CN114367248B - Linear inorganic polymer sol and preparation method thereof - Google Patents
Linear inorganic polymer sol and preparation method thereof Download PDFInfo
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- CN114367248B CN114367248B CN202111391693.8A CN202111391693A CN114367248B CN 114367248 B CN114367248 B CN 114367248B CN 202111391693 A CN202111391693 A CN 202111391693A CN 114367248 B CN114367248 B CN 114367248B
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Abstract
The invention relates to a linear inorganic polymer sol and a preparation method thereof. The method comprises the steps of firstly, sequentially adding a monodentate ligand, a bridging ligand and an inorganic precursor into a composite solvent for multiple coordination reaction, then, carrying out layering reverse stirring, introducing cold moisture, and carrying out reduced pressure distillation to obtain the linear inorganic polymer sol with the non-Newtonian fluid characteristic. Compared with the prior art, the linear inorganic polymer sol has the non-Newtonian fluid characteristic, the branching degree is lower than 0.2, the polymerization degree is 50-500, the conductivity is 0.1-1000 mu C/cm, the surface tension is 30-60 mN/m, the stable storage time is more than 30 days, and the linear inorganic polymer sol can be directly used for electrostatic spinning.
Description
Technical Field
The invention belongs to the technical field of novel sol preparation, and particularly relates to a linear inorganic polymer sol and a preparation method thereof.
Background
The inorganic sol is an important chemical raw material, is prepared from a precursor through wet chemical processes such as hydrolysis, polycondensation, aging and the like, has flexible functionality and excellent applicability, and is widely used for manufacturing materials such as building coatings, electronic devices, catalytic carriers, functional ceramics, high-performance films and the like. Due to good fiber forming performance, the inorganic sol shows unique superiority in preparing ceramic fiber materials, and can be used for producing continuous refractory oxide fibers which cannot be obtained by the traditional process. In recent years, researchers try to prepare ceramic fiber materials with the diameter of nanometer by taking inorganic sol as a raw material, the ceramic fiber materials have the advantages of high temperature resistance, corrosion resistance, abrasion resistance, good photoelectric properties and the like of ceramic materials, and the characteristics of high porosity, large specific surface area, light weight, strong small-size effect and the like of the nanofiber materials, play a key role in the fields of aerospace, electronic information, clean energy, environmental management and the like, have extremely high application value, and can generate huge social and economic benefits.
In the process of preparing ceramic nanofibers by adopting the electrostatic spinning technology, spinning solution must be added with spinning aids such as organic polymer templates besides inorganic sol, otherwise continuous nanofibers cannot be prepared. Due to the addition of spinning aids such as organic polymer templates, pure ceramic nanofibers can be obtained only by removing the polymer templates through processes such as high-temperature calcination and the like in the subsequent processing process, and therefore, the traditional preparation process can cause the defects of poor flexibility of fiber materials, low production efficiency, large production pollution and the like.
In order to overcome the defects: researchers can prepare inorganic sol by following the glue preparation process of dry spinning and directly use the inorganic sol for electrostatic spinning, but the obtained fiber materials are all more than micron-sized; researchers introduce a coupling agent component in the glue preparation process to form inorganic sol with an interpenetrating molecular chain network structure; there are also researchers using salt catalyst methods to prepare inorganic sols for the manufacture of inorganic nanofiber materials. The method can obtain fiber materials by direct electrostatic spinning without using an organic polymer template, but the fiber materials can be spun only by sol with higher viscosity, and because the branching degree of molecular chains in the sol is high and a large number of active groups are remained, the inorganic sol is difficult to store stably, the gelation phenomenon is easy to occur, and the method is not beneficial to continuous production. Some researchers solve the storage problem of the spinning sol by adding a stabilizer into the sol, but the introduction of impurities is caused, the introduction of impurities is not beneficial to the quality of subsequent products, and the problems that the molecular chain of the sol is easy to branch, the structure is difficult to accurately regulate and control, and a large number of residual active groups are not fundamentally solved. Researchers adopt acid catalysis and a method of using ligand to lead the sol to have chain growth tendency at the initial stage of preparation, but only can obtain a chain structure with a shorter molecular chain, and the method can not be used for spinning; when the molecular chain grows further, the chain structure can not be maintained any more.
Therefore, there is a need for the development of a novel inorganic sol that can be directly electrospun without depending on a spinning aid, can stably produce nano-sized fibers, does not undergo gelation, and has good storage stability, and a method for preparing the same.
Disclosure of Invention
Based on the lack of novel inorganic sol which can be directly used for electrostatic spinning, can stably produce nano-sized fibers, does not generate gelation and has good storage stability in the prior art. The invention provides a linear inorganic polymer sol and a preparation method thereof.
The linear inorganic polymer sol provided by the invention is an inorganic sol which has low branching degree and good storage stability of high polymerization degree molecular chains and can be directly used for electrostatic spinning.
The purpose of the invention can be realized by the following technical scheme:
the invention firstly provides a preparation method of linear inorganic polymer sol, which comprises the following steps:
(1) Adding a monodentate ligand, a bridging ligand and an inorganic precursor into a composite solvent, and performing multiple coordination reaction to obtain a homogeneous transparent solution of a bifunctional precursor, wherein the content of the inorganic precursor in the homogeneous transparent solution is 10-50 wt%, the content of the monodentate ligand is 0.1-10 wt%, and the content of the bridging ligand is 0.1-10 wt%;
(2) The obtained homogeneous transparent solution is subjected to layering reverse stirring to generate a plurality of strands of micro-turbulence which impact each other in the solution, so that the materials are uniformly collided and dispersed;
(3) Introducing cold moisture into the layered and reversely-stirred solution to promote the bifunctional precursor to perform hydrolysis-polycondensation reaction, thereby obtaining a linearly-grown prepolymer;
(4) And (4) increasing the viscosity of the solution obtained in the step (3) to obtain the linear inorganic polymer sol with non-Newtonian fluid characteristics.
In one embodiment of the present invention, in step (1), the monodentate ligand is a ligand capable of providing 1 lone pair of electrons, and the bridging ligand is an organic ligand capable of providing 2 to 4 lone pairs of electrons.
In one embodiment of the present invention, in step (1), the monodentate ligand is selected from one or more of the group consisting of chloride, sulfide, bromide, azide, hydroxide, isothiocyanate or nitrite; the bridging ligand is selected from one or more of acetic acid, oxalic acid, citric acid, nitrilotriacetic acid, ethylene diamine tetraacetic acid, ammonium citrate, dithizone, acetylacetone, ethylenediamine or phenanthroline.
In one embodiment of the present invention, in step (1), the inorganic precursor is a metal alkoxide containing 3 or more hydrolyzable coordinating groups.
In one embodiment of the present invention, in step (1), the metal alkoxide is selected from one or more of a silicon source, a titanium source, a zirconium source, or an aluminum source; the silicon source is selected from one or more of tetraethyl orthosilicate, tetra-n-butoxy silane, tetra-n-propoxy silane, trimethylsilyl acetate or vinyl triethoxysilane; the titanium source is selected from one or more of titanium tetramethoxide, titanium tetraethoxide, titanium n-propoxide, titanium isopropoxide, titanium n-butoxide, titanium isobutoxide, titanium tert-butoxide, titanium tetrapentanolate or titanium isooctanoxide; the zirconium source is selected from one or more of zirconium tetramethoxide, zirconium tetraethoxide, zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium isobutanol, zirconium tert-butoxide or zirconium tetrapentanolate; the aluminum source is selected from one or more of trimethoxy aluminum, triethanol aluminum, tri-n-propoxyl aluminum, isopropoxide aluminum, n-butoxide aluminum, sec-butoxide aluminum or tert-butoxide aluminum.
In one embodiment of the present invention, in the step (1), the composite solvent is a composite solvent of an alcohol solvent and a nonpolar solvent, wherein the proportion of the nonpolar solvent is 5 to 20wt%.
In one embodiment of the invention, the alcohol solvent is selected from one or a combination of methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, ethylene glycol, butanediol, hexanediol or glycerol; the nonpolar solvent is selected from one or more of carbon tetrachloride, benzene, toluene, dichloroethane, dichloromethane, chloroform, diethyl ether, diphenyl ether, ethyl acetate, acetone, tetrahydrofuran, N-methylpyrrolidone or N, N-dimethylformamide.
In one embodiment of the present invention, in the step (1), the average number of functional groups of the bifunctional precursor is 2 to 2.5.
In one embodiment of the present invention, the conditions for performing the multiple coordination reaction in step (1) are: under the condition of constant-temperature stirring, the reaction conditions are further preferably as follows: the constant temperature is 10-30 ℃, the stirring condition is 50-1000 rad/min, and the reaction time is 1-48 h.
In an embodiment of the present invention, in the step (2), the layered reverse stirring refers to setting 1 central stirring source and 2 reverse stirring sources in the solution, where the 1 central stirring source and the 2 reverse stirring sources are respectively located at different liquid level heights of the solution. Preferably, the vertical distance from the upper liquid surface of the solution to the bottom surface of the solution is A, the central stirring source is arranged at the position of 0.5A from the upper liquid surface, and the reverse stirring sources are respectively arranged at the positions of 0.25A and 0.75A from the upper liquid surface.
In one embodiment of the present invention, in the step (2), when the form of setting 1 central stirring source and 2 reverse stirring sources in the solution is selected by the stratified reverse stirring, the rotation speed of the central stirring source is 100 to 1000rad/min; the rotating speed of the reverse stirring source is 100-1000 rad/min, and the rotating direction of the reverse stirring source is the reverse direction of the stirring source at the center.
In one embodiment of the present invention, in the step (3), the cold and humid air is composed of air and water, wherein the water content is 1 to 10wt%, the cold and humid air temperature is lower than 10 ℃, the cold and humid air flow rate is 10 to 100mL/min, and the total amount of water introduced is 5 to 20wt% of the mass of the inorganic precursor.
In one embodiment of the present invention, in step (3), the hydrolysis-polycondensation reaction is carried out under a constant temperature condition, preferably, the constant temperature condition is 60 to 100 ℃ and the reaction time is 1 to 8 hours.
In one embodiment of the present invention, in step (3), the linearly-grown prepolymer has a branching degree of less than 0.2 and a polymerization degree of 10 to 50.
In one embodiment of the present invention, in step (4), the viscosity of the solution obtained in step (3) is increased to 10 to 10000 mPas, preferably 200 to 5000 mPas.
In one embodiment of the present invention, in the step (4), the linear inorganic polymer sol has a branching degree of less than 0.2, a polymerization degree of 50 to 500, an electrical conductivity of 0.1 to 1000 μ C/cm, and a surface tension of 30 to 60mN/m.
In one embodiment of the present invention, in the step (4), the stable storage time of the linear inorganic polymer sol is more than 30 days, and can be directly used for electrostatic spinning; the linear inorganic polymer sol has a long-chain molecular chain structure, and the main chain of the molecular chain is formed by alternately arranging oxygen atoms and other non-carbon atoms; the other non-carbon atoms are one or more of silicon, titanium, zirconium and aluminum.
In one embodiment of the present invention, in the step (4), the reduced pressure distillation is selected as a method for increasing the viscosity of the solution obtained in the step (3).
In one embodiment of the present invention, the operating conditions of the reduced pressure distillation are: the reduced pressure distillation is carried out under the conditions that the temperature is between 60 and 100 ℃ and the vacuum degree is between-0.1 and-0.05 MPa.
The invention also provides a linear inorganic polymer sol obtained based on the preparation method of the linear inorganic polymer sol.
The stable storage time of the linear inorganic polymer sol is more than 30 days, and the linear inorganic polymer sol can be directly used for electrostatic spinning; the linear inorganic polymer sol has a long-chain molecular chain structure, and the main chain of the molecular chain is formed by alternately arranging oxygen atoms and other non-carbon atoms; the other non-carbon atoms are one or more of silicon, titanium, zirconium and aluminum.
The mechanism of the invention is introduced as follows:
the inorganic precursor of the linear inorganic polymer sol is a metal alkoxide containing 3 or more hydrolyzable coordinating groups, which has a plurality of reactive alkoxy groups, and the alkoxide undergoes hydrolysis and polycondensation based on nucleophilic reaction to obtain an inorganic sol.
The invention adds two different ligands which provide lone pair electrons, namely monodentate ligand and bridging ligand, into the raw material for preparing the linear inorganic polymer sol, and can perform multiple coordination reaction with alkoxide. Wherein, the monodentate ligand provides 1 pair of lone pair electrons, and through substituting alkoxy of alkoxide, the electropositivity of the central atom is reduced, and the number of active groups is reduced; the bridging ligand provides a plurality of pairs of lone-pair electrons, and is connected with a plurality of alkoxide monomers through substitution and addition to form great steric hindrance, so that the alkoxy groups between the alkoxides are prevented from colliding to react. The content and proportion of the monodentate ligand and the bridging ligand are controlled, and the number of active functional groups of the alkoxide monomer can be accurately controlled.
In addition, alkoxide is easily dissolved in alcohol solvent, but hydroxyl group of alcohol solvent can be adsorbed in central atom to cause shielding effect, so coordination reaction is not easy to proceed. Therefore, the nonpolar solvent is added in the preparation of the linear inorganic polymer sol and is compounded with the alcohol solvent to form the composite solvent, so that the shielding effect of the alcohol solvent can be effectively reduced, and the efficient and stable performance of the coordination reaction is ensured.
After the number of functional groups of the alkoxide monomer is controlled to be about 2, the reaction of the alkoxide along a linear direction can be theoretically ensured, in an actual situation, the material is not uniformly dispersed, and the subsequent water addition causes the local concentration of water molecules in the solution, so that part of alkoxide slips from the ligand, the molecular chain grows and is branched, and the sol with a nonlinear structure is formed. However, the excessive dispersion of the materials leads to extremely low collision probability of active groups, so that the reaction rate is reduced and the production efficiency is reduced. Therefore, the invention adopts a layered reverse stirring mode to form different flow layers in a reaction system, and forms a plurality of strands of micro-turbulence among the different flow layers, thereby ensuring that the materials are uniformly dispersed and have higher collision efficiency; and the method of introducing cold moisture is utilized to ensure that moisture is uniformly dispersed when entering the reaction system, and because the temperature is lower, instant reaction after entering the system can be avoided, and the moisture reacts with alkoxide after being uniformly dispersed and collided with materials. Because the average number of functional groups of the bifunctionality precursor is 2-2.5 and 5, alkoxide reaction can be controlled accurately basically by combining the modes of layered reverse stirring and cold moisture introduction, so that a molecular chain grows along a linear direction, and a prepolymer with a certain polymerization degree is formed. In the subsequent reduced pressure distillation process, the prepolymer further linearly grows to form linear inorganic polymer sol with low branching degree and high polymerization degree, and the residual reactive groups of the linear inorganic polymer sol only exist in end groups, so that gelation does not occur, and the storage time is long; the nano-fiber has non-Newtonian fluid characteristics at a lower concentration, and can be directly used for preparing nano-fibers by electrostatic spinning without adding a spinning auxiliary agent.
Compared with the prior art, the invention has the following beneficial effects:
(1) The linear inorganic polymer sol has the branching degree lower than 0.2, the polymerization degree of 50-500, the conductivity of 0.1-1000 mu C/cm, the surface tension of 30-60 mN/m, the stable storage time of more than 30 days, and can be directly used for electrostatic spinning; the linear inorganic polymer sol has a long-chain molecular chain structure, the main chain of the molecular chain is formed by alternately arranging oxygen atoms and other non-carbon atoms, and the other non-carbon atoms are one or more than one of silicon, titanium, zirconium and aluminum.
(2) The preparation method of the linear inorganic polymer sol is a continuous process, can be applied in a large scale and has better universality.
Detailed Description
The invention firstly provides a preparation method of linear inorganic polymer sol, which comprises the following steps:
(1) Adding a monodentate ligand, a bridging ligand and an inorganic precursor into a composite solvent, and performing multiple coordination reaction to obtain a homogeneous transparent solution of a bifunctional precursor, wherein the content of the inorganic precursor in the homogeneous transparent solution is 10-50 wt%, the content of the monodentate ligand is 0.1-10 wt%, and the content of the bridging ligand is 0.1-10 wt%;
(2) The obtained homogeneous transparent solution is subjected to layering reverse stirring to generate a plurality of strands of micro-turbulence which impact each other in the solution, so that the materials are uniformly collided and dispersed;
(3) Introducing cold moisture into the layered and reversely-stirred solution to promote the bifunctional precursor to perform hydrolysis-polycondensation reaction, thereby obtaining a linearly-grown prepolymer;
(4) And (4) increasing the viscosity of the solution obtained in the step (3) to obtain the linear inorganic polymer sol with non-Newtonian fluid characteristics.
In one embodiment of the present invention, in step (1), the monodentate ligand is a ligand capable of providing 1 lone pair of electrons, and the bridging ligand is an organic ligand capable of providing 2 to 4 lone pairs of electrons.
In one embodiment of the present invention, in step (1), the monodentate ligand is selected from one or more of the group consisting of chloride, sulfide, bromide, azide, hydroxide, isothiocyanate or nitrite; the bridging ligand is selected from one or more of acetic acid, oxalic acid, citric acid, nitrilotriacetic acid, ethylene diamine tetraacetic acid, ammonium citrate, dithizone, acetylacetone, ethylenediamine or phenanthroline.
In one embodiment of the present invention, in step (1), the inorganic precursor is a metal alkoxide containing 3 or more hydrolyzable coordinating groups.
In one embodiment of the present invention, in step (1), the metal alkoxide is selected from one or more of a silicon source, a titanium source, a zirconium source, or an aluminum source; the silicon source is selected from one or more of tetraethyl orthosilicate, tetra-n-butoxy silane, tetra-n-propoxy silane, trimethylsilyl acetate or vinyl triethoxysilane; the titanium source is selected from one or more of titanium tetramethoxide, titanium tetraethoxide, titanium n-propoxide, titanium isopropoxide, titanium n-butoxide, titanium isobutoxide, titanium tert-butoxide, titanium tetrapentanoate or titanium isooctanolate; the zirconium source is selected from one or more of zirconium tetramethoxide, zirconium tetraethoxide, zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium isobutanol, zirconium tert-butoxide or zirconium tetrapentanoate; the aluminum source is selected from one or more of trimethoxy aluminum, triethanol aluminum, tri-n-propoxyl aluminum, isopropoxide aluminum, n-butoxide aluminum, sec-butoxide aluminum or tert-butoxide aluminum.
In one embodiment of the present invention, in the step (1), the composite solvent is a composite solvent of an alcohol solvent and a nonpolar solvent, wherein the proportion of the nonpolar solvent is 5 to 20wt%.
In one embodiment of the invention, the alcohol solvent is one or a combination of several selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, ethylene glycol, butanediol, hexanediol or glycerol; the nonpolar solvent is selected from one or more of carbon tetrachloride, benzene, toluene, dichloroethane, dichloromethane, chloroform, diethyl ether, diphenyl ether, ethyl acetate, acetone, tetrahydrofuran, N-methylpyrrolidone or N, N-dimethylformamide.
In one embodiment of the present invention, in the step (1), the average number of functional groups of the bifunctional precursor is 2 to 2.5.
In one embodiment of the present invention, the conditions for performing the multiple coordination reaction in step (1) are: under the condition of constant-temperature stirring, the reaction conditions are further preferably as follows: the constant temperature is 10-30 ℃, the stirring condition is 50-1000 rad/min, and the reaction time is 1-48 h.
In an embodiment of the present invention, in the step (2), the layered reverse stirring refers to setting 1 central stirring source and 2 reverse stirring sources in the solution, where the 1 central stirring source and the 2 reverse stirring sources are respectively located at different liquid level heights of the solution. Preferably, the vertical distance from the upper liquid surface of the solution to the bottom surface of the solution is A, the central stirring source is arranged at the position of 0.5A from the upper liquid surface, and the reverse stirring sources are respectively arranged at the positions of 0.25A and 0.75A from the upper liquid surface.
In one embodiment of the present invention, in the step (2), when the form of setting 1 central stirring source and 2 reverse stirring sources in the solution is selected by the stratified reverse stirring, the rotation speed of the central stirring source is 100 to 1000rad/min; the rotating speed of the reverse stirring source is 100-1000 rad/min, and the rotating direction of the reverse stirring source is the reverse direction of the central stirring source.
In one embodiment of the present invention, in the step (3), the cold and humid air is composed of air and water, wherein the water content is 1 to 10wt%, the cold and humid air temperature is lower than 10 ℃, the cold and humid air flow rate is 10 to 100mL/min, and the total amount of water introduced is 5 to 20wt% of the mass of the inorganic precursor.
In one embodiment of the present invention, in step (3), the hydrolysis-polycondensation reaction is carried out under a constant temperature condition, preferably, the constant temperature condition is 60 to 100 ℃ and the reaction time is 1 to 8 hours.
In one embodiment of the present invention, in step (3), the linearly-grown prepolymer has a branching degree of less than 0.2 and a polymerization degree of 10 to 50.
In one embodiment of the present invention, in step (4), the viscosity of the solution obtained in step (3) is increased to 10 to 10000 mPas, preferably 200 to 5000 mPas. The method for measuring the viscosity referred to in the present invention is "4-rotation method" in the standard "GB/T10247-2008 viscosity test method".
In one embodiment of the present invention, in the step (4), the linear inorganic polymer sol has a branching degree of less than 0.2, a polymerization degree of 50 to 500, an electrical conductivity of 0.1 to 1000 μ C/cm, and a surface tension of 30 to 60mN/m. In the invention, the branching degree calculation method is DB = (D + T)/(D + L + T), wherein DB is the branching degree, D is the relative number of dendritic units, T is the relative number of terminal units, L is the relative number of linear units, and the numbers of dendritic units, terminals and linear units are obtained by characterization calculation through Fourier infrared spectroscopy, nuclear magnetic spectroscopy and other methods. The polymerization degree is based on the number of repeating units, namely the average value of the number of the repeating units contained in the macromolecular chain of the sol polymer, the average molecular weight of sol molecules is obtained by gel chromatography, and the average molecular weight is divided by the molecular weight of the repeating units to obtain the polymerization degree. The conductivity is tested by adopting a standard GB/T11007-2008 conductivity meter test method. Surface tension was tested using the standard "determination of surface tension of surfactants in GB-T22237-2008".
In one embodiment of the present invention, in the step (4), the stable storage time of the linear inorganic polymer sol is more than 30 days, and can be directly used for electrostatic spinning; the linear inorganic polymer sol has a long-chain molecular chain structure, and the main chain of the molecular chain is formed by alternately arranging oxygen atoms and other non-carbon atoms; the other non-carbon atoms are one or more of silicon, titanium, zirconium and aluminum.
In one embodiment of the present invention, in the step (4), the reduced pressure distillation is selected as a method for increasing the viscosity of the solution obtained in the step (3).
In one embodiment of the present invention, the operating conditions of the reduced pressure distillation are: the reduced pressure distillation is carried out under the conditions that the temperature is between 60 and 100 ℃ and the vacuum degree is between-0.1 and-0.05 MPa.
The invention also provides a linear inorganic polymer sol obtained based on the preparation method of the linear inorganic polymer sol.
The stable storage time of the linear inorganic polymer sol is more than 30 days, and the linear inorganic polymer sol can be directly used for electrostatic spinning; the linear inorganic polymer sol has a long-chain molecular chain structure, and the main chain of the molecular chain is formed by alternately arranging oxygen atoms and other non-carbon atoms; the other non-carbon atoms are one or more of silicon, titanium, zirconium and aluminum.
The present invention will be described in detail with reference to specific examples.
Example 1
A preparation method of linear inorganic polymer sol comprises the following steps:
the first step is as follows: sequentially adding hydrochloric acid, acetylacetone and titanium isopropoxide into a composite solvent of isopropanol and dichloroethane, and stirring at the rotating speed of 500rad/min at the temperature of 30 ℃ to perform multiple coordination reaction for 12 hours to obtain a homogeneous transparent solution of a bifunctional titanium precursor; wherein the content of the inorganic precursor is 30wt%, the content of the monodentate ligand is 0.5wt%, the content of the bridging ligand is 2wt%, the content of isopropanol in the composite solvent accounts for 90wt%, and the average number of functional groups of the bifunctional precursor is 2.2.
The second step is that: and (3) carrying out layered reverse stirring on the homogeneous transparent solution of the titanium precursor, wherein the rotating speed of a central stirring source is 500rad/min, and the rotating speed of a reverse stirring source is 400rad/min. The vertical distance from the upper liquid surface of the solution to the bottom surface of the solution is set as A, the central stirring source is arranged at the position with the vertical distance of 0.5A from the upper liquid surface, and the reverse stirring sources are respectively arranged at the positions with the vertical distances of 0.25A and 0.75A from the upper liquid surface. The rotating direction of the reverse stirring source is the reverse direction of the central stirring source.
The third step: then introducing cold moisture at 5 ℃ into the solution, wherein the flow rate of the cold moisture is 50mL/min, the water content is 3wt%, and the total introduction amount of water is 10wt% of the mass of the precursor; and (3) promoting the bifunctional precursor to perform hydrolysis-polycondensation reaction for 6 hours at the temperature of 80 ℃ to obtain a linearly-grown prepolymer, wherein the branching degree is 0.15, and the polymerization degree is 30.
The fourth step: and (2) carrying out reduced pressure distillation on the solution at the temperature of 80 ℃, collecting a product after the solution viscosity reaches 200mPa & s, thus obtaining the linear inorganic polymer titanium sol, which has the characteristics of shear thinning non-Newtonian fluid, the branching degree of 0.18, the polymerization degree of 300, the conductivity of 25 mu C/cm, the surface tension of 45mN/m, and the stable storage time of 35 days, and can be directly used for electrostatic spinning. The method for calculating the branching degree is DB = (D + T)/(D + L + T), wherein DB is the branching degree, D is the relative number of dendritic units, T is the relative number of terminal units, L is the relative number of linear units, and the numbers of dendritic units, terminal units and linear units are obtained by means of characterization calculation through Fourier infrared spectroscopy, nuclear magnetic spectroscopy and the like. The polymerization degree is based on the number of repeating units, namely the average value of the number of the repeating units contained in the macromolecular chain of the sol polymer, the average molecular weight of sol molecules is obtained by gel chromatography, and then the average molecular weight is divided by the molecular weight of the repeating units to obtain a polymerization degree value. The conductivity is tested by adopting a standard GB/T11007-2008 conductivity meter test method. Surface tension was tested using the standard "determination of surface tension of surfactants" of GB-T22237-2008.
Example 2
A preparation method of linear inorganic polymer sol comprises the following steps:
the first step is as follows: sequentially adding hydrochloric acid, acetic acid and zirconium isopropoxide into a composite solvent of isopropanol and N, N-dimethylformamide, and stirring at the rotating speed of 450rad/min at the temperature of 25 ℃ to perform multiple coordination reaction for 10 hours to obtain a homogeneous transparent solution of a bifunctional titanium precursor; wherein, the content of the inorganic precursor is 28wt%, the content of the monodentate ligand is 1wt%, the content of the bridging ligand is 1.5wt%, the content of the isopropanol in the composite solvent is 92wt%, and the average number of functional groups of the bifunctional precursor is 2.1.
The second step is that: and (3) carrying out layered reverse stirring on the homogeneous transparent solution of the zirconium precursor, wherein the rotating speed of a central stirring source is 400rad/min, and the rotating speed of a reverse stirring source is 300rad/min. The vertical distance from the upper liquid surface of the solution to the bottom surface of the solution is set as A, the central stirring source is arranged at the position with the vertical distance of 0.5A from the upper liquid surface, and the reverse stirring sources are respectively arranged at the positions with the vertical distances of 0.25A and 0.75A from the upper liquid surface. The rotating direction of the reverse stirring source is the reverse direction of the central stirring source.
The third step: then introducing cold moisture at 5 ℃ into the solution, wherein the flow rate of the cold moisture is 20mL/min, the water content is 4wt%, and the total introduction amount of water is 12wt% of the mass of the precursor; and (3) promoting the bifunctional precursor to perform hydrolysis-polycondensation reaction for 7 hours at 70 ℃ to obtain a linearly-grown prepolymer, wherein the branching degree is 0.13, and the polymerization degree is 35.
The fourth step: and (3) carrying out reduced pressure distillation on the solution at 70 ℃, collecting a product after the solution viscosity reaches 150mPa & s, thus obtaining the zirconium sol with a linear inorganic polymer, which has the characteristics of shear thinning non-Newtonian fluid, the branching degree of 0.15, the polymerization degree of 250, the conductivity of 30 mu C/cm, the surface tension of 43mN/m, and stable storage time of 32 days, and can be directly used for electrostatic spinning. The method for calculating the branching degree is DB = (D + T)/(D + L + T), wherein DB is the branching degree, D is the relative number of dendritic units, T is the relative number of terminal units, L is the relative number of linear units, and the numbers of dendritic units, terminals and linear units are obtained by means of Fourier infrared spectroscopy, nuclear magnetic spectroscopy and the like. The polymerization degree is based on the number of repeating units, namely the average value of the number of the repeating units contained in the macromolecular chain of the sol polymer, the average molecular weight of sol molecules is obtained by gel chromatography, and then the average molecular weight is divided by the molecular weight of the repeating units to obtain a polymerization degree value. The conductivity is tested by adopting a standard GB/T11007-2008 conductivity meter test method. Surface tension was tested using the standard "determination of surface tension of surfactants" of GB-T22237-2008.
Example 3
A preparation method of linear inorganic polymer sol comprises the following steps:
the first step is as follows: sequentially adding sodium bromide, acetylacetone and aluminum sec-butoxide into a composite solvent of sec-butyl alcohol and N-methyl pyrrolidone, and stirring at the rotation speed of 400rad/min at the temperature of 25 ℃ to perform multiple coordination reaction for 10h to obtain a homogeneous transparent solution of a bifunctional titanium precursor; wherein, the content of the inorganic precursor is 20wt%, the content of the monodentate ligand is 0.3wt%, the content of the bridging ligand is 3wt%, the sec-butyl alcohol accounts for 93wt% in the composite solvent, and the average number of functional groups of the bifunctional precursor is 2.1.
The second step is that: and (3) carrying out layered reverse stirring on the homogeneous transparent solution of the aluminum precursor, wherein the rotating speed of a central stirring source is 300rad/min, and the rotating speed of a reverse stirring source is 300rad/min. The vertical distance from the upper liquid surface of the solution to the bottom surface of the solution is set as A, the central stirring source is arranged at the position with the vertical distance of 0.5A from the upper liquid surface, and the reverse stirring sources are respectively arranged at the positions with the vertical distances of 0.25A and 0.75A from the upper liquid surface. The rotating direction of the reverse stirring source is the reverse direction of the central stirring source.
The third step: then introducing cold moisture at 3 ℃ into the solution, wherein the flow rate of the cold moisture is 40mL/min, the water content is 5wt%, and the total introduction amount of water is 10wt% of the mass of the precursor; and (3) promoting the bifunctional precursor to perform hydrolysis-polycondensation reaction for 6 hours at 75 ℃ to obtain a linearly-grown prepolymer, wherein the branching degree is 0.12, and the polymerization degree is 20.
The fourth step: and (3) carrying out reduced pressure distillation on the solution at the temperature of 75 ℃, collecting a product after the solution viscosity reaches 180mPa & s, thus obtaining the linear inorganic polymer alumina sol which has the characteristics of shear thinning non-Newtonian fluid, the branching degree of 0.15, the polymerization degree of 200, the conductivity of 35 mu C/cm, the surface tension of 48mN/m, and the stable storage time of 36 days, and can be directly used for electrostatic spinning. The method for calculating the branching degree is DB = (D + T)/(D + L + T), wherein DB is the branching degree, D is the relative number of dendritic units, T is the relative number of terminal units, L is the relative number of linear units, and the numbers of dendritic units, terminal units and linear units are obtained by means of characterization calculation through Fourier infrared spectroscopy, nuclear magnetic spectroscopy and the like. The polymerization degree is based on the number of repeating units, namely the average value of the number of the repeating units contained in the macromolecular chain of the sol polymer, the average molecular weight of sol molecules is obtained by gel chromatography, and then the average molecular weight is divided by the molecular weight of the repeating units to obtain a polymerization degree value. The conductivity is tested by adopting a standard GB/T11007-2008 conductivity meter test method. Surface tension was tested using the standard "determination of surface tension of surfactants" of GB-T22237-2008.
The invention also provides a method for preparing flexible ceramic nanofibers based on the linear inorganic polymer sol, and the linear inorganic polymer sol is directly used for electrostatic spinning to prepare the flexible ceramic nanofibers. The method for preparing the flexible ceramic nanofiber based on the linear inorganic polymer sol comprises the following steps:
(A) Preparing inorganic gel nanofibers from the linear inorganic polymer sol by a temperature/alkali steam assisted electrospinning process;
(B) Introducing the obtained inorganic gel nano-fiber into a resolution bath, and carrying out pressurization resolution treatment to obtain a fiber with an organic component removed;
(C) Introducing the obtained fibers without organic components into a pre-sintering area, and maintaining differential drafting tension compensation treatment on the fibers without organic components to obtain thermal polycondensation fibers;
(D) Introducing the thermal polycondensation fibers into an alternating atmosphere calcining zone to obtain flexible ceramic nanofibers with small grain sizes; the alternating atmosphere calcining zone is formed by alternately arranging an oxidation zone and an inhibition zone, and the oxidation zone, the inhibition zone, the oxidation zone and the inhibition zone are sequentially arranged in the sample introduction direction.
In some preferred embodiments, in the step (a), the method for preparing the inorganic gel nanofibers by the temperature/alkali steam assisted electrospinning process of the linear inorganic polymer sol is specifically as follows:
extruding the linear inorganic polymer sol from a slit nozzle from top to bottom at the speed of 0.1-100 mL/h, and drawing the linear inorganic polymer sol into inorganic sol spinning jet under the condition of applying voltage of 10-100 kV; then, the inorganic sol spinning jet flows through three temperature/alkaline alcohol steam concentration double-gradient spinning areas, so that the inorganic sol spinning jet flows are formed by gelation from outside to inside step by step; finally, inorganic gel fiber is obtained and deposited on a conveyor belt type receiving substrate with the running speed of 0.1-10 m/min.
In some preferred embodiments, in step (A), the three temperature/alkaline alcohol vapor concentration bigradient spinning zones are a spin 1 zone, a spin 2 zone and a spin 3 zone,
the conditions of the inorganic sol spinning jet flow passing through three temperature/alkaline alcohol steam concentration double gradient spinning areas are as follows:
the temperature of the spinning area gradually increases to satisfy T n ＝T 1 +15n, n =2, 3, and T 1 ＝2T 0 Wherein T is 0 At room temperature, T 1 Temperature, T, of zone 1 of spinning 2 Temperature, T, of zone 2 for spinning 3 Is the temperature in zone 3 of spinning. The concentration of the alkaline alcohol vapor in the spinning area is gradually reduced to satisfy C n ＝C 1 -2n, n =2, 3 and C 1 >6g/m 3 。C 1 Concentration of alkaline alcohol vapor in zone 1 for spinning, C 2 Alkaline alcohol evaporation for zone 2 of spinningConcentration of steam, C 3 Is the concentration of the alkaline alcohol vapor in zone 3 of the spin. The length ratio of the spinning 1 area, the spinning 2 area and the spinning 3 area is (a + 2): a + 1): a, a>1。
In some preferred embodiments, in step (A), the length of the temperature/basic alcohol vapor concentration bigradient spinning zone is 5 to 50cm.
In some preferred embodiments, in step (a), the temperature and the concentration of the alkaline alcohol vapor in each zone of the temperature/alkaline alcohol vapor concentration dual gradient spinning zone are regulated by a hot air/steam jet device.
In some preferred embodiments, in step (a), the alkali in the alkaline alcohol vapor is selected from one or more of ammonia water, sodium hydroxide or potassium hydroxide solution, the alcohol in the alkaline alcohol vapor is selected from one or more of ethanol, n-propanol, isopropanol, n-butanol or sec-butanol, and the volume ratio of the alkali solution to the alcohol solution is 0.1-1 v/v.
In one embodiment of the invention, in the step (A), the obtained inorganic gel nanofiber has an average diameter of 50-1000 nm and a length of 1-1000 mm, and meets the requirement that the weight loss rate of the fiber is less than or equal to 5% under the drying condition of 100 ℃. The composition of the obtained inorganic gel nanofiber is inorganic gel and organic components, wherein the content of the organic components is 5-50 wt%.
In some preferred embodiments, in step (B), the resolving bath is an alcohol aqueous solution of an inorganic base, wherein the content of the inorganic base is 0.01 to 10mol/L; the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide, sodium bicarbonate, sodium carbonate or ammonia water, the alcohol-water solution is composed of small molecular alcohol and water, wherein the water content is 5wt%, and the small molecular alcohol is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, ethylene glycol, butanediol, hexanediol or glycerol.
In some preferred embodiments, in the step (B), the conditions of the pressure analysis treatment are: the pressure is 0.3-4 MPa, the temperature is 40-80 ℃, and the treatment time is 10-60 min.
In some preferred embodiments, in step (B), the content of organic components in the de-organic component fibers is less than 1wt%.
In some preferred embodiments, in the step (C), the pre-sintering area is an air atmosphere, the calcining temperature is 150 to 200 ℃, and the pre-sintering time is 1 to 4 hours; the differential drafting tension compensation treatment means that the speed of the fiber sent out of the presintering area is reduced by 10-30% compared with the speed of the fiber sent into the presintering area.
In some preferred embodiments, in step (D), the oxidation zone is an air atmosphere, the calcination temperature is 200 to 400 ℃, and the calcination time is 10 to 30min; the inhibition zone is in a high nitrogen-containing atmosphere, the calcining temperature is 400-1000 ℃, and the calcining time is 30-60 min; the high nitrogen atmosphere consists of nitrogen and other gases, wherein the content of the nitrogen is 80-95 wt%, and the other gases are one or more of argon, helium, carbon dioxide, ammonia and carbon disulfide.
In some preferred embodiments, in the step (D), the flexible ceramic nanofibers have a crystal size of 5 to 30nm, an average fiber diameter of 50 to 500nm, and a softness of less than 300mN.
Further, on the basis of the above examples 1, 2 and 3, the present invention provides a method for preparing a polymer-free template based on the flexible ceramic nanofibers of example 1, which comprises the following specific steps:
the linear inorganic polymer titanium sol of example 1 was extruded from a slit nozzle from the top down at a rate of 1mL/h and drawn into a spinning jet under an applied voltage of 30 kV. Then, the inorganic sol jet flow passes through a spinning 1 area, a spinning 2 area and a spinning 3 area with the temperature/alkaline alcohol steam concentration being in double gradual change, the temperature of the three spinning areas is 35 ℃, 50 ℃ and 65 ℃, and the alkaline alcohol steam concentration is 10g/m 3 、8g/m 3 、6g/m 3 Wherein the alkaline alcohol solvent component comprises ammonia water and ethanol, and the volume ratio of the ammonia water to the ethanol is 0.1v/v; the spinning distance is 60cm, and the lengths of the spinning 1 area, the spinning 2 area and the spinning 3 area are respectively 30cm, 20cm and 10cm. The prepared inorganic titanium gel nanofibers were deposited on a conveyor-type receiving substrate running at a speed of 0.5 m/min.
Introducing the titanium gel nano-fiber with the average diameter of 800nm into an analysis bath, and carrying out pressurized analysis treatment to obtain a fiber with an organic component removed; the analysis bath is ethanol-water solution of sodium hydroxide, the sodium hydroxide content is 0.1mol/L, the pressure condition is 2MPa, the temperature is 60 ℃, and the treatment time is 30min; the content of organic components in the obtained fiber without organic components is 0.5wt%.
Introducing the fibers with the organic components removed into a pre-sintering area, and maintaining differential drafting tension compensation treatment on the fibers to obtain thermal polycondensation fibers; the pre-burning area is in air atmosphere, the calcining temperature is 180 ℃, the pre-burning time is 3 hours, and the speed of the fiber which is sent out of the pre-burning area is reduced by 25 percent compared with the speed of the fiber which is sent into the pre-burning area.
Introducing the thermal polycondensation fibers into an alternating atmosphere calcining area to obtain flexible ceramic nanofibers with the grain size of 21nm, the average fiber diameter of 400nm and the softness of 220 mN; the alternating atmosphere calcining area is sequentially provided with an oxidation area, an inhibition area, an oxidation area and an inhibition area from the sample introduction direction; the oxidation zone is in an air atmosphere, the calcination temperature is 300 ℃, and the calcination time is 20min; the inhibition zone is in a high nitrogen-containing atmosphere, the calcining temperature is 500 ℃, and the calcining time is 50min; the high nitrogen-containing atmosphere consists of nitrogen and helium, wherein the content of nitrogen is 90wt%.
The method for preparing the flexible ceramic nano-fiber by using other different linear inorganic polymer sols can be carried out by referring to the specific technical scheme given above.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (6)
1. A method for preparing a linear inorganic polymer sol, comprising the steps of:
(1) Adding a monodentate ligand, a bridging ligand and an inorganic precursor into a composite solvent, and performing multiple coordination reaction to obtain a homogeneous transparent solution of a bifunctional precursor, wherein the content of the inorganic precursor in the homogeneous transparent solution is 10-50wt%, the content of the monodentate ligand is 0.1-10wt%, and the content of the bridging ligand is 0.1-10wt%;
(2) The obtained homogeneous transparent solution is subjected to layering reverse stirring to generate a plurality of strands of micro-turbulence which impact each other in the solution, so that the materials are uniformly collided and dispersed;
(3) Introducing cold moisture into the layered and reversely-stirred solution to promote the bifunctional precursor to perform hydrolysis-polycondensation reaction, thereby obtaining a linearly-grown prepolymer;
(4) Increasing the viscosity of the solution obtained in the step (3) to obtain a linear inorganic polymer sol with non-Newtonian fluid characteristics;
in step (1), the monodentate ligand is a ligand capable of providing 1 lone pair, and the bridging ligand is an organic ligand capable of providing 2~4 lone pair;
in the step (1), the inorganic precursor is a metal alkoxide containing 3 or more hydrolyzable coordination groups;
in the step (1), the composite solvent is a composite solvent of an alcohol solvent and a nonpolar solvent, wherein the proportion of the nonpolar solvent is 5-20wt%;
the conditions for carrying out the multiple coordination reaction in the step (1) are as follows: stirring at constant temperature of 10-30 ℃, stirring at 50-1000rad/min, and reacting for 1-48h;
in the step (2), the layered reverse stirring means that 1 central stirring source and 2 reverse stirring sources are arranged in the solution, the 1 central stirring source and the 2 reverse stirring sources are respectively positioned at different liquid level heights of the solution, and the rotation direction of the reverse stirring sources is the reverse direction of the central stirring sources;
in the step (3), the cold and wet gas consists of air and water, wherein the water content is 1-10wt%, the cold and wet gas temperature is lower than 10 ℃, the cold and wet gas flow speed is 10-100 mL/min, and the total water introduction amount is 5-20wt% of the mass of the inorganic precursor;
in the step (3), the hydrolysis-polycondensation reaction is carried out under the constant temperature condition of 60 to 100 ℃ for 1 to 8 hours;
in the step (3), the branching degree of the linearly-growing prepolymer is lower than 0.2, and the polymerization degree is 10 to 50.
2. The method of preparing a linear inorganic polymer sol according to claim 1, wherein said monodentate ligand is selected from the group consisting of one or more of a chloride ion, a sulfide ion, a bromide ion, an azide ion, a hydroxide ion, an isothiocyanate ion, and a nitrite ion; the bridging ligand is selected from one or more of acetic acid, oxalic acid, citric acid, nitrilotriacetic acid, ethylene diamine tetraacetic acid, ammonium citrate, dithizone, acetylacetone, ethylenediamine or phenanthroline.
3. The method of claim 1, wherein the metal alkoxide is selected from one or more of a silicon source, a titanium source, a zirconium source, or an aluminum source; the silicon source is selected from one or more of tetraethyl orthosilicate, tetra-n-butoxy silane, tetra-n-propoxy silane, trimethylsilyl acetate or vinyl triethoxysilane; the titanium source is selected from one or more of titanium tetramethoxide, titanium tetraethoxide, titanium n-propoxide, titanium isopropoxide, titanium n-butoxide, titanium isobutoxide, titanium tert-butoxide, titanium tetrapentanolate or titanium isooctanoxide; the zirconium source is selected from one or more of zirconium tetramethoxide, zirconium tetraethoxide, zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium isobutanol, zirconium tert-butoxide or zirconium tetrapentanoate; the aluminum source is selected from one or more of trimethoxy aluminum, triethanol aluminum, tri-n-propoxyl aluminum, isopropoxide aluminum, n-butoxide aluminum, sec-butoxide aluminum or tert-butoxide aluminum.
4. The method for preparing a linear inorganic polymer sol according to claim 1, wherein the alcohol solvent is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, ethylene glycol, butylene glycol, hexylene glycol and glycerol; the nonpolar solvent is selected from one or more of carbon tetrachloride, benzene, toluene, dichloroethane, dichloromethane, chloroform, diethyl ether, diphenyl ether, ethyl acetate, acetone, tetrahydrofuran, N-methylpyrrolidone or N, N-dimethylformamide.
5. Linear inorganic polymer sol obtained on the basis of the production process according to any one of claims 1 to 4.
6. The linear inorganic polymer sol of claim 5, wherein the linear inorganic polymer sol has a branching degree of less than 0.2, a polymerization degree of 50 to 500, an electrical conductivity of 0.1 to 1000 μ C/cm, and a surface tension of 30 to 60mN/m.
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