CN111892729A - Flexible aerogel and preparation method thereof - Google Patents

Flexible aerogel and preparation method thereof Download PDF

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CN111892729A
CN111892729A CN202010599910.1A CN202010599910A CN111892729A CN 111892729 A CN111892729 A CN 111892729A CN 202010599910 A CN202010599910 A CN 202010599910A CN 111892729 A CN111892729 A CN 111892729A
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aerogel
unsaturated silane
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屈洁昊
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Institute of Flexible Electronics Technology of THU Zhejiang
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Abstract

The invention discloses a preparation method of a flexible aerogel, which comprises the following steps: a. uniformly mixing at least two unsaturated silane monomers and an initiator, wherein at least one unsaturated silane monomer contains a siloxane functional group, introducing protective gas to remove oxygen in a system for free radical polymerization reaction, and cooling; b. and c, adding a catalyst into the solution obtained after the reaction in the step a, carrying out hydrolytic polycondensation reaction, and cooling to obtain the flexible aerogel. The preparation method can prepare the powder with the density of 10-320mg/cm3The adjustable and controllable flexible aerogel in the range can realize the intrinsic flexibility of the aerogelAnd high strength, and the thermal conductivity of the prepared aerogel is lower than that of air.

Description

Flexible aerogel and preparation method thereof
Technical Field
The invention belongs to the technical field of functional material preparation, relates to a flexible aerogel, and particularly relates to a preparation method of the flexible aerogel.
Background
Aerogel is a porous and light nano solid material formed by mutually crosslinking colloidal particles or macromolecules, and is widely applied to the fields of heat insulation, noise reduction, sensing, catalysis and the like due to the unique physical properties of low density, high porosity, high specific surface area and the like. However, aerogels are mostly silica matrices, have the defects of low mechanical strength, intrinsic brittleness and the like, have poor processability, and are easy to crack once being subjected to external force, so that the materials are easy to fail. Although the introduction of fillers into aerogels for structural reinforcement is a common optimization method, the problems of porosity reduction and density increase are brought along, and the flexibility of bending and other functions, such as light transmittance, hydrophobicity, heat insulation, adsorption capacity and the like, are reduced to a certain extent, so that the application range of the aerogels is limited. Therefore, there is an urgent need to develop a method for preparing aerogel that can achieve intrinsic flexibility and high strength of aerogel.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, an object of the embodiments of the present invention is to provide a method for preparing a flexible aerogel, which can solve the technical problems of high brittleness, poor processability, increased density, decreased porosity, and the like in the conventional aerogel optimization process, has a low preparation cost, can prepare a flexible aerogel with adjustable density, can realize intrinsic flexibility and high strength of the aerogel, and can prepare an aerogel with a thermal conductivity lower than that of air.
To this end, an embodiment of one aspect of the present invention proposes a method for preparing a flexible aerogel, comprising the steps of:
a. uniformly mixing at least two unsaturated silane monomers and an initiator, wherein at least one unsaturated silane monomer contains a siloxane functional group, introducing protective gas to remove oxygen in a system for free radical polymerization reaction, and cooling;
b. and c, adding a catalyst into the solution obtained after the reaction in the step a, carrying out hydrolytic polycondensation reaction, and cooling to obtain the flexible aerogel.
The preparation method of the flexible aerogel of the embodiment of the invention has the following beneficial effects: 1. the embodiment of the invention is based on a 'double-channel' polymerization strategy, free radical polymerization and hydrolytic polycondensation are creatively carried out between monomers in sequence, and the preparation of the aerogel with intrinsic flexibility, high strength and adjustable density is realized under the condition of no external cross-linking agent; 2. the flexible aerogel prepared by the invention has the characteristics of no structural damage, winding, cutting, 360-degree twisting and high compression ratio of 85 percent, has the adsorption capacity of 23-68 times of self weight on 3 common organic solvents of chloroform, acetone and xylene, has the excellent performance of heat conductivity coefficient smaller than that of air and super hydrophobicity.
In some embodiments of the present invention, in step a, the unsaturated silane monomer is:
allyl unsaturated silane monomer
Figure BDA0002558774230000021
Or
Ethylenically unsaturated silane monomers
Figure BDA0002558774230000022
Wherein R is1、R2、R3Is one of hydrogen atom, methyl, ethyl, methoxy or ethoxy.
In some embodiments of the invention, in the step a, the unsaturated silane monomer is vinyltrimethylsilane, allyltrimethylsilane, vinylmethyldimethoxysilane, allylmethyldimethoxysilane, vinylmethyldiethoxysilane, allylmethyldiethoxysilane, vinyldimethylmethoxysilane, allyldimethylmethoxysilane, vinyldimethylethoxysilane, allyldimethylethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, vinyltriethoxysilane, or allyltriethoxysilane.
In some embodiments of the present invention, the siloxane functional group containing monomer in the unsaturated silane monomer is 90% to 100% of the total molar amount of unsaturated silane monomer.
In some embodiments of the present invention, in the step a, the initiator is an organic peroxide initiator, an azo-based initiator or an oxidation-reduction initiator, and the organic peroxide initiator is selected from at least one of bis (4-tert-butylcyclohexyl) peroxydicarbonate, dicyclohexyl peroxydicarbonate, diisopropyl peroxydicarbonate, tert-butyl peroxypivalate, lauroyl peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, 2-di (tert-butylperoxy) butane, methyl ethyl ketone peroxide, dicumyl peroxide or di-tert-butyl peroxide; the azo initiator is at least one selected from azodiisoheptanonitrile, azodiisobutyronitrile, dimethyl azodiisobutyrate, azodiisovaleronitrile, azodicyclohexyl cyanogen or azoisobutyryl cyano formamide; the oxidation-reduction initiator is at least one selected from dibenzoyl peroxide/N, N-dimethylaniline, dibenzoyl peroxide/N, N-dimethyl toluidine, cumene hydroperoxide/N, N-dimethylaniline, cumene hydroperoxide/N, N-dimethyl toluidine or naphthenate/dibenzoyl peroxide.
In some embodiments of the present invention, in the step a, the molar amount of the initiator is 0.05 to 12% of the total molar amount of the unsaturated silane monomer.
In some embodiments of the invention, in step b, the catalyst is tetramethylammonium hydroxide, tetraethylammonium hydroxide, triethylamine, or isopropylamine.
In some embodiments of the invention, in step b, the molar amount of the catalyst is 0.05 to 0.5 times the total molar amount of the unsaturated silane monomer.
In some embodiments of the invention, the flexible aerogel has a density of 10 to 320mg/cm3。
In some embodiments of the present invention, in the step a, the temperature of the radical polymerization is 20-150 ℃ and the reaction time is 1-60 h; in the step b, the hydrolysis polycondensation reaction temperature is 80-160 ℃, and the reaction time is 24-96 h.
The embodiment of the second aspect of the invention also provides a flexible aerogel prepared by the preparation method of the embodiment.
The flexible aerogel disclosed by the embodiment of the invention has the beneficial effects that the flexible aerogel disclosed by the embodiment of the invention has the characteristics of winding, cutting, 360-degree twisting and high compression ratio of 85% on the basis of no structural damage, the adsorption capacity of the flexible aerogel on 3 common organic solvents such as chloroform, acetone and xylene is 23-68 times of the self weight, and the flexible aerogel has excellent performances such as heat conductivity coefficient smaller than that of air and super-hydrophobicity.
Drawings
Fig. 1 is a schematic view of a reaction mechanism of radical polymerization and hydrolytic polycondensation in a method for preparing a flexible aerogel according to an embodiment of the present invention;
FIG. 2 is a graph comparing the adsorption capacity of the flexible aerogels for 3 common organic solvents in examples 1-5 according to the present invention;
fig. 3 is a graph of compression-rebound mechanics at 85% compression ratio for the flexible aerogel of example 1, wherein the dashed line is the first compression-rebound mechanics curve and the solid line is the 500 cycle compression-rebound mechanics curve.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The following described embodiments are exemplary and are intended to be illustrative of the invention and are not to be construed as limiting the invention.
The preparation method of the flexible aerogel according to the embodiment of the invention comprises the following steps:
a. uniformly mixing at least two unsaturated silane monomers and an initiator, wherein at least one unsaturated silane monomer contains a siloxane functional group, introducing protective gas to remove oxygen in a system for free radical polymerization, preferably, reacting for 1-60h at 20-150 ℃, and cooling to room temperature;
b. and (b) adding a catalyst into the solution obtained after the reaction in the step a, performing hydrolytic polycondensation reaction, preferably, reacting at 80-160 ℃ for 24-96h, and cooling to room temperature to obtain the flexible aerogel.
According to the preparation method of the flexible aerogel disclosed by the embodiment of the invention, based on a 'double-channel' polymerization strategy, free radical polymerization and hydrolytic polycondensation are creatively carried out between monomers in sequence, and the preparation of the aerogel with intrinsic flexibility, high strength and adjustable density is realized under the condition of no external cross-linking agent; the flexible aerogel prepared by the embodiment of the invention has the characteristics of winding, cutting, 360-degree twisting and 85% high compression ratio on the basis of no structural damage, has the adsorption capacity of 23-68 times of self weight on 3 common organic solvents of chloroform, acetone and xylene, and has excellent properties of heat conductivity coefficient smaller than that of air and super-hydrophobicity.
According to some embodiments of the invention, in step a, the unsaturated silane monomer is:
allyl unsaturated silane monomer
Figure BDA0002558774230000031
Or
Ethylenically unsaturated silane monomers
Figure BDA0002558774230000041
Wherein R is1、R2、R3Is one of hydrogen atom, methyl, ethyl, methoxy or ethoxy. In the embodiment of the invention, the unsaturated silane monomers are divided into two types based on the difference of unsaturated bonds, specifically allyl and vinyl. Wherein the groups attached to the Si atom, other than the olefinic bond, may be 5 groups, i.e. R1、R2、R3Specifically, the monomer can be a hydrogen atom, a methyl group, an ethyl group, a methoxy group or an ethoxy group, in the embodiment of the invention, at least 2 monomers are adopted in the process of selecting the reaction monomers, and at least one monomer needs to contain the methoxy group or the ethoxy group so as to perform double-channel crosslinking.
According to some embodiments of the present invention, there is no particular limitation on the unsaturated silane monomer, and preferably, the unsaturated silane monomer is vinyltrimethylsilane, allyltrimethylsilane, vinylmethyldimethoxysilane, allylmethyldimethoxysilane, vinylmethyldiethoxysilane, allylmethyldiethoxysilane, vinyldimethylmethoxysilane, allyldimethylmethoxysilane, vinyldimethylethoxysilane, allyldimethylethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, vinyltriethoxysilane, or allyltriethoxysilane. The embodiment of the invention preferably selects the type of the unsaturated siloxane monomer, the preparation method of the embodiment of the invention can prepare the flexible aerogel of the embodiment of the invention only by adopting the commonly used unsaturated silane monomer, and the raw materials are low in cost and easy to obtain.
According to some embodiments of the invention, the siloxane functional group-containing monomer in the unsaturated silane monomer is 90% to 100% of the total molar amount of unsaturated silane monomer. The embodiment of the invention preferably selects the proportion of the monomer containing the siloxane functional group in the unsaturated silane monomer, and can prepare the flexible aerogel with excellent performance.
According to some embodiments of the present invention, in the step a, the initiator is an organic peroxide initiator, an azo initiator or an oxidation-reduction initiator, and embodiments of the present invention do not particularly limit the initiator, and preferably, the organic peroxide initiator is selected from at least one of bis (4-tert-butylcyclohexyl) peroxydicarbonate, dicyclohexyl peroxydicarbonate, diisopropyl peroxydicarbonate, tert-butyl peroxypivalate, lauroyl peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, 2-di (tert-butylperoxy) butane, methyl ethyl ketone peroxide, dicumyl peroxide or di-tert-butyl peroxide; the azo initiator is at least one selected from azodiisoheptanonitrile, azodiisobutyronitrile, dimethyl azodiisobutyrate, azodiisovaleronitrile, azodicyclohexyl cyanogen or azoisobutyryl cyano formamide; the oxidation-reduction initiator is at least one selected from dibenzoyl peroxide/N, N-dimethylaniline, dibenzoyl peroxide/N, N-dimethyl toluidine, cumene hydroperoxide/N, N-dimethylaniline, cumene hydroperoxide/N, N-dimethyl toluidine or naphthenate/dibenzoyl peroxide; the molar quantity of the initiator is 0.05-12% of the total molar quantity of the unsaturated silane monomer. Embodiments of the present invention may select the initiator based on its half-life and the polymerization time and temperature of the reaction.
According to some embodiments of the invention, in the step a, the introduced protective gas is at least one of nitrogen, argon, helium, neon and krypton. In the embodiment of the invention, the protective gas is added to remove oxygen in the reaction system, so that the reaction system is carried out in an oxygen-free atmosphere, which is beneficial to the generation of free radical polymerization reaction.
According to some embodiments of the invention, in step b, the catalyst is tetramethylammonium hydroxide, tetraethylammonium hydroxide, triethylamine, or isopropylamine; the molar amount of the catalyst is 0.05 to 0.5 times, preferably 0.05 to 0.3 times of the total molar amount of the unsaturated silane monomer. According to the embodiment of the invention, the preferable catalyst is adopted, so that the hydrolytic polymerization reaction can be effectively promoted, and the flexible aerogel with excellent performance is prepared.
According to some embodiments of the invention, the flexible aerogel has a density of 10 to 320mg/cm3。
According to some embodiments of the present invention, when the unsaturated silane monomer is two types of monomers, 1, when the first type of monomer is a monomer containing one siloxane functional group, the second type of monomer is a monomer without siloxane functional group, the molar ratio of the first type of monomer to the second type of monomer is 10, and the amount of the catalyst is 0.08 to 0.12 times of the total molar amount of the unsaturated silane monomer, the aerogel density obtained is 75 to 120mg/cm3When the using amount of the catalyst is 0.15-0.25 times of the total molar amount of the unsaturated silane monomer, the density of the prepared aerogel is 40-60mg/cm3(ii) a In the embodiment, when the dosage of the catalyst is increased from 0.08-0.12 time to 0.15-0.25 time, after the siloxane is hydrolyzed into silanol, the condensation reaction between silanol groups is more fully carried out, the weight loss of dehydration is continuously increased to about 1 time before, and the change of density is mainly caused by the weight loss increase, has small relation with the change of pore diameter and is basically light-proof and whitish. In this embodiment, the incorporation of siloxane-free monomers in the reactive monomers, such as three methyl or ethyl groups attached to Si, improves polymer compliance and lowers surface energy, and the monomer types can be increased from two to three or more, selected for property tuning based on the functional group characteristics of the monomers, such as containing benzene ringsThe amide-containing compound can increase the abrasion resistance, and is preferably aniline methyl triethoxysilane; the cyano-containing group can improve the radiation resistance, and the isocyanate propyl triethoxy silane can improve the ultraviolet resistance. 2. When the first monomer is a monomer containing one siloxane functional group, the second monomer is a monomer containing two siloxane functional groups, the molar ratio of the first monomer to the second monomer is 2, and the dosage of the catalyst is 0.08-0.12 times of the total molar amount of the unsaturated silane monomers, the density of the prepared aerogel is 40-60mg/cm3When the using amount of the catalyst is 0.15-0.25 times of the total molar amount of the unsaturated silane monomer, the density of the prepared aerogel is 15-25mg/cm3And a small amount of siloxane-free third monomer can be introduced into the reaction system, and when the addition amount of the siloxane-free third monomer is less than 0.1 time of the total molar amount of the first type of monomer and the second type of monomer, the density of the prepared aerogel is slightly influenced. In the embodiment, when the catalyst is 0.08-0.12 times of the total amount of the monomers, the crosslinking density is increased, the formed holes are smaller and more, the dehydration weight loss is further increased, and the prepared density is 40-60mg/cm3When the catalyst dosage is nearly doubled, the density of the prepared aerogel is reduced to 15-25mg/cm3Nearby; when the molar ratio of the first monomer to the second monomer is 1 and the dosage of the catalyst is 0.15-0.25 times of the total molar amount of the unsaturated silane monomers, the density of the prepared aerogel is 90-110mg/cm3And a small amount of siloxane-free third monomer can be introduced into the reaction system, and when the addition amount of the siloxane-free third monomer is less than 0.1 time of the total molar amount of the first type of monomer and the second type of monomer, the density of the prepared aerogel is slightly influenced.
According to some embodiments of the present invention, the unsaturated silane monomer is a monomer having three types, the first type is a monomer having one siloxane functional group, the second type is a monomer having two siloxane functional groups, and the third type is a monomer having three siloxane functional groups, 1, when the molar ratio of the first type to the second type is 2, the third type is added in an amount of 0.1 times the total molar amount of the first type and the second type, and the catalyst is not addedWhen the total molar weight of the saturated silane monomer is 0.15-0.25 times, the density of the prepared aerogel is 10-15mg/cm3(ii) a In the embodiment, when the molar ratio of the first monomer to the second monomer is 2, that is, the molar ratio of the mono-siloxane monomer to the bis-siloxane monomer is 2, the third monomer with three siloxane functional groups is introduced, and after the third monomer is added, the density of the prepared aerogel is further reduced, so that the aerogel with the density of 10-15mg/cm can be prepared3The aerogel of (1). 2. When the molar ratio of the first type monomer to the second type monomer is 1, the adding amount of the third type monomer is 0.1 times of the total molar amount of the first type monomer and the second type monomer, and the using amount of the catalyst is 0.08-0.12 times of the total molar amount of the unsaturated silane monomer, the prepared aerogel has the density of 280-3(ii) a In the embodiment, the proportion of the second monomer, namely the disiloxane monomer, is high, the catalyst is relatively absent, more silanol cannot completely complete dehydration weight loss, the functional groups of the silanol in the monomer are relatively close, after one silanol participates in the reaction, the steric hindrance of the ortho-silanol is obviously increased, the reaction space is extruded, and dehydration is inhibited. 3. When the molar ratio of the first type monomer to the second type monomer is 0.5, the addition amount of the third type monomer is 0.1 times of the total molar amount of the first type monomer and the second type monomer, and the dosage of the catalyst is 0.08-0.12 times of the total molar amount of the unsaturated silane monomers, the density of the prepared aerogel is 280-320 mg/cm-3(ii) a When the dosage of the second monomer disiloxane monomer is increased to 2 times of that of the first monomer disiloxane monomer, the catalyst is kept between 0.08 and 0.12 time, the density is basically unchanged, and the prepared aerogel has the density of 280-320 mg/cm-3At this time, the light transmittance of the prepared aerogel is improved, and the light transmittance can reach about 70%. 4. When the molar ratio of the first type of monomer to the second type of monomer is 0.5, the addition amount of the third type of monomer is 0.1 times of the total molar amount of the first type of monomer and the second type of monomer, and the dosage of the catalyst is 0.15-0.25 times of the total molar amount of the unsaturated silane monomer, the density of the prepared aerogel is 130-170mg/cm3. In this example, when the amount of the catalyst is doubled, the density of the prepared aerogel is reduced to 130-170mg/cm3。
According to the preparation method provided by the embodiment of the invention, the difference between the crosslinking density and the dehydration weight loss of the polymer is caused by regulating the monomer type, the monomer ratio and the catalyst dosage in the unsaturated silane monomer, and the corresponding pore size is changed, so that the density is changed finally, and the preparation method provided by the embodiment of the invention can realize that the density is 10-320mg/cm3Control within the scope.
The flexible aerogel according to the example of the second aspect of the present invention is prepared by the preparation method of the above example. The flexible aerogel disclosed by the embodiment of the invention has the characteristics of no structural damage, winding, cutting, 360-degree twisting and high compression ratio of 85%, the adsorption capacity to 3 common organic solvents such as chloroform, acetone and xylene is 23-68 times of the self weight, and the flexible aerogel has excellent performances such as heat conductivity coefficient smaller than that of air and super-hydrophobicity.
Specific embodiments of the present invention are described below with reference to the accompanying drawings.
Example 1
Taking 1mol of allyl dimethyl methoxy silane, 0.1mol of allyl trimethyl silane and 0.05mol of dibenzoyl peroxide, uniformly mixing, introducing nitrogen to remove oxygen in a system, forming a closed space, carrying out free radical polymerization reaction for 6 hours at 90 ℃, cooling to room temperature, adding a tetramethyl ammonium hydroxide aqueous solution consisting of 0.11mol of tetramethyl ammonium hydroxide and 2.2mol of water, uniformly mixing, coating on the surface of a PTFE (polytetrafluoroethylene) base material, reacting for 24 hours at 120 ℃, carrying out sufficient hydrolysis polycondensation reaction, cooling to room temperature, washing with water, and drying to obtain a flaky aerogel, wherein the density of the flaky aerogel is 80mg/cm3。
The principle of the free radical polymerization and hydrolytic polycondensation reaction in the preparation method of the embodiment is shown in fig. 1, the adsorption capacity of the prepared aerogel on 3 common organic solvents is shown in fig. 2, and the compression-rebound mechanics curve of the flexible aerogel under a compression ratio of 85% is shown in fig. 3, wherein the dotted line is the first compression-rebound mechanics curve, and the solid line is the 500-cycle compression-rebound mechanics curve. The data of the performance tests of the aerogel prepared in this example are shown in Table 1.
Example 2
Taking 1mol of allyl dimethyl methoxy silane, 0.5mol of allyl methyl dimethoxy silane, 0.1mol of allyl trimethyl silane and 0.05mol of di-tert-butyl peroxide, uniformly mixing, introducing nitrogen to remove oxygen in a system to form a closed space, carrying out free radical polymerization reaction for 6h at 130 ℃, cooling to room temperature, adding a tetramethyl ammonium hydroxide aqueous solution consisting of 0.4mol of tetramethyl ammonium hydroxide and 4mol of water, uniformly mixing, coating on the surface of a PTFE (polytetrafluoroethylene) base material, reacting for 24h at 120 ℃, carrying out sufficient hydrolytic polycondensation reaction, cooling to room temperature, washing with water, and drying to obtain the sheet aerogel, wherein the density is 15mg/cm3。
The principle of the free radical polymerization and hydrolytic polycondensation reaction in the preparation method of the embodiment is shown in fig. 1, the adsorption capacity of the prepared aerogel on 3 common organic solvents is shown in fig. 2, and the data of various performance tests are shown in table 1.
Example 3
Taking 0.5mol of allyl dimethyl methoxy silane, 0.5mol of allyl methyl dimethoxy silane, 0.1mol of allyl trimethoxy silane and 0.05mol of dibenzoyl peroxide, uniformly mixing, introducing nitrogen to remove oxygen in a system to form a closed space, carrying out free radical polymerization reaction for 6h at 90 ℃, cooling to room temperature, adding a tetramethyl ammonium hydroxide aqueous solution consisting of 0.11mol of tetramethyl ammonium hydroxide and 2.2mol of water, uniformly mixing, coating on the surface of a PTFE (polytetrafluoroethylene) base material, reacting for 24h at 120 ℃, carrying out sufficient hydrolysis polycondensation reaction, cooling to room temperature, washing with water, and drying to obtain the flake aerogel with the density of 300mg/cm3。
The principle of the free radical polymerization and hydrolytic polycondensation reaction in the preparation method of the embodiment is shown in fig. 1, the adsorption capacity of the prepared aerogel on 3 common organic solvents is shown in fig. 2, and the data of various performance tests are shown in table 1.
The aerogel prepared in this example was subjected to a transmittance test, and an ultraviolet-visible-near infrared spectrophotometer (including an integrating sphere attachment) was used to cut a sample into a rectangle having a size of 5mm × 5mm and a thickness of 1mm, and the transmittance was measured to be 55% by taking the percentage of transmitted light at a wavelength of 600nm as the transmittance.
Example 4
Taking 0.5mol of allyl dimethyl methoxy silane, 0.5mol of allyl methyl dimethoxy silane, 0.1mol of allyl trimethyl silane and 0.05mol of di-tert-butyl peroxide, uniformly mixing, introducing nitrogen to remove oxygen in a system to form a closed space, carrying out free radical polymerization reaction for 6h at 130 ℃, cooling to room temperature, adding a tetramethyl ammonium hydroxide solution consisting of 0.22mol of tetramethyl ammonium hydroxide and 2.2mol of water, uniformly mixing, coating on the surface of a PTFE (polytetrafluoroethylene) base material, reacting for 24h at 120 ℃, carrying out full hydrolytic polycondensation reaction, cooling to room temperature, washing with water, and drying to obtain the sheet aerogel with the density of 95mg/cm3。
The principle of the free radical polymerization and hydrolytic polycondensation reaction in the preparation method of the embodiment is shown in fig. 1, the adsorption capacity of the prepared aerogel on 3 common organic solvents is shown in fig. 2, and the data of various performance tests are shown in table 1.
Example 5
Taking 1mol of allyl dimethyl methoxy silane, 0.1mol of allyl trimethyl silane and 0.05mol of dibenzoyl peroxide, uniformly mixing, introducing nitrogen to remove oxygen in a system, forming a closed space, carrying out free radical polymerization reaction for 6 hours at 90 ℃, cooling to room temperature, adding 0.22mol of tetramethyl ammonium hydroxide and 2.2mol of water to form a tetramethyl ammonium hydroxide aqueous solution, uniformly mixing, coating the mixture on the surface of a PTFE (polytetrafluoroethylene) base material, reacting for 24 hours at 120 ℃, carrying out sufficient hydrolysis polycondensation reaction, cooling to room temperature, washing with water, and drying to obtain the flaky aerogel, wherein the density of the flaky aerogel is 50mg/cm3。
The principle of the free radical polymerization and hydrolytic polycondensation reaction in the preparation method of the embodiment is shown in fig. 1, the adsorption capacity of the prepared aerogel on 3 common organic solvents is shown in fig. 2, and the data of various performance tests are shown in tables 1-5.
Example 6
Taking 1mol of allyl dimethyl methoxy silane, 0.1mol of allyl trimethyl silane and 0.05mol of dibenzoyl peroxide/dimethylaniline (wherein, the hydrogen peroxide isDibenzoyl/dimethylaniline with a molar ratio of 2/1), uniformly mixing, introducing nitrogen to remove oxygen in a system, forming a closed space, carrying out free radical polymerization reaction for 2h at 25 ℃, cooling to room temperature, adding a tetramethylammonium hydroxide aqueous solution consisting of 0.11mol of tetramethylammonium hydroxide and 2.2mol of water, uniformly mixing, coating on the surface of a PTFE substrate, reacting for 24h at 120 ℃, carrying out sufficient hydrolysis polycondensation reaction, cooling to room temperature, washing with water, and drying to obtain the flaky aerogel with the density of 85mg/cm3。
Example 7
The same preparation process as in example 1, except that 1mol of allyldimethylmethoxysilane and 0.5mol of allylmethyldimethoxysilane were used as unsaturated silane monomers, 0.15mol of tetramethylammonium hydroxide was used as a catalyst, and the aerogel was obtained to have a density of 50mg/cm3。
Example 8
The same preparation process as in example 7 was conducted except that tetramethylammonium hydroxide as a catalyst was added in an amount of 0.3mol, and the aerogel obtained had a density of 20mg/cm3。
Example 9
The same preparation as in example 1 was conducted except that 1mol of allyldimethylmethoxysilane, 0.5mol of allylmethyldimethoxysilane and 0.15mol of vinyltrimethoxysilane were added as unsaturated silane monomers, 0.413mol of tetramethylammonium hydroxide was added as a catalyst, and the density of the obtained aerogel was 10mg/cm3。
Example 10
The same preparation as in example 9 was conducted except that the unsaturated silane monomers were 1mol of allyldimethylmethoxysilane, 2mol of allylmethyldimethoxysilane and 0.3mol of vinyltrimethoxysilane, the catalyst tetramethylammonium hydroxide was added in an amount of 0.33mol, and the aerogel density was 290mg/cm3The light transmittance was measured to be 70%.
Example 11
The same preparation process as in example 10 was conducted except that tetramethyloxyhydrogen as a catalystThe addition amount of ammonium chloride is 0.6mol, and the density of the prepared aerogel is 150mg/cm3。
Comparative example 1
The same procedure as in example 1, except that only 1.1mol of allyldimethylmethoxysilane and no allyltrimethylsilane were added, was conducted to obtain an aerogel having a density of 100mg/cm3. The data of each performance test is shown in tables 1-5.
Performance testing
Each of the following tests was performed on 10 samples, and the average was used as the final result.
1. Density of
The flexible aerogels obtained in examples 1 to 11 and comparative example 1 were cut into cubes having a size of 3cm × 3cm × 3cm, and after weighing the cubes, density values were calculated from the ratio of mass to volume, and the results are detailed in table 1.
2. Adsorption capacity
The flexible aerogels obtained in examples 1 to 11 and comparative example 1 were cut into cubes having dimensions of 3cm × 3cm × 3cm, and the initial masses were measured and recorded as m0Respectively immersing the aerogel into 3 common organic solvents of chloroform, acetone and xylene at room temperature, taking out after about 10min, weighing the mass after adsorption when no liquid falls off, and recording as m1The adsorption capacity is expressed as (m)1-m0)/m0X 100% rounding.
The aerogels prepared in examples 1 to 11 had adsorption capacities 23 to 68 times as high as their own weights, and the aerogels prepared in comparative example 1 had significantly weaker adsorption capacities than those of examples 1 to 11 of the present invention, and the results are shown in Table 1.
3. Water contact angle
The flexible aerogels prepared in examples 1 to 11 and comparative example 1 were cut into cubes having dimensions of 3cm × 3cm × 3cm, the volumes of the low-dropping water drops were 3 μ L using a water contact angle tester at room temperature, the aerogels prepared in examples 1 to 11 all had static water contact angles of > 150 ° and had strong hydrophobicity, and the aerogels prepared in comparative example 1 had static water contact angles of 142 ° and less than 150 ° and the results are shown in table 1.
4. Coefficient of thermal conductivity
The average thermal conductivity of the samples was tested based on the requirements of the Standard "GB/T10295-. The thermal conductivity of air is 0.25 W.m-1·k-1The thermal conductivity of the flexible aerogels prepared in examples 1 to 11 is less than that of air, and the flexible aerogels have excellent heat insulation performance, and the thermal conductivity of comparative example 1 is 0.32 W.m-1·k-1。
5. Resilience to compression
The flexible aerogel obtained in example 1 was cut into cubes having dimensions of 3cm × 3cm × 3cm, and subjected to a compression-rebound mechanical property test by a universal testing machine, and the results are shown in fig. 3: after the flexible aerogel is subjected to compression-rebound cycles under a compression ratio of 85% for 500 times, the mechanical curve of the flexible aerogel is still basically consistent with that of the initial state, and the mechanical curves of the flexible aerogel in the examples 2 to 11 are sequentially tested under the same condition, so that the result is similar to that of the example 1, and the aerogel prepared by the embodiment of the invention has extremely high internal structure stability, can still maintain the initial mechanical property after being subjected to cyclic pressing under a high compression ratio, has excellent fatigue resistance, and has the first maximum compression stress shown in table 1. Comparative example 1 when the compression resilience test is performed, after 500 compression-rebound cycles at a compression ratio of 85%, the sample has local cracks and damages, which indicates that the stability of the internal structure of the aerogel is low, the initial mechanical properties cannot be maintained after cyclic pressing at a high compression ratio, the fatigue resistance is lower than that of other examples, and the first maximum compression stress of comparative example 1 is only 8 MPa.
6. 360 winding
The aerogels prepared in the embodiments 1 to 11 can be wound and then unreeled, and can be repeatedly carried out without changing the structure, and can be cut into any shape by using scissors, the twisting angle is larger than 360 degrees, while the aerogels prepared in the comparative example 1 are difficult to twist by 360 degrees when being wound.
TABLE 1
Figure BDA0002558774230000101
The reaction mechanism of radical polymerization and hydrolytic polycondensation in fig. 1 of the present invention is a schematic diagram of a process of a two-channel crosslinking reaction, the reaction mainly consists of radical polymerization and hydrolytic polycondensation, wherein the kind or number of siloxane groups on Si atoms in the polymer is not particularly limited and is selected only for convenience of illustration, and siloxane forms silanol during hydrolysis, and then is dehydrated and polycondensed into a second crosslinking channel.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (10)

1. The preparation method of the flexible aerogel is characterized by comprising the following steps:
a. uniformly mixing at least two unsaturated silane monomers and an initiator, wherein at least one unsaturated silane monomer contains a siloxane functional group, introducing protective gas to remove oxygen in a system for free radical polymerization reaction, and cooling;
b. and c, adding a catalyst into the solution obtained after the reaction in the step a, carrying out hydrolytic polycondensation reaction, and cooling to obtain the flexible aerogel.
2. The method for preparing a flexible aerogel according to claim 1, wherein in the step a, the unsaturated silane monomer is:
Figure FDA0002558774220000011
wherein R is1、R2、R3Is one of hydrogen atom, methyl, ethyl, methoxy or ethoxy.
3. The method for preparing a flexible aerogel according to claim 2, wherein in the step a, the unsaturated silane monomer is vinyltrimethylsilane, allyltrimethylsilane, vinylmethyldimethoxysilane, allylmethyldimethoxysilane, vinylmethyldiethoxysilane, allylmethyldiethoxysilane, vinyldimethylmethoxysilane, allyldimethylmethoxysilane, vinyldimethylethoxysilane, allyldimethylethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, vinyltriethoxysilane, or allyltriethoxysilane.
4. The method for preparing a flexible aerogel according to claim 1, wherein in the step a, the monomer containing siloxane functional groups in the unsaturated silane monomers accounts for 90-100% of the total molar amount of the unsaturated silane monomers.
5. The method for preparing a flexible aerogel according to claim 1, wherein in the step a, the initiator is an organic peroxide initiator, an azo initiator or an oxidation-reduction initiator, and the organic peroxide initiator is at least one selected from bis (4-t-butylcyclohexyl) peroxydicarbonate, dicyclohexyl peroxydicarbonate, diisopropyl peroxydicarbonate, t-butyl peroxypivalate, lauroyl peroxide, dibenzoyl peroxide, t-butyl peroxybenzoate, 2-di (t-butylperoxy) butane, methyl ethyl ketone peroxide, dicumyl peroxide or di-t-butyl peroxide; the azo initiator is at least one selected from azodiisoheptanonitrile, azodiisobutyronitrile, dimethyl azodiisobutyrate, azodiisovaleronitrile, azodicyclohexyl cyanogen or azoisobutyryl cyano formamide; the oxidation-reduction initiator is at least one selected from dibenzoyl peroxide/N, N-dimethylaniline, dibenzoyl peroxide/N, N-dimethyl toluidine, cumene hydroperoxide/N, N-dimethylaniline, cumene hydroperoxide/N, N-dimethyl toluidine or naphthenate/dibenzoyl peroxide; the molar quantity of the initiator is 0.05-12% of the total molar quantity of the unsaturated silane monomer.
6. The method for preparing a flexible aerogel according to claim 1, wherein in the step b, the catalyst is tetramethylammonium hydroxide, tetraethylammonium hydroxide, triethylamine or isopropylamine.
7. The method for preparing a flexible aerogel according to claim 1 or 6, wherein in the step b, the molar amount of the catalyst is 0.05 to 0.5 times of the total molar amount of the unsaturated silane monomers.
8. Method for preparing flexible aerogels according to claim 1, characterised in that the density of said flexible aerogels is comprised between 10 and 320mg/cm3。
9. The method for preparing flexible aerogel according to claim 1, wherein in the step a, the temperature of the free radical polymerization is 20-150 ℃ and the reaction time is 1-60 h; in the step b, the hydrolysis polycondensation reaction temperature is 80-160 ℃, and the reaction time is 24-96 h.
10. A flexible aerogel produced by the production method according to any one of claims 1 to 9.
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Publication number Priority date Publication date Assignee Title
JPH08104710A (en) * 1994-10-06 1996-04-23 Nippon Steel Chem Co Ltd Production of silicon-base hybrid material
RU2659077C1 (en) * 2017-12-13 2018-06-28 Федеральное государственное бюджетное учреждение науки Институт элементоорганических соединений им. А.Н. Несмеянова Российской академии наук (ИНЭОС РАН) Method for producing flexible siloxane aerogels
CN109485905A (en) * 2018-11-26 2019-03-19 淮阴工学院 A kind of double cross-linked network silica-based aerogels and preparation method thereof
CN109796018A (en) * 2019-01-29 2019-05-24 同济大学 A kind of preparation method of elasticity double cross connection aeroge
CN111154036A (en) * 2020-01-20 2020-05-15 南京工业大学 Preparation method of ethylene-silane copolymerized composite aerogel

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08104710A (en) * 1994-10-06 1996-04-23 Nippon Steel Chem Co Ltd Production of silicon-base hybrid material
RU2659077C1 (en) * 2017-12-13 2018-06-28 Федеральное государственное бюджетное учреждение науки Институт элементоорганических соединений им. А.Н. Несмеянова Российской академии наук (ИНЭОС РАН) Method for producing flexible siloxane aerogels
CN109485905A (en) * 2018-11-26 2019-03-19 淮阴工学院 A kind of double cross-linked network silica-based aerogels and preparation method thereof
CN109796018A (en) * 2019-01-29 2019-05-24 同济大学 A kind of preparation method of elasticity double cross connection aeroge
CN111154036A (en) * 2020-01-20 2020-05-15 南京工业大学 Preparation method of ethylene-silane copolymerized composite aerogel

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