollow Si or Ge electrospun fluid stock.
  • FIG. 36 illustrates a schematic of the process and system for producing Al 2 O 3 /ITO hybrid nanofibers suitable for use in flexible solar cells.
  • FIG. 37 illustrates micrographs, x-ray diffraction plots and a schematic for a solar cell with a plurality of components made from inorganic nanofibers.
  • FIG. 38 illustrates a graphic comparing the effect of calcination conditions on electrical conductivity and magnetic coercivity of Ni nanofibers.
  • FIG. 39 illustrates a graphic comparing the effect of fiber alignment conditions on electrical conductivity in the axial and perpendicular direction of a Ni nanofiber mat.
  • FIG. 40 illustrates a Ragone plot depicting energy densities and power densities typical of electrochemical devices.
  • FIG. 41 illustrates an exemplary principle of operation and energy level scheme of a dye-sensitize nanocrystalline solar cell.
  • FIG. 42 illustrates an exemplary principle of operation of a thin film nanocrystal/nanowire hybrid solar cell.
  • FIG. 43 illustrates a schematic of tri-axial electrospinning.
  • FIG. 44 illustrates a TEM image of tri-axial nanofibers of SiO 2 (core)/PI-b-PS with Fe 3 O 4 (middle)/SiO 2 (sheath).
  • FIG. 45 illustrates a cross-sectional view of an electrolytic double layer ultracapacitor.
  • FIG. 46 illustrates a cross-sectional view of barium titanate nanofibers laid on the activated carbon of an ultracapacitor.
  • Nanotechnology is the manipulation of matter at an atomic and molecular scale and is a diverse field involving many different structures, techniques and potential applications. Of them, one structure is a nanofiber, which generally has a diameter of less than 5,000 nm and has various lengths. There is a need for high quality nanofibers, such as metal nanofibers, ceramic nanofibers, hybrid nanofibers, and the like. Such nanofibers and processes for preparing such nanofibers are provided in certain embodiments herein. In some embodiments, provided herein are high quality nanofibers that have good structural integrity, few voids, few structural defects, tunable length, and the like. In some embodiments, the present disclosure includes methods for making long, high quality nanofibers.
  • methods provided herein use a fluid stock comprising a precursor and a polymer that interact with each other and/or are compatible with each other such that the polymer facilitates solubilization (e.g., dissolution, dispersion, or the like) of the precursor.
  • a nanofiber e.g., a precursor nanofiber
  • a nanofiber comprising a polymer and a precursor.
  • a nanofiber comprising a metal component (e.g., a metal, such as a single metal or a metal alloy, a metal oxide, such as a metal oxide, a ceramic, or the like).
  • a continuous matrix metal component nanofiber e.g., a metal, such as a single metal or a metal alloy, a metal oxide, such as a metal oxide, a ceramic, or the like.
  • a continuous matrix metal component nanofiber e.g., a metal, such as a single metal or a metal alloy, a metal oxide, such as a metal oxide, a ceramic, or the
  • a process for the conversion of electrospun fluid stock e.g., a precursor nanofiber comprising a polymer and a precursor
  • this process leaves defects such as gaps, voids, and the like in the resultant nanofiber.
  • these defects are reduced by increasing the proportion of a metal or ceramic precursor in the fluid stock relative to the amount of polymer.
  • ensuring that the fluid stock is homogenous reduces the voids and/or defects in the nanofiber compared to when the fluid stock is not homogenous.
  • the precursor is solubilized by associating the precursor with a ligand.
  • the polymer is water soluble.
  • water-based (aqueous) fluid stocks are advantageous over fluid stocks based on other solvents (e.g., where a non-aqueous solvent is toxic). In some embodiments, it is advantageous to perform the process in an aqueous environment.
  • associating the precursor with the polymer results in long, high quality nanofibers with few defects compared to embodiments without an association between the precursor and polymer.
  • the precursor is distributed relatively homogenously on the polymer (e.g., such that electrospinning of the fluid stock having such homogenous associations provides nanofibers with few voids and defects).
  • the increased proportion of precursor and homogenous distribution of the precursor to create high quality nanofibers results in nanofibers with complex geometries or advanced properties.
  • These geometries include long hollow nanofibers and nanofibers that are hybrids of more than one material.
  • these materials are without limitation, metals, ceramics, or combinations thereof.
  • the process includes electrospinning a fluid stock.
  • the fluid stock comprises metal precursor (e.g., a precursor comprising a metal-ligand compound that, depending on downstream treatment can be converted into a metal, a metal oxide, a ceramic, or the like) and polymer.
  • the metal precursor and polymer are present in a precursor-polymer association.
  • the weight to weight ratio of the precursor to polymer is at least 1:2.
  • the weight to weight ratio of the precursor to polymer is over 1:2.
  • the wt. precursor to wt. polymer ratio is at least 1:1.
  • the wt. precursor to wt. polymer ratio is over 1:1.
  • the polymer is water soluble (e.g., completely dissolvable in water, or at least swellable in water).
  • the fluid stock is aqueous (i.e., comprising water).
  • the precursor e.g., as measured by the metal component of the precursor is at least 200 mM in the fluid stock.
  • the fluid stock comprises metal precursor and polymer, the weight-to-weight ratio of the precursor to polymer of over 1:2 (e.g., at least 1:1.75).
  • the fluid stock is prepared by combining precursor and polymer in a weight-to-weight ratio of over 1:2 (e.g., at least 1:1.75).
  • the fluid stock is aqueous.
  • the metal precursor and polymer are present in the fluid stock in a precursor-polymer association.
  • a process described herein comprises associating or binding a metal to a solubilizing ligand to produce a first metal precursor, optionally in an aqueous solution.
  • the precursor solution is mixed to provide a homogenous precursor composition (e.g., solution).
  • the precursor composition is then combined with a composition of polymer (e.g., water-soluble polymer) to provide a fluid stock.
  • the (first) precursor molecules associate with, or bind to (which terms are understood to be used interchangeably herein—reference to association or binding indicates formation of a covalent bond, a metal-ligand complex, an ionic bond, a Lewis base/Lewis acid interaction, or the like), the polymer (e.g., to provide a precursor-polymer association—a polymer+a second metal precursor).
  • the fluid stock is mixed to provide a homogenous fluid stock, where the precursor is optionally associated with the polymer substantially evenly (e.g., as determined by measuring the variation of viscosity in the composition).
  • the fluid stock is then electrospun into an electrospun fluid stock.
  • the electrospun fluid stock is then calcinated, optionally by heating. In some embodiments, heating in a reducing environment results in a pure metal nanofiber and heating in an oxidizing environment leads to a ceramic nanofiber.
  • the polymer is a nucleophilic polymer (e.g., a polymer comprising alcohol groups, such as PVA).
  • the polymer is a nucleophilic polymer and a first precursor (e.g., reagent precursor) is an electrophilic precursor (e.g., a metal acetate, metal chloride, or the like).
  • a first precursor e.g., reagent precursor
  • an electrophilic precursor e.g., a metal acetate, metal chloride, or the like.
  • the precursor-polymer association is a reaction product between a nucleophilic polymer and an electrophilic first precursor (e.g., reagent precursor).
  • the polymer is an electrophilic polymer (e.g., a polymer comprising chloride or bromide groups, such as polyvinyl chloride).
  • the polymer is an electrophilic polymer and a first precursor (e.g., reagent precursor) is a nucleophilic precursor (e.g., metal-ligand complex comprising “ligands” with nucleophilic groups, such as alcohols or amines).
  • a first precursor e.g., reagent precursor
  • a nucleophilic precursor e.g., metal-ligand complex comprising “ligands” with nucleophilic groups, such as alcohols or amines.
  • the precursor-polymer association is a reaction product between an electrophilic polymer and a nucleophilic first precursor.
  • the fluid stock comprises a high loading of precursor.
  • the fluid stock comprises a high loading of the precursor on the polymer and/or associations between the precursor and polymer.
  • the polymer has a precursor loading of at least 20% (i.e., at least 20% of the reactive sites of the polymer—nucleophilic or electrophilic sites—are associated with a metal compound; this is also described herein as being at least 20% saturated with precursor).
  • the polymer loaded with metal precursor form (i) a composition comprising a polymer and a metal precursor and (ii) a polymer-precursor association.
  • the polymer has a loading of at least 35%.
  • the polymer has a loading of at least 50%. In yet more specific embodiments, the polymer has a loading of at least 75%. Loading can be determined by any suitable mechanism, e.g., nuclear magnetic resonance (NMR) spectrometry, infrared (IR) spectrometry, or the like.
  • NMR nuclear magnetic resonance
  • IR infrared
  • FIG. 2B illustrates the increased loading of precursor on the polymer (e.g., by the decreasing intensity of the —OH peak).
  • the methods for creating a homogenous fluid stock are used to produce structures with geometries other than nanofibers (e.g., nanoparticles, spheres, meshes, thin films, nano-robotic parts such as a gear). As with nanofibers, it is desirable in some embodiments to make these structures with few defects, so are suitable applications of the present disclosure.
  • the present invention includes pure metal, ceramic, or hybrid nanostructures including spheres, meshes, gears and the like.
  • the process comprises electrospinning a fluid stock. Any suitable method for electrospinning is used.
  • elevated temperature electrospinning is utilized. Exemplary methods for comprise methods for electrospinning at elevated temperatures as disclosed in U.S. Pat. No. 7,326,043 and U.S. Pat. No. 7,901,610, which are incorporated herein for such disclosure.
  • elevated temperature electrospinning improves the homogeneity of the fluid stock throughout the electrospinning process.
  • gas assisted electrospinning is utilized (e.g., about a common axis with the jet electrospun from a fluid stock described herein).
  • gas-assisted electrospinning is described in PCT Patent Application PCT/US2011/024894 (“Electrospinning apparatus and nanofibers produced therefrom”), which is incorporated herein for such disclosure.
  • the gas is optionally air or any other suitable gas (such as an inert gas, oxidizing gas, or reducing gas).
  • gas assistance increases the throughput of the process and/or reduces the diameter of the nanofibers.
  • gas assisted electrospinning accelerates and elongates the jet of fluid stock emanating from the electrospinner.
  • incorporating a gas stream inside a fluid stock produces hollow nanofibers.
  • the fluid stock is electrospun using any method known to those skilled in the art.
  • nanofibers are produced from an aqueous fluid stock (e.g., comprising water, a water soluble polymer and metal and/or ceramic precursor).
  • aqueous fluid stocks are cheaper, more environmentally friendly, avoid the use of organic solvents and/or have other advantages in certain applications.
  • the use of aqueous fluid stocks allows for higher loading of both polymers and precursors.
  • higher precursor loading provides for metal, metal oxide, and ceramic nanofibers that have good structural integrity, reduced void structures, and/or reduced structural defects.
  • coaxial electrospinning electrospinning two or more fluids about a common axis
  • coaxial electrospinning with a second fluid is used to add coatings, make hollow nanofibers, make nanofibers comprising more than one material, and the like.
  • the second fluid is either outside (i.e., at least partially surrounding) or inside (e.g., at least partially surrounded by) the aqueous (first) fluid stock.
  • the second fluid is a gas (gas-assisted electrospinning).
  • gas assistance increases the throughput of the process, reduces the diameter of the nanofibers, and/or is used to produce hollow nanofibers.
  • the method for producing nanofibers comprises coaxially electrospinning an aqueous fluid stock and a gas.
  • the second fluid is a second fluid stock having the characteristics as described herein (i.e., comprising a polymer and precursor according to the instant disclosure).
  • a hybrid nanofiber comprising a core and at least one layer thereon is formed.
  • a method for producing a nanofiber comprising electrospinning a first fluid with a second fluid, at least one of the first or second fluids being an aqueous fluid.
  • the first fluid and second fluid are positioned relative to each other in any suitable orientation and/or shape.
  • the first fluid and second fluids are next two each other as they exit the electrospinner.
  • one of either the first fluid or second fluid surrounds the other.
  • the first and second fluids are electrospun about the same or similar axis.
  • the first fluid is an aqueous fluid comprising water, a water soluble polymer, and metal and/or ceramic precursor.
  • the second fluid is a second aqueous fluid, comprising water, a water soluble polymer, and a second metal and/or ceramic precursor, wherein the water soluble polymer of the second fluid is the same or different than the water soluble polymer of the first fluid.
  • the method includes “co-axially” electrospinning, producing “co-axial” hybrid nanofibers, and such.
  • co-axial refers to concentric cylinders of material that have a common (the same) center axis (e.g., a cylindrical nanofiber with a core material surrounded by one or more coatings or cylindrical layers).
  • Co-axial nanofibers are hollow in some embodiments. There is no limit to the number of layers of material (i.e., co-axial does not imply two layers).
  • the terms “co-axial” and “multi-axial” are used interchangeably.
  • Multi-axial electrospinning refers to electrospinning multiple fluids (e.g., multiple fluid stocks as described herein and/or one or more gas) about a common axis.
  • the use of metal precursors increases the electrical conductivity, which may lead to more vigorous whipping of the electrospinning filament.
  • Increasing the electrical conductivity of the fluid stock through choice of precursor for example may also increase the productivity of the process in some instances.
  • increased productivity is achieved by increasing the conductivity of the fluid stock.
  • increased conductivity causes more repulsion by the jets emanating from adjacent spinnerets.
  • the jets are less likely to touch each other prematurely because of this increased repulsion, which allows the practitioner to space the spinnerets more closely together. More closely spaced spinnerets generally results into increased overall productivity (as long as the productivity per spinneret is not substantially reduced).
  • the electrospinning process described herein comprises dispersing and/or keeping the fluid stock relatively evenly dispersed (e.g., uniformly dispersed or homogenously dispersed).
  • the fluid stock is heated, especially if the fluid stock solidifies at ambient temperature.
  • the fluid stock is agitated, optionally in combination with heating. Agitation includes but is not limited to stirring, mixing, sonicating, vortexing, and the like and creates or maintains a substantially homogenous fluid stock.
  • the fluid stock is stirred continuously during the electrospinning process. In one particular embodiment, the fluid stock is stirred for about an hour to get a homogenous dispersion.
  • the procedure for forming the nanofiber is not electrospinning Electrospinning is but one method of producing nanofibers.
  • Other suitable methods include the sol-gel technique or interfacial polymerization or “fast mixing” techniques (Huang, Pure Appl. Chem., Vol. 78, No. 1, pp. 15-27, 2006).
  • the present disclosure further includes methods for making nano-geometries other than fibers such as for making nano-spheres by electrospraying.
  • the composition of the fluid stock and methods for making same are agnostic to the particular geometry (i.e., are applicable to any geometry) and method for producing the geometry.
  • high loading of precursor on the polymer in the fluid stock is beneficial for obtaining pure and/or uniform nanofibers.
  • few defects and/or voids are created in the nanofiber when the polymer is removed compared to the number of defects and/or voids created when having lower precursor loading.
  • Loading is represented as the weight ratio of the precursor to polymer in or combined to form the fluid stock.
  • the weight ratio of the precursor to polymer is any value resulting in a nanofiber with suitable properties in a given embodiment.
  • the weight ratio of the precursor to polymer is at least 1:2 in some embodiments. In some embodiments, there is more precursor than polymer by weight.
  • the weight ratio of the precursor to polymer is at least 1.25:1, at least 1.5:1, at least 1.75:1, at least 2:1, at least 3:1, at least 4:1, at least 5:1, at least 6:1, at least 7:1, at least 8:1, at least 9:1, at least 10:1, at least 15:1, at least 20:1, at least 30:1, at least 40:1, at least 50:1, or at least 100:1.
  • the weight ratio of the precursor to polymer is about 1.25:1, about 1.5:1, about 1.75:1, about 2:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1 about 10:1, about 15:1, about 20:1, about 30:1, about 40:1, about 50:1, or about 100:1.
  • the weight ratio of precursor to polymer is between about 1:2 and 10:1, between 1:1 and 4:1, between about 2:1 and 10:1, or between about 3:1 and 8:1.
  • the weight ratio is determined by comparing the un-associated, un-reacted theoretical weights of the polymer and the precursor (e.g., a first precursor that is reacted with the polymer, such as a metal acetate).
  • a process described herein comprises preparing and/or using a fluid stock that is prepared by combining precursor with a polymer and, optionally, a fluid (e.g., water, or water containing fluid—an aqueous fluid) and the precursor/polymer weight-to-weight ratio is determined by the amount of precursor (e.g., a first precursor) combined with a polymer (e.g., a polymer not associated with a precursor).
  • a fluid e.g., water, or water containing fluid—an aqueous fluid
  • the precursor/polymer weight-to-weight ratio is determined by the amount of precursor (e.g., a first precursor) combined with a polymer (e.g., a polymer not associated with a precursor).
  • the precursor/polymer weight-to-weight ratio is x:y (e.g., regardless of whether or not the precursor ultimately associates with the polymer in the stock).
  • a precursor e.g., a first precursor, such as ML b , wherein M is a metal and L is one or more ligand as described herein, and b is a suitable number, such as 1-10)
  • P a polymer-precursor association
  • P-ML b-1 , ML b-1 being a second precursor in association with the polymer.
  • all or part of the first precursor is associated with the polymer and the precursor/polymer weight-to-weight ratio is determined by the ratio of the sum of the first and second precursors to the polymer.
  • a process provided herein comprises: (a) preparing a fluid stock by combining a first metal precursor, a polymer, and a fluid (e.g., aqueous fluid), the first fluid precursor being combined with the polymer in a weight-to-weight ratio of at least 1:2; and (b) electrospinning a fluid stock.
  • a process provided herein comprises electrospinning a fluid stock prepared by combining a first metal precursor, a polymer, and a fluid (e.g., aqueous fluid), the first metal precursor being combined with the polymer in a weight-to-weight ratio of at least 1:2.
  • FIG. 2A illustrates a first precursor of Al(OCOCH 3 ) 3 reacting with a polymer to form a polymer-precursor association comprising a polymer (polyvinyl alcohol) in association with a second precursor of Al(OCOCH 3 ) 2 .
  • the weight to weight ratio of the first precursor to polymer is over 1:2.
  • the wt. first precursor to wt. polymer ratio is at least 1:1.
  • the wt. first precursor to wt. polymer ratio is over 1:1.
  • the fluid stock includes metal and/or ceramic precursor and polymer.
  • the nanofiber comprises metal or ceramic precursor and polymer.
  • the precursor and/or nanofiber is not metal and/or ceramic.
  • the methods described herein are used to make nanostructures that have few voids or defects in some instances (e.g., no matter the material).
  • the methods for making a substantially uniform fluid feed described herein are applicable to materials other than metals and/or ceramics.
  • FIG. 1 illustrates an exemplary schematic of a process described herein.
  • a first composition comprising metal precursor 101 (e.g., an acetate of Ag, Al, Co, Fe, Ni, Zn, Zr, Si, etc.) is combined 102 with a second composition comprising a polymer 103 (e.g., PVA, PVAc, PVEO, etc.) to prepare a fluid stock comprising a fluid stock composition 104 .
  • a fluid stock provided herein is electrospun using, e.g., a syringe system 105 , through a nozzle 106 , wherein the nozzle is optionally heated.
  • electrospinning of the fluid stock produces a precursor nanofiber 108 , comprising metal precursor and polymer (e.g., in a weight ratio of over 1:2 and up to 4:1), the precursor nanofiber being collected on a collector 107 .
  • Treatment 109 e.g., thermal and/or chemical treatment
  • ceramic, metal, or composite nanofibers e.g., pure ceramic, metal, or composite nanofibers
  • FIG. 34 illustrates another exemplary schematic of a process described herein.
  • a first composition comprising metal precursor 3401 (e.g., an acetate of Ag, Al, Co, Fe, Ni, Zn, Zr, Si, etc.) is combined 3402 with a second composition comprising a polymer 3403 (e.g., PVA, PVAc, PEO, etc.) to prepare a fluid stock comprising a fluid stock composition 3404 .
  • a fluid stock is provided 3406 to an apparatus 3408 comprising a plurality of electrospinning nozzles/needles 3409 .
  • the fluid stock is electrospun with another fluid 3407 (e.g., via connection to an air pump) that is also provided to the apparatus 3409 .
  • apparatus 3409 comprises a fluid stock chamber 3410 and a second fluid chamber (e.g., high pressure gas chamber) 3411 . Electrospinning of the fluid stock may then be electrospun from a center needle or nozzle (e.g., aligned along a longitudinal axis) 3413 while a second fluid is being coaxially expressed from an outer needle or nozzle (e.g., aligned along the same longitudinal axis) 3412 .
  • the fluid stock nozzle (needle) 3413 is optionally heated.
  • the gas and fluid stock chambers and needles may be switched (see, e.g., FIG. 35 ).
  • electrospinning of the fluid stock produces a precursor nanofiber 3415 , comprising metal precursor and polymer (e.g., in a weight ratio of over 1:2 and up to 4:1), the precursor nanofiber being collected on a collector 3414 .
  • Treatment 3416 e.g., thermal and/or chemical treatment
  • ceramic, metal, or composite nanofibers e.g., pure ceramic, metal, or composite nanofibers
  • the metal nanofiber may be a metal alloy nanofiber, such as a platinum-iron alloy 3418 .
  • FIG. 35 illustrates an exemplary schematic of a process for preparing hollow (i.e., hollow core) metal, metal oxide, or ceramic nanofibers described herein.
  • a fluid stock is provided to a fluid stock chamber 3502 of an apparatus described herein.
  • the fluid stock chamber comprises a supply end and a nozzle end, out of which the fluid stock is electrospun with the assistance of gas, which is provided via a gas chamber 3501 comprising a supply end and a nozzle end, the nozzle end being positioned coaxially (i.e., along substantially the same longitudinal axis) with the nozzle end of the fluid stock chamber 3503 .
  • coaxial electrospinning of the fluid stock with the gas in such a manner produces a hollow precursor nanofiber 3506 , which may be collected on a collector 3505 .
  • the hollow precursor nanofibers comprising metal precursor and polymer is illustrated 3506 in FIG. 35 .
  • these hollow precursor nanofibers are then treated 3507 (e.g., thermally) to produce hollow metal nanofibers 3508 .
  • Exemplary hollow nanofibers include hollow Si or Ge nanofibers.
  • FIG. 36 illustrates yet another exemplary schematic of a process described herein, particularly a layered nanocomposite nanofiber that is prepared by a coaxial gas assisted electrospinning process.
  • a first fluid stock 3601 e.g., comprising a metal precursor and a polymer
  • a second fluid stock 3602 e.g., comprising a second metal precursor and a second polymer, the second precursor and polymer independently being either the same or different from the first
  • a third fluid e.g., gas
  • the fluid stocks may be provided to the apparatus by any device, e.g., by a syringe 3605 .
  • the gas may be provided from any source 3606 (e.g., air pump).
  • such an apparatus comprises a plurality of co-axial needles 3604 .
  • Exemplary needles as illustrates by the cross section 3707 , comprise an outer sheath tube 3608 , at least one intermediate tube 3609 , and a core tube 3610 .
  • each of the tubes are coaxially aligned (i.e., aligned along the substantially same axis).
  • such a process may be utilized to prepare a nanofiber comprising a core and a layer, wherein the core comprises a metal, metal oxide, or ceramic, and the layer comprises a metal, metal oxide or ceramic.
  • the core and layer comprise the same or different materials.
  • the core comprises aluminum (from an aluminum precursor fluid stock), and the layer may comprise ITO (from an ITO precursor fluid stock).
  • a nanofiber or a plurality (used interchangeably herein with “a collection”) of nanofibers comprising a polymer and a metal precursor described herein.
  • the nanofiber is prepared according to a process as described above.
  • the polymer and the metal precursor are present in the nanofiber in the form of a polymer-precursor association.
  • polymer and precursor ratios of the polymer/precursor nanofibers are as described herein, e.g., for the fluid stock.
  • the nanofiber(s) comprise polymer and metal precursor.
  • the polymer and metal precursor comprise an optional first metal-precursor and a polymer-precursor association, the polymer-precursor association comprising a polymer bound to one or more second metal-precursor.
  • the weight ratio of metal precursor to polymer is at least 1:2 in some embodiments. In other embodiments there is about equal weights of precursor and polymer. In some embodiments, there is more precursor than polymer by weight.
  • the weight ratio of the precursor to polymer is at least 1.25:1, at least 1.5:1, at least 1.75:1, at least 2:1, at least 3:1, at least 4:1, at least 5:1, at least 6:1, at least 7:1, at least 8:1, at least 9:1, at least 10:1, at least 15:1, at least 20:1, at least 30:1, at least 40:1, at least 50:1, or at least 100:1.
  • the weight ratio of the precursor to polymer is about 1.25:1, about 1.5:1, about 1.75:1, about 2:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1 about 10:1, about 15:1, about 20:1, about 30:1, about 40:1, about 50:1, or about 100:1.
  • the weight ratio of precursor to polymer is between about 1:2 and 10:1, between 1:1 and 4:1, between about 2:1 and 10:1, or between about 3:1 and 8:1.
  • a precursor nanofiber provided herein comprises an optional first metal precursor having the formula ML b (wherein M is a metal and L is one or more ligand as described herein, and b is a suitable number, such as 1-10) and the polymer-precursor association having the formula P-(ML b-1 ) g (P being a polymer and g being the precursor saturation or loading number, such a number greater than or equal to 1).
  • g is understood to be a number less than or equal to the number of monomeric units or reactive sites (especially if monomeric units having more than one reactive site are uses) present in P.
  • some cross-linking between polymers (P), e.g., through a metal precursor, will be present (e.g., forming a P-ML b-2 -P; if ML b , ML b-1 and ML b-2 are all present, the ML b-2 residue may be considered a third metal precursor).
  • combining a first precursor and a polymer under controlled conditions reduces crosslinking between polymers.
  • the polymers are less than 20% cross-linked (e.g., less than 20% of the metal precursors are associated with 2 or more polymers and/or less than 20% of the monomeric units of the polymer are connected, e.g., via a metal precursor, to another polymer).
  • the polymers are less than 10% cross-linked. In specific embodiments, the polymers are less than 5% cross-linked. In more specific embodiments, the polymers are less than 3% cross-linked. In still more specific embodiments, the polymers are less than 2% cross-linked. In yet more specific embodiments, the polymers are less than 1% cross-linked.
  • the polymer of the polymer-precursor association is at least 20% saturated with precursor. In specific embodiments, the polymer of the polymer-precursor association is at least 35% saturated with precursor. In more specific embodiments, the polymer of the polymer-precursor association is at least 50% saturated with precursor. In still more specific embodiments, the polymer of the polymer-precursor association is at least 75% saturated with precursor.
  • the polymer is (e.g., on average) at least 20%, at least at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% saturated. In some instances, the polymer is on average between about 50% and 100%, between about 70% and 100%, between about 90% and 100%, between about 50% and 90%, between about 60% and 80%, or between about 20% and 50% saturated.
  • a nanofiber or plurality of nanofibers provided herein comprise a polymer and (e.g., on average) at least 5 elemental wt. % metal. In certain embodiments, a nanofiber or plurality of nanofibers provided herein comprise a polymer and (e.g., on average) at least 10 elemental wt. % metal. In specific embodiments, a nanofiber or plurality of nanofibers provided herein comprise a polymer and (e.g., on average) at least 15 elemental wt. % metal. In more specific embodiments, a nanofiber or plurality of nanofibers provided herein comprise a polymer and (e.g., on average) at least 20 elemental wt. % metal.
  • metal constitutes (e.g., on average) at least 25 elemental wt. % of the nanofiber(s). In still more specific embodiments, metal constitutes (e.g., on average) at least 30 elemental wt. % of the nanofiber(s). In yet more specific embodiments, metal constitutes (e.g., on average) at least 35 elemental wt. % of the nanofiber(s). In more specific embodiments, metal constitutes (e.g., on average) at least 40 elemental wt. % of the nanofiber(s). In various embodiments, metal constitutes (e.g., on average) at least 10 elemental wt. %, at least 15 elemental wt. %, at least 45 elemental wt. %, at least 50 elemental wt. % of the nanofiber(s).
  • an electrospun precursor nanofiber comprises metal precursor and polymer, wherein the metal precursor and polymer when taken together make up at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 98% of the total mass of the nanofiber.
  • the polymer is an organic polymer.
  • the metal precursor of the precursor may also be optionally solvated (e.g., hydrated if the fluid stock of the fluid medium is water). It is to be understood that disclosures herein are intended to contemplate such solvates.
  • a process provided herein comprises one or more processes for treating (e.g., further treating for those embodiments wherein the treatment is combined with the electrospinning process described above) an electrospun fluid stock (e.g., a precursor nanofiber comprising a polymer and precursor, such as any precursor nanofiber described herein).
  • an electrospun fluid stock e.g., a precursor nanofiber comprising a polymer and precursor, such as any precursor nanofiber described herein.
  • the further treatment comprises converting a precursor nanofiber (the electrospun nanofiber, comprising a polymer and precursor) into a metal, metal oxide (e.g., metal oxide ceramic), or ceramic nanofiber.
  • a process described herein comprises removing the polymer from the electrospun fluid stock (i.e., precursor nanofiber).
  • treatment (calcination) of the precursor nanofiber includes removing the polymer (e.g., optionally thermally or chemically removing the polymer).
  • removing the polymer creates voids and/or defects in the nanofiber.
  • the polymer is removed in a substantially unmodified state.
  • the polymer is degraded by any suitable means (e.g., degraded by heat, evaporated, or sublimated).
  • the polymer is removed by chemical means (e.g., by solubilizing the polymer or chemically degrading the polymer).
  • the polymer is chemically degraded in a strong acid or base.
  • calcination includes removal of the ligand that is optionally a component of the precursor.
  • the ligand is degraded or removed whole, removed by heat or chemicals, and the like.
  • the treatment (calcination) process also comprises converting the precursor(s) to metal (e.g., single metal, or metal alloy), metal oxide (e.g., metal oxide ceramic), and/or ceramic. Such a conversion is also intended to be encompassed herein by the term “calcination”.
  • An exemplary calcination is the conversion of a precursor nanofiber comprising a polymer and metal and/or ceramic precursors into a metal and/or ceramic nanofiber.
  • the conversion of precursors to metal(s), metal oxide(s), and/or ceramic(s) occurs simultaneously with the removal of the polymer.
  • the conversion of precursors and the removal of the polymer occur at different times. In various embodiments, polymer removal and precursor conversion occur under the same conditions, or under different conditions.
  • treatment (calcination) is performed in a gaseous environment.
  • the gaseous environment is inert (i.e., consisting of non-reactive gases).
  • treatment (calcination) occurs under an inert atmosphere, such as a noble gas.
  • the noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), or mixtures thereof.
  • the inert gas is or comprises argon.
  • the inert gas is or comprises nitrogen (N 2 ) gas.
  • treatment of the electrospun fluid stock comprises chemical treatment thereof.
  • chemical treatment comprises treatment under oxidative conditions.
  • oxidative treatment comprises treating the electrospun fluid stock with a gas comprising oxygen (e.g., air).
  • the oxidative treatment also comprises thermal treatment.
  • thermal treatment occurs upon calcination, optionally oxidation reactions.
  • oxidation converts metal precursors to metal oxide (e.g., a metal oxide ceramic) or ceramic nanofibers.
  • oxidative reactions are performed in an oxygen-rich environment, such as air. In one particular example (e.g., where the nanofiber is a ceramic nanofiber), calcination is performed in air at about 600° C. for about 2 hours.
  • chemical treatment comprises treatment under reduction conditions.
  • Reduction is the gain of electrons, which is the opposite reaction from oxidation.
  • reducing environments are employed.
  • the reductive environment prevents or minimizes the conversion of metal precursors to metal oxides (and/or may reduce metal oxides back to metals if oxidation has occurred).
  • the reducing environment comprises metal such as Mg under vacuum.
  • the reducing environment comprises hydrogen gas (H 2 ).
  • the reductive environment is a mixture of inert gas and hydrogen gas.
  • the strength of the reductive environment is varied by blending H 2 with an inert gas in various proportions.
  • the present disclosure encompasses hydrogen-nitrogen mixtures and the like.
  • the reductive environment is any environment in which oxidation is prevented or minimized (e.g., an environment substantially devoid of oxygen).
  • treatment is performed under a mixture of argon and hydrogen at about 800° C. for about 2 hours to produce a pure metal nanofiber.
  • treatment is performed in a liquid environment.
  • the liquid environment is aqueous.
  • the liquid environment comprises a different solvent than water, such as an organic solvent.
  • the liquid environments comprise oxidative, reductive, or inert conditions.
  • An exemplary liquid-based reducing environment is a solution NaBH 4 .
  • An exemplary oxidizing solution comprises hydrogen peroxide H 2 O 2 .
  • calcination uses a catalyst (i.e., whether conducted in the gas phase or liquid phase).
  • Calcination is performed at any suitable temperature for any suitable amount of time. In some instances, higher temperature calcinations produce nanofibers of a smaller diameter. In some instances, low temperature and/or short time may generate small crystal domains in amorphous metal or metal oxides, while high temperature calcination may lead to nanofibers with pure metal or pure metal oxide crystals. In certain instances, crystal size may impact electric conductivity or magnetic properties. In some instances, low temperature calcination of magnetically active metal or metal oxides may generate superparamagnetic nanofibers. In some instances, high temperature calcination may produce metal nanofibers with increased electric conductivity.
  • calcination is performed at about 100° C., about 150° C., about 200° C., about 300° C., about 400° C., about 500° C., about 600° C., about 700° C., about 800° C., about 900° C., about 1,000° C., about 1,500° C., about 2,000° C., and the like.
  • calcination is performed at a temperature of at least 100° C., at least 150° C., at least 200° C., at least 300° C., at least 400° C., at least 500° C., at least 600° C., at least 700° C., at least 800° C., at least 900° C., at least 1,000° C., at least 1,500° C., at least 2,000° C., and the like.
  • calcination is performed at a temperature of at most 100° C., at most 150° C., at most 200° C., at most 300° C., at most 400° C., at most 500° C., at most 600° C., at most 700° C., at most 800° C., at most 900° C., at most 1,000° C., at most 1,500° C., at most 2,000° C., and the like. In some embodiments, calcination is performed at a temperature of between about 300° C. and 800° C., between about 400° C. and 700° C., between about 500° C. and 900° C., between about 700° C. and 900° C., between about 800° C.
  • calcination is performed between 300° C. and 1200° C. In more specific embodiments, calcination is performed between 400° C. and 1000° C. In still more specific embodiments, calcination is performed between 500° C. and 900° C. In some specific embodiments, calcination is performed at 600° C. In other specific embodiments, calcination is performed at 800° C.
  • calcination is performed at a constant temperature.
  • the temperature changes over time.
  • the temperature increases from a first temperature (e.g., the temperature of the electrospinning process, optionally room temperature) to a second temperature.
  • calcination then proceeds for a given time at the second temperature.
  • the temperature continues to vary.
  • the rate of increase in temperature during calcination is varied in certain instances. Any suitable rate of increase is permissible, whereby a nanofiber of the desired properties is obtained. In certain embodiments, the rate of temperature increase is about 0.1° C./min.
  • the rate of temperature increase is at least about 0.1° C./min, at least about 0.3° C./min, at least about 0.5° C./min, at least about 0.7° C./min, at least about 1.0° C./min, at least about 1.5° C./min, at least about 2° C./min, at least about 2.5° C./min, at least about 3° C./min, at least about 4° C./min, at least about 5° C./min, at least about 10° C./min, at least about 20° C./min, and the like.
  • the rate of temperature increase is at most about 0.1° C./min, at most about 0.3° C./min, at most about 0.5° C./min, at most about 0.7° C./min, at most about 1.0° C./min, at most about 1.5° C./min, at most about 2° C./min, at most about 2.5° C./min, at most about 3° C./min, at most about 4° C./min, at most about 5° C./min, at most about 10° C./min, at most about 20° C./min, and the like.
  • the rate of temperature increase is between about 0.1° C./min and 0.5° C./min, between about 0.5° C./min and 2° C./min, between about 2° C./min and 10° C./min, between about 0.1° C./min and 2° C./min, and the like.
  • Calcination is performed for any suitable amount of time (e.g., as necessary to arrive at a nanofiber with the desired properties).
  • the time and temperature of calcination are related to each other. For example, choice of a higher temperature reduces the amount of time needed to produce a nanofiber with a given property. The converse is also true; increasing the time of calcination reduces the necessary temperature, which is advantageous if the nanofiber includes temperature-sensitive materials for example.
  • calcination is performed for about 5 minutes, about 15 minutes, about 30 minutes, about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 8 hours, about 12 hours, about 1 day, about 2 days, and the like.
  • calcination is performed for at least 5 minutes, at least 15 minutes, at least 30 minutes, at least 1 hour, at least 2 hours, at least 3 hours, at least 4 hours, at least 8 hours, at least 12 hours, at least 1 day, at least 2 days, and the like. In some embodiments, calcination is performed for at most 5 minutes, at most 15 minutes, at most 30 minutes, at most 1 hour, at most 2 hours, at most 3 hours, at most 4 hours, at most 8 hours, at most 12 hours, at most 1 day, at most 2 days, and the like. In yet other embodiments, calcination is performed for between about 10 minutes and 60 minutes, between about 1 hour and about 5 hours, between about 5 hours and 1 day, and the like.
  • calcination of a precursor nanofiber results in a desired nanofiber (e.g., a pure metal or pure ceramic nanofiber).
  • the nanofiber consists essentially of pure metal or ceramic (i.e., optionally including small amounts of other materials).
  • the other materials are residual polymer, residual carbonaceous material (e.g., degraded ligand and/or polymer), minor amounts of oxygen (e.g., in the form of a metal oxide if the nanofiber is “pure metal”), or other components of the fluid stock.
  • the process has a high yield (e.g., which is desirable for embodiments in which the precursor is expensive). Yield may be quantified by comparing the number of molecules (e.g., in moles) of precursor molecules in the nanofiber to the number of molecules (e.g., in moles) of precursor molecules that get converted into their final form (e.g., metal, metal oxide, or ceramic) and are incorporated in the nanofiber.
  • Yield may be quantified by comparing the number of molecules (e.g., in moles) of precursor molecules in the nanofiber to the number of molecules (e.g., in moles) of precursor molecules that get converted into their final form (e.g., metal, metal oxide, or ceramic) and are incorporated in the nanofiber.
  • the yield may be calculated by solving for the number of precursor molecules (or y*the number of precursor molecules if the precursor molecule has more than one metal atom (i.e., y metal atoms) therein) in the fluid stock divided by the number of metal atoms in the nanofiber(s) (i.e., metal atoms in fluid stock/metal atoms in nanofiber(s)).
  • higher loading of precursor on the polymer may result in higher yield. For example, in one trial loading precursor to polymer at a ratio of 4:1 resulted in an 80% yield.
  • the metal atoms in the nanofiber are about 10%, about 20%, about 30%, about 33%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 98%, or about 100% of the number of (e.g., in moles) precursor molecules in the fluid stock.
  • the metal atoms in the nanofiber are at least 10%, at least 20%, at least 30%, at least 33%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98%, or at least 99% of the moles of precursor molecules in the fluid stock.
  • the moles of precursor molecules in the nanofiber are between about 10% and about 40%, between about 20% and about 50%, or between about 50% and about 100% of the moles of precursor molecules in the fluid stock.
  • fluid stocks Described herein are fluid stocks, fluid stocks having certain characteristics, fluid stocks prepared according to the methods herein disclosed, fluid stocks preparable by the methods herein disclosed, fluid stocks incorporating the precursors herein disclosed, fluid stocks incorporating the polymers herein disclosed, and fluid stocks suitable for the methods and systems herein disclosed.
  • the present disclosure also includes methods for using the fluid stocks, and the like.
  • a composition (e.g., for use as an electrospinning fluid stock) provided or used in a process herein comprises metal precursor and polymer.
  • the metal precursor is present in a weight-to-weight ratio of over 1:2 with the polymer.
  • the metal precursor is present in a weight-to-weight ratio of over 1:1 with the polymer.
  • the precursor to polymer weight ratio is as described throughout this disclosure.
  • the fluid stock further comprises water (i.e., the fluid stock is aqueous).
  • the metal precursor is present in a concentration of at least 200 mM. In other embodiments, the precursor is present in any suitable amount described herein.
  • the fluid stock comprises a substantially uniform and/or homogenous dispersion or solution (e.g., as measured by viscosity deviations, UV absorbance, or the like).
  • the fluid stock comprises at least two different metal precursors.
  • the at least two different metal precursors comprise different metals.
  • use of at least two different metal precursors provides an alloy or composite nanofiber following electrospinning and treatment according to the processes described herein.
  • metal precursor of the fluid stock is at least partially in the form of a polymer-precursor association.
  • the metal precursor is partially in the form of a polymer-precursor association (e.g., P-(ML b-1 ) g as described herein) and partially in a form that is not associated with a polymer (e.g., ML b as described herein).
  • the precursor present in the fluid stock is at least 80% associated with the polymer.
  • the precursor present in the fluid stock is at least 90% associated with the polymer.
  • the precursor present in the fluid stock is at least 95% associated with the polymer.
  • the precursor present in the fluid stock is at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 75%, at least 85%, at least 98%, or at least 99% associated with the polymer.
  • some cross-linking between polymers (P), e.g., through a metal precursor, will be present (e.g., forming a P-ML b-2 -P; which is considered to be in “associated” form).
  • the polymers of a fluid stock described herein are less than 20% cross-linked (e.g., less than 20% of the metal precursors are associated with 2 or more polymers and/or less than 20% of the monomeric units of the polymer are connected, e.g., via a metal precursor, to another polymer).
  • the polymers are less than 10% cross-linked.
  • the polymers are less than 5% cross-linked.
  • the polymers are less than 3% cross-linked.
  • the polymers are less than 2% cross-linked.
  • the polymers are less than 1% cross-linked.
  • increasing the amount of precursor relative to the amount of polymer and/or distributing the precursor relatively uniformly in the fluid stock produces nanofibers with reduced voids and/or fewer defects relative to nanofibers where the amount of precursor is lower or the fluid stock is not uniform.
  • the fluid stock is a solution, optionally an aqueous solution.
  • the polymer is water soluble and the precursor is solubilized by associating with a ligand.
  • one or more components are not fully dissolved and the fluid stock is a dispersion.
  • the fluid stock is uniform or homogenous (e.g., no matter whether the fluid stock is a solution or dispersion).
  • homogeneity and/or uniformity of the fluid stock is determined by measuring the standard deviation of the viscosity of the fluid stock.
  • the viscosity of fractions of the fluid stock deviate from the viscosity of the fluid stock as a whole by less than 5%, less than 10%, less than 20%, or any suitable amount to effectively produce nanofibers described herein.
  • the fluid stock is kept uniform or homogenous, e.g., by agitating.
  • a process described herein further comprises maintaining uniformity of the fluid stock, e.g., by heating and/or agitating the fluid stock.
  • Methods of agitating include, by way of non-limiting example, mixing, stirring, shaking, sonicating, or otherwise inputting energy to prevent or delay the formation of more than one phase in the fluid stock. Any of these methods or equivalents are employed in various embodiments.
  • the fluid stock is continually agitated.
  • the fluid stock is agitated to create a uniform dispersion or solution, which is then used in an electrospinning step before the fluid stock (e.g., dispersion or solution) loses uniformity and/or homogeneity (e.g., it before it separates into more than one phase).
  • exemplary phases are an aqueous phase and an oil phase, or an aqueous phase and a phase that includes polymer or precursor (e.g., a solid/precipitate phase) for example.
  • a uniform fluid stock is made by first agitating a solution of precursor or uniform dispersion of precursor.
  • the fluid stock is made by uniformly distributing precursor in a first dispersion before combining the first dispersion with a second dispersion (e.g., which includes polymer).
  • the precursor solution or uniform dispersion is continually agitated in some embodiments, optionally mixed while being combined with the polymer dispersion to create the fluid stock.
  • the fluid stock is an aqueous fluid stock and/or comprises polymer dissolved in water.
  • the continuous phase of the fluid stock is water (e.g., when the fluid stock is a dispersion).
  • the solvent is water (e.g., when the fluid stock is a solution).
  • the solution or dispersion of precursor is aqueous
  • the solution or dispersion of polymer is aqueous
  • both solutions or dispersions are aqueous.
  • the fluid stock is heated (e.g., optionally in combination with agitation) to create a substantially uniform or substantially homogenous dispersion or solution.
  • the fluid stock is made by uniformly distributing precursor in a first dispersion before combining the first dispersion with a second dispersion (e.g., which includes polymer).
  • the first dispersion is heated, optionally in combination with agitation.
  • the polymer concentration in the fluid stock is related to (e.g., proportional to) the average molecular weight of the polymer. For example, in some embodiments when the polymer has a molecular weight of about 1,000,000 atomic mass units, the polymer is present at 1% of the fluid stock by weight. In another example, when the polymer has a molecular weight of about 50,000 atomic mass units, the polymer is present at 20% of the fluid stock by weight. In general, the higher the molecular weight of the polymer, the lower the required concentration of polymer in the fluid stock to achieve high quality metal and/or ceramic nanofibers.
  • the fluid stock contains any suitable amount of polymer.
  • the weight percent of polymer in the fluid stock is represented as the weight percent of polymer alone, or as the combined weight percent of polymer with associated precursor. In some embodiments, the fluid stock is about 10 weight % polymer or polymer associated with precursor.
  • the fluid stock comprises about 0.5 weight %, about 1 weight %, about 2 weight %, about 3 weight %, about 4 weight %, about 5 weight %, about 6 weight %, about 7 weight %, about 8 weight %, about 9 weight %, about 10 weight %, about 12 weight %, about 14 weight %, about 16 weight %, about 18 weight %, about 20 weight %, about 30 weight %, or about 40 weight % polymer or polymer associated with precursor.
  • the fluid stock comprises at least about 0.5 weight %, at least about 1 weight %, at least about 2 weight %, at least about 3 weight %, at least about 4 weight %, at least about 5 weight %, at least about 6 weight %, at least about 7 weight %, at least about 8 weight %, at least about 9 weight %, at least about 10 weight %, at least about 12 weight %, at least about 14 weight %, at least about 16 weight %, at least about 18 weight %, at least about 20 weight %, at least about 30 weight %, or at least about 40 weight % polymer or polymer associated with precursor.
  • the fluid stock comprises at most about 0.5 weight %, at most about 1 weight %, at most about 2 weight %, at most about 3 weight %, at most about 4 weight %, at most about 5 weight %, at most about 6 weight %, at most about 7 weight %, at most about 8 weight %, at most about 9 weight %, at most about 10 weight %, at most about 12 weight %, at most about 14 weight %, at most about 16 weight %, at most about 18 weight %, at most about 20 weight %, at most about 30 weight %, or at most about 40 weight % polymer or polymer associated with precursor.
  • the fluid stock comprises from about 1 weight % to about 20 weight % polymer or polymer associated with precursor. In some embodiments, the fluid stock comprises from about 1 weight % to about 10 weight %, from about 1 weight % to about 5 weight %, from about 5 weight % to about 20 weight %, from about 5 weight % to about 10 weight %, from about 10 weight % to about 15 weight %, or from about 15 weight % to about 20 weight % polymer or polymer associated with precursor.
  • polymer concentration in the fluid stock is determined on a monomeric residue concentration.
  • concentration of the polymer is determined based on the concentration of polymeric repeat units present in the stock.
  • polymer concentration of polyvinyl alcohol may be measured based on the concentration of (—CH 2 CHOH—) present in the fluid stock.
  • the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 100 mM.
  • the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 200 mM.
  • the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 400 mM.
  • the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 500 mM. In at least 5 mM, at least 100 mM, at least 150 mM, at least 200 mM, at least 250 mM, at least 300 mM, at least 350 mM, at least 400 mM, at least 500 mM, at least 700 mM, at least 900 mM, at least 1.2 M, at least 1.5 M, at least 2 M, at least 5 M, and the like. In some embodiments, the concentration of the precursor in the fluid stock is between 5 mM and 5 M, between 200 mM and 1 M, between 100 mM and 700 mM, and the like.
  • the concentration of precursor in the fluid stock to monomeric residue in the fluid stock is at least 1:4. In specific embodiments, the concentration of precursor in the fluid stock to monomeric residue in the fluid stock is at least 1:3. In more specific embodiments, the concentration of precursor in the fluid stock to monomeric residue in the fluid stock is at least 1:2. In still more specific embodiments, the concentration of precursor in the fluid stock to monomeric residue in the fluid stock is at least 1:1.2. In yet more specific embodiments, the concentration of precursor in the fluid stock to monomeric residue in the fluid stock is about 1:1 (e.g., within 5%). In other embodiments, the concentration of precursor in the fluid stock to monomeric residue in the fluid stock is at least 1:10, at least 1:8, at least 1:6, at least 1:1.5, at least 1:3.5, at least 1:2.5, or any suitable ratio.
  • the fluid stock comprises precursor and polymer, wherein at least 5 elemental wt. % of the total mass of the precursor and polymer is metal. In certain embodiments, at least 10 elemental wt. % of the total mass of the precursor and polymer is metal. In specific embodiments, at least 15 elemental wt. % of the total mass of the precursor and polymer is metal. In more specific embodiments, at least 20 elemental wt. % of the total mass of the precursor and polymer is metal. In specific embodiments, at least 25 elemental wt. % of the total mass of the precursor and polymer is metal. In still more specific embodiments, at least 30 elemental wt. % of the total mass of the precursor and polymer is metal.
  • At least 35 elemental wt. % of the total mass of the precursor and polymer is metal. In more specific embodiments, at least 40 elemental wt. % of the total mass of the precursor and polymer is metal. In various embodiments, at least 10 elemental wt. %, at least 15 elemental wt. %, at least 45 elemental wt. %, at least 50 elemental wt. % of the total mass of the precursor and polymer is metal.
  • the concentration of precursor in the fluid stock is high.
  • the concentration is any suitable concentration.
  • the concentration of the precursor in the fluid stock is about 5 mM, about 10 mM, about 20 mM, about 40 mM, about 60 mM, about 80 mM, about 100 mM, about 150 mM, about 200 mM, about 250 mM, about 300 mM, about 350 mM, about 400 mM, about 500 mM, about 700 mM, about 900 mM, about 1.2 M, about 1.5 M, about 2 M, about 5 M, and the like.
  • the concentration of the precursor in the fluid stock is at least 5 mM, at least 10 mM, a at least 20 mM, at least 40 mM, at least 60 mM, at least 80 mM, at least 100 mM, at least 150 mM, at least 200 mM, at least 250 mM, at least 300 mM, at least 350 mM, at least 400 mM, at least 500 mM, at least 700 mM, at least 900 mM, at least 1.2 M, at least 1.5 M, at least 2 M, at least 5 M, and the like.
  • the concentration of the precursor in the fluid stock is at most 5 mM, at most 10 mM, a at most 20 mM, at most 40 mM, at most 60 mM, at most 80 mM, at most 100 mM, at most 150 mM, at most 200 mM, at most 250 mM, at most 300 mM, at most 350 mM, at most 400 mM, at most 500 mM, at most 700 mM, at most 900 mM, at most 1.2 M, at most 1.5 M, at most 2 M, at most 5 M, and the like. In some embodiments, the concentration of the precursor in the fluid stock is between 5 mM and 5 mM, between 20 mM and 1 M, between 100 mM and 700 mM, between 100 mM and 300 mM, and the like.
  • a fluid stock is prepared by (i) dissolving or dispersing a precursor in a first fluid (e.g., water, or another aqueous medium) to form a first composition; (ii) dissolving or dispersing a polymer in a second fluid (e.g., water, or another aqueous medium) to form a second composition; and (iii) combining at least a portion of the first and second compositions to form the fluid stock.
  • a first fluid e.g., water, or another aqueous medium
  • a second fluid e.g., water, or another aqueous medium
  • a metal precursor provided herein may be present in a fluid stock described herein, present in a precursor nanofiber described herein, used in an electrospinning process described herein, or the like.
  • the precursor is any molecule or molecules convertible into a metal, ceramic, or metal oxide (such as a metal oxide ceramic).
  • metal precursors are optionally converted, upon treatment of the precursor (e.g., the precursor present in a precursor/polymer nanofiber), into a metal (e.g., a single metal, a metal alloy), a metal oxide (e.g., a metal oxide ceramic) or a ceramic (e.g., metal oxide, or otherwise).
  • the precursor is a molecule or molecules that associates with polymers, such as those described herein. In some embodiments, the precursor is a molecule or molecules that distributes substantially uniformly along the polymers or within the fluid stock. In some embodiments, an increased weight ratio of precursor in the fluid stock and distribution of the precursor uniformly in the fluid stock results in high quality nanofibers with few voids and/and defects (e.g., compared with a nanofiber where the weight ratio is lower or the fluid stock is not uniform).
  • precursor having certain characteristics
  • precursor prepared according to the methods herein disclosed precursor preparable by the methods herein disclosed
  • precursor incorporating the ligands herein disclosed precursor incorporating the metals herein disclosed
  • precursor suitable for the methods and systems herein disclosed precursor suitable for the methods and systems herein disclosed.
  • methods for using the precursor to produce nanofibers includes the nanofibers comprising (precursor nanofibers) and/or prepared by the precursors (e.g., metal-, metal oxide-, ceramic-containing nanofibers), and the like.
  • the precursor is a metal containing compound that is associated with at least one ligand.
  • the metal-ligand association (used interchangeably herein with “metal-ligand complex”) is associated via any suitable type of bond or interaction.
  • the interaction between the metal and the ligand in the metal-ligand association (metal-ligand complex) is an ionic bond (e.g., cationic metal-anionic ligand salt), a covalent bond, a metal-ligand complex (e.g., coordination complex between ligand and metal), or the like.
  • a precursor described herein is associated with a polymer instead of, or in addition to, other ligands—such compounds are intended to be considered was metal-ligand associations (whether or not additional ligands are present).
  • a precursor provided herein is a metal compound in association with a ligand and free of any association with a polymer (e.g., ML b , wherein M is metal and L is one or more ligand as described herein, and b is a suitable number, such as a number of at least 1, e.g., 1-10); a metal compound is association with a polymer and, optionally, in association with a ligand (e.g., P-ML b-1 , ML b-1 being a second precursor in association with the polymer (P); with a ligand if b is >1); a metal compound in association with more than one polymer and, optionally, in association with a ligand (e.g., P-ML b-2 -P; with a ligand if b is >2).
  • a metal compound in association with more than one polymer and, optionally, in association with a ligand (e.g., P-ML b-2 -P
  • the precursor is a molecule that is substantially identical to the material comprising the nanofiber, optionally a metal.
  • the precursor is convertible to the material comprising the nanofiber.
  • the precursor is converted by performing the calcination procedures disclosed herein.
  • metal precursors in complex with a ligand are converted to metal oxide nanofibers by employing oxidizing conditions and heat.
  • precursors of metal in complex with a ligand are converted to a metal nanofiber by calcinating in reducing conditions and heat.
  • precursors of metal in complex with a ligand are converted to a metal nanofiber by calcinating in inert conditions and heat. In other embodiments, these processes may be performed in the absence of heat.
  • pure metal or ceramic nanofibers have attractive properties such as high conductivity for use in devices such as batteries, ultracapacitors, solar cells, and the like.
  • nanofibers are also useful in the field of catalysis on account of the high surface area to volume ratio.
  • the precursor comprises a metal.
  • the metal is a transition metal, alkali metal, alkaline earth metal, post-transition metal, lanthanide, or actinide.
  • Transition metals include: scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), and hasium (Hs).
  • Alkali metals include: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr).
  • Alkaline earth metals include: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
  • Post-transition metals include: aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), lead (Pb), and bismuth (Bi).
  • Lanthanides include the elements with atomic number 57 to 71 on the periodic table.
  • Actinides include the elements with atomic number 89 to 103 on the periodic table.
  • silicon Si
  • germanium Ge
  • antimony Sb
  • polonium Po
  • silicon is used in the process described herein to produce silicon nanofibers.
  • the metal of the precursor is a transition metal.
  • the metal of the precursor is silicon.
  • the metal of the precursor is not silicon.
  • the metal of the precursor is aluminum.
  • the metal of the precursor is not aluminum.
  • the precursor comprises at least two different metals.
  • the metal is an alkali metal. In other specific embodiments, the metal is an alkaline earth metal. In still other embodiments, the metal is a transition metal. In more specific embodiments, the metal is a period IV transition metal. In other specific embodiments, the metal is a period V transition metal. In some embodiments, the metal is a group XIII metal. In certain embodiments, the metal is a group XIV metal. In certain embodiments, the metal is a metalloid.
  • the metal is lithium, beryllium, sodium, magnesium, aluminum, silicon, potassium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, zirconium, palladium, silver, cadmium, tin, barium, hafnium, tungsten, lead, or the like.
  • the precursor comprises at least two precursors (i.e., at least a first and second precursor), each precursor comprising a different metal than the other precursor.
  • at least one of the metals is silicon.
  • at least one of the metals is aluminum.
  • at least one of the metals is zirconium.
  • the metal of the first precursor is silicon, aluminum, or zirconium
  • the metal of the second precursor is not silicon, aluminum, or zirconium.
  • the metal precursor is a metal-ligand association (complex) (e.g., a coordination complex), each metal precursor comprising metal atom(s) associated (complexed) with one or more ligand(s) (e.g., 1-10, 2-9, or any suitable number of ligands).
  • the precursor described herein comprises at least two different types of ligand (e.g., at least one acetate and at least one halide).
  • the precursor is a metal carboxylate (e.g., —OCOCH 3 or another —OCOR group, wherein R is an alkyl, substituted alkyl, aryl, substituted aryl, or the like).
  • the precursor is lithium acetate, beryllium acetate, sodium acetate, magnesium acetate, aluminum acetate, silicon acetate, potassium acetate, calcium acetate, titanium acetate, vanadium acetate, chromium acetate, manganese acetate, iron acetate, cobalt acetate nickel acetate, copper acetate, zinc acetate, gallium acetate, germanium acetate, zirconium acetate, palladium acetate, silver acetate, cadmium acetate, tin acetate, barium acetate, hafnium acetate, tungsten acetate, lead acetate, or the like.
  • the precursor is a metal nitrate.
  • the precursor is lithium nitrate, beryllium nitrate, sodium nitrate, magnesium nitrate, aluminum nitrate, silicon nitrate, potassium nitrate, calcium nitrate, titanium nitrate, vanadium nitrate, chromium nitrate, manganese nitrate, iron nitrate, cobalt nitrate nickel nitrate, copper nitrate, zinc nitrate, gallium nitrate, germanium nitrate, zirconium nitrate, palladium nitrate, silver nitrate, cadmium nitrate, tin nitrate, barium nitrate, hafnium nitrate, tungsten nitrate, lead nitrate, or the like.
  • the precursor is a metal alkoxide (e.g., a methoxide, ethoxide, isopropyl oxide, t-butyl oxide, or the like).
  • the precursor is lithium alkoxide, beryllium alkoxide, sodium alkoxide, magnesium alkoxide, aluminum alkoxide, silicon alkoxide, potassium alkoxide, calcium alkoxide, titanium alkoxide, vanadium alkoxide, chromium alkoxide, manganese alkoxide, iron alkoxide, cobalt alkoxide nickel alkoxide, copper alkoxide, zinc alkoxide, gallium alkoxide, germanium alkoxide, zirconium alkoxide, palladium alkoxide, silver alkoxide, cadmium alkoxide, tin alkoxide, barium alkoxide, hafnium alkoxide, tungsten alkoxide, lead alk
  • the precursor is a metal halide (e.g., chloride, bromide, or the like).
  • the precursor is lithium halide, beryllium halide, sodium halide, magnesium halide, aluminum halide, silicon halide, potassium halide, calcium halide, titanium halide, vanadium halide, chromium halide, manganese halide, iron halide, cobalt halide nickel halide, copper halide, zinc halide, gallium halide, germanium halide, zirconium halide, palladium halide, silver halide, cadmium halide, tin halide, barium halide, hafnium halide, tungsten halide, or the like.
  • the precursor is a diketone (e.g., acetylacetone, hexafluoroacetylacetone, or the like).
  • the precursor is lithium diketone, beryllium diketone, sodium diketone, magnesium diketone, aluminum diketone, silicon diketone, potassium diketone, calcium diketone, titanium diketone, vanadium diketone, chromium diketone, manganese diketone, iron diketone, cobalt diketone nickel diketone, copper diketone, zinc diketone, gallium diketone, germanium diketone, zirconium diketone, palladium diketone, silver diketone, cadmium diketone, tin diketone, barium diketone, hafnium diketone, tungsten diketone, lead diketone, or the like.
  • the precursor comprises mixtures or combinations of precursors.
  • mixtures of metal precursors are used to form metal alloy nanofibers.
  • metal alloy nanofibers are made from precursors that are alloys of metal.
  • Exemplary metal alloys include CdSe, CdTe, PbSe, PbTe, FeNi (perm alloy), Fe—Pt intermetallic compound, Pt—Pb, Pt—Pd, Pt—Bi, Pd—Cu, and Pd—Hf.
  • metal precursors used herein generally comprise a metal in association with a ligand.
  • Ligands are associated with the metal in any suitable way, such as through ionic, covalent, coordination complexes, conjugation, or any other suitable association.
  • precursor molecules do not have a high solubility in the fluid stock (e.g., optionally not a high solubility in an aqueous fluid stock).
  • a poor solubility of precursor may make it difficult to achive (a) an increased weight ratio of precursor in the fluid stock and (b) a substantially uniform distribution of precursor in the fluid stock.
  • the precursor is solubilized.
  • the precursor molecules comprise a metal atom in association with a solvating molecule (i.e., a ligand that improves the solubility and/or dispersibility of the metal precursor in the fluid medium, e.g., water).
  • the a first precursor may be added to a fluid (e.g., water), but forms a second precursor in the fluid (e.g., a solvate and/or an association with a polymer of the fluid stock).
  • a fluid e.g., water
  • the solvating molecule is substantially similar to the monomers of the polymer (e.g., ligand is acetate and polymer is polyvinyl acetate).
  • solubility and uniform distribution of the precursor is achieved by associating the solvating molecule to both the precursor and the polymer.
  • the solvating molecule is a ligand.
  • the ligand is suitable for solubilizing or improving the dispersibility of a metal, optionally in an aqueous solution, optionally in the fluid stock.
  • the present disclosure includes achieving a more uniform fluid stock by first solubilizing or distributing the precursor in a first solution.
  • the solvating molecule or ligand also improves the solubility or dispersibility of the precursor in a first fluid (e.g., dispersion or solution) (i.e., that is mixed with at least one second solution to make a fluid stock).
  • Some embodiments comprise solubilizing the precursor by associating a metal with a ligand, optionally complexing the metal with a ligand.
  • the precursor comprises a metal-ligand association (e.g., complex), as discussed herein.
  • the ligands are referred to herein as “molecules” in association with the metal.
  • the association between the metal and ligand or molecules is optionally being a chemical bond (e.g., covalent bond), ionic bond, conjugation, or coordination complex.
  • the precursor is a metal-ligand complex.
  • association between the solvating molecule or ligand and the precursor is any physical, chemical, or electromagnetic force known in the art of chemistry.
  • An example of an association is a chemical bond.
  • bonds are covalent bonds, non-covalent bonds, ionic bonds, hydrogen bonds, and the like.
  • Further examples of associations are hydrophilic interactions and hydrophobic interactions.
  • the skilled practitioner will be aware of many other types of interactions or associations that may be employed such as a Lewis acid-Lewis base interaction between the precursor and the solvating molecule or ligand.
  • the ligand is generally the “Lewis base”, meaning that it furnishes an electron pair to share with a Lewis acid.
  • the association is a metal-ligand coordination complex.
  • Metal-ligand coordination complexes are also known as “metal complexes” or “chelation complexes”. These complexes generally include a central atom or ion (usually metallic), bonded to a surrounding array of molecules or anions, which in turn are known as ligands or complexing agents. In nature, most compounds containing metals consist of coordination complexes. The association between the metal and ligand is strong or weak in various embodiments.
  • ligands per metal atom there are any suitable number of ligands per metal atom (e.g., optionally a number suitable to solvate, i.e., increase solubility or dispersibility of, the metal).
  • the number of ligands per metal atom is referred to as the “coordination number”.
  • the coordination numbers is between two and nine (for ML b compounds, the coordination number is b). Large numbers of ligands are not uncommon for the lanthanides and actinides.
  • the number of bonds depends on the size, charge, and electron configuration of the metal ion and the ligands.
  • Metal ions may have more than one coordination number (e.g., depending on oxidation state of the metal).
  • the precursor is essentially saturated with ligand.
  • it may be determined that the precursor is substantially saturated when no more ligand complexes with the metal precursor at successively higher amounts of ligand or at successively longer times.
  • the ligand is acetate.
  • the precursor molecules are metal acetates and the polymer is polyvinyl acetate.
  • the precursor molecules are metal acetates and the polymer is polyvinyl alcohol.
  • a precursor described herein comprises one or more ligand selected from the group consisting of ketones, diketones (e.g., a 1,3-diketone, such as ROCCHR′COR group, wherein R is an alkyl, substituted alkyl, aryl, substituted aryl and R′ is R or H), carboxylates (e.g., acetate or —OCOR group, wherein each R is independently an alkyl, substituted alkyl, aryl, substituted aryl), halides, nitrates, amines (e.g., NR′ 3 , wherein each R′′ is independently R or H or two R′′, taken together form a heterocycle or heteroaryl), and combinations thereof.
  • ketones e.g., a 1,3-diketone, such as ROCCHR′COR group, wherein R is an alkyl, substituted alkyl, aryl, substituted aryl and R′ is R or H
  • carboxylates
  • iodide bromide, sulfide (e.g., —SR), thiocyanate, chloride, nitrate, azide, fluoride, hydroxide, oxalate, water, nitrite (e.g., RN 3 ), isothiocyanate, acetonitrile, pyridine, ammonia, ethylenediamine, 2,2′-bipyridine, 1,10-phenanthroline, nitrite, triphenylphosphate, cyanide, carbon monoxide, or alko-oxide.
  • the precursor is a metal complex such as metal acetate, metal halide (e.g., metal chloride), metal nitrate, or metal alko-oxide (e.g., methoxide or ethoxide).
  • metal and/or ceramic precursors are metal atoms associated (complexed) with a ligand.
  • Exemplary metal and/or ceramic precursors include nickel acetate, copper acetate, iron acetate, nickel nitrate, copper nitrate, iron alko-oxide, and the like.
  • the present disclosure also encompasses the use of combinations of ligands.
  • a first ligand imparts increased solubility to the precursor, while a second ligand preferentially associates with the polymer.
  • a polymer described herein is a polymer (e.g., homopolymer or copolymer) comprising a plurality of reactive sites.
  • the reactive sites are nucleophilic (i.e., a nucleophilic polymer) or electrophilic (i.e., an electrophilic polymer).
  • a nucleophilic polymer described herein comprises a plurality of alcohol groups (such as polyvinyl alcohol—PVA—or a cellulose), ether groups (such as polyethylene oxide—PEO—or polyvinyl ether—PVE), and/or amine groups (such as polyvinyl pyridine, ((di/mono)alkylamino)alkyl alkacrylate, or the like).
  • alcohol groups such as polyvinyl alcohol—PVA—or a cellulose
  • ether groups such as polyethylene oxide—PEO—or polyvinyl ether—PVE
  • amine groups such as polyvinyl pyridine, ((di/mono)alkylamino)alkyl alkacrylate, or the like.
  • fluid stocks comprising and/or methods comprising electrospinning a fluid stock comprising a polymer.
  • the methods described herein optionally utilize an aqueous fluid stock.
  • a water-based process is desirable, for instance if one wants to avoid potential health, environmental, or safety problems associated with organic solvents.
  • the fluid stock is homogenous (e.g., which comprises a water-soluble polymer).
  • polymers used in the compositions and processes described herein are hydrophilic polymers, including water-soluble and water swellable polymers.
  • the polymer is soluble in water, meaning that it forms a solution in water.
  • the polymer is swellable in water, meaning that upon addition of water to the polymer the polymer increases its volume up to a limit.
  • Water soluble or swellable polymers are generally at least somewhat hydrophilic.
  • Exemplary polymers suitable for the present methods include but are not limited to polyvinyl alcohol (“PVA”), polyvinyl acetate (“PVAc”), polyethylene oxide (“PEO”), polyvinyl ether, polyvinyl pyrrolidone, polyglycolic acid, hydroxyethylcellulose (“HEC”), ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate, and the like.
  • PVA polyvinyl alcohol
  • PVAc polyvinyl acetate
  • PEO polyethylene oxide
  • polyvinyl ether polyvinyl pyrrolidone
  • polyglycolic acid polyglycolic acid
  • HEC hydroxyethylcellulose
  • ethylcellulose cellulose ethers
  • polyacrylic acid polyisocyanate
  • polyisocyanate polyacrylic acid
  • the polyisocyanate and the like.
  • the polymer is isolated from biological material.
  • the polymer is starch, chitosan
  • the polymer imparts a suitable elongational viscosity to the fluid stock for electrospinning nanofibers.
  • low shear viscosity leads to beaded nanofibers.
  • uniform distribution of the precursor in the fluid feed helps to maintain a suitably high elongational viscosity.
  • Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. Viscosity is measured in units of poise. In various embodiments, the viscosity of the polymer or fluid stock is measured with or without associated precursor. The polymer or fluid stock has any suitable elongational viscosity. In some embodiments, the polymer or fluid stock has an elongational viscosity of about 10 poise, 50 poise, about 100 poise, about 200 poise, about 300 poise, about 400 poise, about 500 poise, about 600 poise, about 800 poise, about 1000 poise, about 1500 poise, about 2000 poise, about 2500 poise, about 3000 poise, about 5,000 poise, and the like.
  • the polymer or fluid stock has an elongational viscosity of at least 50 poise, at least 100 poise, at least 200 poise, at least 300 poise, at least 400 poise, at least 500 poise, at least 600 poise, at least 800 poise, at least 1,000 poise, at least 1,500 poise, at least 2,000 poise, at least 2,500 poise, at least 3,000 poise, at least 5,000 poise, and the like.
  • the polymer or fluid stock has an elongational viscosity of at most 50 poise, at most 100 poise, at most 200 poise, at most 300 poise, at most 400 poise, at most 500 poise, at most 600 poise, at most 800 poise, at most 1,000 poise, at most 1,500 poise, at most 2,000 poise, at most 2,500 poise, at most 3,000 poise, at most 5,000 poise, and the like. In some embodiments, the polymer or fluid stock has an elongational viscosity of between about 100 and 3,000 poise, or between about 1,000 and 5,000 poise, and the like.
  • Molecular weight is related to the mass of the monomers comprising the polymer and the degree of polymerization. In some embodiments, molecular weight is a factor that affects viscosity.
  • the polymer has any suitable molecular weight. In some embodiments, the polymer has a molecular weight of at least 20,000 atomic mass units (“amu”), at least 50,000 amu, at least 100,000 amu, at least 200,000 amu, at least 300,000 amu, at least 400,000 amu, at least 500,000 amu, at least 700,000 amu, or at least 1,000,000 amu and the like.
  • the polymer has a molecular weight of at most 20,000 amu, at most 50,000 amu, at most 100,000 amu, at most 200,000 amu, at most 300,000 amu, at most 400,000 amu, at most 500,000 amu, at most 700,000 amu, or at most 1,000,000 amu and the like. In some embodiments, the polymer has a molecular weight of about 20,000 amu, about 50,000 amu, about 100,000 amu, about 200,000 amu, about 300,000 amu, about 400,000 amu, about 500,000 amu, about 700,000 amu, or about 1,000,000 amu and the like.
  • the polymer has a molecular weight of from about 50,000 amu to about 1,00,000 amu, from about 100,000 amu to about 500,000 amu, from about 200,000 amu to about 400,000 amu, or from about 500,000 amu to about 1,00,000 amu and the like.
  • the polydispersity index (“PDI”) is a measure of the distribution of molecular mass in a given polymer sample.
  • the PDI is the weight average molecular weight divided by the number average molecular weight, which is calculated by formula known to those skilled in the art of polymer science.
  • the polymer has any suitable polydispersity index.
  • the polymer has a polydispersity index of about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 15, about 20, and the like.
  • the polymer has a polydispersity index of at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 15, at least 20, and the like.
  • the polymer has a polydispersity index of at most 1, at most 2, at most 3, at most 4, at most 5, at most 6, at most 7, at most 8, at most 9, at most 10, at most 15, at most 20, and the like. In some embodiments, the polymer has a polydispersity index of about 1 to about 10, about 2 to about 5, and the like.
  • the present disclosure includes polymers, includes polymers having the characteristic herein disclosed, includes polymers prepared according to the methods herein disclosed, includes polymers preparable by the methods herein disclosed, includes polymers incorporating the precursor herein disclosed, and includes polymers suitable for the methods and systems herein disclosed.
  • the present disclosure also includes methods for using the polymers, and the like.
  • the fluid stock comprises mixtures or combinations of polymers.
  • a first polymer binds to a first precursor and a second polymer binds to a second precursor (e.g., to form a composite nanofiber following treatment of the precursor nanofiber).
  • a first polymer associates with a high amount of precursor and a second polymer is chosen to create high quality nanofibers when electrospun (e.g., elongational viscosity).
  • the fluid stock includes a high-precursor loading polymer and a highly spinnable polymer.
  • the fluid stock comprises co-polymers including block co-polymers.
  • the co-polymer comprises at least one vinylalcohol, vinylpyrrolidone, vinylacetate, ethylene oxide, dimethylacrylamide, and/or polyacrylamide block.
  • the various blocks of the co-polymer associate with different precursors.
  • a first polymer block associates with nickel precursor and a second polymer block associates with iron precursor (e.g., to form a composite nanofiber following treatment of a precursor nanofiber that has nano-domains of nickel interspersed with nano-domains of iron corresponding to the distribution of the blocks of their respective polymer associations).
  • such a nanofiber has different properties than a nickel-iron alloy nanofiber (i.e., where the nickel and iron are substantially uniformly mixed on the molecular level).
  • a nanocomposite nanofiber comprising a first material and a second material.
  • the first material is a continuous matrix material.
  • the second material makes up discrete, isolated domains of the nanofiber (e.g., on the surface of the nanofiber).
  • the first material is a ceramic or metal oxide (e.g., forming a continuous matrix).
  • the second material is a metal.
  • the polymer is removed from the nanofiber following electrospinning (e.g., by the calcination methods herein disclosed). In some embodiments, calcination degrades the polymer. In some embodiments, the fluid stock comprises degradable polymers (e.g., polymers removable by the calcination methods herein disclosed). The polymer is optionally degraded or removed by any suitable means including, but not limited to thermal degradation, chemical degradation, sublimation, evaporation, and the like. In some embodiments, lower molecular weight polymers are easier to remove by evaporation or sublimation.
  • associating the precursor with the polymer achieves at least one of a high proportion of precursor in the fluid stock and a uniform distribution of precursor in the fluid stock. In some instances the association reduces the amount of voids or defects in the nanofiber. In some embodiments, associating the precursor with the polymer increases the solubility of one or more of the precursor and the polymer in the fluid stock.
  • the present disclosure encompasses precursor in association with polymer and encompasses methods for associating precursor with polymer.
  • a moiety (e.g., a hydroxyl, amine, ether, etc.) of the polymer may displace and replace a ligand of the precursor (i.e., converting a first precursor to a second precursor).
  • a moiety of the polymer may react directly with the ligand (e.g., a nucleophilic group of a polymer may react with an electrophilic group of the ligand, or vis versa).
  • FIG. 2A illustrates one mechanism by which a polymer may be associated with a precursor.
  • the precursor associates with the polymer in the fluid stock.
  • the process described herein utilizes an association of the precursor with the polymer to provide a fluid stock wherein precursor is uniformly distributed in the fluid stock.
  • the fluid stock remains a solution or substantially uniform dispersion (e.g., in part because the precursor associates with the polymer in the fluid stock).
  • the association is a physical, chemical, or electromagnetic force between the precursor and the polymer. Examples of associations are chemical bonds. Examples of bonds are covalent bonds, non-covalent bonds, ionic bonds, hydrogen bonds, and the like. Further examples of associations are hydrophilic interactions and hydrophobic interactions. Other types of suitable interactions or associations are a Lewis acid-Lewis base interaction between the precursor and the polymer. In some embodiments, the association is a metal-ligand complex.
  • the monomers along the polymer chain provide sites to which precursor associates.
  • these sites are chemical groups including but not limited to hydroxyl groups, carbonyl groups, aldehyde groups, esters, amines, coarboxyamide, imines, nitrates and the like.
  • groups contain hydrocarbons, halogens, oxygen, nitrogen, sulfur, phosphorus and the like. Those skilled in the art will be familiar with chemical groups. Chemical groups are also known as “functional groups”.
  • precursors associate with chemical groups on the polymer through chemical bonds.
  • the polymer comprises a plurality of moieties. In some embodiments, these moieties are chemical groups, optionally chemical groups of the monomers bound along the polymer chain. In some embodiments, the moieties complex or bind with precursors, including metals. In some embodiments, the moieties displace the ligand of a metal-ligand precursor. In some embodiments, the polymer includes on average at least 100 functional groups, chemical groups, or moieties per polymer molecule that are capable of associating with a precursor (e.g., optionally with a metal precursor).
  • the precursors are iron acetates (a metal ligand complex) and the polymer is polyvinyl alcohol.
  • the moiety or functional group is an alcohol group.
  • the polymer has a plurality of alcohol groups along its backbone suitable for associating with the iron acetate.
  • the acetate either binds to the alcohol groups while still being complexed with the iron, or the alcohol groups displace the acetate ligand and associate directly with the iron.
  • the amount of precursor associated or loaded onto the polymer is high. In some embodiments, higher loading is related to the number of functional groups in the polymer (which depends in part on the molecular weight of the polymer and concentration of the functional groups). In some instances, more functional groups provide more sites for precursor to associate, thereby enabling higher precursor loading.
  • the quantity of precursor associated with the polymer is determined at least in part by the number of ligands per precursor. In some embodiments, more ligands per metal increase the probability of a ligand associating with a functional group on the polymer. In one example, there are three acetate ligands per aluminum in the precursor.
  • the polymer is essentially saturated with precursor molecules, meaning that substantially no more precursors will associate with the polymer.
  • the saturation is determined by adding an excess of precursor to the polymer, separating the polymer from the precursor and determining what quantity of precursor bound to the polymer. The amount of precursor is measured using any suitable technique known in the art of analytical chemistry. In some instances, following separation, the practitioner determines the amount of unassociated precursor, the amount precursor associated with the polymer, or both the amount of unassociated precursor and the amount precursor associated with the polymer. Tests of this nature are conducted with progressively more precursor added to the fluid stock until no more precursor binds to the polymer, indicating that the precursor is present in excess amount and the polymer is saturated.
  • measurements are conducted over progressively longer time periods of contact between the precursor and the polymer to verify that no more precursor associates with the polymer at longer times, and the polymer is saturated with precursor.
  • Another suitable method for determining saturation is to calculate the stoichiometry of the association. For example in some instances, one compares the moles of chemical groups on the polymer in the fluid stock and the moles of precursor molecules associated with those functional groups. If one precursor associates with one chemical group, the polymer is saturated when the moles of precursor is substantially equal to the moles of chemical groups.
  • the polymer is saturated with precursor up to any suitable level.
  • various samples of polymer have a distribution of precursor saturation levels. Individual polymer samples accordingly exceed or fall short of the average precursor saturation.
  • the polymer is on average less than 100% saturated with precursor.
  • the polymer is on average at least 20%, at least at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% saturated.
  • the polymer is on average between about 50% and 100%, between about 70% and 100%, between about 90% and 100%, between about 50% and 90%, between about 60% and 80%, or between about 20% and 50% saturated.
  • a polymer type e.g., PVA
  • PVA polymer type
  • reference to PVA includes reference to unassociated polymer of the P—OH type (including partially or completely ionized forms), and the associated P—O-ML b-1 type (wherein the reference to “PVA” refers to the P—O portion and the ML b-1 refers to a precursor that may be present to the exclusion of ML b or in addition to ML b , depending on the extent to which the ML b precursor is loaded upon or associated with the PVA).
  • nanofibers e.g., nanofibers having any one or more of the characteristics herein disclosed, nanofibers prepared according to the methods described herein, and nanofibers preparable by the methods described herein. Also provided herein are processes for using the nanofibers, devices comprising the nanofibers and the like.
  • the nanofibers have few defects and/or voids.
  • a voids and defects in the nanofiber include breaks in the nanofiber, regions of nanofiber wherein the diameter is so narrow as to be easily broken (e.g., having a diameter of less than 10% or less than 5% of the average nanofiber diameter), regions of the nanofiber wherein the nanofiber material has anomalous morphologies (e.g., crystalline domains in a substantially amorphous nanofiber—such crystalline domains may increase fracturing and brittleness of the nanofiber), and the like.
  • the nanofibers have fewer defects and/or voids, wherein the number of defects and/or voids in the nanofiber is in comparison to a nanofiber not produced by the methods of the disclosure (for example with a low loading of precursor).
  • a metal nanofiber provided herein comprises about 99.99%, about 99.95%, about 99.9%, about 99%, about 98%, about 97%, about 96%, about 95%, about 90%, about 80%, and the like of metal by mass.
  • the metal nanofiber comprises at least about 99.99%, at least about 99.95%, at least about 99.9%, at least about 99%, at least about 98%, at least about 97%, at least about 96%, at least about 95%, at least about 90%, at least about 80%, and the like of metal by mass (e.g., elemental mass).
  • metal nanofibers provided herein comprise at least 50%, at least 60%, at least 70%, or at least 75% metal by mass (e.g., elemental mass).
  • metal nanofibers provided herein comprise at least 80% metal by mass.
  • metal nanofibers provided herein comprise at least 90% metal by mass.
  • metal nanofibers provided herein comprise at least 95% metal by mass.
  • metal nanofibers provided herein comprise a continuous matrix of crystalline metal.
  • the continuous matrix of crystalline metal with few or no defects, provides for improved performance of the metal nanofibers (e.g., improved electrical conductivity).
  • the metal nanofibers comprise a single metal. In other embodiments, the metal nanofibers comprise two or more metals. In some embodiments, provided herein are metal nanofibers comprising two or more metals and the metals are in the form of an alloy. In other embodiments, provided herein are metal nanofibers comprising two or more metals and the metals are in the form of a composite (e.g., a layered hybrid nanofiber, a composite with distinct metal segments, a composite with a first metal that forms a continuous matrix and a second metal that is present in isolated domains within the nanofiber, or the like).
  • a composite e.g., a layered hybrid nanofiber, a composite with distinct metal segments, a composite with a first metal that forms a continuous matrix and a second metal that is present in isolated domains within the nanofiber, or the like.
  • metal nanofibers provided herein comprises less than 10% carbon by mass (e.g., elemental mass). In certain embodiments, metal nanofibers provided herein comprise less than 7% carbon by mass. In specific embodiments, metal nanofibers provided herein comprise less than 5% carbon by mass. In more specific embodiments, metal nanofibers provided herein comprise less than 3% carbon by mass. In still more specific embodiments, metal nanofibers provided herein comprise less than 1% carbon by mass. In some embodiments, metal nanofibers provided herein comprises less than 5% oxygen by mass (e.g., elemental mass). In certain embodiments, metal nanofibers provided herein comprise less than 3% oxygen by mass. In specific embodiments, metal nanofibers provided herein comprise less than 2% oxygen by mass. In more specific embodiments, metal nanofibers provided herein comprise less than 2% oxygen by mass. In still more specific embodiments, metal nanofibers provided herein comprise less than 0.5% oxygen by mass.
  • FIG. 15 illustrates the elemental analysis of nickel nanofibers prepared according to a process herein.
  • the nanofiber is observed to have high nickel content.
  • the elemental ratios of nickel to oxygen to carbon were about 64:1:0.25 in the dark region and 62:5:0.1 in the light region.
  • the metal is any metal, including: transition metal, alkali metal, alkaline earth metal, post-transition metal, lanthanide, or actinide.
  • Suitable transition metals include: scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium
  • Suitable alkali metals include: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr).
  • Suitable alkaline earth metals include: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
  • Suitable post-transition metals include: aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), lead (Pb), and bismuth (Bi).
  • Suitable lanthanides include the elements with atomic number 57 to 71 on the periodic table.
  • Suitable actinides include the elements with atomic number 89 to 103 on the periodic table.
  • the nanofiber is germanium (Ge), antimony (Sb) and polonium (Po), or silicon (Si).
  • germanium Ge
  • Sb antimony
  • Po polonium
  • Si silicon
  • certain methods for producing metal nanofibers are disclosed herein and optionally include calcination under reducing conditions.
  • nanofiber comprises an alkali metal. In further or alternative embodiments, the nanofiber comprises an alkaline earth metal. In certain embodiments, the nanofiber comprises a transition metal. In some embodiments, the nanofiber comprises a period IV transition metal. In certain embodiments, the nanofiber comprises a period V transition metal. In some embodiments, the nanofiber comprises a group XIII metal. In certain embodiments, nanofiber comprises is a group XIV metal. In certain embodiments, the nanofiber comprises a metalloid.
  • the nanofiber comprises lithium, beryllium, sodium, magnesium, aluminum, silicon, potassium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, zirconium, palladium, silver, cadmium, tin, barium, hafnium, tungsten, lead, combinations thereof, or the like.
  • the nanofiber comprises silicon.
  • FIGS. 3 , 5 , 7 , 8 , 12 , 22 , 23 , 26 , 27 , and 28 illustrate precursor and metal nanofibers provided herein and/or as prepared according to the processes described herein.
  • FIG. 3 illustrates nickel precursor nanofibers 301 having average diameters of 500-700 nm, and nickel nanofibers 302 , having average diameters of 400-500 nm, prepared from the nickel precursor nanofibers 301 after treatment at 600° C. for 2 hours in Argon.
  • FIG. 3 also illustrates the crystal x-ray diffraction pattern 303 of the nickel nanofibers 302 .
  • FIG. 3 illustrates the crystal x-ray diffraction pattern 303 of the nickel nanofibers 302 .
  • FIG. 5 illustrates copper precursor nanofibers 501 having average diameters of 600-800 nm, and copper nanofibers 502 , having average diameters of 300-500 nm, prepared from the copper precursor nanofibers 501 after treatment at 800° C. for 2 hours in a Argon/Hydrogen mixture.
  • FIG. 5 also illustrates the crystal x-ray diffraction pattern 503 of the copper nanofibers 502 .
  • FIG. 7 illustrates silver precursor nanofibers 701 having average diameters of 900-1200 nm, and silver nanofibers 702 , having average diameters of 600-800 nm, prepared from the silver precursor nanofibers 701 after treatment at 600° C. for 2 hours in air.
  • FIG. 7 also illustrates the crystal x-ray diffraction pattern 703 of the silver nanofibers 702 .
  • FIG. 8 illustrates iron precursor nanofibers 801 having average diameters of 300-600 nm, and iron nanofibers 802 , having average diameters of 200-500 nm, prepared from the iron precursor nanofibers 801 after treatment at 600° C. for 2 hours in argon.
  • FIG. 8 also illustrates the crystal x-ray diffraction pattern 803 of the iron nanofibers 802 .
  • FIG. 12 illustrates lead precursor nanofibers 1201 having average diameters of 500-1100 nm, and lead nanofibers 1202 , having average diameters of 250-700 nm, prepared from the lead precursor nanofibers 1201 after treatment at 600° C.
  • FIG. 12 also illustrates the crystal x-ray diffraction pattern 1203 of the lead nanofibers 1202 .
  • FIG. 13 illustrates nickel precursor nanofibers (Panel B) and nickel nanofibers (Panel D). Depending on the precursor loading (Panel A), based on the weight-to-weight ratio of nickel acetate and PVA combined into a fluid stock, different diameters of precursor nanofibers (Panel C) and metal nanofibers (Panel E) were obtained.
  • FIG. 14 also illustrates nickel nanofibers prepared from fluid stocks prepared from nickel acetate and PVA (Panel A illustrates the loading based on the weight-to-weight ratio of polymer-to-precursor).
  • FIG. 15 illustrates an elemental analysis of metal nanofibers prepared according to the instant disclosure.
  • FIGS. 22 and 23 illustrate metal alloy nanofibers prepared according to the instant disclosure.
  • FIG. 22 illustrates cadmium-selenium precursor nanofibers 2201 having average diameters of 300-1000 nm, and cadmium-selenium alloy nanofibers 2202 , having average diameters of 500-700 nm, prepared from the cadmium-selenium precursor nanofibers 2201 after treatment at 600° C. for 2 hours in argon.
  • FIG. 22 also illustrates the crystal x-ray diffraction pattern 2203 of the cadmium-selenium alloy nanofibers 2202 .
  • FIG. 23 illustrates lead-selenium precursor nanofibers 2301 having average diameters of 700-1300 nm, and lead-selenium alloy nanofibers 2302 , having average diameters of 600-900 nm, prepared from the lead-selenium precursor nanofibers 2301 after treatment at 600° C. for 2 hours in argon.
  • FIG. 23 also illustrates the crystal x-ray diffraction pattern 2303 of the lead-selenium alloy nanofibers 2302 .
  • FIG. 24 illustrates a more zoomed view of the cadmium-selenium and lead-selenium alloy nanofibers
  • FIG. 25 illustrates an elemental analysis of the lead-selenium alloy nanofibers.
  • FIG. 26 illustrates cadmium-tellurium precursor nanofibers 2601 having average diameters of 500-900 nm, and cadmium-tellurium alloy nanofibers 2602 , having average diameters of 300-650 nm, prepared from the cadmium-tellurium precursor nanofibers 2601 after treatment at 600° C. for 2 hours in argon.
  • FIG. 26 also illustrates the crystal x-ray diffraction pattern 2603 of the cadmium-tellurium alloy nanofibers 2602 .
  • FIG. 27 illustrates lead-tellurium precursor nanofibers 2701 having average diameters of 400-700 nm, and lead-tellurium alloy nanofibers 2702 , having average diameters of 300-550 nm, prepared from the lead-tellurium precursor nanofibers 2701 after treatment at 600° C. for 2 hours in argon.
  • FIG. 27 also illustrates the crystal x-ray diffraction pattern 2703 of the lead-tellurium alloy nanofibers 2702 .
  • FIG. 28 illustrates iron-nickel precursor nanofibers 2801 having average diameters of 600-1000 nm, and iron-nickel alloy nanofibers 2802 , having average diameters of 200-750 nm, prepared from the iron-nickel precursor nanofibers 2801 after treatment at 600° C. for 2 hours in an argon/hydrogen mixture.
  • FIG. 28 also illustrates the crystal x-ray diffraction pattern 2803 of the iron-nickel alloy nanofibers 2802 .
  • FIG. 29 illustrates TEM images for iron oxide
  • the ceramic nanofiber comprises about 99.99%, about 99.95%, about 99.9%, about 99%, about 98%, about 97%, about 96%, about 95%, about 90%, about 80%, and the like of ceramic by mass. In some embodiments, the ceramic nanofiber comprises at least about 99.99%, at least about 99.95%, at least about 99.9%, at least about 99%, at least about 98%, at least about 97%, at least about 96%, at least about 95%, at least about 90%, at least about 80%, and the like of ceramic by mass (e.g., elemental mass).
  • ceramic nanofibers provided herein comprise at least 50%, at least 60%, at least 70%, or at least 75% ceramic by mass (e.g., elemental mass). In specific embodiments, ceramic nanofibers provided herein comprise at least 80% ceramic by mass. In more specific embodiments, ceramic nanofibers provided herein comprise at least 90% ceramic by mass. In still more specific embodiments, ceramic nanofibers provided herein comprise at least 95% ceramic by mass.
  • the metal oxide nanofiber comprises about 99.9%, about 99%, about 98%, about 97%, about 96%, about 95%, about 90%, about 80%, and the like of ceramic by mass.
  • the metal oxide nanofiber comprises at least about at least about 99%, at least about 98%, at least about 97%, at least about 96%, at least about 95%, at least about 90%, at least about 80%, and the like of metal oxide by mass (e.g., elemental mass).
  • metal oxide nanofibers provided herein comprise at least 50%, at least 60%, at least 70%, or at least 75% metal oxide by mass (e.g., elemental mass). In specific embodiments, metal oxide nanofibers provided herein comprise at least 80% metal oxide by mass. In more specific embodiments, metal oxide nanofibers provided herein comprise at least 90% metal oxide by mass. In still more specific embodiments, metal oxide nanofibers provided herein comprise at least 95% metal oxide by mass. In some embodiments, metal oxide nanofibers provided herein comprise at least 80% metal and oxygen by mass. In more specific embodiments, metal oxide nanofibers provided herein comprise at least 90% metal and oxygen by mass. In still more specific embodiments, metal oxide nanofibers provided herein comprise at least 95% metal and oxygen by mass. In yet more specific embodiments, metal oxide nanofibers provided herein comprise at least 98% metal and oxygen by mass.
  • metal nanofibers provided herein comprises less than 10% carbon by mass (e.g., elemental mass). In certain embodiments, metal nanofibers provided herein comprise less than 7% carbon by mass. In specific embodiments, metal nanofibers provided herein comprise less than 5% carbon by mass. In more specific embodiments, metal nanofibers provided herein comprise less than 3% carbon by mass. In still more specific embodiments, metal nanofibers provided herein comprise less than 1% carbon by mass.
  • the ceramic of a nanofiber provided herein is a metal oxide.
  • Exemplary ceramics or metal oxides include but are not limited to Al 2 O 3 , ZrO 2 , Fe 2 O 3 , CuO, NiO, ZnO, CdO, SiO 2 , TiO 2 , V 2 O 5 , VO 2 , Fe 3 O 4 , SnO, SnO 2 , CoO, CoO 2 , Co 3 O 4 , HfO 2 , BaTiO 3 , SrTiO 3 , and BaSrTiO 3 .
  • Methods for producing ceramic (and/or metal oxide) nanofibers are disclosed herein and optionally include calcination under oxidizing conditions.
  • the metal of the metal oxide or ceramic is any metal, including: transition metal, alkali metal, alkaline earth metal, post-transition metal, lanthanide, or actinide.
  • Suitable transition metals include: scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (R
  • Suitable alkali metals include: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr).
  • Suitable alkaline earth metals include: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
  • Suitable post-transition metals include: aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), lead (Pb), and bismuth (Bi).
  • Suitable lanthanides include the elements with atomic number 57 to 71 on the periodic table.
  • Suitable actinides include the elements with atomic number 89 to 103 on the periodic table.
  • the metal of the metal oxide is a metalloid, such as, germanium (Ge), antimony (Sb) and polonium (Po), or silicon (Si).
  • a metalloid such as, germanium (Ge), antimony (Sb) and polonium (Po), or silicon (Si).
  • certain methods for producing ceramic or metal oxide nanofibers are disclosed herein and optionally include calcination under oxidizing conditions.
  • nanofiber comprises an oxide of or ceramic comprising an alkali metal. In further or alternative embodiments, the nanofiber comprises an oxide of or ceramic comprising an alkaline earth metal. In certain embodiments, the nanofiber comprises a transition metal. In some embodiments, the nanofiber comprises an oxide of or ceramic comprising a period IV transition metal. In certain embodiments, the nanofiber comprises an oxide of or ceramic comprising a period V transition metal. In some embodiments, the nanofiber comprises an oxide of or ceramic comprising a group XIII metal. In certain embodiments, nanofiber comprises an oxide of or ceramic comprising is a group XIV metal. In certain embodiments, the nanofiber comprises an oxide of or ceramic comprising a metalloid.
  • the nanofiber comprises an oxide of or ceramic comprising aluminum, silicon, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, zirconium, cadmium, tin, barium, hafnium, tungsten, lead, combinations thereof, or the like.
  • the oxide is not an oxide of silicon, zirconium, or aluminum.
  • the oxide is an oxide of silicon, zirconium, or aluminum, and further comprises an additional material (e.g., a metal, metal alloy, or the like), such as in a composite material (e.g., a layered hybrid nanofiber, a composite with distinct segments, a composite with a first material that forms a continuous matrix and a second material that is present in isolated domains within the nanofiber—e.g., wherein the oxide is the matrix material, or the like).
  • a composite material e.g., a layered hybrid nanofiber, a composite with distinct segments, a composite with a first material that forms a continuous matrix and a second material that is present in isolated domains within the nanofiber—e.g., wherein the oxide is the matrix material, or the like).
  • the ceramic and metal oxide nanofibers comprise a single metal type. In other embodiments, the ceramic and metal oxide nanofibers comprise a two or more metal types (e.g., BaTiO3, SrTiO3, BaSrTiO3 (e.g., Ba0.55Sr0.45TiO3), and the like). In some embodiments, provided herein are ceramic and metal oxide nanofibers comprising two or more metal types together form a multi-metal oxide or in an ordered alloy type crystalline lattice.
  • the two or more metal types form separate oxide materials in an amorphous mixture, in a composite (e.g., a layered hybrid nanofiber, a composite with distinct oxide segments, a composite with a first material that forms a continuous matrix and a second material that is present in isolated domains within the nanofiber, or the like), or the like.
  • a composite e.g., a layered hybrid nanofiber, a composite with distinct oxide segments, a composite with a first material that forms a continuous matrix and a second material that is present in isolated domains within the nanofiber, or the like
  • FIGS. 4 , 6 , 9 , 10 , and 11 illustrate metal precursor and metal oxide (e.g., metal oxide ceramic) nanofibers provided herein and/or as prepared according to the processes described herein.
  • FIG. 4 illustrates nickel precursor nanofibers 401 having average diameters of 500-700 nm, and nickel oxide nanofibers 402 , having average diameters of 300-500 nm, prepared from the nickel precursor nanofibers 401 after treatment at 600° C. for 2 hours in air.
  • FIG. 4 also illustrates the crystal x-ray diffraction pattern 403 of the nickel oxide nanofibers 402 .
  • FIG. 6 illustrates copper precursor nanofibers 601 having average diameters of 600-800 nm, and copper oxide nanofibers 602 , having average diameters of 200-600 nm, prepared from the copper precursor nanofibers 601 after treatment at 600° C. for 2 hours in air.
  • FIG. 6 also illustrates the crystal x-ray diffraction pattern 603 of the copper oxide nanofibers 602 .
  • FIG. 9 illustrates zinc precursor nanofibers 901 having average diameters of 500-1000 nm, and zinc oxide nanofibers 902 , having average diameters of 400-700 nm, prepared from the zinc precursor nanofibers 901 after treatment at 600° C. for 2 hours in air.
  • FIG. 9 illustrates zinc precursor nanofibers 901 having average diameters of 500-1000 nm, and zinc oxide nanofibers 902 , having average diameters of 400-700 nm, prepared from the zinc precursor nanofibers 901 after treatment at 600° C. for 2 hours in air.
  • FIG. 9 also illustrates the crystal x-ray diffraction pattern 903 of the zinc oxide nanofibers 902 .
  • FIG. 10 illustrates cadmium precursor nanofibers 1001 having average diameters of 800-1200 nm, and cadmium oxide nanofibers 1002 , having average diameters of 600-900 nm, prepared from the cadmium precursor nanofibers 1001 after treatment at 800° C. for 2 hours in air.
  • FIG. 10 also illustrates the crystal x-ray diffraction pattern 1003 of the cadmium oxide nanofibers 1002 .
  • FIG. 10 illustrates cadmium precursor nanofibers 1001 having average diameters of 800-1200 nm, and cadmium oxide nanofibers 1002 , having average diameters of 600-900 nm, prepared from the cadmium precursor nanofibers 1001 after treatment at 800° C. for 2 hours in air.
  • FIG. 10 also illustrates the crystal x-ray diffraction pattern 1003 of the cadmium oxide nano
  • FIG. 11 illustrates zirconium precursor nanofibers 1101 having average diameters of 800-1000 nm, and zirconia nanofibers 1102 , having average diameters of 300-600 nm, prepared from the zirconium precursor nanofibers 1101 after treatment at 800° C. for 2 hours in air.
  • FIG. 11 also illustrates the crystal x-ray diffraction pattern 1103 of the zirconia nanofibers 1102 .
  • the metal alloy is any suitable metal alloy including: transition metal, alkali metal, alkaline earth metal, post-transition metal, lanthanide, or actinide, additionally, germanium (Ge), antimony (Sb) and polonium (Po), and silicon (Si).
  • the alloy is a metal-metal alloy. In other embodiments, the alloy is a metal-non-metal alloy.
  • metal-metal alloys are prepared by utilizing a first metal precursor, a second metal precursor, and optional further metal precursors in a fluid stock in a process described herein described herein (e.g., evenly dispersing the at least two metal precursors), wherein the first and second metal precursors comprise different metals.
  • metal-non-metal alloys are prepared by utilizing a metal precursor and a non-metal stock (e.g., powder of the non-metal material) in a fluid stock in a process described herein described herein (e.g., evenly dispersing the metal precursor and the non-metal stock in the fluid stock), wherein the first and second metal precursors comprise different metals.
  • metal alloys optionally comprise any metal discussed above for metal nanofibers (as the metal alloy nanofibers discussed are considered within the scope of metal nanofibers for the purposes of this disclosure).
  • any suitable non-metal material such as boron, carbon, phosphorus, sulfur, selenium, or the like, may be utilized.
  • FIG. 25 illustrates a lead selenium metal-non-metal alloy prepared according to the disclosure provided herein.
  • metal alloy nanofibers comprising metal alloy, or nanofibers substantially comprised of metal alloy.
  • the metal alloy nanofiber comprises about 99%, about 98%, about 97%, about 96%, about 95%, about 90%, about 80%, and the like of metal alloy by mass.
  • the metal alloy nanofiber comprises at least about 99%, at least about 98%, at least about 97%, at least about 96%, at least about 95%, at least about 90%, at least about 80%, and the like of ceramic by mass (e.g., elemental mass).
  • metal alloy nanofibers provided herein comprise at least 50%, at least 60%, at least 70%, or at least 75% metal alloy by mass (e.g., elemental mass). In specific embodiments, metal alloy nanofibers provided herein comprise at least 80% metal alloy by mass. In more specific embodiments, metal alloy nanofibers provided herein comprise at least 90% metal alloy by mass. In still more specific embodiments, metal alloy nanofibers provided herein comprise at least 95% metal alloy by mass.
  • the metal alloy nanofibers comprise low amounts of carbon and/or oxygen as discussed herein for metal nanofibers.
  • the metal-non metal alloy is a metal-carbon alloy
  • at least 50%, at least 60%, at least 70%, or at least 75% metal and carbon by mass e.g., elemental mass.
  • metal alloy nanofibers provided herein comprise at least 80% metal and carbon by mass.
  • metal alloy nanofibers provided herein comprise at least 90% metal and carbon by mass.
  • metal alloy nanofibers provided herein comprise at least 95% metal and carbon by mass.
  • Exemplary metal alloys include, but are not limited to CdSe, CdTe, PbSe, PbTe, FeNi (perm alloy), Fe—Pt intermetallic compound, Pt—Pb, Pt—Pd, Pt—Bi, Pd—Cu, and Pd—Hf.
  • Methods for producing metal alloy nanofibers are disclosed herein and optionally include electrospinning a fluid stock comprising a mixture of the metal precursors of the alloy and calcinating under reducing conditions.
  • a CdSe alloy nanofiber is produced by electrospinning a fluid stock comprising a mixture of cadmium acetates and selenium acetates, followed by calcinating under reducing conditions.
  • a nanofiber of virtually any material is produced using the methods described herein (e.g., as long as the material is convertible from suitable precursors distributed substantially evenly and in a high proportion of the fluid stock).
  • the nanofiber is a calcium phosphate (Ca—P) nanofiber.
  • the methods of the present disclosure produce high quality Ca—P nanofibers, optionally wherein the nanofiber is at least 50 ⁇ m long on average.
  • the methods of the present disclosure are combined with other methods to produce yet more embodiments.
  • the nanofibers undergo further modifications following their synthesis.
  • biologically functional additives are added to calcium phosphate nanofibers for culturing bone and dental cells or as implants to treat bone, dental or periodontal diseases and defects.
  • the nanofibers are surface-modified.
  • enzymes are immobilized on the nanofiber surface to create a biological catalyst.
  • doping processes from the semiconductor industry are employed to introduce impurities into a pure semiconductor nanofiber (e.g., for the purpose of modulating its electrical properties).
  • a nanofiber comprising a segment comprising a continuous matrix of a metal, a metal oxide, a metal alloy, a ceramic, or a combination thereof.
  • a continuous matrix is conductive from one end of the segment to the other end of the segment.
  • a continuous matrix defines a single unified volume of the metal, metal oxide, metal alloy, ceramic, or a combination thereof.
  • the metal, metal oxide, metal alloy, ceramic, or a combination thereof is in contact with metal, metal oxide, metal alloy, ceramic, or a combination thereof all along the length of the continuous matrix.
  • the segment or plurality of segments comprise any suitable proportion of the nanofiber, including about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, and the like of the length of the nanofiber.
  • the segment or segments comprise at most 5%, at most 10%, at most 20%, at most 30%, at most 40%, at most 50%, at most 60%, at most 70%, at most 80%, at most 90%, at most 95%, and the like of the length of the nanofiber.
  • the segment or segments comprise at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, and the like of the length of the nanofiber.
  • a continuous matrix described herein comprises less than half of the mass of the nanofiber, but forms the continuous matrix that runs along the length of the nanofiber. In some instances, the continuous matrix runs along at least 50% the length of the nanofiber (e.g., on average for populations of nanofibers). In specific instances, the continuous matrix runs along at least 70% the length (e.g., on average) of the nanofiber(s).
  • the continuous matrix runs along at least 80% the length (e.g., on average) of the nanofiber(s). In still more specific embodiments, the continuous matrix runs along at least 90% of the length (e.g., on average) of the nanofiber(s). In yet more specific embodiments, the continuous matrix runs along at least 95% of the length (e.g., on average) of the nanofiber(s).
  • Previous methods for producing nanofibers do not generally produce nanofibers of a high enough quality to be any form other than a solid monolithic cylinder.
  • the number and size of voids and defects in nanofibers are substantially reduced, allowing more complex geometries such as hollow nanofibers and composite or hybrid nanofibers made of more than one material.
  • the hybrid or hollow nanofibers are suitably long and continuous (i.e., high quality).
  • a composite nanofiber comprising a first material and a second material.
  • at least one or both of the first and second materials comprise a metal or metal oxide (e.g., metal oxide ceramic).
  • the first material forms a continuous matrix of the nanofiber.
  • the first material is a metal, a ceramic, or carbon.
  • the first material is a metal or carbon and the second material is a metal, metal oxide (e.g., metal oxide ceramic), or ceramic.
  • the first material is a ceramic and the second material is a metal, metal oxide, or ceramic.
  • the first material is a ceramic and the second material is a metal.
  • the first material forms a continuous matrix and the second material forms isolated domains within the nanofiber.
  • both the first and second materials form continuous matrices within the nanofiber (e.g., a layered hybrid nanofiber, such as a layered hybrid nanofiber formed via coaxial electrospinning—a layered coaxial hybrid nanofiber).
  • the first and second materials form different (e.g., alternating) segments of the nanofiber (i.e., alternating segments along the length of the nanofiber).
  • hybrid nanofibers are useful in flexible solar cells for example.
  • “Hybrid” is used interchangeably with “composite” and means that the nanofiber comprises at least two materials. The materials are found in distinct locations on or in the nanofiber. Such locations are arranged in any suitable geometric matter.
  • One exemplary geometry is a fiber with various annular rings or layers made of different materials.
  • each layer is coaxial.
  • coaxial hybrid nanofibers are produced by the methods described herein (e.g., comprising at least two layers—one of which may form a core of the nanofiber, the other a layer at least partially surrounding the core).
  • the spinneret is modified to comprise a first conduit containing a first fluid stock surrounded by a second conduit containing a second fluid stock ( FIG. 35 ).
  • the fluid stocks are drawn or forced through the conduits.
  • Such a configuration produces an annular fluid jet with the second fluid stock surrounding the first fluid stock.
  • the first and second fluid stocks do not substantially mix, so are converted into different materials in the nanofiber.
  • a hybrid nanofiber e.g., including a coaxial nanofiber
  • various layers are any material suitable.
  • the coaxial layers are referred to in any manner unless the context clearly indicates otherwise.
  • the first layer may surround the second layer or the second layer may surround the first layer.
  • the first coaxial layer comprises a ceramic.
  • the second coaxial layer comprises a ceramic.
  • the first coaxial layer comprises a metal.
  • the second coaxial layer comprises a metal.
  • the hybrid nanofiber is metal-on-metal, ceramic-on-metal, ceramic-on-ceramic, or metal-on-ceramic.
  • the hybrid nanofiber has at least 3 components, including any integer with all types of materials in all types of combinations.
  • composite nanofibers comprise metal, metal oxide, and/or ceramic, as disclosed herein.
  • the metals, metal oxides, and/or ceramics used in such composite nanofibers include any such metals, metal oxides, or ceramics described herein for metal (e.g., single metal or alloys), metal oxide (e.g., metal oxide ceramics), and ceramic nanofibers.
  • a metal like Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, Al is hybridized with a ceramic like Al 2 O 3 , ZrO 2 , Fe 2 O 3 , CuO, MO, ZnO, CdO, SiO 2 , TiO 2 , V 2 O 5 , VO 2 , Fe 3 O 4 , SnO, SnO 2 , CoO, CoO 2 , CO 3 O 4 , HfO 2 , BaTiO 3 , SrTiO 3 , BaSrTiO 3 .
  • a first co-axial layer comprises Ni or Fe.
  • a second co-axial layer comprises Al 2 O 3 , ZrO 2 , SiO 2 or TiO 2 .
  • a first co-axial layer comprises Ni and a second co-axial layer comprises ZrO 2 .
  • a first coaxial layer comprises Al 2 O 3
  • a second co-axial layer comprises ITO.
  • a first coaxial layer comprises ZrO 2 and a second co-axial layer comprises ZnO.
  • a first and a second material are disposed along different parts of the length of the nanofiber.
  • such a nanofiber is produced by alternating the fluid stock between a first fluid stock comprising a first material and a second fluid stock comprising a second material in the electrospinning process.
  • a nanofiber upon calcination a nanofiber is produced that alternates along its length between a first material and a second material.
  • the first and second materials are any suitable material, including ceramics and metals.
  • a composite nanofiber comprises a metal-metal hybrid, a metal-ceramic hybrid, or the like.
  • the nanofiber is a hybrid of both metal and ceramic.
  • the mass percentages of the total mass of the metal and ceramic components of the nanofiber are added (to the extent that either or both are present) and comprise about 99.99%, about 99.95%, about 99.9%, about 99%, about 98%, about 97%, about 96%, about 95%, about 90%, about 80%, and the like of the nanofiber.
  • the sum of the metal and ceramic components of the nanofiber are at least about 99.99%, at least about 99.95%, at least about 99.9%, at least about 99%, at least about 98%, at least about 97%, at least about 96%, at least about 95%, at least about 90%, at least about 80%, and the like of the nanofiber.
  • the total mass of the metal and ceramic components (to the extent that either or both are present) comprise at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or the like. In some instances, these lower metal/ceramic content composite nanofibers are present nanofibers comprising a continuous matrix that is neither metal nor ceramic.
  • FIGS. 16-21 and 31 - 33 illustrate metal precursor and metal composite/hybrid nanofibers provided herein and/or as prepared according to the processes described herein.
  • FIG. 16 illustrates zirconium-zinc precursor nanofibers 1601 (i.e., nanofibers comprising zirconium precursor, zinc precursor, and polymer) having average diameters of 600-1000 nm, and zirconia-zinc oxide composite nanofibers 1602 , having average diameters of 300-600 nm, prepared from the precursor nanofibers 1601 after treatment at 600° C. for 2 hours in argon.
  • FIG. 16 also illustrates the crystal x-ray diffraction peaks for zirconia 1603 and zinc oxide 1604 for the composite nanofibers 1602 .
  • FIG. 17 illustrates zirconium-silver precursor nanofibers 1701 having average diameters of 700-900 nm, and zirconia-silver composite nanofibers 1702 , having average diameters of 400-700 nm, prepared from the precursor nanofibers 1701 after treatment at 800° C. for 2 hours in an argon/hydrogen mixture.
  • FIG. 17 also illustrates the crystal x-ray diffraction peaks for zirconia 1703 and silver 1704 for the composite nanofibers 1702 .
  • FIG. 18 illustrates zirconium-nickel precursor nanofibers 1801 having average diameters of 800-1200 nm, and zirconia-nickel composite nanofibers 1802 , having average diameters of 600-800 nm, prepared from the precursor nanofibers 1801 after treatment at 600° C. for 2 hours in argon.
  • FIG. 18 also illustrates the crystal x-ray diffraction peaks for zirconia 1803 and nickel 1804 for the composite nanofibers 1802 .
  • FIG. 19 illustrates zirconium-iron precursor nanofibers 1901 having average diameters of 600-1000 nm, and zirconia-iron composite nanofibers 1902 , having average diameters of 400-700 nm, prepared from the precursor nanofibers 1901 after treatment at 600° C.
  • FIG. 19 also illustrates the crystal x-ray diffraction peaks for zirconia 1903 and iron 1904 for the composite nanofibers 1902 .
  • FIG. 20 further illustrates TEM images for such nanocomposites.
  • FIG. 21 illustrates aluminum-nickel precursor nanofibers 2101 having average diameters of 400-1100 nm, and alumina-nickel composite nanofibers 2102 , having average diameters of 150-700 nm, prepared from the precursor nanofibers 2101 after treatment at 600° C. for 2 hours in argon.
  • FIG. 21 also illustrates the crystal x-ray diffraction peaks for nickel 2103 (and no peaks for the amorphous alumina) for the composite nanofibers 2102 .
  • FIG. 31 illustrates zirconium-nickel precursor nanofibers 3101 (nickel precursor+polymer core and zirconium precursor+polymer sheath) having average diameters of 450-700 nm, and zirconia-nickel layered composite nanofibers 3102 , having average diameters of 300-550 nm, prepared from the precursor nanofibers 3101 after treatment at 600° C. for 2 hours in argon.
  • FIG. 31 also illustrates the crystal x-ray diffraction peaks for zirconia and nickel 3103 for the layered (i.e., coaxial) composite nanofibers 3102 (nickel metal core and zirconia sheath).
  • FIG. 31 illustrates zirconium-nickel precursor nanofibers 3101 (nickel precursor+polymer core and zirconium precursor+polymer sheath) having average diameters of 450-700 nm, and zirconia-nickel layered composite nanofibers 3102 , having average diameters of 300-550 n
  • FIG. 32 illustrates TEM images for coaxial/layered layered nickel/zirconia nanofibers and FIG. 33 illustrates elemental analysis of coaxial/layered layered nickel/zirconia nanofibers.
  • Panel A of FIG. 33 illustrates a hybrid nanofiber comprising a zirconium oxide layer outside of a nickel layer (core).
  • Panel B of FIG. 33 illustrates the high content of zirconium and oxygen relative to nickel and carbon (in a ratio of about 18:32:4:2, respectively).
  • the present disclosure encompasses methods for producing hollow nanofibers, methods for using hollow nanofibers, devices incorporating hollow nanofibers, and the hollow nanofibers themselves.
  • hollow nanofibers are useful in lithium ion batteries in some instances.
  • hollow nanofibers are produced using a spinneret that comprises a first conduit containing a first fluid surrounded by a second conduit containing a second fluid.
  • the first fluid is any fluid that does not become an integral part of the nanofiber (e.g., a gas).
  • the first fluid is inert.
  • the first fluid is a gas, optionally air.
  • a gas as the inner annular fluid as described in the gas-assisted electrospinning technique as disclosed in PCT Patent Application PCT/US2011/024894 (“Electrospinning apparatus and nanofibers produced therefrom”).
  • the gas jet accelerates and elongates the fluid stock stream emanating from the electrospinner, leading to thinner fibers.
  • the methods disclosed herein lead to thinner nanofibers (e.g., when using the gas-assisted method) and nanofibers that have few defects (e.g., so are therefore high quality).
  • the first (inert) fluid is a liquid, optionally mineral oil for example.
  • the mineral oil core does not mix with the electrospun fluid stock.
  • the mineral oil core is removed following calcination to leave a hollow nanofiber.
  • hollow nanofibers are produced without an inert inner annular fluid.
  • a coaxial hybrid nanofiber is produced, then the inner annual material is removed, leaving a hollow nanofiber.
  • the inner material is removed by any suitable technique including dissolving, subliming, evaporating, degrading, etching, or equivalents that result in a hollow nanofiber.
  • the hollow core of the nanofiber has any suitable diameter.
  • a given collection of nanofibers comprise nanofibers that have a distribution of fibers with various diameters of the hollow core.
  • a single nanofiber has a hollow core diameter that varies along its length. In some embodiments, certain fibers of a population or portions of a fiber exceed or fall short of the average inner diameter.
  • the diameter of the hollow core is on average about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 15 nm, about 20 nm, about 40 nm, about 60 nm, about 80 nm, about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm, and the like.
  • the diameter of the hollow core is on average at most about 1 nm, at most about 2 nm, at most about 3 nm, at most about 4 nm, at most about 5 nm, at most about 6 nm, at most about 7 nm, at most about 8 nm, at most about 9 nm, at most about 10 nm, at most about 15 nm, at most about 20 nm, at most about 40 nm, at most about 60 nm, at most about 80 nm, at most about 100 nm, at most about 200 nm, at most about 300 nm, at most about 400 nm, at most about 500 nm, and the like.
  • the diameter of the hollow core is on average at least about 1 nm, at least about 2 nm, at least about 3 nm, at least about 4 nm, at least about 5 nm, at least about 6 nm, at least about 7 nm, at least about 8 nm, at least about 9 nm, at least about 10 nm, at least about 15 nm, at most least 20 nm, at least about 40 nm, at least about 60 nm, at least about 80 nm, at least about 100 nm, at least about 200 nm, at least about 300 nm, at least about 400 nm, at least about 500 nm, and the like.
  • the diameter of the hollow core is on average between about 1 nm and 10 nm, between about 5 nm and 20 nm, between about 5 nm and 10 nm, between about 10 nm and 50 nm, between about 20 nm and 50 nm, between about 1 nm and 50 nm, between about 100 nm and 500 nm, and the like.
  • the nanofibers described herein are unique compositions of matter, having never before been described.
  • described herein are nanofibers having certain novel properties.
  • these nanofibers have certain dimensions, aspect ratios, specific surface areas, porosities, conductivities, flexibilities, and the like that are beyond what was previously achievable.
  • the nanofibers described herein offer improvement upon devices that comprise the nanofibers.
  • the metal nanofibers described herein have an electrical conductivity that is at least 70% of the conductivity of the material when formed into a sheet in some instances.
  • high conductivity improves the function of solar cells based on the novel metal nanofibers.
  • certain applications favor smaller diameter nanofibers (e.g., which are achieved without sacrificing quality by practicing the methods described herein).
  • gas-assisted electrospinning techniques are utilized to create thin nanofibers (i.e., by accelerating the jet stream of fluid stock leaving the electrospinner).
  • the diameter of the nanofiber changes upon calcination, optionally shrinking.
  • copper nanofibers were 600 to 800 nm in diameter when electrospun and 300 to 500 nm after calcination.
  • the loading of precursor on the polymer affects the diameter of the nanofiber.
  • thicker nanofibers result from higher precursor loadings (e.g., because there is more precursor material converted into the nanofiber).
  • Methods for measuring the diameter of a nanofiber include, but are not limited to microscopy, optionally transmission electron microscopy (“TEM”) or scanning electron microscopy (“SEM”).
  • nanofibers or processes for producing nanofibers having any suitable diameter comprise nanofibers that have a distribution of fibers of various diameters.
  • a single nanofiber has a diameter that varies along its length. In some embodiments, certain fibers of a population or portions of a fiber exceed or fall short of the average diameter.
  • the nanofiber has on average a diameter of about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 130 nm, about 150 nm, about 200 nm, about 250 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, about 1,000 nm, about 1,500 nm, about 2,000 nm and the like.
  • the nanofiber has on average a diameter of at most 20 nm, at most 30 nm, at most 40 nm, at most 50 nm, at most 60 nm, at most 70 nm, at most 80 nm, at most 90 nm, at most 100 nm, at most 130 nm, at most 150 nm, at most 200 nm, at most 250 nm, at most 300 nm, at most 400 nm, at most 500 nm, at most 600 nm, at most 700 nm, at most 800 nm, at most 900 nm, at most 1,000 nm, at most 1,500 nm, at most 2,000 nm and the like.
  • the nanofiber has on average a diameter of at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, at least 60 nm, at least 70 nm, at least 80 nm, at least 90 nm, at least 100 nm, at least 130 nm, at least 150 nm, at least 200 nm, at least 250 nm, at least 300 nm, at least 400 nm, at least 500 nm, at least 600 nm, at least 700 nm, at least 800 nm, at least 900 nm, at least 1,000 nm, at least 1,500 nm, at least 2,000 nm and the like.
  • the nanofiber has on average a diameter between about 50 nm and about 300 nm, between about 50 nm and about 150 nm, between about 100 nm and about 400 nm, between about 100 nm and about 200 nm, between about 500 nm and about 800 nm, between about 60 nm and about 900 nm, and the like.
  • nanofibers e.g., metal, metal oxide, ceramic, and/or composite nanofibers described herein
  • nanofibers e.g., metal, metal oxide, ceramic, and/or composite nanofibers described herein have a (e.g., average) diameter of 100 nm to 1000 nm. In some embodiments, nanofibers described herein (e.g., those comprising metal/metal oxide/ceramic) have a (e.g., average) diameter of 500 nm or less. In some embodiments, nanofibers described herein (e.g., those comprising metal/metal oxide/ceramic) have a (e.g., average) diameter of 400 nm or less.
  • nanofibers described herein (e.g., those comprising metal/metal oxide/ceramic) have a (e.g., average) diameter of 200 nm to 500 nm. In other specific embodiments, precursor nanofibers described herein have a (e.g., average) diameter of less than 2000 nm. In more specific embodiments, precursor nanofibers described herein have a (e.g., average) diameter of 300 nm to 1500 nm.
  • the nanofiber is long.
  • the methods of the present disclosure produce long nanofibers (e.g., because the high loading and uniform distribution of precursor creates nanofibers that are highly “continuous” or “coherent”, meaning that they have few defects).
  • such high quality nanofibers are statistically more likely to be long because the probability is reduced that there is a defect along any particular length that is severe enough to define an end of the nanofiber.
  • Methods for measuring the length of a nanofiber include, but are not limited to microscopy, optionally transmission electron microscopy (“TEM”) or scanning electron microscopy (“SEM”).
  • the nanofibers have any suitable length.
  • a given collection of nanofibers comprise nanofibers that have a distribution of fibers of various lengths.
  • certain fibers of a population exceed or fall short of the average length.
  • the nanofiber has an average length of about 20 ⁇ m, about 50 ⁇ m, about 100 ⁇ m, about 500 ⁇ m, about 1,000 ⁇ m, about 5,000 ⁇ m, about 10,000 ⁇ m, about 50,000 ⁇ m, about 100,000 ⁇ m, about 500,000 ⁇ m, and the like.
  • the nanofiber has an average length of at least about 20 ⁇ m, at least about 50 ⁇ m, at least about 100 ⁇ m, at least about 500 ⁇ m, at least about 1,000 ⁇ m, at least about 5,000 ⁇ m, at least about 10,000 ⁇ m, at least about 50,000 ⁇ m, at least about 100,000 ⁇ m, at least about 500,000 ⁇ m, and the like.
  • aspect ratio is the length of a nanofiber divided by its diameter. In some instances, aspect ratio is a useful metric for quantifying the coherence of a nanofiber, with higher aspect ratios indicating that a nanofiber or population of nanofibers have few voids or defects. In some embodiments, aspect ratio refers to a single nanofiber. In some embodiments, aspect ratio refers to a plurality of nanofibers and is reported as a single average value (i.e., the aspect ratio being the average length of the nanofibers of a sample divided by their average diameter). In some instances, diameters and/or lengths are measured by microscopy. The nanofibers have any suitable aspect ratio.
  • the nanofiber has an aspect ratio of about 5, about 10, about 10 2 , about 10 3 , about 10 4 , about 10 5 , about 10 6 , about 10 7 , about 10 8 , about 10 9 , about 10 10 , about 10 11 , about 10 12 , and the like. In some embodiments the nanofiber has an aspect ratio of at least about 5, at least 10, at least 10 2 , at least 10 3 , at least 10 4 , at least 10 5 , at least 10 6 , at least 10′, at least 10 8 , at least 10 9 , at least 10 10 , at least 10 11 , at least 10 12 , and the like. In some embodiments, the nanofiber is of substantially infinite length and has an aspect ratio of substantially infinity.
  • the aspect ratio (e.g., average aspect ratio) of nanofibers provided herein is at least 100. In more specific embodiments, the aspect ratio (e.g., average aspect ratio) of nanofibers provided herein is at least 1,000 (e.g., at least 5,000). In still more specific embodiments, the aspect ratio (e.g., average aspect ratio) of nanofibers provided herein is at least 10,000.
  • the nanofibers have a high surface area.
  • the nanofiber is used as a catalyst where reactions take place on the surface of the nanofiber.
  • a high surface area reduces the size of the process equipment and/or reduces the amount of expensive material required in the catalyst.
  • the “specific surface area” is the surface area per mass or volume one of a fiber (or an average of a plurality of fibers). In various instances, the specific surface area is calculated based on a single nanofiber, or based on a collection of nanofibers and reported as a single average value. Techniques for measuring mass are known to those skilled in the art. In some instances, the surface area is calculated by measuring the diameter and length of nanofiber in the sample and applying the equation for the surface area of a cylinder (i.e., 2 times pi times half of the diameter of the nanofiber times the sum of the length of the nanofiber and half of the diameter of the nanofiber).
  • the surface area is measured by physical or chemical methods, for example by the Brunauer-Emmett, and Teller (BET) method where the difference between physisorption and desorption of inert gas is utilized.
  • BET Brunauer-Emmett, and Teller
  • the surface area is measured by titrating certain chemical groups on the nanofiber to estimate the number of groups on the surface, which is related to the surface area by a previously determined titration curve.
  • BET Brunauer-Emmett, and Teller
  • the nanofiber has any suitable specific surface area.
  • the specific surface area is about 0.1 m 2 /g, about 0.5 m 2 /g, about 1.0 m 2 /g, about 5 m 2 /g, about 10 m 2 /g, about 40 m 2 /g, about 60 m 2 /g, about 80 m 2 /g, about 100 m 2 /g, about 200 m 2 /g, about 400 m 2 /g, about 600 m 2 /g, about 800 m 2 /g, about 1,000 m 2 /g, about 1,500 m 2 /g, about 2,000 m 2 /g, and the like.
  • the specific surface area is at least 0.1 m 2 /g, at least 0.5 m 2 /g, at least 1.0 m 2 /g, at least 5 m 2 /g, at least 10 m 2 /g, at least 40 m 2 /g, at least 60 m 2 /g, at least 80 m 2 /g, at least 100 m 2 /g, at least 200 m 2 /g, at least 400 m 2 /g, at least 600 m 2 /g, at least 800 m 2 /g, at least 1,000 m 2 /g, at least 1,500 m 2 /g, at least 2,000 m 2 /g, and the like.
  • the specific surface area is between about 0.1 m 2 /g and 1 m 2 /g, between about 1 m 2 /g and 1,000 m 2 /g, between about 10 m 2 /g and 100 m 2 /g, between about 600 m 2 /g and 2,000 m 2 /g, between about 10 m 2 /g and 1,000 m 2 /g, between about 100 m 2 /g and 600 m 2 /g, between about 300 m 2 /g and 500 m 2 /g, and the like.
  • methods disclosed herein reduce the number and size of pores.
  • Porosity is also called “void fraction” and is a measure of the void spaces in a material.
  • porosity is a fraction of the volume of voids over the total volume and is reported as a percentage between 0% and 100%. In various embodiments, the porosity depends on many factors including loading and distribution of precursor in the fluid stock, calcination conditions, and the like.
  • Methods for measuring or estimating porosity include microscopy. Methods also include first measuring the surface area of a sample of nanofibers by any direct or indirect method, then comparing the measured surface area with the surface area of an idealized cylinder having the average length and diameter of the nanofibers in the sample. In some embodiments, the difference between the measured and expected surface area is converted to a volume, then to a volume fraction by assuming that the pores are in the shape of spheres or cylinders having an average diameter. In some embodiments, the porosity is measured by immersing the nanofibers in a fluid that penetrates the pores.
  • the porosity is estimated by comparing the total volume of nanofiber plus fluid with the volume that would be obtained from immersing a collection of idealized non-porous cylinders having the diameter and length of the nanofibers.
  • the void volume is the difference between these volumes, which is converted to porosity by dividing the void volume by the volume of the idealized cylinders.
  • the nanofibers have any suitable porosity.
  • the porosity is about 1%, about 2%, about 4%, about 6%, about 8%, about 10%, about 15%, about 20%, about 25%, about 30%, about 40%, about 50%, about 60%, about 70% and the like.
  • the porosity is at most 1%, at most 2%, at most 4%, at most 6%, at most 8%, at most 10%, at most 15%, at most 20%, at most 25%, at most 30%, at most 40%, at most 50%, at most 60%, at most 70% and the like.
  • the porosity is at least 1%, at least 2%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70% and the like. In some embodiments, the porosity is between about 1% and 10%, between about 10% and 50%, between about 20% and 30%, between about 30% and 70%, between about 1% and 50%, between about 5% and 20%, and the like.
  • nanofibers provided herein have improved performance over other nano-materials.
  • Young's modulus, fracture toughness, ultimate strength, electrical conductivity, thermal conductivity, flexibility, and/or other characteristics of the nanofibers described herein (and/or their composite materials) are improved over other nanostructures of the same material and/or over the bulk/sheet form of the same material.
  • Table 1 illustrates the physical properties of certain nanofibers provided herein and the physical properties of bulk materials having similar structure.
  • ceramic or metal oxide nanofibers or nanofibers having a continuous matrix of ceramic and/or metal oxide having an average Young's Modulus at least the level (or at least 90% the level) of a ceramic set forth in Table 1 (particularly rows 1 or 2 for amorphous ceramics, row 3 from crystalline ceramics, or row 4 or 5 for metal oxides).
  • ceramic or metal oxide nanofibers or nanofibers having a continuous matrix of ceramic and/or metal oxide having an average Fracture Toughness at least the level (or at least 90% the level) as set forth in Table 1 (particularly rows 1 or 2 for amorphous ceramics, row 3 from crystalline ceramics, or row 4 or 5 for metal oxides).
  • ceramic or metal oxide nanofibers or nanofibers having a continuous matrix of ceramic and/or metal oxide having an average Ultimate Strength at least the level (or at least 90% the level) as set forth in Table 1 (particularly rows 1 or 2 for amorphous ceramics, row 3 from crystalline ceramics, or row 4 or 5 for metal oxides).
  • metal nanofibers or nanofibers having a continuous matrix of metal having an average Young's Modulus at least the level (or at least 90% the level) of a ceramic set forth in Table 1 (particularly rows 6, 7, or 8).
  • metal nanofibers or nanofibers having a continuous matrix of metal having an average Fracture Toughness at least the level (or at least 90% the level) as set forth in Table 1 (particularly rows 6, 7, or 8).
  • metal nanofibers or nanofibers having a continuous matrix of metal having an average Ultimate Strength at least the level (or at least 90% the level) as set forth in Table 1 (particularly rows 6, 7, or 8).
  • metal nanofibers or nanofibers having a continuous matrix of metal having an average electrical conductivity of at least the level (or at least 90% the level) as set forth in Table 1 (particularly rows 6, 7, or 8).
  • nanofibers described herein have improved Young's modulus over similar materials in other nanostructure or bulk forms.
  • nanofibers having a mean or median nanofiber Young's modulus-to-diameter ratio of at least 0.18 GPa/nm In still more specific instances, provided herein are nanofibers having a mean or median nanofiber Young's modulus-to-diameter ratio of at least 0.2 GPa/nm. In yet more specific instances, provided herein are nanofibers having a mean or median nanofiber Young's modulus-to-diameter ratio of at least 0.25 GPa/nm. In specific instances, provided herein are nanofibers having a mean or median nanofiber Young's modulus-to-diameter ratio of at least 0.3 GPa/nm. In some instances, provided herein are nanofibers having a mean or median nanofiber Young's modulus-to-diameter ratio of at least 0.05 GPa/nm or at least 0.5 GPa/nm.
  • amorphous ceramic nanofibers e.g., pure amorphous ceramic nanofibers, as described herein, or nanofibers comprising a amorphous ceramic continuous matrix
  • amorphous ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 0.15 GPa/nm.
  • amorphous ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 0.2 GPa/nm.
  • amorphous ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 0.3 GPa/nm.
  • amorphous ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 0.35 GPa/nm. In some embodiments, provided herein are amorphous ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.05 MPa/nm. In specific embodiments, provided herein are amorphous ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.075 MPa/nm. In yet more specific embodiments, provided herein are amorphous ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.1 MPa/nm.
  • amorphous ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.15 MPa/nm. In yet more specific embodiments, provided herein are amorphous ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.2 MPa/nm. In some embodiments, provided herein are amorphous ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.075 MPa/nm and an average Young's modulus-to-diameter ratio of at least 0.15 GPa/nm.
  • amorphous ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.15 MPa/nm and an average Young's modulus-to-diameter ratio of at least 0.3 GPa/nm.
  • amorphous ceramic nanofibers having a fracture toughness of at least 0.5 MPa ⁇ m 1/2 In specific embodiments, provided herein are amorphous ceramic nanofibers having a fracture toughness of at least 0.6 MPa ⁇ m 1/2 . In more specific embodiments, provided herein are amorphous ceramic nanofibers having a fracture toughness of at least 0.7 MPa ⁇ m 1/2 .
  • crystalline ceramic nanofibers e.g., pure crystalline ceramic nanofibers, as described herein, or nanofibers comprising a crystalline ceramic continuous matrix
  • crystalline ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 1 GPa/nm.
  • crystalline ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 1.5 GPa/nm.
  • crystalline ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 2 GPa/nm.
  • crystalline ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 3 GPa/nm. In more specific embodiments, provided herein are crystalline ceramic nanofibers comprising an average Young's modulus-to-diameter ratio of at least 4 GPa/nm. In some embodiments, provided herein are crystalline ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 3 MPa/nm. In specific embodiments, provided herein are crystalline ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 5 MPa/nm.
  • crystalline ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 7.5 MPa/nm. In still more specific embodiments, provided herein are crystalline ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 10 MPa/nm. In yet more specific embodiments, provided herein are crystalline ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 12.5 MPa/nm. In some embodiments, provided herein are crystalline ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 5 MPa/nm and an average Young's modulus-to-diameter ratio of at least 1.5 GPa/nm.
  • crystalline ceramic nanofibers comprising an average ultimate strength-to-diameter ratio of at least 12.5 MPa/nm and an average Young's modulus-to-diameter ratio of at least 4 GPa/nm.
  • crystalline ceramic nanofibers having an average fracture toughness of at least 1.5 MPa ⁇ m 1/2 .
  • metal nanofibers e.g., pure metal nanofibers, as described herein, or nanofibers comprising a metal continuous matrix
  • metal nanofibers comprising an average Young's modulus-to-diameter ratio of at least 0.8 GPa/nm.
  • metal nanofibers comprising an average Young's modulus-to-diameter ratio of at least 1.1 GPa/nm.
  • metal nanofibers comprising an average Young's modulus-to-diameter ratio of at least 1.5 GPa/nm.
  • metal nanofibers comprising an average Young's modulus-to-diameter ratio of at least 2 GPa/nm. In more specific embodiments, provided herein are metal nanofibers comprising an average Young's modulus-to-diameter ratio of at least 2.9 GPa/nm. In some embodiments, provided herein are metal nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.2 MPa/nm. In specific embodiments, provided herein are metal nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.35 MPa/nm.
  • metal nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.5 MPa/nm. In still more specific embodiments, provided herein are metal nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.7 MPa/nm. In yet more specific embodiments, provided herein are metal nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.9 MPa/nm. In some embodiments, provided herein are metal nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.35 MPa/nm and an average Young's modulus-to-diameter ratio of at least 1.1 GPa/nm.
  • metal nanofibers comprising an average ultimate strength-to-diameter ratio of at least 0.9 MPa/nm and an average Young's modulus-to-diameter ratio of at least 2.9 GPa/nm.
  • metal nanofibers having an average fracture toughness of at least 3 MPa ⁇ m 1/2 In specific embodiments, provided herein are metal nanofibers having an average fracture toughness of at least 3.5 MPa ⁇ m 1/2 . In more specific embodiments, provided herein are metal nanofibers having a average fracture toughness of at least 4.1 MPa ⁇ m 1/2 .
  • the average electrical conductivity of a metal nanofiber provided herein has a log(S/m) to log(S/m) ratio with an identical bulk material of at least 0.75 (i.e., log of the electrical conductivity along the length of the metal nanofiber divided by log of the electrical conductivity of the same metal, in bulk).
  • the average electrical conductivity of a metal nanofiber provided herein has a log(S/m) to log(S/m) ratio with an identical bulk material of at least 0.85.
  • the average electrical conductivity of a metal nanofiber provided herein has a log(S/m) to log(S/m) ratio with an identical bulk material of at least 0.9.
  • the average electrical conductivity of a metal nanofiber provided herein has a log(S/m) to log(S/m) ratio with an identical bulk material of at least 0.95.
  • applications of the nanofibers described herein benefit from nanofibers having a high conductivity.
  • a high electrical conductivity is desirable in energy generation applications that involve moving electrons through the nanofiber (e.g., as an electrode of a battery).
  • nanofibers that are long and continuous with a reduced number or size of defects have a higher conductivity.
  • conductivity means either “thermally conductivity”, “electrically conductivity”, or both thermally and electrically conductivity unless context clearly dictates otherwise.
  • Electrical conductivity is a measure of a material's ability to conduct electric current. Electrical conductivity is measured in units of Siemens per length (e.g., S/cm). The reciprocal of conductivity is resistivity. Electrical resistivity is a measure of how strongly a material opposes the flow of electric current and is reported in units of ohm meter (em). In some instances, thermal conductivity is reported in units of watts per meter Kelvin (W/m/K). Thermal resistivity is the reciprocal thereof. Inspection of the units indicates whether the value is electrical or thermal conductivity.
  • the nanofiber has a conductivity (e.g., electrical or thermal) which is compared to a thin sheet of the material from which the nanofiber is made.
  • a conductivity e.g., electrical or thermal
  • a copper nanofiber is compared with a thin sheet of copper.
  • the nanofibers have any suitable conductivity as a percentage of the conductivity of the material is formed into a sheet.
  • the conductivity is variable over different portions of a collection of nanofibers, or along different directions.
  • conductivity is reported as either an average value, or a value specific to a certain condition or direction of measurement (i.e., for anisotropic materials).
  • the nanofiber has a conductivity of about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about 100% when compared with the conductivity of the material when formed into a sheet. In some embodiments, the nanofiber has a conductivity of at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, or at least about 100% when compared with the conductivity of the material when formed into a sheet.
  • the nanofiber has a conductivity of at most about 5%, at most about 10%, at most about 20%, at most about 30%, at most about 40%, at most about 50%, at most about 60%, at most about 70%, at most about 80%, at most about 90%, at most about 95%, or at most about 100% when compared with the conductivity of the material when formed into a sheet.
  • the nanofiber has a conductivity of between about 5% and 10%, between about 10% and 20%, between about 20% and 30%, between about 30% and 40%, between about 40% and 50%, between about 50% and 60%, between about 60% and 70%, between about 70% and 80%, between about 80% and 90%, between about 90% and 95%, between about 95% and 100%, when compared with the conductivity of the material when formed into a sheet.
  • conductivity is reported without reference to the conductivity of the material when formed into a sheet.
  • electrical conductivity is reported on an absolute, rather than relative basis.
  • Electrical conductivity is measured by any suitable method known to those skilled in the art.
  • the nanofibers have any suitable electrical conductivity.
  • electrical conductivity is measured as an average value, at a specific condition, or along a specific direction of the nanofiber sample.
  • the conductivity is about 1 S/cm, about 10 S/cm, about 100 S/cm, about 10 3 S/cm, about 10 4 S/cm, about 10 5 S/cm, about 10 6 S/cm, about 10 7 S/cm, about 10 8 S/cm, and the like.
  • the conductivity is at least 1 S/cm, at least 10 S/cm, at least 100 S/cm, at least 10 3 S/cm, at least 10 4 S/cm, at least 10 5 S/cm, at least 10 6 S/cm, at least 10 7 S/cm, at least 10 8 S/cm, and the like.
  • the conductivity is at most 1 S/cm, at most 10 S/cm, at most 100 S/cm, at most 10 3 S/cm, at most 10 4 S/cm, at most 10 5 S/cm, at most 10 6 S/cm, at most 10 7 S/cm, at most 10 8 S/cm, and the like.
  • the conductivity is between about 1 S/cm and 10 S/cm, between about 10 S/cm and 100 S/cm, between about 100 S/cm and 1,000 S/cm, between about 1,000 S/cm and 10 4 S/cm, between about 10 4 S/cm and 10 5 S/cm, between about 10 5 S/cm and 10 6 S/cm, between about 10 6 S/cm and 10 7 S/cm, between about 10 7 S/cm and 10 8 S/cm, between about 10 5 S/cm and 10 8 S/cm, and the like.
  • the nanofibers or collections of nanofibers of the present disclosure are flexible.
  • flexible nanofibers are advantageous in applications such as in the manufacture of flexible solar panels.
  • flexibility is quantified by the Young's modulus, which is the slope of the initial linear portion of a stress-strain curve.
  • the Young's modulus has units of pressure, such as mega Pascals (MPa).
  • MPa mega Pascals
  • flexibility is different along different directions of the material, so may be reported with respect to a certain direction, or is reported as an average value.
  • the flexibility is at least partially determined by the calcination temperature.
  • the calcination temperature is about 200° C.
  • the Young's modulus is at least 100 MPa.
  • lower calcination temperatures lead to a significantly higher fraction of amorphous metal or ceramic in the nanofiber, which results in higher flexibility.
  • the nanofibers have any suitable flexibility.
  • the nanofiber has a Young's modulus of about 10 MPa, about 20 MPa, about 40 MPa, about 60 MPa, about 80 MPa, about 100 MPa, about 150 MPa, about 200 MPa, about 250 MPa, about 300 MPa, about 400 MPa, about 1,000 MPa, and the like.
  • the nanofiber has a Young's modulus of at least about 10 MPa, at least about 20 MPa, at least about 40 MPa, at least about 60 MPa, at least about 80 MPa, at least about 100 MPa, at least about 150 MPa, at least about 200 MPa, at least about 250 MPa, at least about 300 MPa, at least about 400 MPa, at least about 1,000 MPa, and the like.
  • the nanofibers described herein are collected or formed into any suitable structure (e.g., suitable for the desired application). Structures include, but are not limited to spheres, cones, cylinders, slabs, helixes, polygons, and the like. For simplicity of terminology, all possible shapes or assemblage of nanofibers are herein referred to as a “mat”. In various embodiments, nanofiber mats comprise nanofibers of a single type, or nanofibers of at least two types.
  • coherent nanofibers lead to a mat having desirable properties (e.g., a less brittle nanofiber mat). In some instances, these desirable properties emerge from the properties of the component nanofibers and/or depend on the method in which the nanofibers are formed into the mat.
  • the present disclosure includes the nanofiber mats.
  • nanofiber mats formed by the nanofibers of the present disclosure.
  • described herein are methods for preparing nanofiber mats, optionally using an electrospinning process.
  • nanofibers are collected in a given geometry as they are produced (e.g., by moving the collection plate relative to the spinnerets, i.e., 3-D printing).
  • nanofibers are formed into a given geometry after collection (optionally before calcination), or formed into a given geometry after calcination.
  • the nanofiber mat comprises nanofibers arranged in a controlled manner (e.g., on a mesh with a perpendicular lattice). In some embodiments, the nanofibers are arranged randomly.
  • the mats are patterned in any level of detail including different fibers of different types, laid in different directions, in contact with various other nanofibers or insulated from various other nanofibers, and the like.
  • the nanofibers are cross-linked and/or surface modified.
  • the nanofiber surface proves a high surface area for mass transfer of a chemical product. These nanofibers are particularly applicable as catalysts for example. In some embodiments, the nanofiber surface proves a high surface area for mass transfer of a protons or electrons in the nanofiber mat. These nanofibers are particularly applicable as electrodes for example.
  • nanofibers provided herein are assembled into a nanofiber mat.
  • use of nanofiber mats provide for the improvement of certain nanofiber performance characteristics.
  • FIG. 39 shows a graphic comparing the effect of fiber alignment conditions on electrical conductivity in the axial and perpendicular direction of a Ni nanofiber mat.
  • the nanofiber mat has substantially the same properties as the nanofibers from which it is comprised. For example, a similar porosity, similar specific surface area, similar specific conductivity, and the like. In some instances, the nanofiber mat has different properties from the nanofibers from which it is comprised. For example, a different porosity, different specific surface area, different conductivity, and the like. In various embodiments, the property of the mat is either greater than or less than the property of an individual nanofiber.
  • the nanofiber mat is “isotropic” or has isotropic properties (e.g., meaning that the nanofiber mat has the same or substantially similar properties in all orientations and along all directions of the material).
  • the mat is “anisotropic” (e.g., meaning that it has different properties in various orientations or along different directions of the material).
  • anisotropic properties are created by controlling the orientation of the nanofibers in the mat. For example, in one embodiment where nanofiber direction was uniformly controlled, there was an approximately 100 fold difference in electric conductivity of copper nanofibers between the axial direction (direction of the nanofiber) and the perpendicular direction.
  • a given property differs in a second orientation or direction compared to a first orientation or direction by about 5%, about 10%, about 15%, about 20%, about 30%, about 40%, about 50%, about 60%, about 80%, about 100%, about 150%, about 200%, about 300%, about 400%, about 500%, and the like.
  • a given property is about 10 times, about 20 times, about 50 times, about 100 times, about 200 times, about 500 times, about 1,000 times, about 10,000 times, and the like higher in a second direction or orientation than in a first direction or orientation.
  • a given property differs in a second orientation or direction compared to a first orientation or direction by at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 80%, at least about 100%, at least about 150%, at least about 200%, at least about 300%, at least about 400%, at least about 500%, and the like.
  • a given property is at least about 10 times, at least about 20 times, at least about 50 times, at least about 100 times, at least about 200 times, at least about 500 times, at least about 1,000 times, at least about 10,000 times, and the like higher in a second direction or orientation than in a first direction or orientation.
  • a given property differs in a second orientation or direction compared to a first orientation or direction by at most about 5%, at most about 10%, at most about 15%, at most about 20%, at most about 30%, at most about 40%, at most about 50%, at most about 60%, at most about 80%, at most about 100%, at most about 150%, at most about 200%, at most about 300%, at most about 400%, at most about 500%, and the like.
  • a given property is at most about 10 times, at most about 20 times, at most about 50 times, at most about 100 times, at most about 200 times, at most about 500 times, at most about 1,000 times, at most about 10,000 times, and the like higher in a second direction or orientation than in a first direction or orientation.
  • the mat has a conductivity in a first direction and a conductivity in a second direction, wherein the conductivity in the first direction is at least one hundred times higher than in the second direction. In some embodiments, the mat has a conductivity of at least 1.0 S/cm in either the first or second direction.
  • the porosity of the nanofiber mat is a consideration, for example in filtration applications. For example, in order to remove particles of a certain diameter, it is desirable to have a mat with pores smaller than the diameter of the smallest particle to be removed in some instances.
  • the porosity of the nanofiber mat is greater than the porosity of the nanofibers that comprise the mat. In some embodiments, the porosity of the mat is the combination of the spaces between the nanofiber strands and the pores within the nanofibers themselves. In some instances, microscopy is used to estimate porosity. In some instances, the porosity of a nanofiber mat having a first volume defined by its external surface is measured by submersing the nanofiber mat in a fluid having a second volume. The volume of the fluid plus submersed nanofiber mat defines a third volume. A fourth volume is obtained by subtracting the second volume from the third volume. The porosity is one minus the ratio of the fourth volume to the first volume. In some embodiments, porosity is expressed as a percentage.
  • the nanofiber mat has any suitable porosity.
  • the porosity is about 1%, about 2%, about 4%, about 6%, about 8%, about 10%, about 15%, about 20%, about 25%, about 30%, about 40%, about 50%, about 60%, about 70% and the like.
  • the porosity is at most 1%, at most 2%, at most 4%, at most 6%, at most 8%, at most 10%, at most 15%, at most 20%, at most 25%, at most 30%, at most 40%, at most 50%, at most 60%, at most 70% and the like.
  • the porosity is at least 1%, at least 2%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70% and the like. In some embodiments, the porosity is between about 1% and 10%, between about 10% and 50%, between about 20% and 30%, between about 30% and 70%, between about 1% and 50%, between about 5% and 20%, and the like.
  • porosity has units of length.
  • the porous length is the distance between a point on a nanofiber strand and the nearest point on another nanofiber strand. In some instances, objects having a dimension longer than this porous length will not generally be able to pass through the mat. In some instances, the porous length is measured by bombarding the nanofiber mat with particles of a plurality of diameters until the particles of a certain size pass through the nanofiber mat, indicating that the nanofiber mat has a porous length approximately equal to the diameter of said particles.
  • the pores of the nanofiber mat have any suitable size.
  • the pores are about 0.1 microns, about 0.2 microns, about 0.5 microns, about 0.7 microns, about 1 microns, about 2 microns, about 4 microns, about 6 microns, about 8 microns, about 10 microns, about 15 microns, about 20 microns, about 30 microns, about 40 microns, about 50 microns, about 70 microns, about 100 microns, about 200 microns, and the like on their longest dimension.
  • the pores are at most about 0.1 microns, at most about 0.2 microns, at most about 0.5 microns, at most about 0.7 microns, at most about 1 microns, at most about 2 microns, at most about 4 microns, at most about 6 microns, at most about 8 microns, at most about 10 microns, at most about 15 microns, at most about 20 microns, at most about 30 microns, at most about 40 microns, at most about 50 microns, at most about 70 microns, at most about 100 microns, at most about 200 microns, and the like on their longest dimension.
  • the pores are at least about 0.1 microns, at least about 0.2 microns, at least about 0.5 microns, at least about 0.7 microns, at least about 1 microns, at least about 2 microns, at least about 4 microns, at least about 6 microns, at least about 8 microns, at least about 10 microns, at least about 15 microns, at least about 20 microns, at least about 30 microns, at least about 40 microns, at least about 50 microns, at least about 70 microns, at least about 100 microns, at least about 200 microns, and the like on their longest dimension.
  • the pores are between about 0.5 microns and 50 microns, between about 1 microns and 10 microns, between about 10 microns and 50 microns, between about 0.1 microns and 5 microns, between about 2 microns and 10 microns, between about 40 microns and 100 microns, and the like on their longest dimension.
  • the density of the nanofiber mat is another characteristic to consider in certain applications.
  • the concentration of the polymer in the fluid stock has an impact on the density of the mat (e.g., potentially with decreased amounts of polymer leading to a denser mat, e.g., because fewer voids are left when the polymer is removed in calcination).
  • the density of the mat was at least about 1 g/m 3 where the polymer was less than about 30% in the fluid stock.
  • the nanofiber mat has any suitable density.
  • the mat has a density of about 0.01 g/cm 3 , about 0.05 g/cm 3 , about 0.1 g/cm 3 , about 0.2 g/cm 3 , about 0.4 glcm 3 , about 0.8 g/cm 3 , about 1 g/cm 3 , about 5 g/cm 3 , about 10 g/cm 3 , and the like.
  • the mat has a density of at least about 0.01 g/cm 3 , at least about 0.05 g/cm 3 , at least about 0.1 g/cm 3 , at least about 0.2 g/cm 3 , at least about 0.4 g/cm 3 , at least about 0.8 g/cm 3 , at least about 1 g/cm 3 , at least about 5 g/cm 3 , at least about 10 g/cm 3 , and the like.
  • the mat has a density of at most about 0.01 g/cm 3 , at most about 0.05 g/cm 3 , at most about 0.1 g/cm 3 , at most about 0.2 g/cm 3 , at most about 0.4 g/cm 3 , at most about 0.8 g/cm 3 , at most about 1 g/cm 3 , at most about 5 g/cm 3 , at most about 10 g/cm 3 , and the like.
  • the mat has a density of between about 0.01 g/cm 3 and 0.05 g/cm 3 , between about 0.05 g/cm 3 and 0.3 g/cm 3 , between about 0.1 g/cm 3 and 1 g/cm 3 , between about 1 g/cm 3 and 5 g/cm 3 , and the like.
  • the mat has any suitable number of strands per area or volume. In some instances, microscopy is used to determine the number of strands per area or volume. In some embodiments, the mat comprises about 5 strands, about 10 strands, about 50 strands, about 100 strands, about 150 strands, about 250 strands, about 500 strands, about 1,000 strands, about 5,000 strands, about 50,000 strands, and the like per square millimeter or per cubic millimeter.
  • the mat comprises at least about 5 strands, at least about 10 strands, at least about 50 strands, about 100 strands, at least about 150 strands, at least about 250 strands, at least about 500 strands, at least about 1,000 strands, at least about 5,000 strands, at least about 50,000 strands, and the like per square millimeter or per cubic millimeter.
  • the mat comprises between about 5 strands to 50 strands, between about 50 strands to 500 strands, between about 500 strands to 5,000 strands, between about 5,000 strands to 50,000 strands, and the like per square millimeter or per cubic millimeter.
  • the sizes of the crystal domains in the nanofiber have an effect on properties of the nanofiber or nanofiber mat (e.g., including magnetic strength and electrical conductivity).
  • calcination conditions have an effect on crystallization domains.
  • FIG. 38 shows that by tuning calcination conditions with Ni nanofibers, a 5-fold difference in magnetic strength was obtained and a 10,000 fold difference in electric conductivity was obtained. Described herein are nanofibers or nanofiber mats having crystal domains of a certain size.
  • the present disclosure also encompasses nanofibers or nanofiber mats with tunable properties and methods for tuning the properties of nanofiber or nanofiber mats (e.g., including magnetic or conductivity properties).
  • the domains are metal oxide domains. In various embodiments, these domains have various sizes, for example about 1 nm, about 5 nm, about 10 nm, about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 40 nm, about 50 nm, about 70 nm, about 90 nm, and the like.
  • the domains are at least about 1 nm, at least about 5 nm, at least about 10 nm, at least about 15 nm, at least about 20 nm, at least about 25 nm, at least about 30 nm, at least about 40 nm, at least about 50 nm, at least about 70 nm, at least about 90 nm, and the like in size.
  • the domains are at most about 1 nm, at most about 5 nm, at most about 10 nm, at most about 15 nm, at most about 20 nm, at most about 25 nm, at most about 30 nm, at most about 40 nm, at most about 50 nm, at most about 70 nm, at most about 90 nm, and the like in size.
  • the domains have a size between about 1 nm and 100 nm, between about 20 nm and 30 nm, between about 1 nm and 20 nm, between about 30 nm and 90 nm, between about 40 nm and 70 nm, between about 15 nm and 40 nm, and the like.
  • the nanofiber and/or nanofiber mat is magnetic.
  • the coercivity (also called the coercive field or coercive force) of a ferromagnetic material is the intensity of the applied magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has been driven to saturation. Coercivity is usually measured in oersted (Oe) or ampere/meter units.
  • the nanofiber mat has any suitable magnetic coercivity.
  • the nanofiber mat has a magnetic coercivity of about 10 Oe, about 20 Oe, about 40 Oe, about 60 Oe, about 80 Oe, about 100 Oe, about 125 Oe, about 150 Oe, about 175 Oe, about 200 Oe, about 250 Oe, about 300 Oe, about 350 Oe, about 400 Oe, about 500 Oe, about 1,000 Oe, and the like.
  • the nanofiber mat has a magnetic coercivity of at least about 10 Oe, at least about 20 Oe, at least about 40 Oe, at least about 60 Oe, at least about 80 Oe, at least about 100 Oe, at least about 125 Oe, at least about 150 Oe, at least about 175 Oe, at least about 200 Oe, at least about 250 Oe, at least about 300 Oe, at least about 350 Oe, at least about 400 Oe, at least about 500 Oe, at least about 1,000 Oe, and the like.
  • the nanofiber mat has a magnetic coercivity of at most about 10 Oe, at most about 20 Oe, at most about 40 Oe, at most about 60 Oe, at most about 80 Oe, at most about 100 Oe, at most about 125 Oe, at most about 150 Oe, at most about 175 Oe, at most about 200 Oe, at most about 250 Oe, at most about 300 Oe, at most about 350 Oe, at most about 400 Oe, at most about 500 Oe, at most about 1,000 Oe, and the like.
  • the nanofiber mat has a magnetic coercivity of between about 50 Oe and 2000e, between about 100 Oe and 300 Oe, between about 200 Oe and 500 Oe, between about 300 Oe and 1,000 Oe, between about 10 Oe and 100 Oe, between about 175 Oe and 300 Oe, between about 200 Oe and 250 Oe, and the like.
  • the nanofiber and/or nanofiber mat is paramagnetic or superparamagnetic.
  • Paramagnetism is a form of magnetism that occurs in the presence of an externally applied magnetic field.
  • Superparamagnetism is a form of magnetism which appears in small ferromagnetic or ferrimagnetic nanoparticles or nanofibers.
  • magnetization randomly flips direction under the influence of temperature. The time between two flips is called the Néel relaxation time.
  • the time used to measure the magnetization of the nanoparticles is much longer than the Néel relaxation time, their magnetization appears to be on average zero. That is, they are said to be in the superparamagnetic state. In this state, an external magnetic field is able to magnetize the nanoparticles or nanofibers, similarly to a paramagnet.
  • a number of components of a system interact to produce nanofibers.
  • these include an electrospinning apparatus and a module for collecting the electrospun fluid stock or nanofiber. These two components are related by a voltage difference such that the thin jet of fluid stock emanating from the electrospinner is attracted to and deposits on the collection module.
  • the electrospinning component of the system is a gas-assisted electrospinner. The gas used to accelerate the jet of fluid stock is optionally air.
  • the system also includes a fluid stock.
  • the fluid stock interacts with the electrospinner to produce a nanofiber.
  • the fluid stock has an elongational viscosity that allows for a jet of fluid stock to erupt from a charged droplet.
  • the fluid stock is a system of polymer and precursor that interact with each other to at least in part determine the spinnability of the fluid stock and the properties of the nanofiber.
  • the system also includes an apparatus for calcinating the nanofiber (e.g., a heater or a gas chamber).
  • an apparatus for calcinating the nanofiber e.g., a heater or a gas chamber.
  • the gas is part of the system, wherein the gas is optionally air, hydrogen, nitrogen, an inert gas, and the like.
  • Electrochemical devices include fuel cells, batteries, capacitors and ultra-capacitors, among others.
  • solar cells are electrochemical devices.
  • other electrochemical devices do not fit within the categories listed herein.
  • electrochemical devices have a wide range of energy densities and power densities that are summarized graphically on a Ragone chart ( FIG. 40 ).
  • Energy density is reported in units of watt-hours per kilogram (W ⁇ h/kg) or equivalents and is a measure of the amount of useful energy stored in a given size device (by mass or volume).
  • Power density is reported in units of watts per kilogram (W/kg) or equivalents and is a measure of how quickly energy can be utilized.
  • fuel cells have a high energy density, but a low power density.
  • capacitors have a high power density but a low energy density.
  • batteries and ultracapacitors have energy densities and power densities between capacitors and fuel cells.
  • nanofibers in electrochemical devices are used as electrodes in fuel cells or batteries (e.g., where they may have beneficial properties such as a high conductivity and surface area). In some embodiments, they are utilized as the dielectric layer in an ultracapacitor.
  • the present disclosure includes an electrochemical device that includes the nanofibers described herein, includes an electrochemical device that includes a nanofiber produced by the methods described herein, and includes an electrochemical device that includes a nanofiber produced by the system described herein. In some aspects, the disclosure also includes methods for making and methods for using electrochemical devices that comprise nanofibers.
  • devices are built that comprise the nanofibers described herein.
  • such a device is created by substituting a component of the device with nanofibers (e.g., thus improving the function of the device), but substantially preserving the overall architecture and design of the device.
  • the architecture and overall design of the device comprising nanofibers is markedly different than a fuel cell, battery, ultracapacitor and the like.
  • an electrochemical device with both high energy density and high power density, for example to energize an electric vehicle that has both a long driving range (i.e., energy density) and can be charged and accelerate quickly (i.e., high power density).
  • the electrochemical device has any suitable energy and power density.
  • the power density is at least about 100 W/kg
  • the energy density is at least about 10 W ⁇ h/kg, at least about 50 W ⁇ h/kg, at least about 100 W ⁇ h/kg, at least about 500 W ⁇ h/kg, at least about 1,000 W ⁇ h/kg, at least about 5,000 W ⁇ h/kg, and the like.
  • the energy density is at least about 10 W ⁇ h/kg, at least about 50 W ⁇ h/kg, at least about 100 W ⁇ h/kg, at least about 500 W ⁇ h/kg, at least about 1,000 W ⁇ h/kg, at least about 5,000 W ⁇ h/kg, and the like. In some embodiments where the power density is at least about 1,000 W/kg, the energy density is at least about 10 W ⁇ h/kg, at least about 50 W ⁇ h/kg, at least about 100 W ⁇ h/kg, at least about 500 W ⁇ h/kg, at least about 1,000 W ⁇ h/kg, at least about 5,000 W ⁇ h/kg, and the like.
  • the energy density is at least about 10 W ⁇ h/kg, at least about 50 W ⁇ h/kg, at least about 100 W ⁇ h/kg, at least about 500 W ⁇ h/kg, at least about 1,000 W ⁇ h/kg, at least about 5,000 W ⁇ h/kg, and the like. In some embodiments where the power density is at least about 10,000 W/kg, the energy density is at least about 10 W ⁇ h/kg, at least about 50 W ⁇ h/kg, at least about 100 W ⁇ h/kg, at least about 500 W ⁇ h/kg, at least about 1,000 W ⁇ h/kg, at least about 5,000 W ⁇ h/kg, and the like.
  • a fuel cell is an electrochemical cell that converts chemical energy into electrical energy.
  • electricity is generated from the reaction between a fuel supply and an oxidizing agent.
  • the reactants flow into the cell, and the reaction products flow out of it, while the electrolyte remains within it.
  • fuel cells are different from electrochemical cell batteries in that they consume a reactant from an external source (i.e., which is replenished).
  • fuel cells are made up of three segments which are sandwiched together: the anode, the electrolyte, and the cathode.
  • two chemical reactions occur at the interfaces of the three different segments.
  • the net result of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current is created (e.g., which can be used to power electrical devices, normally referred to as the load).
  • fuels and oxidants are possible.
  • a hydrogen fuel cell uses hydrogen as its fuel and oxygen (e.g., from air) as its oxidant.
  • Other possible fuels include hydrocarbons and alcohols.
  • Other possible oxidants include chlorine and chlorine dioxide.
  • a catalyst oxidizes the fuel, (e.g., hydrogen), turning the fuel into a positively charged ion and a negatively charged electron.
  • the electrolyte is a substance specifically designed so ions can pass through it, but the electrons do not.
  • the freed electrons travel through a wire creating the electric current.
  • the ions travel through the electrolyte to the cathode.
  • the ions once reaching the cathode, the ions are reunited with the electrons and the two react with a third chemical, (e.g., oxygen), to create water or carbon dioxide.
  • a fuel cell has higher energy conversion efficiency than other power sources (e.g., since it converts chemical energy directly into electricity).
  • fuel cells produce no pollution (e.g., when hydrogen is used as the fuel) or less pollution (e.g., when hydrocarbon is used as the fuel) compared to combustion.
  • fuel cells operate quietly, reducing noise pollution.
  • a fuel cell operates continuously and generates electricity as long as the fuel is supplied. In some instances, fuel cells are used in applications including portable electronic devices, automobiles, and stationary power generation.
  • the catalyst for hydrogen oxidation at the anode is carbon supported platinum.
  • the Pt/C anode system exhibits certain drawbacks in some instances.
  • the use of carbon generally leads to the corrosion of the electrode in some embodiments.
  • the platinum is an expensive catalyst.
  • the fuel cells described herein comprise electrodes based on nanofibers (e.g., avoiding the corrosion by carbon and reduce the expensive Pt loading).
  • the nanofibers comprise intermetallic Fe—Pt.
  • nanofibers in fuel cells.
  • they are used as electrodes, optionally anodes or cathodes.
  • described herein is a fuel cell that comprises a nanofiber described herein, a fuel cell that comprises a nanofiber produced by the methods described herein, and includes a fuel cell that comprises a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using fuel cells that comprise nanofibers.
  • the nanofiber comprises any suitable material including, but not limited to iron (Fe), platinum (Pt), or any mixture thereof.
  • the nanofiber is a pure metal nanofiber or a metal alloy nanofiber, including any hybrid or hollow geometry.
  • the atoms have a certain arrangement (e.g., including a face-centered tetragonal structure).
  • the ratio of Fe to Pt atoms in the nanofiber of the fuel cell is about 1 Fe to 5 Pt, or about 4 Fe to 5 Pt for example.
  • the Fe and Pt atoms are substantially evenly distributed amongst each other (i.e., the nanofiber does not comprise aggregates of Pt or Fe).
  • the creation of the face-centered tetragonal structure of Fe—Pt is pursued to enhance oxygen reduction and durability under the minimized Pt loading.
  • the optional face-centered tetragonal structure also provides connectivity of the Pt.
  • a Pt/C fuel cell mixes Pt particles with C and forms an electrode by vapor deposition of the mixture.
  • the nanofibers and electrodes described herein significantly reduce the cost of the fuel cell (e.g., by using less platinum).
  • a gas-assisted electrospinning procedure is a cheaper and faster process than vapor deposition.
  • the fuel cell comprises an anode and the anode comprises nanofibers.
  • a reduced amount of platinum is preferred (e.g., because of cost).
  • the anode has any suitable amount of platinum (including no platinum).
  • the anode has by mass percentage about 5% Pt, about 10% Pt, about 15% Pt, about 20% Pt, about 25% Pt, about 30% Pt, about 40% Pt, about 50% Pt, about 70% Pt, and the like.
  • the anode has by mass percentage at most about 5% Pt, at most about 10% Pt, at most about 15% Pt, at most about 20% Pt, at most about 25% Pt, at most about 30% Pt, at most about 40% Pt, at most about 50% Pt, at most about 70% Pt, and the like.
  • the fuel cell has at least 10 fold less or at least 30 fold less Pt than a traditional Pt/C fuel cell.
  • the amount of corrosion of the cathode is reduced compared with a traditional Pt/C fuel cell.
  • the nanofibers described herein reduce or substantially eliminate corrosion in the fuel cell.
  • reduced corrosion improves the performance of the fuel cell.
  • the fuel cells described herein consist of substantially no carbon. In one aspect, the fuel cells described herein consist of substantially no carbon in the anode.
  • the fuel cells described herein have a high current density.
  • the current density is any suitable value.
  • the current density is about ⁇ 0.01 mA/cm 2 , about ⁇ 0.02 mA/cm 2 , about ⁇ 0.04 mA/cm 2 , about ⁇ 0.06 mA/cm 2 , about ⁇ 0.08 mA/cm 2 , about ⁇ 0.1 mA/cm 2 , about ⁇ 0.3 mA/cm 2 , and the like.
  • the current density is at least about ⁇ 0.01 mA/cm 2 , at least about ⁇ 0.02 mA/cm 2 , at least about ⁇ 0.04 mA/cm 2 , at least about ⁇ 0.06 mA/cm 2 , at least about ⁇ 0.08 mA/cm 2 , at least about ⁇ 0.1 mA/cm 2 , at least about ⁇ 0.3 mA/cm 2 , and the like. In some embodiments, the current density is about 4 times higher than a traditional Pt/C fuel cell.
  • the fuel cell has increased reaction stability. In some instances, reaction stability is reported as the number of CV cycles. Cyclic voltammetry or CV is a type of potentiodynmic electrochemical measurement. In some cyclic voltammetry experiments, the working electrode potential is ramped linearly versus time (e.g., like linear sweep voltammetry). In some instances, cyclic voltammetry takes the experiment a step further than linear sweep voltammetry (which ends when it reaches a set potential). When cyclic voltammetry reaches a set potential, the working electrode's potential ramp is inverted. In some embodiments, this inversion happens multiple times during a single experiment.
  • the current at the working electrode is plotted versus the applied voltage to give the cyclic voltammogram trace.
  • cyclic voltammetry is used to study the electrochemical properties of an analyte in solution.
  • the fuel cells described herein have about 1.5 ⁇ more, about 2 ⁇ more, about 3 ⁇ more, about 4 ⁇ more, about 5 ⁇ more, about 10 ⁇ more, and the like CV cycles than a traditional Pt/C fuel cell.
  • the fuel cell is significantly thinner than a traditional Pt/C fuel cell.
  • reduced thickness allows packing of more fuel cells into a given volume, increasing overall performance and/or reducing cost.
  • the fuel cells have any suitable thickness.
  • the fuel cell has a thickness of about 0.2 mm, about 0.5 mm, about 0.7 mm, about 1 mm, about 1.5 mm, about 2 mm, about 5 mm, and the like when measured along its shortest dimension.
  • the fuel cell has a thickness of at most about 0.2 mm, at most about 0.5 mm, at most about 0.7 mm, at most about 1 mm, at most about 1.5 mm, at most about 2 mm, at most about 5 mm, and the like when measured along its shortest dimension.
  • a battery is composed of electrochemical cells that are connected in series and/or in parallel to provide the required voltage and capacity.
  • each cell consists of a positive and a negative electrode (both sources of chemical reactions) separated by an electrolyte solution, which enables ion transfer between the two electrodes. Once these electrodes are connected externally, chemical reactions proceed in tandem at both electrodes (i.e., thereby liberating electrons and enabling the current to be used).
  • the amount of electrical energy (typically expressed per unit of weight, e.g., W ⁇ h/kg or mW ⁇ h/g) that a battery is able to deliver is a function of the cell potential (V) and capacity (A ⁇ h/kg), which is linked directly to the chemistry of the system.
  • described herein are batteries comprising nanofibers.
  • the nanofibers are used in electrodes, optionally anodes or cathodes.
  • described herein is a battery that includes a nanofiber as described herein, includes a battery that includes a nanofiber produced by the methods described herein, and includes a battery that includes a nanofiber produced by the system described herein.
  • the described herein are methods for making and methods for using batteries that include nanofibers.
  • the battery is a rechargeable lithium battery.
  • the nanofiber, the anode, and the cathode are any suitable material.
  • silicon or germanium are used as anode material (e.g., because these materials have a low discharge potential and high theoretical charge capacity (about 4200 mA ⁇ h/g, and 1,600 mA ⁇ h/g respectively) compared to that of graphitic carbon (373 mA ⁇ h/g)).
  • the nanofiber is a Si or Ge nanofiber.
  • the anode includes Si or Ge nanofibers.
  • silicon anodes have limited applications because silicon's volume changes upon insertion and extraction of lithium, which results in pulverization and capacity fading.
  • hollow nanofibers can accommodate volume changes without pulverization.
  • the nanofibers described herein are hollow.
  • the batteries described herein comprise a hollow Si or Ge (or combination Si/Ge) nanofiber.
  • hollow Si and/or Ge nanofibers are produced via water-based, multi-axial electrospinning.
  • the nanofibers comprise pure SiO 2 , and their hybrids with V 2 O 5 , ZrO 2 , TiO 2 , Fe, Ni, and carbon with Fe 3 O 4 .
  • pure ceramic nanofibers such as SiO 2 , Al 2 O 3 and ZrO 2 , etc. are produced via electrospinning of aqueous polymer solution containing their precursors, followed by thermal treatment.
  • Hollow Si or Ge nanofibers are produced in any suitable manner.
  • mineral oil and aqueous polymer solution with Si or Ge precursor are coaxially electrospun as core and sheath layer, respectively, followed by the removal of mineral core to create a hollow structure.
  • gas-assisted coaxial electrospinning is employed (e.g., where an air stream is used as core) to create a hollow structure during the spinning (e.g., and to stretch the sheath layer jet of precursor solution for higher throughput).
  • Any suitable method of reduction is employed (e.g., following electrospinning of hollow Si or Ge precursor nanofibers).
  • thermal treatment and/or chemical reduction are applied to obtain pure hollow Si or Ge nanofibers.
  • the degree of volume expansion upon insertion and extraction of lithium in Li-ion battery applications is evaluated.
  • the nanofibers described herein have any suitable amount of volume expansion.
  • the volume expansion is about 100%, about 200%, about 300%, about 400%, about 600%, about 800%, and the like. In some embodiments, the volume expansion is at most about 100%, at most about 200%, at most about 300%, at most about 400%, at most about 600%, at most about 800%, and the like.
  • the batteries described herein have any suitable recharging efficiency.
  • the recharging efficiency is about 500 mAh/g, about 800 mAh/g, about 1,200 mAh/g, about 1,600 mAh/g, about 2,000 mAh/g, about 3,000 mAh/g, about 5,000 mAh/g, about 10,000 mAh/g, and the like.
  • the recharging efficiency is at least about 500 mAh/g, at least about 800 mAh/g, at least about 1,200 mAh/g, at least about 1,600 mAh/g, at least about 2,000 mAh/g, at least about 3,000 mAh/g, at least about 5,000 mAh/g, at least about 10,000 mAh/g, and the like.
  • energy is generally stored by the removal of charge carriers, typically electrons, from one metal plate and depositing them on another. In some instances, this charge separation creates a potential between the two plates, which is harnessed in an external circuit. In some instances, the total energy stored increases with both the amount of charge stored and the potential between the plates. In some instances, the amount of charge stored per unit voltage is a function of the size, the distance, and the material properties of the plates and the material in between the plates (the dielectric), while the potential between the plates is limited by breakdown of the dielectric. In some instances, the dielectric controls the capacitor's voltage. In some instances, changing the dielectric material leads to higher energy density for a given size of capacitor.
  • charge carriers typically electrons
  • the present disclosure includes a capacitor that comprises the nanofibers described herein, includes a capacitor that includes a nanofiber produced by the methods described herein, and includes a capacitor that includes a nanofiber produced by the system described herein. In some aspects, the disclosure also includes methods for making and methods for using capacitors that include nanofibers.
  • An ultracapacitor also known as an electric double-layer capacitor (EDLC), a supercapacitor, supercondenser, pseudocapacitor, or electrochemical double layer capacitor, is an electrochemical capacitor with relatively high energy density. In some instances, the energy density is on the order of hundreds of times greater compared to conventional electrolytic capacitors. In some instances, ultra-capacitors have a higher power density in comparison with batteries or fuel cells.
  • EDLC electric double-layer capacitor
  • a supercapacitor supercondenser, pseudocapacitor, or electrochemical double layer capacitor
  • ultra-capacitors have a higher power density in comparison with batteries or fuel cells.
  • ultra-capacitors do not have a conventional dielectric.
  • ultra-capacitors use “plates” that are two layers of a substrate (optionally the same substrate), rather than two separate plates separated by an intervening substance.
  • this “electrical double layer” results in the separation of charge despite the thin physical separation of the layers (e.g., on the order of nanometers).
  • the lack of a bulky layer of dielectric in an ultra-capacitor permits the packing of plates with much larger surface area into a given size, resulting in high capacitances compared with a capacitor.
  • any of the components of an ultracapacitor comprise nanofibers (for example, porous carbon/BaTiO 3 /separator).
  • the nanofibers are produced from a water-based, gas-assisted electrospinning process.
  • dielectric double layer comprises nanofibers.
  • described herein are ultracapacitors comprising nanofibers.
  • the present disclosure includes an ultracapacitor that includes the nanofibers described herein, includes an ultracapacitor that includes a nanofiber produced by the methods described herein, and includes an ultracapacitor that includes a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using ultracapacitors that comprise nanofibers.
  • the ultracapacitor comprises porous carbon electrodes with a dielectric layer.
  • the porous carbon electrodes are formed of nanofibers.
  • nanofibers are disposed on the carbon electrodes.
  • the nanofibers comprise any material with a suitable dielectric constant. Non-limiting examples are StTiO 3 , BaTiO 3 , SrBaTiO 3 , mixtures thereof, and combinations thereof.
  • the nanofibers are of any suitable geometry including hybrid or hollow nanofibers.
  • the process includes electrospinning a fluid stock, wherein the fluid stock comprises precursor molecules bound to a polymer.
  • the precursor molecules comprise Ba, St, Ti, or mixtures thereof.
  • the process includes thermally treating the spun nanofibers.
  • the ultracapacitor comprises a thin layer of dielectric nanofibers at the interface between the electrolyte and the electrode (e.g., activated carbon electrode). In some instances, this nanofiber layer results in an increased capacitance. Capacitance density is reported in units of farads per cubic centimeter (F/cm 3 ) or equivalents. In some embodiments, the ultra-capacitors described herein have a capacitance density of about 10 F/cm 3 , about 20 F/cm 3 , about 50 F/cm 3 , about 100 F/cm 3 , about 200 F/cm 3 , about 500 F/cm 3 , about 1,000 F/cm 3 , and the like.
  • the ultracapacitor have a capacitance density of at least about 10 F/cm 3 , at least about 20 F/cm 3 , at least about 50 F/cm 3 , at least about 100 F/cm 3 , at least about 200 F/cm 3 , at least about 500 F/cm 3 , at least about 1,000 F/cm 3 , and the like.
  • FIG. 45 shows a cross-sectional view of an electrolytic double layer ultracapacitor comprising an electrolyte 4501 , a separator 4502 , and an activated carbon electrode 4503 .
  • FIG. 46 shows a cross-sectional view of barium titanate nanofibers B laid on the activated carbon A of an ultracapacitor (with electrolyte C).
  • a solar cell also called photovoltaic cell or photoelectric cell
  • a solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect.
  • assemblies of cells are used to make modules (e.g., solar panels), which are used to capture energy from sunlight.
  • Photovoltaics is a field of technology related to the use of photovoltaic cells to producing electricity from light (though it is often used specifically to refer to the generation of electricity from sunlight).
  • photovoltaic devices are based on the concept of charge separation at an interface of two materials of different conduction mechanism.
  • photovoltaic devices are solid-state junction devices, usually made of silicon, (e.g., and profiting from the experience and material availability resulting from the semiconductor industry), however other designs and materials can be utilized.
  • any of the components of a solar cell comprise nanofibers.
  • exemplary components include an anode, an n-layer, an active layer, a p-layer and a cathode.
  • the nanofibers are produced by the water-based, gas-assisted electrospinning process described herein.
  • the n-layer, active layer and p-layer comprise nanofibers.
  • the present disclosure includes uses of nanofibers in solar cells.
  • the present disclosure includes solar cells that include a nanofiber of the invention, includes solar cells that include a nanofiber produced by the methods of the invention, and includes thin film solar cells that include a nanofiber produced by the system of the invention.
  • the disclosure also includes methods for making and methods for using solar cells that include nanofibers.
  • the cathode comprises nanofibers (e.g., aluminum).
  • any suitable material is used as the cathode including pure metal nanofibers such as gold (Au), silver (Ag), nickel (Ni), copper (Co), and/or calcium (Ca).
  • the n-layer provides for transfer of electrons.
  • the n-layer comprises ZnO nanofibers. Any suitable bandgap material is used as the n-layer including nanofibers of any suitable pure metal oxides such as TiO 2 .
  • the photoactive layer comprises PbSe nanofibers (e.g., where the PbSe crystals are nanoscale in size).
  • Any suitable bandgap material is used as the photoactive layer including nanofibers of any suitable hybrid materials such as CdTe, CdS, PbS, and/or PbTe.
  • the p-layer provides the transfer of holes.
  • the p-layer comprises NiO nanofibers. Any suitable bandgap material is used as the p-layer including nanofibers of any suitable pure metal oxides such as CuInGaSe 2 .
  • ITO Indium Tin Oxide
  • the anode comprises ITO nanofibers.
  • any suitable conducting, transparent material is used as the anode including nanofibers of any suitable pure inorganic materials such as carbon.
  • the cathode comprises Al
  • the n-layer comprises ZnO
  • the photoactive layer comprises PbSe
  • the p-layer comprises NiO
  • the anode comprises ITO.
  • any one or more of the components comprise nanofibers.
  • the solar cells based on the nanofibers have good connectivity among nanocrystals in each layer with minimal recombination losses. In some instances, the solar cells based on the nanofibers remove the complications associated with incompatibility among processes for each component.
  • FIG. 37 illustrates an schematic of an embodiment of a solar cell device using nanofibers provided herein.
  • inorganic solid-state junction devices are being replaced by cells based on nanocrystalline and conducting films (i.e., thin films).
  • thin-film structures reduce the cost of photovoltaic devices (e.g., by eliminating the use of the expensive silicon wafers).
  • it is now possible to depart completely from solid-state junction devices by replacing the contacting phase to the semiconductor by an electrolyte, liquid, gel or solid, thereby forming a photo-electrochemical cell.
  • the prototype of this family of devices is the dye-sensitized solar cell (see FIG. 41 ).
  • the dye-sensitized solar cell performs the optical absorption and the charge separation processes by the association of a sensitizer as light-absorbing material with a wide band gap semiconductor of nanocrystalline morphology.
  • described herein are thin film solar cells and photo-electrochemical cells comprising nanofibers.
  • the present disclosure includes thin film solar cells and photo-electrochemical cells that include the nanofibers described herein, includes thin film solar cells and photo-electrochemical cells that include a nanofiber produced by the methods described herein, and includes thin film solar cells and photo-electrochemical cells that include a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using thin film solar cells and photo-electrochemical cells that include nanofibers.
  • the thin film solar cells and photo-electrochemical cells are flexible.
  • ITO Indium Tin Oxide
  • various flexible substrates based on transparent polymers have been developed, but they do not provide enough thermal stability for thermal treatment of electrode materials (>450° C.) or good adhesion between the substrate and electrodes.
  • described herein are coaxial nanofibers of alumina (core) and ITO (sheath) (e.g., for use as substrates for flexible solar cell applications).
  • the alumina/ITO nanofibers have good thermal stability and good adhesion between the substrate and the electrodes.
  • inorganic materials such as alumina, alumina-magnesia and zirconia have been fabricated as flexible substrates for catalytic applications.
  • insertion of these flexible inorganic materials in the ITO sheath of coaxial nanofibers results in improved flexibility without losing transparency and conductivity.
  • coaxial nanofibers of alumina and ITO are synthesized via water-based spinning (e.g., as substrates for flexible solar cells).
  • the development of alumina/ITO nanofibers cathodes is carried out in two steps.
  • aqueous polymer solutions containing high loading of Al precursor and ITO precursor are coaxially electrospun as core and sheath layer, respectively, followed by the thermal treatment to create alumina/ITO coaxial nanofibers.
  • a high speed air stream is incorporated into the coaxial procedure as an additional skin layer (i.e., tri-axial jets of alumina precursor (core)/ITO (middle)/air (sheath)).
  • the gas flow produces nanofibers at a faster rate.
  • tri-axial electrospinning is utilized in the confined assembly of block copolymers sandwiched by silica layers.
  • the present disclosure includes flexible solar cells that include the nanofibers described herein, includes flexible solar cells that include a nanofiber produced by the methods described herein, and includes flexible solar cells that include a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using flexible solar cells that comprise nanofibers.
  • the disclosure includes solar cells comprising a substrate comprising nanofibers comprising alumina, ITO, or a mixture of alumina and ITO.
  • FIG. 42 shows the principle of operation of a thin film nanocrystal/nanowire hybrid solar cell.
  • FIG. 44 shows a TEM image of tri-axial nanofibers of SiO 2 (core)/PI-b-PS with Fe 3 O 4 (middle)/SiO 2 (sheath).
  • the pure metal and/or ceramic nanofibers other than in electrochemical devices e.g., filters, sensors, catalysts, membranes, electrodes, tissue regeneration matrixes, and the like.
  • Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst.
  • a catalyst is not consumed by the reaction itself.
  • a catalyst participates in multiple chemical transformations.
  • catalysts that speed the reaction are called positive catalysts.
  • substances that interact with catalysts to slow the reaction are called inhibitors (or negative catalysts).
  • substances that increase the activity of catalysts are called promoters, and substances that deactivate catalysts are called catalytic poisons.
  • solid-state catalysts (sometimes known as a heterogeneous catalyst) catalyze reactions on their surface.
  • Exemplary solid-state catalysts are metals and metal alloys.
  • metals and metal alloys are expensive (e.g., precious metals) and reactions are surface-catalyzed.
  • it is advantageous to use a catalyst with a high surface to mass ratio (e.g., to maximize performance per cost).
  • long, thin nanofibers have a high surface area to mass ratio, so are a desirable material from which to make catalysts.
  • described herein are catalysts.
  • the present disclosure includes a catalyst that comprises the nanofibers described herein, includes a catalyst that comprises a nanofiber produced by the methods described herein, and includes a catalyst that comprises a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using catalysts that comprise nanofibers.
  • the catalyst comprises composite nanofibers comprising a first layer (e.g., comprising Fe or Ni) and a second layer (e.g., comprising SiO 2 , ZrO 2 or Al 2 O 3 ).
  • the catalyst is capable of producing H 2 from glucose or cellulose.
  • the catalyst has a maximum temperature for H 2 production of about 60° C. (e.g., increased from about 40° C.).
  • hydrogen sulfide is a poisonous gas that is a pollutant in some industrial processes.
  • hydrogen sulfide is removed by a catalyst.
  • the catalyst comprises composite nanofibers (e.g., comprising ZnO on ZrO 2 ).
  • the catalyst is capable of removing H 2 S from flue gas.
  • the catalyst is capable of removing H 2 S to a concentration of 10 ppm.
  • filters are used to purify particles from a fluid stream.
  • the present disclosure includes filters.
  • the present disclosure includes a filter that comprises the nanofibers described herein, includes a filter that includes a nanofiber produced by the methods described herein, and includes a filter that includes a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using filters that comprise nanofibers.
  • the filter is a water filter. In some embodiments, the filter is an air filter. In some embodiments, the filter is designed to remove particles of a certain size.
  • the nanofibers described herein are used in sensors.
  • the sensor comprises nanofibers comprising metal oxides.
  • the metal oxides are dispersed in a conducting metal.
  • a molecule is sensed by a change in current.
  • the nanofiber comprises V 2 O 5 and the molecule is ammonia.
  • the present disclosure includes sensors.
  • the present disclosure includes a sensor that comprises the nanofibers described herein, includes a sensor that includes a nanofiber produced by the methods described herein, and includes a sensor that includes a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using sensors that comprise nanofibers.
  • a membrane is a general or selective barrier, which is often thin.
  • the nanofibers described herein are formed into membranes.
  • the membrane comprises nanofibers (e.g., SiO 2 comprising metal oxides).
  • the membrane is capable of removing metal ions from wastewater.
  • the membrane comprises nanofibers comprising TiO 2 .
  • the membrane is capable of degrading organic pollutants.
  • the pollutant is a pesticide or volatile organic compound.
  • the degradation of the pollutant is photocatalytic (i.e., catalyzed by light).
  • the present disclosure includes membranes.
  • the present disclosure includes a membrane that comprises the nanofibers described herein, includes a membrane that comprises a nanofiber produced by the methods described herein, and includes a membrane that comprises a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using membranes that comprise nanofibers.
  • an electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g., a semiconductor, an electrolyte or a vacuum).
  • electrodes are utilized in electrochemical devices (e.g., fuel cells, batteries, ultra-capacitors and solar cells).
  • the present disclosure includes electrodes.
  • the present disclosure includes an electrode that comprises the nanofibers described herein, includes an electrode that comprises a nanofiber produced by the methods described herein, and includes an electrode that comprises a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using electrodes that comprise nanofibers.
  • the nanofibers are used in medicine, including in tissue culture.
  • described herein are tissue regeneration matrixes.
  • the nanofibers are used for constructing a porous scaffold onto which cells are seeded that grow to fill the scaffold (e.g., thereby producing a material suitable for tissue supplementation or replacement).
  • the present disclosure includes an electrode that comprises the nanofibers described herein, includes an electrode that comprises a nanofiber produced by the methods described herein, and includes an electrode that comprises a nanofiber produced by the system described herein.
  • described herein are methods for making and methods for using electrodes that comprise nanofibers.
  • the nickel acetate solution was then combined with the PVA solution to create a fluid stock.
  • the precursor solution was added gradually to the polymer solution while being continuously vigorously stirred for 2 hours.
  • the mass ratio of precursor to polymer for the fluid feed was 2:1.
  • the fluid stock of Example 1 was electrospun by a gas-assisted technique.
  • the overall process and apparatus is depicted in FIG. 1 .
  • the fluid stock was loaded into a syringe pump connected to a spinneret with an inner nozzle diameter (fluid stock) of 4.13 ⁇ 10 ⁇ 4 m and an outer (air) diameter of 1.194 ⁇ 10 ⁇ 3 m.
  • the distance between the nozzle and the collection plate was kept at about 15 cm and the fluid stock was spun at a rate of 0.1 ml/min.
  • a charge of +15 kV was maintained at the collector.
  • the air velocity at the nozzle was 100 m/s.
  • the temperature of the air and fluid stock at the nozzle was 300 K.
  • the electrospun fluid stock of Example 3 was heated for 2 hours at 600° C. in an atmosphere of 100% Ar gas.
  • an SEM image was taken before and after calcination as depicted in FIG. 3 .
  • the diameter of the nanofiber was approximately 500-700 nm as spun and 400-500 nm after calcination.
  • an x-ray diffraction measurement was conducted a Scintag Theta-Theta X-ray Diffractometer, indicating that the nanofiber was substantially pure nickel as depicted in FIG. 3 .
  • the electrospun fluid stock of Example 3 was heated for 2 hours at 600° C. in an atmosphere of air.
  • an SEM image was taken before and after calcination as depicted in FIG. 4 .
  • the diameter of the nanofiber was approximately 500-700 nm as spun and 300-500 nm after calcination.
  • An x-ray diffraction measurement indicates that that the nanofiber was substantially pure nickel oxide as depicted in FIG. 4 .
  • Example 2 a fluid stock of copper acetate and PVA were prepared with the ratio of precursor:polymer of 2:1. These fluid stocks were electrospun by the procedure of Example 3. The electrospun fluid stock was heated for 2 hours at 800° C. in an atmosphere of 94% Ar and 6% H 2 gas. In order to visualize the nanofiber before and after calcination an SEM image was taken before and after calcination as depicted in FIG. 5 . The diameter of the nanofiber was approximately 600-800 nm as spun and 300-500 nm after calcination. An x-ray diffraction measurement indicates that that the nanofiber was substantially pure copper as depicted in FIG. 5 .
  • the electrospun fluid stock of Example 6 was heated for 2 hours at 600° C. in an atmosphere of air.
  • an SEM image was taken before and after calcination as depicted in FIG. 6 .
  • the diameter of the nanofiber was approximately 600-800 nm as spun and 200-600 nm after calcination.
  • An x-ray diffraction measurement indicates that that the nanofiber was substantially pure copper oxide as depicted in FIG. 6 .
  • Example 2 Following the procedure of Example 1, a fluid stock of silver acetate and PVA were prepared with ratio of precursor:polymer of 2:1. These fluid stocks were electrospun by the procedure of Example 3. The electrospun fluid stock was heated for 2 hours at 600° C. in an atmosphere of air. In order to visualize the nanofiber before and after calcination an SEM image was taken before and after calcination as depicted in FIG. 7 . The diameter of the nanofiber was approximately 900-1200 nm as spun and 600-800 nm after calcination. An x-ray diffraction measurement indicates that that the nanofiber was substantially pure silver as depicted in FIG. 7 .
  • Example 2 a fluid stock of iron acetate and PVA were prepared with the ratio of precursor:polymer of 2:1. These fluid stocks were electrospun by the procedure of Example 3. The electrospun fluid stock was heated for 2 hours at 600° C. in an atmosphere of air. In order to visualize the nanofiber before and after calcination an SEM image was taken before and after calcination as depicted in FIG. 8 . The diameter of the nanofiber was approximately 300-500 nm as spun and 200-400 nm after calcination. An x-ray diffraction measurement indicates that that the nanofiber was substantially pure iron as depicted in FIG. 8 .
  • Example 2 a fluid stock of zinc acetate and PVA were prepared with the ratio of precursor:polymer of 2:1. These fluid stocks were electrospun by the procedure of Example 3. The electrospun fluid stock was heated for 2 hours at 600° C. in an atmosphere of air. In order to visualize the nanofiber before and after calcination an SEM image was taken before and after calcination as depicted in FIG. 9 . The diameter of the nanofiber was approximately 500-1000 nm as spun and 400-700 nm after calcination. An x-ray diffraction measurement indicates that that the nanofiber was substantially pure zinc oxide as depicted in FIG. 9 .
  • Example 2 a fluid stock of cadmium acetate and PVA were prepared with the ratio of precursor:polymer of 2:1. These fluid stocks were electrospun by the procedure of Example 3. The electrospun fluid stock was heated for 2 hours at 800° C. in an atmosphere of air. In order to visualize the nanofiber before and after calcination an SEM image was taken before and after calcination as depicted in FIG. 10 . The diameter of the nanofiber was approximately 800-1200 nm as spun and 600-900 nm after calcination. An x-ray diffraction measurement indicates that that the nanofiber was substantially pure cadmium as depicted in FIG. 10 .
  • Example 2 a fluid stock of zirconium acetate and PVA were prepared with the ratio of precursor:polymer of 2:1. These fluid stocks were electrospun by the procedure of Example 3. The electrospun fluid stock was heated for 2 hours at 800° C. in an atmosphere of air or 94% Ar and 6% H 2 gas. In order to visualize the nanofiber before and after calcination an SEM image was taken before and after calcination as depicted in FIG. 10 . The diameter of the nanofiber was approximately 800-1000 nm as spun and 300-600 nm after calcination. An x-ray diffraction measurement indicates that that the nanofiber was substantially pure zirconia as depicted in FIG. 11 .
  • Example 2 a fluid stock of lead acetate and PVA were prepared with the ratio of precursor:polymer of 2:1. These fluid stocks were electrospun by the procedure of Example 3. The electrospun fluid stock was heated for 2 hours at 600° C. in an atmosphere of 94% Ar and 6% H 2 gas. In order to visualize the nanofiber before and after calcination an SEM image was taken before and after calcination as depicted in FIG. 10 . The diameter of the nanofiber was approximately 500-1200 nm as spun and 250-700 nm after calcination. An x-ray diffraction measurement indicates that that the nanofiber was substantially pure lead as depicted in FIG. 12 .
  • Nanofibers are prepared by calcination under appropriate conditions.
  • Example 2 Following the procedure of Example 1, various fluid stocks of nickel acetate and PVA were prepared with ratios of precursor:polymer of 1:2, 1:1, 2:1, and 4:1. These fluid stocks were electrospun by the procedure of Example 3. At that point, 4 SEM micrographs were taken of the electrospun fluid stock. The electrospun fluid stock was then calcinated by the procedure of Example 4 to create pure Ni nanofibers. At that point, 4 micrographs were taken of the calcinated nanofibers. FIG. 13 shows that the diameter of the nanofibers increased with higher loading of precursor. It also shows that continuous, high-quality nanofibers were formed, particularly at high loading of precursor. TEM micrographs were also taken of the calcinated nanofibers. FIG. 14 shows that there are no voids in the nanofibers, confirming that they are dense and coherent.
  • FIG. 15 shows that for both dark (left) and bright (right) regions of the TEM images, the majority of the nanofiber is Ni with a small oxygen content. Negligible amounts of carbon are detected.
  • a mixture of 50% Pb and 50% Se were formed from lead acetate and Se powder according to the procedures of Example 1.
  • the precursors were further made into a fluid stock with PVA according to the procedure of Example 1 and electrospun according to the procedure of Example 3.
  • the electrospun fluid stock was calcinated by heating for 2 hours at 600° C. in an atmosphere of 100% Ar.
  • Micrographs FIG. 23
  • TEM micrographs FIG. 24
  • EDX Energy-dispersive x-ray spectroscopy
  • FIG. 30 shows that calcinated pure metal nanofibers prepared by the methods of the disclosure (Treatment Scheme 2 and 3) exhibit very high conductivity (greater than 10 6 S/m) and are nearly as conductive as the known conductivity of the metal when formed into a sheet. On the contrary, metal fibers with Treatment Scheme 1 and from low precursor loading exhibit much lower conductivity (lower than 10 3 S/m).
  • Fluid feeds of Zr acetate and Ni acetate were prepared according to the procedure of Example 1.
  • the two fluid stocks were then electrospun in a co-axial manner using a spinneret similar to the one depicted in FIG. 35 .
  • the center conduit contained Ni acetate fluid stock (not air as depicted in FIG. 35 ) and the outer conduit contained ZrO 2 fluid stock.
  • the electrospinning procedure was gas-assisted.
  • the electrospun hybrid fluid stock was calcinated by heating for 2 hours at 600° C. in an atmosphere of air, followed by 2 hours at 600 C in an atmosphere of 94% Ar and 6% H 2 gas.
  • Micrographs FIG. 31
  • TEM micrographs FIG. 32
  • EDX Energy-dispersive x-ray spectroscopy
  • Fuel cell electrodes that include Fe—Pt nanofibers. These nanofibers may be prepared according to the procedures and system depicted in FIG. 34 . Water-soluble Fe and Pt acetates are mixed with a water-soluble polymer such as PVA to create a fluid stock as in Example 1. The ratio of precursor to polymer is 4:1 in this example.
  • gas assisted electrospinning will be adapted to increase the throughput.
  • the nanofiber production rate can be increased by more than ten times by incorporate air flow into the sheath jet layer in a coaxial scheme. As depicted in FIG.
  • the spinning dope can be prepared by adding an adequate ratio of Fe to Pt precursors to aqueous polymer solution and is used as the core jet in coaxial electrospinning, while a high-speed air stream is used as the sheath layer jet to stretch the core jet of precursor solution.
  • the creation of the face-centered tetragonal structure of Fe—Pt is pursued to enhance oxygen reduction and durability under the minimized Pt loading.
  • FIG. 35 shows an apparatus suitable for producing hollow Si or Ge nanofibers suitable for use as anodes in lithium ion batteries.
  • the high speed air and Si or Ge precursor solution form the core and sheath jets in gas-assisted coaxial electrospinning
  • FIG. 36 shows a schematic of the process and system for producing Al 2 O 3 /ITO hybrid nanofibers suitable for use in flexible solar cells. Triaxial configuration of Al 2 O 3 /ITO/air in gas-assisted electrospinning is utilized to produce a coaxial Al 2 O 3 /ITO nanofiber.
  • FIG. 37 shows micrographs, x-ray diffraction plots and a schematic for a solar cell with a plurality of components made from nanofibers.
  • FIG. 16 shows micrographs and an x-ray diffraction plot of ZnO/ZrO 2 hybrid nanofibers
  • FIG. 17 shows micrographs and an x-ray diffraction plot of Ag/ZrO 2 hybrid nanofibers
  • FIG. 18 shows micrographs and an x-ray diffraction plot of Ni/ZrO 2 hybrid nanofibers
  • FIG. 19 shows micrographs and an x-ray diffraction plot of Fe/ZrO 2 hybrid nanofibers
  • FIG. 16 shows micrographs and an x-ray diffraction plot of ZnO/ZrO 2 hybrid nanofibers
  • FIG. 17 shows micrographs and an x-ray diffraction plot of Ag/ZrO 2 hybrid nanofibers
  • FIG. 18 shows micrographs and an x-ray diffraction plot of Ni/ZrO 2 hybrid nanofibers
  • FIG. 19 shows micrographs and an x-ray diffraction plot of Fe/ZrO 2 hybrid nanofibers
  • FIG. 21 shows micrographs and an x-ray diffraction plot of Ni/Al 2 O 3 hybrid nanofibers
  • FIG. 22 shows micrographs and an x-ray diffraction plot of CdSe alloy nanofibers
  • FIG. 26 shows micrographs and an x-ray diffraction plot of CdTe alloy nanofibers
  • FIG. 27 shows micrographs and an x-ray diffraction plot of PbTe alloy nanofibers
  • FIG. 28 shows micrographs and an x-ray diffraction plot of Fe 3 O 4 /FeNi alloy nanofibers
  • FIG. 29 shows TEM micrographs of Fe 3 O 4 /FeNi alloy nanofibers.
  • processes describe in the examples herein were utilized to make the nanofibers of Table 1.
  • FIG. 20 shows TEM micrographs of various hybrid nanofibers.

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