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  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
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  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/44—Carbon
  • C09C1/48—Carbon black
  • C09C1/56—Treatment of carbon black ; Purification
  • C09C1/565—Treatment of carbon black ; Purification comprising an oxidative treatment with oxygen, ozone or oxygenated compounds, e.g. when such treatment occurs in a region of the furnace next to the carbon black generating reaction zone
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  • C01B2202/00—Structure or properties of carbon nanotubes
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  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/20—Nanotubes characterized by their properties
  • C01B2202/36—Diameter
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Definitions

• the present invention was made in connection with research pursuant to grant numbers NASA-JSC-NCC 9-77 from the National Aeronautics and Space Administration; grant number NSR- DMR-0073046 from the National Science Foundation; and grant number N00014-99-1-0406 from the DARPA/ONR.
• the present invention relates broadly to carbon nanotubes. More specifically, the invention relates to derivatization of carbon nanotubes with diazonium compounds and to uses for the derivatized carbon nanotubes.
• Fullerenes are closed-cage molecules composed entirely of sp -hybridized carbons, arranged in hexagons and pentagons. Fullerenes (e.g., C 60 ) were first identified as closed spheroidal cages produced by condensation from vaporized carbon. Fullerene tubes are produced in carbon deposits on the cathode in carbon arc methods of producing spheroidal fullerenes from vaporized carbon.
• Such tubes are referred to herein as carbon nanotubes.
• Many of the carbon nanotubes made by these processes were multi-wall nanotubes, i.e., the carbon nanotubes resembled concentric cylinders.
• Carbon nanotubes having up to seven walls have been described in the prior art. Ebbesen II; lijima et al., "Helical Microtubules Of Graphitic Carbon,”
• Nanotubes are one of the more striking discoveries in the chemistry and materials genre in recent years. Nanotubes posses tremendous strength, an extreme aspect ratio, and are excellent thermal and electrical conductors. A plethora of potential applications for nanotubes have been hypothesized, and some progress is being made towards commercial applications. Accordingly, chemical modification of single-wall carbon nanotubes, as well as multi- wall carbon nanotubes, will be necessary for some applications.
• such applications may require grafting of moieties to the nanotubes: to allow assembly of modified nanotubes, such as single-wall carbon nanotubes, onto surfaces for electronics applications; to allow reaction with host matrices in composites; and to allow the presence of a variety of functional groups bound to the nanotubes, such as single-wall carbon nanotubes, for sensing applications.
• These functionalized nanotubes may either be de-fluorinated by treatment with hydrazine or allowed to react with strong nucleophiles, such as alkyllithium reagents.
• strong nucleophiles such as alkyllithium reagents.
• fluorinated nanotubes may well provide access to a variety of functionalized materials, the two-step protocol and functional group intolerance to organolithium reagents may render such processes incompatible with certain, ultimate uses of the carbon nanotubes.
• the invention incorporates new processes for the chemical modification of carbon nanotubes.
• Such processes involve the derivatization of multi- and single-wall carbon nanotubes, including small diameter (ca. 0.7 nm) single-wall carbon nanotubes, with diazonium species.
• the method allows the chemical attachment of a variety of organic compounds to the side and ends of carbon nanotubes.
• These chemically modified nanotubes have applications in polymer composites, molecular electronic applications, and sensor devices.
• the methods of derivatization include electrochemical induced reactions, thermally induced reactions (via in-situ generation of diazonium compounds or via preformed diazonium compounds), and photochemically induced reactions.
• the derivatization causes significant changes in the spectroscopic properties of the nanotubes.
• the estimated degree of functionality is ca. 1 out of every 20 to 30 carbons in a nanotube bearing a functionality moiety.
• the electrochemical induced processes include procedures utilizing an assembly of nanotubes, such as a piece of "bucky paper" or mat, which can be held with a silver paste covered alligator clip and immersed in an acetonitrile solution of a diazonium salt and a supporting electrolyte salt, while applying a potential (typically a negative potential) to the assembly of nanotubes.
• a molecular wire such as an oligo(phenylene ethynylene) molecular wire
• a molecular electronic device have been covalently attached to a nanotube.
• Such electrochemical processes can be adapted to apply site-selective chemical functionalization of nanotubes. Moreover, it allows for the controlled attachment of two or more different chemical functionalities to different locations on the nanotubes.
• the thermally induced processes include procedures in which a dispersion of carbon nanotubes in an organic solvent mixture is treated with a precursor to a reactive diazonium species. This precursor is then transformed in-situ to the reactive species, and its thermal decomposition leads to chemical attachment to the carbon nanotubes. It is believed that such a process has the advantage of scalability and avoids the necessity of isolating and storing potentially unstable diazonium compounds, i.e., the species that reacts with the carbon nanotubes.
• the thermal induced processes also include procedures utilizing pre-formed diazonium species.
• the reactive species can be prepared beforehand, isolated, and added to the mixture. Additional variations include variations in the temperature of the process (ambient temperature and higher and lower temperatures), ratio of reactants, and a variety of organic solvents.
• the photochemical induced processes are similar to the thermal induced reaction except that a photochemical process (not a thermal process) is utilized to cause the decomposition of the diazonium species that leads to the chemical attachment of the moieties to the carbon nanotubes.
• the nanotubes When modified with suitable chemical groups, the nanotubes are chemically compatible with a polymer matrix, allowing transfer of the properties of the nanotubes (such as mechanical strength) to the properties of the composite material as a whole.
• the modified carbon nanotubes can be thoroughly mixed (physically blended) with the polymeric material, and/or, if desired, allowed to react at ambient or elevated temperature. These methods can be utilized to append functionalities to the nanotubes that will further covalently bond to the host polymer matrix, or directly between two tubes themselves.
• polyethylene polyethylene
• various epoxy resins polypropylene, polycarbonate etc.
• composite materials could be made with chemically modified nanotubes and thermoplastics, thermosets, elastomers, and others.
• chemical groups that can be attached to the nanotubes. The specific group will be chosen to enhance compatibility with the particular polymer matrix desired and, if desired, to cause chemical bonding to the host material.
• the nanotubes can be used as a generator of polymer growth. I.e., the nanotubes would be derivatized with a functional group that could be an active part of a polymerization process, which would also result in a composite material in which the carbon nanotubes are chemically involved.
• FIGURE 1 shows the structure of certain aryl diazonium salts used to derivatize single-wall carbon nanotubes.
• FIGURE 2 shows the scheme utilized to prepare Compounds 9 and 11 as reflected in Figure
• FIGURE 3 shows the absorption spectra in dimethylformamide for (A) SWNT-p and (B) SWNT-1.
• FIGURE 4 shows the absorption spectra in dimethylformamide for (A) SWNT-p and (B) SWNT-8.
• FIGURE 5 shows the Raman spectra from solid samples, with excitation at 782 nm, for (A) SWNT-p and (B) SWNT-1.
• FIGURE 6 shows the Raman spectra in the radial breathing mode region for (A) SWNT-4 and (B) SWNT-p.
• FIGURE 7 shows the infrared spectra (attenuated total reflectance) of derivatized nanotubes for (A) SWNT-4 and (B) SWNT-6.
• FIGURE 8 shows the thermogravimetric analysis data in argon for SWNT-10.
• FIGURE 9 shows the Raman spectra for (A) SWNT-p, (B) SWNT-2, and (C) SWNT-2 after TGA.
• FIGURE 10 shows the high-resolution TEM images for (A) SWNT-p and (B) SWNT-4. The scale bar applies to both images.
• FIGURE 11 shows electrochemical grafting of an aryl diazonium salt onto a carbon surface.
• FIGURE 12 shows the reaction sequence for derivatization of single-wall carbon nanotubes by in-situ generation of the diazonium species, and examples of functionalized phenyl moieties employed in reactions.
• FIGURE 13 shows the absorption spectra in dimethylformamide for (A) SWNT-p and (B) 18.
• the spectra for 16, 17, and 19 are similar, with little or no visible structure.
• the spectrum of the material from the sequence to produce 20 was essentially equivalent to that shown for SWNT-p.
• FIGURE 14 shows the Raman spectra from solid samples, with excitation at 782 nm, for (A) SWNT-p and (B) 17.
• the Raman spectra of 16, 18, and 19 are similar, but with differing ratios of the peak intensities. In all these cases, the relative intensity of the disorder mode is increased.
• the spectrum of the material from the sequence to produce 20 was essentially equivalent to that shown for SWNT-p.
• FIGURE 15 shows the reaction sequence for photochemical derivatization of a single-wall carbon nanotube.
• FIGURE 16 shows an example of the portions comprising an epoxy resin.
• FIGURE 17 shows examples of nanotubes that are chemically modified with groups compatible with the curing agent portion, and reactive with the epoxy portion of a thermosetting resin.
• FIGURE 18 shows a schematic depiction of carbon nanotube containing composite material where the freehand lines represent the polymer matrix that is cross-linked by the chemically modified carbon nanotubes, creating a thermosetting composite material.
• FIGURE 19 shows a depiction of chemically modified carbon nanotubes cross-linked via disulfide linkages.
• FIGURE 20 shows the preparation of nanotubes chemically modified with thiophenol moieties.
• FIGURE 21 shows the preparation of carbon nanotubes chemically modified with pendant epoxy groups that are compatible with the epoxy portion of a resin and reactive with the curing agent portion of a thermosetting resin, as reflected in FIGURE 16.
• FIGURE 22 shows an example of a composite material based on poly(methylmethacrylate) and chemically modified carbon nanotubes, based on a hydrogen bonding motif (indicated by the dashed lines).
• FIGURE 23 shows an example of chemically modified nanotubes being used in a polymerization process to grow the polymer from the nanotubes.
• Aryl diazonium salts are known to react with electron deficient olefi s, known as the Meerwein reaction. Obushak, M. D., et al., Tett. Lett. 1998, 39, 9567-9570. In such solution phase reactions, diazonium salt decomposition is typically catalyzed by a metal salt such as copper(l) chloride, giving a reactive aryl radical. In some cases, the reaction is believed to proceed through an aryl cation. This type of chemistry has been successfully applied to the modification of carbon surfaces via grafting of electrochemically reduced aryl diazonium salts.
• Methylene chloride and acetonitrile were distilled from calcium hydride.
• Dimethylformamide was distilled and stored over molecular sieves.
• Tetrahydrofuran was distilled from sodium/benzophenone ketyl. All other reagents were obtained commercially and used without further purification.
• Carbon Nanotubes A method for producing small diameter (ca. 0J nm) single-wall carbon nanotubes has been developed by Smalley, et al. Nikolaev, P., et al., Chem. Phys. Lett. 1999, 313, 91-97. This method is disclosed in a co-pending application commonly assigned to the assignee of the Application, United States Patent Application Serial No. 09/830,642 "Gas-Phase Nucleation and Growth of Single-Wall Carbon Nanotubes from High Pressure CO,” to Smalley et al., filed April 27, 2001, which is incorporated herein by reference. This material is now commercially available (Carbon Nanotechnologies Inc., HiPco material).
• these nanotubes are understood to display enhanced reactivity relative to the larger diameter tubes typically produced by laser oven methods, since the reactivity of C 6 o has been attributed in part to curvature strain. While the present invention is also pertinent to multi-wall carbon nanotubes and larger diameter single-wall carbon nanotubes, these small diameter nanotubes were primarily utilized during the examples demonstrating the present process. A variety of diazonium salts have been used, including those that provide moieties conducive to further elaboration after attachment of the nanotubes. Also, an oligo (phenylene ethynylene) molecular device similar to the one that has been shown to exhibit memory and room temperature negative resistance (Chen, J. et al., App. Phys. Lett. 2000, 77, 1224-1226) has been attached to the nanotubes.
• oligo phenylene ethynylene
• Examples Nos. 1-11 For the electrochemical derivatization experiments, a piece of bucky paper, formed by filtration of a suspension, was used as the working electrode in a 3-electrode cell and immersed in an acetonitrite solution containing the diazonium salt and an electrolyte.
• the diazonium salts were probably reduced to aryl radicals at the surface of the bucky paper, and subsequently become covalently attached to the nanotubes.
• the conductivity of single-wall carbon nanotubes has been well documented.
• aryl diazonium salts are easily prepared under conditions that tolerate a variety of functional groups. Consequently, the method described herein allows functionalization of nanotubes with a wide variety of diazonium salts, including those that provide chemical handles for additional elaboration after attachment to nanotubes.
• the purified single-wall nanotubes (hereafter, SWNT-p) used in this investigation contained little amorphous or other extraneous carbon contaminants.
• the purification technique for the nanotubes is discussed in more detail below.
• the fact the SWNT-p contained little amorphous or other extraneous carbon contaminants is significant, as the presence of such material may have hindered the ability to determine whether previous derivatization efforts were successful. (although the lack of impurities was an issue in the initial demonstrations respecting the operability of the reactions, it should be noted that these reactions will work on raw, impurified multi- and single-wall carbon nanotubes, i.e.
• the small diameter single-wall carbon nanotubes used in this investigation were produced by a gas-phase catalytic technique, using carbon monoxide as the feedstock and iron carbonyl as the catalyst.
• Nanotechnologies Inc., HiPco material The raw production material was purified by air oxidation at 150°C for a period of 12 hours, followed by annealing in argon at 800°C for 6 hours. This material was sonicated in concentrated hydrochloric acid (ca. 30 mg in 60 mL), filtered, washed extensively with water and 2-propanol, and dried under vacuum. The purity of these samples was verified by SEM, TEM, and EMPA.
• Bucky Paper The use of bucky paper as a working electrode for the derivatization raises several unique issues. Electrical contact between the source and the bucky paper during the electrochemical process is an issue. This situation can be improved by application of colloidal silver paste to the alligator clip used to hold the bucky paper. It is also believed that the success of the reaction is at least partially dependent on the quality of the bucky paper employed as the working electrode. Accordingly, it was helpful to achieve a suspension that contained little or no visible particulate prior to filtration to form the bucky paper.
• the apparatus used for the electrochemical derivatization experiments was a 3-electrode cell, with Ag/AgN0 3 reference electrode and platinum wire counter electrode.
• a piece of bucky paper (1-2 mg) served as the working electrode.
• the bucky paper was prepared by filtration of a 1 ,2-dichlorobenzene suspension over a 0.2 ⁇ M PTFE (47 mm, Sartorius) membrane. After drying under vacuum, the paper was peeled off the membrane, and a piece was excised for use in the derivatization.
• the bucky paper was held with an alligator clip, previously treated with colloidal silver paste (Ted Pella, Inc.), and immersed in an acetonitrile solution of the diazonium salt (0.5 mM for SWNT-1-SWNT-7 and SWNT-
• TGA data were collected in argon, on a TA Instruments SDT-2960.
• AFM experiments were performed in tapping mode on a Digital Multi-mode SPM. Samples for these experiments were dispersed by sonication and spin coated on a freshly cleaved mica substrate.
• EMPA experiments were performed on a Cameca SX- 50. The instrument was calibrated, and data were taken from several different points on each sample. The average of these points is reported below.
• NMR data were collected on a Bruker Avance 400. Chemical shifts are reported in ppm downfield from TMS, and referenced to solvent. Melting points are not corrected.
• the features (van Hove bands) in the spectrum of SWNT-p are due to singularities in the density of states (DOS), and, in this spectral region, are attributed to the band gap transitions in semiconducting nanotubes.
• the width of these features is due to the overlap of features from tubes of different diameters and chiral indices. These transitions are no longer visible for SWNT-1, and the spectrum is essentially featureless.
• the absorption spectra of SWNT-2 - SWNT-7 and SWNT-11 - SWNT-12 are similar, with no apparent features.
• Raman Spectroscopy Raman spectroscopy of single-wall carbon nanotubes is also well developed both theoretically and experimentally. Richter, E., et al., Phys. Rev. Lett. 1997, 79, 2738- 2740; Rao, A. M, et al., Science 1997, 275, 187-191; Li, H. D., et al., App. Phys. Lett. 2000, 76, 2053-2055.
• the Raman spectrum of SWNT-p ( Figure 5A) displays two strong bands; the radial breathing ( ⁇ r ⁇ 230 cm "1 ) and tangential ( ⁇ t ⁇ 1590 cm "1 ) modes.
• SWNT-8 1292 1.0 : 0.7 : : 3.0
• the intensity of this mode increased relative to the intensity of the other two modes in all cases.
• the intensity of the tangential mode is also increased relative to the radial breathing mode in most cases, and the overall intensity is lower.
• Raman spectra collected after functionalization revealed changes in the relative intensities of the peaks within the radial breathing mode region. For example, the Raman spectra in this region is shown in Figure 6 for SWNT-p and SWNT-4.
• Electron Microprobe analysis Electron microprobe analysis (EMPA) experiments revealed 2.7 atomic% chlorine for SWNT-2 (average of four points), and 3.5 atomic% fluorine for SWNT-3
• Nanotube carbons bearing a functionalized phenyl moiety are compensated for weight loss at low temperatures due to solvent evaporation and degassing (ca. 2-4% in all cases).
• Table 2 reflects that the degree of functionality for these compounds is at least about one moiety to fortoy carbon atoms, and typically at least about one moiety to thirty carbon atoms.
• the estimated degree of functionality is ca. out of every 20 to 30 carbons in the nanotube bearing a functionality moiety.
• SWNT-4 was the only material found to offer significantly improved solubility in organic solvents.
• SWNT-4 was even found to be somewhat soluble in tetrahydrofuran (THF), as opposed to a complete lack of solubility for SWNT-p in that solvent.
• THF tetrahydrofuran
• the THF solution was found to contain approximately 50 mg L "1 of SWNT-4, with no visible particulate. After 36 hours, some visible particulate was present, but the solvent was still almost black. This dark color was retained for at least several weeks.
• Solubility in dimethylformamide, chloroform, and 1,2- dichlorobenzene was also improved, with suspensions being formed much more rapidly than in the case of SWNT-p, and higher concentrations being achievable. It is believed that this improvement in solubility is probably due to the blocking effect of the bulky ferf-butyl group, which could inhibit the close contact necessary for "roping" of the nanotubes.
• SWNT-5 and SWNT-8 were found to be more soluble in dimethylformamide, but solubility in other solvents (tetrahydrofuran, toluene, 2-propanol, carbon disulfide) was not improved.
• SWNT-9 was prepared in an effort to effect improved solubility in water and other hydrogen bonding solvents. This functionalization, however, had quite the opposite result.
• SWNT-9 was not dispersible in water or water/0.2 %Triton X. Considerable difficulty was encountered in suspending SWNT-9 in dimethylformamide. Robustness. In an effort to assess the robustness of the functionalization and preclude simple intercalation or adsorption, SWNT-1 was subjected to a variety of conditions.
• SWNT-3 was re-examined by EMPA after additional sonication in acetonitrile, followed by filtration and washing.
• the fluorine content was 3.6 atomic %, as compared to 3.5 atomic % (w ' cfe supra), and hence within experimental limits C.
• the aryl radical that is presumably generated on reduction may react with a nanotube, leaving an adjacent radical that may further react or be quenched by a solvent or some impurity, or oxygen.
• the propensity of the initial aryl radical to dimerize or abstract a hydrogen atom from the solvent is minimized by the fact that the radical is generated at the surface of the nanotube where reaction is desired. It is noted that although the reaction may proceed through an aryl cation, the mechanism is irrelevant to the final product.
• Derivatization with aryl diazonium species is not limited to the electrochemically induced reaction. That is, both direct treatment of single-wall carbon nanotubes with aryl diazonium tetrafluoroborate salts in solution, and in-situ generation of the diazonium with an alkyl nitrite are effective means of functionalization. In-situ generation of the diazonium species has advantages in that this method can avoid the necessity of isolating and storing potentially unstable or light sensitive aryl diazonium species.
• the temperature utilized during the thermal reaction would be at most about 200°C, and typically at most about 60°C. In some cases, direct treatment with pre-formed diazonium salts is observed to be effective at moderate or even room temperature, and it is expected that reactions could be observed at temperatures below room temperature.
• the nanotubes used in this investigation were again produced by a gas-phase catalytic process developed by Smalley et al., and are now commercially available (Carbon Nanotechnologies Inc., HiPco material).
• the production material was purified by oxidation in wet air at 250°C for 24 hours, then stirring in concentrated hydrochloric acid at room temperature for 24 hours. The resulting material was washed with copious amounts of water, then 10% aqueous sodium bicarbonate, and finally with additional water. After drying under vacuum, the material was used for the functionalization reactions.
• the suspension was diluted with 30 mL of dimethylformamide (DMF), filtered over a Teflon (0.45 ⁇ M) membrane, and washed extensively with DMF. Repeated sonication in, and further washing with DMF constituted purification of the material.
• DMF dimethylformamide
• the intensity of the disorder mode (1290 cm “1 ) is significantly increased.
• the increase in the relative intensity of the disorder mode can be attributed to an increased number of sp 3 -hybridized carbons in the nanotube framework, and can be taken as a crude measure of the degree of functionalization.
• the functionalized phenyl moieties attached to the nanotubes can be removed by heating in an argon atmosphere, and that thermal gravimetric analysis (TGA) consequently provides a quantitative estimate of the degree of functionalization.
• the mass loss for 19 corresponds to an estimated 1 in 37 carbons in the nanotubes being functionalized, versus the 1 in 34 ratio achieved by the electrochemical method. It is believed that the thermal technique is then comparable in its effectiveness to the electrochemical method for the equivalent material (SWNT-5). It is believed that optimization of the conditions could provide a higher degree of functionalization. The observed efficacy is sufficient to significantly alter the properties of the single-wall carbon nanotubes, and will likely be satisfactory for numerous applications, such as cross-linked materials and composite formation as discussed below.
• the thermal reaction of the present invention was found to be nearly as efficacious as the electrochemical process of the present invention, although, in certain respects, this thermal reaction is simpler to execute and more adaptable for scalability.
• the chemical derivatization of nanotubes can also be successfully performed using pre-formed diazonium species.
• the diazonium species can be prepared beforehand, isolated, and added to the mixture.
• the derivatization can then be induced thermally. Additional variations include variations in the temperature of the process (ambient temperature and higher and lower temperatures), ratio of reactants, and a variety of organic solvents.
• Derivatization with aryl diazonium species can also be induced photochemically. A photochemical reaction was performed utilizing 4-chlorobenzenediazonium tetrafluoroborate, which is the same diazonium species prepared and utilized in Example No. 2.
• directed functionalization of the crossed-nanotube junctions can be performed by applying a potential to the ends of the nanotubes (as is known in the art) in the presence of ⁇ , ⁇ -bis(diazonium) salts or mono-diazonium salts with an interacting group at the opposite end would permit functionalization at the cross point domain.
• any cross bar array of nanotubes could be functionalized by such processes.
• a crossbar architecture of nanotubes will be prepared by fluid flow over a patterned substrate, or by direct tube growth between posts, or by some other method.
• the diazonium salt assembly described here could occur in a diazonium solution, with voltages on orthogonal tubes, regardless of the assembly method for the tube arrays. Application of potentials to the nanotubes in the presence of diazonium salts would permit functionalization at the cross point domain.
• the diazonium species are directed by the potential existing at the junction to react with the surface of the nanotube, thus placing functional molecular devices at the junctions.
• Site-specific functionalization could enable the use of nanotubes in molecular electronic applications since device functionality is critical at the cross points.
• the crossed nanotubes therefore provide a method of directly addressing the functionalized molecules, including molecules that function as molecular switches, molecular wires, and in other capacities and uses as is generally known in the art.
• this process would allow for attachment of different molecules to nanotube cross points, i.e., controlled attachment of two or more different chemical functionalities to different locations on nanotubes. This would be performed by applying a potential at a specified set of positions while in a solution of a first diazonium salt , then moving to a solution of a second diazonium salt and applying a potential at other positions, etc.
• site specific functionalization will allow individual molecules or groups of molecules to be electrically addressed by metallic contact pads or other contact means as are known in the art. Just such a molecule of electronic interest is incorporated into SWNT-8.
• Polymer and polymer/composite materials are widely used for structural materials and a variety of other applications.
• the derivatized carbon nanotubes made using the processes disclosed herein can be used in combination with existing polymer matrices to create new polymer/composite materials.
• possible composite materials could be made with chemically modified nanotubes and thermoplastics, thermosets, elastomers, and others.
• chemical structure of the polymer matrix i.e. polyethylene, various epoxy resins, polypropylene, polycarbonate efc.
• chemical groups that can be attached to the nanotubes. According, it is possible to select a specific polymer and specific moiety to enhance the properties of the particular polymer/composite material desired.
• the polymer/composite material will have significantly enhanced properties, such as, for example, enhanced strength and/or conductivity.
• the nanotubes when modified with suitable chemical groups, the nanotubes will be chemically compatible with the polymer matrix, allowing transfer of the properties of the nanotubes (especially mechanical strength) to the properties of the composite material as a whole.
• the modified carbon nanotubes can be thoroughly mixed (physically blended) with the polymeric material, and allowed to react at ambient or elevated temperature.
• thermosets It may be desired to form a polymer/composite material in which the carbon nanotubes are chemically bound at multiple points to the polymer (thermosets). For example, this can be done, for example, utilizing an epoxy resin. Epoxy resins are typically composed of two portions that are mixed in a certain ratio. The resulting mixture then hardens, or "cures,” over a period of time into an adhesive or structural material. The two parts are the epoxy portion (labeled
• A in Figure 16 in this case derived from the reaction of bisphenol-A with epichlorohydrin
• B the curing agent
• the curing agent contains chemical groups that react with a repeatedly occurring chemical group in the epoxy portion. I.e., the cured or cross-linked resin results from the reaction of A (specifically, the terminal epoxide functionalities) with B (specifically, the terminal amine functionalities). Because both the epoxy portion and the curing agent contain numerous reactive groups, a "cross-linked” material is created, with numerous chemical bonds that impart strength to the cured material (labeled "C” in Figure 16). The result of the reaction is a highly cross-linked thermoset material.
• curing agents may be based on diamines, polymercaptans, phenol containing materials, etc., and may be polymeric.
• the addition of chemically modified carbon nanotubes to this type of system will greatly increase the strength of the resulting material, due to the strength of the nanotubes themselves.
• the nanotubes can be chemically modified with groups that are compatible with either the epoxy portion or the curing agent portion.
• modified nanotubes can be prepared as shown in Figure 17. (In the figures, the shaded cylinder represents the carbon nanotubes).
• Carbon nanotubes thus modified will be thoroughly mixed with either the curing agent portion or the epoxy portion.
• the resulting material will then be thoroughly mixed with the second portion and allowed to react, or cure at either ambient or elevated temperature, depending on the particular system.
• the resulting composite material will then be cross-linked not only by the curing agent, but also by the modified carbon nanotubes, via, for example, aryl-thioether linkages, as shown in Figure 18, where the freehand lines schematically represent the polymer matrix.
• the linkages between the polymer matrix and the nanotubes could be ether, thioether, amine, salt bridge (such as SWNT-11 in an amine contaning host polymer) or other linkages.
• the direct chemical bond between the nanotubes and the surrounding polymer matrix will enable the transference of the strength properties of the nanotubes to the composite material itself.
• enhancement of the material properties by the nanotubes may be caused by factors other than such direct chemical bonding; for example, improved dispersion of the nanotubes within the polymer matrix, enabled by the functionalization, may allow enhancement.
• the derivatized nanotubes reflected in Figure 20 were prepared. From this, what is believed to be a step of deprotection of the thiol was performed by treatment with trifluoroacetic acid in 1 ,2-dichlorobenzene (acid hydrolysis). Alternatively, this step could be performed by treatment with trifluoroacetic acid in dimethylformamide, or by thermolysis at or about 175°C. Again, the functionalized nanotubes formed as reflected in Figure 20 would chemically react with, for example an epoxy resin, with the free thiol group (SH) acting as a crosslinking agent.
• SH free thiol group
• derivatized nanotubes can be utilized for thermoplastics.
• the derivatized nanotubes may or may not be chemically bound to the polymer matrix. It is understood that a modest degree of chemical attachment between the derivatized nanotubes and the polymer matrix could be tolerated, while retaining the thermoplastic properties (specifically, the ability to heat and reform the material without significant degradation).
• physical blending of the carbon nanotubes with the polymer can be enhanced by the derivatization process (specifically by making the nanotubes more compatible with, or more soluble in, the host polymer).
• a polymer/composite material containing pure (and underivatized) single-wall carbon nanotubes may be desired so that the polymer would have certain enhanced conductive properties; however, the pure and underivatized carbon nanotubes may not sufficiently disperse in the polymer.
• the derivatized nanotubes could then be dispersed adequately. Because the derivatization of the nanotube may likely have affected the conductivity of the nanotube (and will thus effect the conductivity of the polymer/composite), it may be desirable to reverse the derivatization process to remove the functional groups from the nanotubes after dispersal. In this manner, the conductivity of the material can be recovered. This can be done by any process that reverses the derivatization, such as raising the temperature of the polymer/composite material to a temperature at which the functional group disassociates. Typically, this temperature appears to be at least about 250°C.
• thermoplastic may also be formed utilizing the derivatized carbon nanotube.
• the functional groups while not necessarily chemically bond to the polymer, would be physical extensions from the tube (like branches from a tree) that will afford additional strength to the polymer/composite materials. This enhancement may be due to a roughening effect on the nanotube surface, increasing friction and reducing sliding of the polymer matrix along the nanotube length. As is understood in the art, such as an effect would further enable transference of the desirable nanotube properties to the composite material.
• This derivatized material (17) was dispersed in High-Impact-Polystyrene (HIPS) at various concentrations. Tensile strength, tensile modulus, and % strain to failure data of the resulting composite material were then gathered. The results of these examples are reflected in Table 3.
• HIPS High-Impact-Polystyrene
• SWNT-p unfunctionalized nanotubes
• a polymer that includes carbon nanotubes can be formed by derivatizing the carbon nanotubes with a functional group that is capable of polymerizing or initiating a polymerization. Once the functional group is attached, standard polymerization techniques can then be employed to grow the polymer from the functional group in situ. I.e., the functional group attached to the nanotube could be used as a generator of polymer growth.
• standard polymerization techniques could be any of the standard known types, such as radical, cationic, anionic, condensation, ring-opening, methathesis, or ring-opening-metathesis (ROMP) polymerizations, when appropriate groups are bound to the nanotubes.
• Figure 23 reflects an example of a carbon nanotube that has been derivatized with a functional group 4- aminophenyl that is subsequently polymerized with styrene to grow the polymer from the functional group. Accordingly, the functional group attached to the nanotube would be a chemically active part of the polymerization, which would result in a composite material in which the nanotubes are chemically involved.
• compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

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