CN119461388A

CN119461388A - Preparation method and application of fluorosilane modified silica aerogel

Info

Publication number: CN119461388A
Application number: CN202411532665.7A
Authority: CN
Inventors: 任丽霞; 高友美; 袁晓燕
Original assignee: Tianjin University
Current assignee: Tianjin University
Filing date: 2024-10-30
Publication date: 2025-02-18

Abstract

The present invention relates to a preparation method and application of fluorosilane-modified silica aerogel. Silica aerogel is modified by a one-step method using fluorosilane, and the fluorosilane is added into the preparation process as a co-precursor and an aging modifier, respectively, to improve the hydrophobicity and enhance the mechanical properties. The hydrophobicity of solids is controlled by surface chemistry and morphology. Fluorosilane is introduced into silica aerogel. Due to the introduction of fluorine element, the hydrophobicity of silica aerogel changes from general hydrophobicity to super hydrophobicity, and the contact angle reaches 152°; the introduced small molecule alkyl chain enhances the bonding strength of silica particles, thereby improving the strength and toughness of aerogel, the fracture strength increases to 1.2MPa, and the fracture deformation increases to 22%; in addition, the thermal conductivity of the modified aerogel is less than 30.0mW/(m·K). There is great potential in thermal insulation and self-cleaning.

Description

Preparation method and application of fluorosilane modified silica aerogel

Technical Field

The invention relates to preparation of fluorosilane modified silica aerogel and related characterization thereof in heat insulation application. In particular to a preparation method and application of fluorosilane modified silica aerogel. More specifically, the method is a preparation method of modifying the silicon dioxide aerogel by using fluorosilane through a one-step method and the practical application of the method in the aspects of heat insulation and superhydrophobicity.

Background

The heat insulation materials commonly used at present mostly have loose and porous structures, and can effectively prevent convection heat conduction among gases. Silica aerogel is a relatively common insulating material, and by aerogel is meant a special material that replaces the liquid in the wet gel with air and is able to retain its original pore structure. The silica aerogel skeleton is a continuous irregular three-dimensional porous network formed by mutually agglomerating SiO ₂ nano particles, the particles are formed by connecting Si-O-Si bonds, and the pores inside the network are filled with air. The air molecules are positioned in the nanometer holes, the smaller the aperture is, the worse the fluidity of the air is, when the air does not flow, the gas molecules are adsorbed on the surface of the hole wall, and the vacuum state is formed inside the holes, so that the heat convection phenomenon is reduced. Because of this particular structure, aerogels can be effective in reducing heat transfer and convection, thereby reducing thermal conductivity. At present, the silicon dioxide aerogel is widely applied to the fields of military, aerospace, petrochemical industry and the like in the forms of aerogel felts, aerogel plates, aerogel coatings and the like, can be used for protecting pipelines at ultralow temperature to reduce energy loss, and can also be used for protecting safety at ultrahigh temperature.

SiO ₂ aerogel was first prepared in 1931 by Kistler at the university of Stanford, USA, using sol-gel method and supercritical drying technique. In 1985, tewari and the like used TEOS with toxicity far less than TMOS as a precursor and used CO ₂ for supercritical drying to prepare the silica aerogel with the same quality, and the improvement reduces the toxicity of a silicon source and greatly reduces the risk of supercritical drying.

With the intensive research, the need for silica aerogel modification is increasing, and the possibility of improving the implementation of the aerogel in practical applications is becoming more and more urgent. However, the disadvantages of silica aerogel itself limit the application. Firstly, because the silica aerogel is mostly composed of air, the framework is formed by randomly connecting silica nanoparticles, so that the brittleness is high, and the strength and toughness are poor. In addition, the surface of the pure silica aerogel is relatively hydrophilic, and the phenomenon that water is absorbed in the low-temperature application process to freeze easily occurs is avoided, so that the heat preservation performance is reduced. So the aim of application is mainly achieved by improving the strength and the hydrophobicity of the aerogel. The mechanical properties of silica aerogel can be improved by (i) preparing a polyorganosiloxane aerogel using an organosiloxane such as methyltrimethoxysilane as a precursor, (ii) crosslinking the silica skeleton with polymers such as epoxide, polyimide and isocyanate to adhere the polymers to the surface of the silica skeleton and increase the contact area between nanoparticles, (iii) adding a three-dimensional fiber network to the silica aerogel, and (iii) incorporating inorganic substances is also a viable method for enhancing the mechanical properties of silica aerogel. There are two main approaches to increase hydrophobicity, one is to add silylating agents (e.g., hexamethyldisiloxane, methyltrimethoxysilane, phenyltrimethoxysilane, etc.) during sol-gel process, and the second is to modify the dried aerogel surface by reacting with ethanol in the gas phase to form ethoxy groups. In order to improve the mechanical property and the hydrophilcity of the silica aerogel, in the patent, organic macromolecular fluorosilane is added in the process of cohydrolysis and aging, so that the hydrophobicity of the surface of the aerogel is enhanced due to the introduction of fluorine element, and meanwhile, the introduced flexible chains are attached to the silica framework, so that the bonding strength among particles is enhanced, and the strength and toughness of the aerogel are improved. The silica aerogel with improved mechanical properties and hydrophobicity can be obtained only by modifying through a one-step method, and doped monomers can be directly subjected to cohydrolysis and copolycondensation without separate operations such as prepolymerization, so that the operation is simple and convenient.

Disclosure of Invention

In the invention, the silicon dioxide aerogel is modified by using the fluorosilane through a one-step method, and the fluorosilane is respectively used as a co-precursor and an aging modifier to be added into the preparation process, so that the hydrophobicity is improved and the mechanical property is enhanced. The hydrophobicity of a solid is controlled by the surface chemistry and morphology, which can be quantified using the water contact angle, which depends on the magnitude of the intermolecular interactions between the surface and the contact liquid. The solid surface exhibiting a water contact angle exceeding 150 ° is considered to be superhydrophobic, and the hydrolysis antenna of the aerogel surface in the present patent can reach 152 ° to conform to the superhydrophobic characteristic, thereby satisfying the function of the fluorosilane modified aerogel for daily antifouling. In addition, the heat conductivity of the pure silica aerogel is 18.5 mW/(m.K), the heat conductivity after the fluorosilane is added is about 23 mW/(m.K), and the heat conductivity modified by the organic polymer is about 40 mW/(m.K), compared with the heat conductivity of the fluorosilane modified aerogel by other methods, the heat conductivity increment of the fluorosilane modified aerogel is smaller, the heat insulation capacity is excellent, and the method is simple and convenient, easy to operate, low in cost, easy to compound with fiber felt and the like, only needs to be subjected to vacuum impregnation for a period of time in the sol process, and is expected to be produced in a large scale to a certain extent.

The invention aims to provide a preparation method of fluorosilane modified silica aerogel, which improves the mechanical property and hydrophobicity of silica-based aerogel so as to increase the feasibility in practical application.

The technical scheme of the invention is as follows:

The preparation method of the fluorosilane modified silica aerogel comprises the following steps:

1) The fluorosilane is used as a co-precursor, tetraethyl silicate (TEOS), water and ethanol are uniformly mixed and stirred, then an acid catalyst is dripped to adjust the pH of a system to be about 2-3, fluorosilane is added into silica sol to carry out co-hydrolysis, stirring and hydrolysis are carried out for 5-10 hours at room temperature under a sealed condition, an alkaline catalyst is dripped to adjust the pH to 6-8 after the hydrolysis is finished, standing is carried out at room temperature for waiting for gelation, after gelation, wet gel is soaked in an aging liquid of the mixture of the tetraethyl silicate and the ethanol, and then the wet gel is aged for 24-48 hours in an oven, so that further reinforcement of a silica framework is promoted;

or:

The fluorosilane is used as an aging modifier, tetraethyl silicate (TEOS), water and ethanol are uniformly mixed and stirred, then an acid catalyst is dripped to adjust the pH of the system to be about 2-3, and the system is stirred and hydrolyzed for 5-8 hours at room temperature under the sealed condition;

2) Solvent replacement, namely taking out the gel from the oven, naturally cooling the gel to room temperature, adding ethanol, and performing solvent replacement to remove unreacted tetraethyl silicate, fluorosilane and redundant water;

3) And (3) performing supercritical drying, namely after solvent replacement is finished, putting a container which is completely immersed in the ethanol and is subjected to the supercritical drying in an ethanol supercritical drying reaction kettle, after the temperature is raised to 240-245 ℃, preserving the heat for 1-2 hours in the temperature state, then releasing ethanol steam in the reaction kettle until the internal pressure and the external pressure are balanced, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to the room temperature.

Preferably, in the step 1, the molar ratio of the fluorosilane obtained by the co-precursor method to the silicon dioxide in the system is 1% -30%;

Preferably, the fluorosilane in step 1 comprises trifluoropropyl trimethoxysilane, triethoxy [4- (trifluoromethyl) phenyl ] silane, tridecafluorooctyl trimethoxysilane, heptadecafluorodecyl triethoxysilane, perfluorooctyl trichlorosilane, nonafluorohexyl trimethoxysilane, triethoxy [5,5,6,6,7,7,7-heptafluoro-4, 4-bis (trifluoromethyl) heptyl ] silane;

Preferably, the acid catalyst of the step 1 can be hydrochloric acid, nitric acid, acetic acid or oxalic acid, and the base catalyst can be ammonia water, propylene oxide, tetramethylammonium hydroxide or 3-aminopropyl triethoxysilane;

Preferably, the aging liquid in the co-precursor method in the step 1 is a mixed solution of tetraethyl silicate and ethanol in a volume ratio of 1:5-1:10, and the aging time is 12-48 h.

Preferably, the aging liquid in the aging modification method in the step 1 is a mixed solution of fluorosilane and ethanol in a volume ratio of 1:5-1:10, and the aging time is 12-48 h.

Preferably, the solvent replacement in the step 2 is performed once every 5-8 hours, and the total number of the replacement is 3-6.

In the method, fluorosilane is introduced into the silica aerogel, and fluorine is introduced, so that the hydrophobicity of the silica aerogel is changed from general hydrophobicity to superhydrophobicity, the contact angle reaches 152 degrees, the introduced small molecular alkyl chain enhances the bonding strength of silica particles, so that the strength and toughness of the aerogel are improved, the breaking strength is increased to 1.2MPa, the breaking deformation is increased to 22%, and in addition, the heat conductivity coefficient of the modified aerogel is less than 30.0 mW/(m.K).

The fluorosilane modified silica aerogel of the invention is applied to heat insulation.

The fluorosilane modified silica aerogel of the invention is applied to self-cleaning.

The fluorosilane-modified silica aerogel has good thermal insulation capability when applied in environments of-100 ℃ and 200 ℃ and has a surface temperature of about 15 ℃ and 65 ℃ in contact with the air environment.

The invention also relates to the application in the aspects of heat insulation and self-cleaning. The fluoro silane and the silicon source are used as co-precursors by a one-step modification method, fluorine on the alkyl chain is exposed outside the holes when gel is formed, so that the hydrophobicity is improved, and meanwhile, the alkyl chain is attached to the surface of the gel and plays a role of buffering when external force is applied, so that the compressive strength and toughness of the gel are improved. The aerogel prepared by the technical scheme provided by the invention has the characteristics of simple operation, mild reaction conditions, readily available raw materials and low heat conductivity coefficient, and has great potential in the aspect of heat insulation in the future.

Compared with the existing pure silica aerogel, the silica aerogel with improved mechanical properties and hydrophobicity is successfully prepared by the technical scheme of the invention. The hydrophobicity of the aerogel is changed from general hydrophobicity to superhydrophobic, so that the aerogel can be applied to antifouling, anticorrosion and anti-icing in daily life. In addition, as the pure silica aerogel is only randomly connected by nano particles, the skeleton is fragile, and the introduced micromolecular fluoro-silane can be attached to the surface of the skeleton of the silica nano particles, so that the buffer effect can be realized when the external force acts, the compressive strength of the aerogel is increased from 0.4MPa to 1.2MPa, the fracture deformation is increased from 10% to 22%, and the toughness and strength of the aerogel are effectively enhanced.

Drawings

FIG. 1 is a scanning electron micrograph of silica aerogel prepared in example 1

FIG. 2 is an EDS diagram of silica aerogel prepared in example 2

FIG. 3 is the thermal conductivity results of aerogels prepared in examples 3-5 and comparative example

FIG. 4 is a graph showing the mechanical properties of aerogels prepared in examples 6-8 and comparative examples

FIG. 5 is a photograph of the contact angle of silica prepared in example 9

FIG. 6 is an infrared thermal imaging of silica aerogel prepared in accordance with example 10

FIG. 7 is a self-cleaning test chart of silica aerogel prepared in example 11

Detailed Description

Example 1

Step 1, respectively weighing 10.2g of tetraethyl silicate (TEOS), 22.3g of ethanol and 3.5g of water, wherein silicon dioxide accounts for 9.0% of the mole of the system, uniformly mixing and stirring the three materials for 10min, dropwise adding acetic acid to adjust the pH of the system to be about 2-3, then adding 0.11g of trifluoropropyl trimethoxysilane into silica sol to carry out cohydrolysis, wherein the content is 1% of the mole of silicon dioxide in the system, and finally stirring and hydrolyzing for 6h at room temperature under the sealed condition. And (3) after the hydrolysis is finished, dropwise adding ammonia water to adjust the pH to 6-7, and standing at room temperature to wait for gel. After gelation, the wet gel is soaked in ageing liquid with the volume ratio of tetraethyl silicate to ethanol of 1:5 and aged for 24 hours in a 50 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 2, solvent replacement, namely taking out the gel from the oven, naturally cooling the gel to room temperature, adding fresh and clean ethanol, and performing solvent replacement to remove unreacted TEOS and redundant water, wherein the gel is replaced once every 8 hours for 3 times.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample into an ethanol supercritical drying reaction kettle for supercritical drying after solvent replacement is finished, preserving heat for 1h in the temperature state after the temperature is raised to 240 ℃ of the ethanol, then releasing ethanol steam in the reaction kettle until internal and external pressure balance is achieved, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to room temperature.

Test example 1

In this test example, the microscopic morphology of the heat insulating material prepared in example 1 was observed, and the porous heat insulating material prepared in example 1 was subjected to microscopic morphology test by using an S-4800 cold field emission scanning electron microscope. Fig. 1 is an SEM photograph of the aerogel prepared in example 1, in which the pearl chain shape is clearly observed, the overall pore distribution is relatively uniform, and no obvious phase separation is observed, thus proving that the fluorosilane and the original silicon source are well combined.

Example 2

Step 1, respectively weighing 25.3g of tetraethyl silicate (TEOS), 48.1g of ethanol and 8.5g of water, wherein silicon dioxide accounts for 8.8% of the mole of the system, uniformly mixing and stirring the three materials for 10min, dropwise adding oxalic acid to adjust the pH of the system to be about 2-3, then adding 1.85g of triethoxy [4- (trifluoromethyl) phenyl ] silane into silica sol to carry out cohydrolysis, wherein the content is 5% of the mole of the silicon dioxide in the system, and finally stirring and hydrolyzing for 6h at room temperature under the sealed condition. And after the hydrolysis is finished, dropwise adding propylene oxide to adjust the pH to 6-8, and standing at room temperature to wait for gel. After gelation, the wet gel is soaked in ageing liquid with the volume ratio of tetraethyl silicate to ethanol of 1:6 and aged for 24 hours in a 60 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 2, solvent replacement, namely taking out the gel from the oven, naturally cooling the gel to room temperature, adding fresh and clean ethanol, and performing solvent replacement to remove unreacted TEOS and redundant water, wherein the gel is replaced once every 6 hours, and the total replacement is performed for 4 times.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample after solvent replacement is finished into an ethanol supercritical drying reaction kettle for supercritical drying, preserving heat for 1.5 hours at the temperature state after the temperature is increased to 243 ℃ of the ethanol, then releasing ethanol steam in the reaction kettle until the internal pressure and the external pressure are balanced, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to the room temperature.

Test example 2

In this test example, the porous heat insulation material prepared in example 1 was subjected to microscopic morphology test by using an S-4800 type cold field emission scanning electron microscope on the aerogel prepared in example 2. Fig. 2 is an elemental analysis EDS image of the insulation material prepared in example 2 of the present invention, in which fluorine is uniformly distributed, advantageously demonstrating the incorporation of fluorine into silica aerogel.

Example 3

Step 1, respectively weighing 30.0g of tetraethyl silicate (TEOS), 66.1g of ethanol and 10.2g of water, wherein silicon dioxide accounts for 8.1% of the mole of the system, uniformly mixing the three materials, vigorously stirring for 10min, dropwise adding hydrochloric acid to adjust the pH of the system to be about 2-3, then adding 8.63g of tridecafluorooctyl trimethoxysilane into silica sol to carry out cohydrolysis, wherein the content is 13% of the mole of the silicon dioxide in the system, and finally stirring and hydrolyzing for 8h at room temperature under the sealed condition. And after the hydrolysis is finished, dropwise adding tetramethylammonium hydroxide to adjust the pH to 6-8, and standing at room temperature to wait for gel. After gelation, the wet gel is soaked in ageing liquid with the volume ratio of tetraethyl silicate to ethanol of 1:8 and aged for 24 hours in a 70 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 2, solvent replacement, namely taking out the gel from the oven, naturally cooling the gel to room temperature, adding fresh and clean ethanol, and performing solvent replacement to remove unreacted TEOS and redundant water, wherein the gel is replaced once every 7 hours, and the total replacement is performed for 4 times.

And 3, supercritical drying, namely after solvent replacement is finished, placing a container which is completely immersed in the ethanol and is subjected to sample supercritical drying in a reaction kettle for supercritical drying, after the temperature is raised to 245 ℃ of the ethanol, preserving the heat for 1.4 hours in the state of the temperature, then releasing ethanol steam in the reaction kettle until the internal pressure and the external pressure are balanced, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to the room temperature.

Test example 3

This test example carries out the measurement of the thermal conductivity of the aerogels prepared in examples 3 to 5 and the unmodified silica aerogel, and specifically the thermal conductivity of the thermal insulation materials prepared in examples and comparative examples was measured by a TC2120 thermal conductivity meter. FIG. 3 is a graph showing the results of the thermal conductivities of the aerogels of comparative examples and examples 3-5, wherein the prepared aerogels have low thermal conductivities and good thermal insulation properties. The aerogels prepared in comparative examples and examples 3, 4, and 5 had thermal conductivities of 18.5 mW/(mK), 20.5 mW/(mK), 24.7 mW/(mK), and 26.2 mW/(mK), respectively.

Example 4

Step 1, respectively weighing 20.5g of tetraethyl silicate (TEOS), 52.2g of ethanol and 6.9g of water, wherein silicon dioxide accounts for 7.4% of the mole of the system, uniformly mixing the three materials, vigorously stirring for 10min, dropwise adding nitric acid to adjust the pH of the system to be about 2-3, then adding 6.51g of nonafluorohexyl trimethoxysilane into silica sol to carry out cohydrolysis, wherein the content is 18% of the mole of silicon dioxide in the system, and finally stirring and hydrolyzing for 12h at room temperature under the sealed condition. And (3) dropwise adding ammonia water after the hydrolysis is finished, adjusting the pH to 6-7, and standing at room temperature for waiting for gel. After gelation, the wet gel is soaked in ageing liquid with the volume ratio of tetraethyl silicate to ethanol of 1:10 and aged for 24 hours in a 55 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 2, solvent replacement, namely taking out the gel from the oven, naturally cooling the gel to room temperature, adding fresh and clean ethanol, and performing solvent replacement to remove unreacted TEOS and redundant water, wherein the gel is replaced once every 5 hours, and the total replacement is performed for 6 times.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample after solvent replacement is finished into an ethanol supercritical drying reaction kettle for supercritical drying, preserving heat for 1.8 hours at the temperature after the temperature is increased to 242 ℃ of ethanol critical temperature, then releasing ethanol steam in the reaction kettle until internal and external pressure balance is achieved, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to room temperature.

Example 5

Step 1, respectively weighing 15.2g of tetraethyl silicate (TEOS), 48.3g of ethanol and 6.5g of water, wherein silicon dioxide accounts for 6.2% of the molar weight of the system, uniformly mixing the three materials, vigorously stirring for 20min, dropwise adding nitric acid to adjust the pH of the system to be about 2-3, then adding 7.66g of perfluorooctyl trichlorosilane into silica sol to carry out cohydrolysis, wherein the content is 22% of the molar weight of the silicon dioxide in the system, and finally stirring and hydrolyzing for 5h at room temperature under a sealed condition. And (3) dropwise adding ammonia water after the hydrolysis is finished, adjusting the pH to 6-8, and standing at room temperature for waiting for gel. After gelation, the wet gel is soaked in ageing liquid with the volume ratio of tetraethyl silicate to ethanol of 1:9 and aged for 24 hours in a 70 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample after solvent replacement is finished into an ethanol supercritical drying reaction kettle for supercritical drying, preserving heat for 1.6 hours at the temperature after the temperature is increased to 244 ℃ of ethanol critical temperature, then releasing ethanol steam in the reaction kettle until internal and external pressure balance is achieved, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to room temperature.

Example 6

Step 1, respectively weighing 42.3g of tetraethyl silicate (TEOS), 93.4g of ethanol and 21.9g of water, wherein silicon dioxide accounts for 7.7% of the mole of the system, uniformly mixing the three materials, vigorously stirring for 15min, dropwise adding oxalic acid to adjust the pH of the system to be about 2-3, then adding 12.35g of heptadecafluorodecyl triethoxysilane into silica sol to carry out cohydrolysis, wherein the content is 10% of the mole of the silicon dioxide in the system, and finally stirring and hydrolyzing for 12h at room temperature under the sealed condition. And (3) dropwise adding ammonia water after the hydrolysis is finished, adjusting the pH to 6-7, and standing at room temperature for waiting for gel. After gelation, the wet gel is soaked in ageing liquid with the volume ratio of tetraethyl silicate to ethanol of 1:10 and aged for 24 hours in a 60 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample replacement into an ethanol supercritical drying reaction kettle for supercritical drying after the solvent replacement is finished, preserving heat for 1.2 hours at the temperature after the temperature is raised to 241 ℃ of ethanol, then releasing ethanol steam in the reaction kettle until the internal and external pressure balance is achieved, and finally taking out the prepared aerogel after the solvent replacement of the solvent is finished when the temperature in the reaction kettle is reduced to room temperature, and performing supercritical drying to obtain the prepared aerogel.

Test example 4

Test example mechanical properties of aerogels prepared in examples 6 to 8 and comparative example (unmodified silica aerogel) were tested, specifically, compression test was performed on aerogel materials prepared in examples and comparative example using a CMT4203 microcomputer controlled electronic universal tester, and the surface of the sample was polished flat with 1000 mesh sand paper before the test. The aerogels prepared in comparative examples and examples 6,7,8 had breaking strengths of 0.4MPa, 0.75MPa, 1.2MPa, 0.78MPa, respectively.

Example 7

Step 1, respectively weighing 10.2g of tetraethyl silicate (TEOS), 22.5g of ethanol and 3.7g of water, wherein silicon dioxide accounts for 7.6% of the mole amount of the system, uniformly mixing the three materials, vigorously stirring for 10min, dropwise adding hydrochloric acid to adjust the pH of the system to be about 2-3, then adding 7.635g of triethoxy [5,5,6,6,7,7,7-heptafluoro-4, 4-bis (trifluoromethyl) heptyl ] silane into silica sol to carry out cohydrolysis, wherein the content is 30% of the mole amount of the silicon dioxide in the system, and finally stirring and hydrolyzing for 12h at room temperature under a sealed condition. And after the hydrolysis is finished, 3-aminopropyl triethoxysilane is dropwise added to adjust the pH to 6-7, and the mixture is stood at room temperature for waiting for gel. After gelation, the wet gel is soaked in ageing liquid with the volume ratio of tetraethyl silicate to ethanol of 1:8 and aged for 24 hours in a 75 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample after solvent replacement is finished into an ethanol supercritical drying reaction kettle for supercritical drying, preserving heat for 1.6 hours at the temperature after the temperature is raised to 240 ℃ of the ethanol critical temperature, then releasing ethanol steam in the reaction kettle until the internal pressure and the external pressure are balanced, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to the room temperature.

Example 8

And 1, respectively weighing 30.5g of tetraethyl silicate, 68.5g of water and 12.6g of water, wherein silicon dioxide accounts for 8.1% of the mole of the system, uniformly mixing the three materials, stirring for 10min, dropwise adding hydrochloric acid to adjust the pH of the system to be about 2-3, and stirring and hydrolyzing for 6h at room temperature under a sealed condition. And (3) after the hydrolysis is finished, dropwise adding ammonia water to adjust the pH to 6-8, and standing at room temperature to wait for gel. After gelation, the wet gel is soaked in an aging liquid with the volume ratio of ethoxy [4- (trifluoromethyl) phenyl ] silane to ethanol of 1:6 and aged for 48 hours in a 60 ℃ oven, so that the further reinforcement of the silica framework is promoted.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample after solvent replacement is finished into an ethanol supercritical drying reaction kettle for supercritical drying, preserving heat for 1.7 hours at the temperature state after the temperature is increased to 243 ℃ of the ethanol, then releasing ethanol steam in the reaction kettle until the internal pressure and the external pressure are balanced, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to the room temperature.

Example 9

And 1, respectively weighing 50.2g of tetraethyl silicate, 127.5g of water and 17.9g of water, wherein silicon dioxide accounts for 7.4% of the mole of the system, uniformly mixing the three materials, stirring for 10min, dropwise adding nitric acid to regulate the pH of the system to be about 2-3, and stirring and hydrolyzing for 6h at room temperature under a sealed condition. And (3) after the hydrolysis is finished, dropwise adding ammonia water to adjust the pH to 6-8, and standing at room temperature to wait for gel. After gelation, the wet gel is soaked in aging liquid with the volume ratio of nonafluorohexyl trimethoxysilane to ethanol of 1:7 and aged for 36 hours in a 75 ℃ oven, so as to promote further reinforcement of the silica framework.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample after solvent replacement is finished into an ethanol supercritical drying reaction kettle for supercritical drying, preserving heat for 1.9 hours at the temperature after the temperature is increased to 244 ℃ of ethanol critical temperature, then releasing ethanol steam in the reaction kettle until internal and external pressure balance is achieved, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to room temperature.

Test example 5

The test example is to test the hydrophobic property of the aerogel prepared in example 9, and specifically to measure the angle by using a JC200D optical contact angle tester. Fig. 5 is a photograph of the contact angle of the aerogel prepared in example 9, with an angle of 152 °.

Example 10

And step 1, respectively weighing 29.2g of tetraethyl silicate, 80.2g of water and 15.8g of water, wherein silicon dioxide accounts for 6.7% of the mole of the system, uniformly mixing the three materials, stirring for 10min, dropwise adding acetic acid to regulate the pH of the system to be about 2-3, and stirring and hydrolyzing for 6h at room temperature under a sealed condition. And after the hydrolysis is finished, dropwise adding tetramethylammonium hydroxide to adjust the pH to 6-8, and standing at room temperature to wait for gel. After gelation, the wet gel is soaked in aging liquid with the volume ratio of trifluoropropyl trimethoxy silane to ethanol of 1:9 and aged for 30 hours in a 70 ℃ oven, so as to promote further reinforcement of the silica framework.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample into an ethanol supercritical drying reaction kettle for supercritical drying after solvent replacement is finished, preserving heat for 2.0h in the temperature state after the temperature is raised to 240 ℃ of the ethanol, then releasing ethanol steam in the reaction kettle until the internal pressure and the external pressure are balanced, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to room temperature.

Test example 6

The test example was a test of the thermal insulation performance of the aerogels prepared in example 10 and comparative example (unmodified silica aerogel), and the concrete operation was to take an aerogel having a height of about 10mm, place it on a 200 ℃ hot stage and a-120 ℃ cold stage, respectively, and then record the temperature change condition of the upper surface of the aerogel by using a thermal infrared imager.

FIG. 6 is a photograph of an infrared thermal image of the aerogel prepared in example 10 and comparative example after being stabilized on a 200℃hot stage and a-120℃cold stage for 10 minutes (comparative example on the left, example 10 on the right), showing that the thermal insulation properties of the unmodified silica aerogel and the modified aerogel are not very different, and that the modified aerogel has excellent thermal insulation capability although the mechanical properties are increased.

Example 11

And step 1, respectively weighing 25.3g of tetraethyl silicate, 68.5g of water and 8.6g of water, wherein silicon dioxide accounts for 7.1% of the mole of the system, uniformly mixing the three materials, stirring for 10min, dropwise adding oxalic acid to regulate the pH of the system to be about 2-3, and stirring and hydrolyzing for 6h at room temperature under a sealed condition. And after the hydrolysis is finished, 3-aminopropyl triethoxysilane is dropwise added to adjust the pH to 6-8, and the mixture is stood at room temperature for waiting for gel. After gelation, the wet gel is soaked in aging liquid with the volume ratio of trifluoropropyl trimethoxy silane to ethanol of 1:9 and aged for 30 hours in a 70 ℃ oven, so as to promote further reinforcement of the silica framework.

And 2, solvent replacement, namely taking out the gel from the oven, naturally cooling the gel to room temperature, adding fresh and clean ethanol, and performing solvent replacement to remove unreacted TEOS and redundant water, wherein the gel is replaced once every 7 hours for 5 times.

And 3, performing supercritical drying, namely placing a container which is completely immersed in the ethanol and used for sample after solvent replacement is finished into an ethanol supercritical drying reaction kettle for supercritical drying, preserving heat for 1.0h in the temperature state after the temperature is raised to 245 ℃ of the ethanol, then releasing ethanol steam in the reaction kettle until the internal pressure and the external pressure are balanced, and finally taking out the prepared aerogel when the temperature in the reaction kettle is reduced to the room temperature.

Test example 7

The test example is to prove that the modified aerogel has certain self-cleaning capability due to the improvement of the hydrophobic property, and specifically the aerogel prepared in the example 11 and the comparative example is placed in a methylene blue solution for soaking for 1min, and then taken out to observe the surface changes of the two. FIG. 7 shows the self-cleaning performance test (upper: comparative example; lower: example 11) of the aerogels prepared in example 11 and comparative example (unmodified silica aerogel) as seen in FIG. 7, the aerogel of comparative example had a blue residual liquid after soaking, while the aerogel of example 11 was still clean and stain-free, demonstrating the improved hydrophobicity of the modified silica aerogel.

The technical scheme disclosed and proposed by the invention can be realized by a person skilled in the art by appropriately changing the condition route and other links in consideration of the content of the present invention, although the method and the preparation technology of the invention have been described by the preferred embodiment examples, the related person can obviously modify or recombine the method and the technical route described herein to realize the final preparation technology without departing from the content, spirit and scope of the invention. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be included within the spirit, scope and content of the invention.

Claims

1. The preparation method of the fluorosilane modified silica aerogel is characterized by comprising the following steps:

1) The fluorosilane is used as a co-precursor, tetraethyl silicate, water and ethanol are uniformly mixed and stirred, then an acid catalyst is dripped to adjust the pH of a system to be about 2-3, fluorosilane is added into silica sol to carry out co-hydrolysis, stirring and hydrolysis are carried out for 5-10 hours at room temperature under a sealed condition, an alkaline catalyst is dripped to adjust the pH to 6-8 after the hydrolysis is finished, standing is carried out at room temperature to wait for gel, after gelation, wet gel is soaked in an aging liquid mixed by the tetraethyl silicate and the ethanol, and then the wet gel is aged for 24-48 hours in an oven to promote further reinforcement of a silica framework;

or:

The fluorosilane is used as an aging modifier, tetraethyl silicate, water and ethanol are mixed and stirred uniformly, then an acid catalyst is dripped to adjust the pH of the system to be about 2-3, and the system is stirred and hydrolyzed for 5-8 hours at room temperature under the sealed condition;

2. The method of claim 1, wherein the molar ratio of fluorosilane from the co-precursor process to silica in the system in step1 is 1% to 30%.

3. The method of claim 1, wherein the fluorosilane of step 1 comprises trifluoropropyl trimethoxysilane, triethoxy [4- (trifluoromethyl) phenyl ] silane, tridecafluorooctyl trimethoxysilane, heptadecafluorodecyl triethoxysilane, perfluorooctyl trichlorosilane, nonafluorohexyl trimethoxysilane, or triethoxy [5,5,6,6,7,7,7-heptafluoro-4, 4-bis (trifluoromethyl) heptyl ] silane.

4. The process according to claim 1, wherein the acid catalyst of step 1 is hydrochloric acid, nitric acid, acetic acid, oxalic acid, and the base catalyst is ammonia, propylene oxide, tetramethylammonium hydroxide, or 3-aminopropyl triethoxysilane.

5. The method of claim 1, wherein the aging liquid in the co-precursor method of step 1 is a mixed solution of tetraethyl silicate and ethanol in a volume ratio of 1:5-1:10, and the aging time is 12-48 h.

6. The method of claim 1, wherein the aging liquid in the aging modification method of step 1 is a mixed solution of fluorosilane and ethanol in a volume ratio of 1:5-1:10, and the aging time is 12-48 h.

7. The method of claim 1, wherein the solvent replacement in step 2 is performed every 5 to 8 hours for 3 to 6 times.

8. The application of the fluorosilane modified silica aerogel prepared by the method of claim 1 in heat insulation.

9. The use of the fluorosilane-modified silica aerogel prepared by the method of claim 1 in self-cleaning.