Preparation method for preparing super-hydrophobic silicon dioxide aerogel by using combined modifier

Abstract

The invention provides a method for preparing super-hydrophobic silicon dioxide aerogel by using a combined modifier. The method comprises the following steps: S1, mixing silane, ethanol and deionized water, adding a catalyst, and uniformly stirring to obtain a precursor solution A; s2, sequentially adding a combined modifier into the precursor solution A, and uniformly stirring to obtain a mixed solution B; s3, the mixed solution B is poured into a mold for standing, and wet gel is obtained; s4, carrying out replacement aging treatment on the wet gel to obtain alcogel; and S5, carrying out drying treatment on the alcogel by adopting a supercritical carbon dioxide drying technology to obtain the super-hydrophobic silicon dioxide aerogel material. The preparation process is greatly simplified, the preparation period is shortened, and the consistency of product quality is improved. And compared with the existing production process, the preparation method is more environment-friendly and energy-saving, and is more environment-friendly. The application field of the super-hydrophobic aerogel material can be expanded, and remarkable economic and social benefits are brought.

Description

Technical Field

[0001] The invention belongs to the technical field of silica aerogel preparation, and relates to a method for preparing super-hydrophobic silica aerogel by using a combined modifier. Background Art

[0002] Silica aerogel is a new type of material with a nanoporous structure, with excellent properties such as low density, high porosity, and low thermal conductivity. It has broad application prospects in the fields of thermal insulation, adsorption, and catalysis. However, traditional silica aerogel materials are usually hydrophilic and easily absorb water during long-term use in a humid environment, affecting their performance and service life. Therefore, silica aerogel materials with super-hydrophobic properties are required in special use scenarios. At present, the methods for preparing super-hydrophobic silica aerogel materials mainly include surface modification, template method, sol-gel method, etc. The surface modification method is to achieve super-hydrophobic properties by grafting or coating hydrophobic substances on the surface of silica aerogel, but the method is complex and costly, and it is easy to affect the pore structure of the aerogel, resulting in a decrease in the comprehensive performance of the aerogel. The template method is to control the structure and morphology of the aerogel by a template agent, and then remove the template agent to obtain a super-hydrophobic aerogel, but the removal process of the template agent is relatively difficult, and it is easy to leave residual template agents, affecting the performance of the aerogel. The sol-gel method is to prepare silica aerogel through a sol-gel process, and then achieve super-hydrophobic properties through surface modification and other methods. However, this method is cumbersome, has a long cycle, and requires the use of a large amount of organic solvents, which is easy to pollute the environment. In order to improve the production process of super-hydrophobic silica aerogel, researchers have tried to introduce various modifiers. For example, patent application number 202210574518.0 discloses a method for preparing super-hydrophobic silica aerogel powder, which is prepared by multi-step operations such as sol preparation and two hydrophobic modifications. Although silica aerogel powder with super-hydrophobic properties can be obtained, the process is complicated and has certain requirements for equipment and environment. At the same time, a certain amount of waste liquid is generated during the preparation process; patent application number 201910270914.2 discloses a method for preparing super-hydrophobic silica aerogel at normal pressure Method, this patent prepares super-hydrophobic silica aerogel at normal pressure, which requires precise control of parameters. The preparation cycle is long and is not conducive to large-scale rapid production. Drying at normal pressure may lead to uneven drying; Patent with application number 202110575394.3 discloses super-hydrophobic silica aerogel and its preparation method, super-hydrophobic porous membrane and its preparation method and application. This patent has strict requirements on raw materials, the freeze-drying time is long and the equipment energy consumption is high, which limits the improvement of production efficiency and increases production costs.

[0003] In summary, the existing methods for preparing super-hydrophobic silica aerogel materials have the problems of complex process, high cost, long cycle, and environmental pollution. Therefore, it is of great practical significance to develop a simple, efficient and environmentally friendly method for preparing super-hydrophobic silica aerogel materials. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for preparing super hydrophobic silica aerogel by combining modifiers, which specifically comprises the following steps: S1: Preparation of precursor solution: silane, ethanol, deionized water and other raw materials are mixed, and after mixing evenly, a catalyst is added and stirred evenly to obtain a precursor solution A. Among them, silane is ethyl orthosilicate or methyl orthosilicate, and the catalyst is hydrochloric acid or ammonia water. When preparing the precursor solution, the molar ratio of silane, ethanol and deionized water is ensured to be 1: (5-10): (3-5). When mixing, silane, ethanol and deionized water are first mixed and stirred. During the stirring process, the temperature is controlled at 50-60°C, the stirring speed is maintained at 200-300r / min, and the entire stirring time is controlled at 30-60min. The stirring process requirements are strictly implemented to ensure that each component is fully mixed and evenly mixed.

[0005] S2: Introducing the combined modifier, the combined modifier is sequentially added to the precursor solution A for hydrophobic modification, and the precursor solution A mixed with the combined modifier is stirred uniformly to obtain a mixed solution B. As a priority of the present invention, the combined modifier is composed of a fluorine-containing silane coupling agent, a long-chain alkyl silane coupling agent and a silane coupling agent with a special functional group.

[0006] Fluorine-containing silane coupling agents have extremely low surface energy, and the fluorine atoms in their molecular structure can strongly repel water molecules, thus giving aerogel materials excellent superhydrophobic properties. Long-chain alkyl silane coupling agents can enhance the hydrophobicity and stability of the material, and can form an orderly hydrophobic film on the surface of the aerogel, thereby improving the water resistance and chemical stability of the material. Silane coupling agents with special functional groups help to improve the structural stability of the material and its compatibility with other components. Its functional groups can react with the hydroxyl groups on the surface of silica to form a strong chemical bond, thereby enhancing the structural strength of the aerogel. The functional group can also interact with other modifier molecules to improve the overall effect of the combined modifier. In order to achieve the best performance, the fluorine-containing silane coupling agent is tridecafluorooctyltrimethoxysilane, the long-chain alkyl silane coupling agent is octadecyltrimethoxysilane, and the silane coupling agent with special functional groups is composed of γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0007] When adding the combined modifier, the order and amount of the three modifiers must be strictly controlled to achieve the best hydrophobic effect. When preparing, first add the fluorinated silane coupling agent and stir for 20 to 30 minutes, then add the long-chain alkyl silane coupling agent and stir for 20 to 30 minutes, and finally add the silane coupling agent with special functional groups and stir for 1.5 to 2 hours. The mass ratio of the fluorinated silane coupling agent, the long-chain alkyl silane coupling agent and the silane coupling agent with special functional groups is 2:3:1, and the amount added to the combined modifier is 8% to 20% of the mass of silane.

[0008] S3: Gelation reaction: Pour the mixed solution B into the mold and let it stand. During the process, keep the temperature at 40-60°C and the relative humidity at 40%-60%. The total reaction time is controlled at 20-36h. Strictly control the reaction conditions within the temperature and humidity range to ensure that the gelation reaction rate is appropriate, so as to obtain a wet gel with uniform and stable structure.

[0009] S4: Solvent replacement and aging, the wet gel obtained in step S3 is subjected to replacement aging, and an organic solvent is used for replacement aging, wherein the organic solvent used is ethanol, acetone or isopropanol, and the aging temperature is ensured to be 50-60°C, and the time is 30-50 hours to obtain alcohol gel. During the aging process, the structure of the wet gel gradually becomes more stable, and the incompletely reacted substances continue to react, so that the performance of the aerogel is further improved.

[0010] S5: Drying treatment: using supercritical carbon dioxide drying technology to dry the alcohol gel can effectively remove the solvent in the alcohol gel while avoiding the shrinkage and cracking of the aerogel caused by solvent volatilization in the traditional drying method, and maintaining the nanoporous structure of the aerogel. The supercritical carbon dioxide drying temperature is 40~60℃, the pressure is 10~15MPa, and the time is 5~10h. After drying treatment, a superhydrophobic silica aerogel material is obtained.

[0011] The preparation method of the combined modifier provided by the present invention for preparing super-hydrophobic silica aerogel is compared with the prior art, and the one-step preparation process using a new combined modifier is concise and efficient, greatly simplifies the preparation process, shortens the preparation cycle, reduces production costs, and can reduce production errors and improve the consistency of product quality. The super-hydrophobic performance of aerogel is significantly improved by adopting a new combined modifier, and the excellent performances such as super-hydrophobicity of the material can be better given. In the hydrophobic performance test, the contact angle can reach more than 160 °, and the rolling angle is less than 8 °, and the prepared aerogel material has excellent stability in a humid environment. In the preparation process, a large amount of organic solvents are not required, which is more environmentally friendly and energy-saving than the existing production process, and is more friendly to the environment. It is possible to promote the further development of materials science, and a new path is opened up for the preparation of super-hydrophobic materials. It is possible to expand the application field of super-hydrophobic aerogel materials, and there is great potential in the fields of construction, aerospace, electronics, environmental protection, and significant economic and social benefits are brought. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention is further described in detail below with reference to the accompanying drawings.

[0013] Figure 1 This is a diagram showing the hydrophobicity test results of Example 2; Figure 2 This is a hydrophobic performance test result diagram of Comparative Example 1; Figure 3 This is a diagram showing the hydrophobic performance test results of Comparative Example 2. DETAILED DESCRIPTION

[0014] To further illustrate the concept of the present invention, the present invention will be further described in detail by specific examples below. The following examples are only for illustrative purposes to illustrate and explain the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the contents of the present invention are included in the scope of protection intended by the present invention. Embodiment 1

[0015] Weigh 1 mol of tetraethyl orthosilicate, 8 mol of ethanol, and 4 mol of deionized water, add the weighed raw materials into a reaction vessel with a stirring device, add 1 mol / L hydrochloric acid as a catalyst, turn on the stirrer and stir continuously at 250 r / min at 55°C for 30 min to ensure that all components are fully mixed. At this time, the solution is transparent and stable, and a precursor solution A is obtained.

[0016] Weigh 0.4 g of tridecafluorooctyltrimethoxysilane, 0.6 g of octadecyltrimethoxysilane, and 0.2 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, first slowly add tridecafluorooctyltrimethoxysilane to precursor solution A, stir for 20 minutes to make it initially dispersed evenly, then add octadecyltrimethoxysilane, and continue stirring for 30 minutes. It is observed that the viscosity of the solution gradually increases. Finally, add γ-(2,3-epoxypropoxy)propyltrimethoxysilane and continue stirring for 2 hours to ensure that the three modifiers are fully integrated to obtain a mixed solution B.

[0017] Pour the mixed solution B into a polytetrafluoroethylene mold, and place the mold in a constant temperature and humidity chamber at 50°C and 50% relative humidity for gelation. The gelation process is closely observed, and a wet gel with uniform structure and soft texture is obtained after 24 hours. The polytetrafluoroethylene mold has good corrosion resistance and shape stability, which can ensure that the wet gel maintains a regular shape during the molding process.

[0018] The wet gel was immersed in isopropanol solvent for solvent replacement aging treatment. The aging temperature was 55°C and the aging time was 48 hours. The isopropanol was replaced every 16 hours for a total of 3 times to obtain an alcohol gel.

[0019] Finally, the alcohol gel was placed in a supercritical drying device, and the drying temperature was set to 50°C, the pressure was set to 12 MPa, and the time was set to 6 hours to obtain a superhydrophobic silica aerogel material. Embodiment 2

[0020] Weigh 1 mol of tetraethyl orthosilicate, 10 mol of ethanol, and 5 mol of deionized water, add the weighed raw materials into a reaction container with a stirring device, add ammonia water as a catalyst, turn on the stirrer and stir at a speed of 300 r / min at 50°C for 40 minutes to fully mix the components. At this time, the solution is transparent and stable, and a precursor solution A is obtained.

[0021] Weigh 0.5 g of tridecafluorooctyltrimethoxysilane, 0.75 g of octadecyltrimethoxysilane, and 0.25 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, first slowly add tridecafluorooctyltrimethoxysilane to precursor solution A, stir for 30 minutes to make it initially dispersed evenly, then add octadecyltrimethoxysilane, continue stirring for 30 minutes, observe that the viscosity of the solution gradually increases, finally add γ-(2,3-epoxypropoxy)propyltrimethoxysilane and continue stirring for 1.5 hours to obtain a mixed solution B.

[0022] Pour the mixed solution B into a glass mold and place the mold in a constant temperature and humidity chamber at 55°C and 55% relative humidity for gelation. The gelation process is closely observed and a wet gel with uniform structure and soft texture is obtained after 30 hours. The glass mold has good transparency and can easily observe the gelation process.

[0023] The wet gel was immersed in isopropanol solvent for solvent replacement aging treatment. The aging temperature was 60°C and the aging time was 40 hours. The isopropanol was replaced every 10 hours for a total of 4 times to obtain an alcohol gel.

[0024] Finally, the alcohol gel was placed in a supercritical carbon dioxide drying device, and the drying temperature was set to 55°C, the pressure was set to 13 MPa, and the time was set to 8 hours to obtain a superhydrophobic silica aerogel material.

[0025] Comparative Example 1 Weigh 1 mol of tetraethyl orthosilicate, 7 mol of ethanol, and 4 mol of deionized water, stir at 200 r / min at 55°C for 120 min to obtain precursor solution A, add a certain amount of ammonia water, pour it into a mold, and let it stand at room temperature for 24 h to allow it to gel naturally to form silica hydrogel.

[0026] The formed silica hydrogel was immersed in ethanol, and the ethanol was replaced every 8 hours for a total of 3 times to remove moisture and residual impurities in the hydrogel. The silica hydrogel after solvent replacement was immersed in an ethanol solution containing 10% hexamethyldisilazane by volume and reacted at 55°C for 12 hours to allow the hexamethyldisilazane to react with the hydroxyl groups on the silica surface to achieve surface modification.

[0027] The surface-modified silica hydrogel was placed in a supercritical drying device, and carbon dioxide gas was introduced. The drying temperature was 55° C., the pressure was 12 MPa, and the time was 8 h to obtain a hydrophobic silica aerogel.

[0028] Comparative Example 2: Weigh 1 mol of tetraethyl orthosilicate, 0.5 mol of methyltrimethoxysilane, 6 mol of ethanol, and 5 mol of deionized water, stir at 220 r / min at 55°C for 180 min to obtain precursor solution A, add a certain amount of ammonia water, pour it into a mold, and let it stand at room temperature for 20 h to allow it to gel naturally to form a silica hydrogel.

[0029] The formed silica hydrogel was immersed in ethanol, and the ethanol was replaced every 8 h for a total of 3 times to remove moisture and residual impurities in the hydrogel.

[0030] The soaked silica gel was placed in a supercritical drying device, and carbon dioxide gas was introduced. The drying temperature was 55° C., the pressure was 12 MPa, and the time was 6 h to obtain a hydrophobic silica aerogel.

[0031] The super hydrophobic silica aerogel materials prepared in the above examples and comparative examples were subjected to performance tests, and the test items included hydrophobicity, internal structure parameters, thermal insulation performance and material stability. The test results are shown in the following table:

[0032] The hydrophobic performance test results of Example 2 are as follows Figure 1 As shown, the hydrophobic performance test results of comparative example 1 are as follows Figure 2 As shown, the hydrophobic performance test results of comparative example 2 are as follows Figure 3 As shown, by comparison, it can be seen that the super hydrophobic silica aerogel material prepared by the present invention has obvious advantages. The contact angle of water droplets on the material can reach more than 160°. Compared with Comparative Examples 1 and 2, the contact angle is increased by nearly 10°, reaching a maximum of 16°, and the rolling angle is less than 8°. Compared with Comparative Examples 1 and 2, it is increased by 2°, reaching a maximum of 7°, and has better hydrophobic performance. From the perspective of thermal insulation performance, the internal structure porosity of Example 1 and Example 2 reached 95% and 96% respectively, and the density was 0.12g / cm³ and 0.13g / cm³ respectively. Compared with Comparative Example 1 and Comparative Example 2, the internal structure density was effectively reduced, and the internal void density was further increased, so that the thermal conductivity was reduced to 0.018W / (m·K) and 0.016W / (m·K) respectively, compared with 0.019W / (m·K) and 0.021W / (m·K) of Comparative Example 1 and Comparative Example 2, which have lower thermal conductivity and better thermal insulation function. When conducting stability tests in humid environments, Example 1 and Example 2 can have better stability in humid environments, and will not absorb water and penetrate, effectively ensuring hydrophobic performance; while Comparative Example 1 can also be hydrophobic, but the hydrophobic performance will decrease during the test, and the stability is poor; while Comparative Example 2 not only has the problem of decreased hydrophobic performance, but also will penetrate as time goes by. In summary, the super-hydrophobic silica aerogel prepared by the method provided by the present invention can have better hydrophobic properties, better thermal insulation effect, and better stability in use.

[0033] There are many methods and approaches to implement the technical solutions of the present invention, and the above are only preferred implementations provided by way of example. Those skilled in the art may think of many changes, modifications and substitutions without departing from the present invention. It should be understood that various alternatives to the implementations of the present invention described herein may be adopted in the practice of the present invention. The attached claims are intended to limit the scope of the present invention and therefore cover methods within the scope of these claims and their equivalents. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing super hydrophobic silica aerogel by combining modifiers, characterized in that: The following steps are involved: S1: Preparing a precursor solution, mixing silane, ethanol and deionized water, adding a catalyst and stirring evenly to obtain a precursor solution A; S2: introducing the combined modifier, adding the combined modifier into the precursor solution A in sequence, stirring evenly to obtain a mixed solution B; The combined modifier includes a fluorine-containing silane coupling agent, a long-chain alkyl silane coupling agent and a silane coupling agent with a special functional group; S3: gelation reaction, pouring the mixed solution B into a mold and letting it stand to obtain a wet gel; S4: solvent replacement and aging, the wet gel is subjected to a replacement aging treatment with an organic solvent to obtain an alcohol gel; S5: Drying treatment: using supercritical carbon dioxide drying technology to dry the alcohol gel to obtain a superhydrophobic silica aerogel material.

2. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 1, wherein: The fluorine-containing silane coupling agent is tridecafluorooctyltrimethoxysilane, the long-chain alkyl silane coupling agent is octadecyltrimethoxysilane, and the silane coupling agent with a special functional group is gamma-(2,3-epoxypropoxy)propyltrimethoxysilane.

3. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 2, characterized in that: In the step S2, when adding the combined modifier, first add the fluorine-containing silane coupling agent and stir for 20 to 30 minutes, then add the long-chain alkyl silane coupling agent and stir for 20 to 30 minutes, and finally add the silane coupling agent with special functional groups and stir for 1.5 to 2 hours.

4. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 3, characterized in that: The mass ratio of the fluorine-containing silane coupling agent, the long-chain alkyl silane coupling agent and the silane coupling agent with special functional groups is 2:3:1, and the amount added to the combined modifier is 8% to 20% of the mass of the silane.

5. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 1, characterized in that: Silane, ethanol and deionized water are mixed and stirred at 50-60° C., with a stirring speed of 200-300 r / min and a stirring time of 30-60 min.

6. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 1, characterized in that: The catalyst is hydrochloric acid or ammonia water.

7. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 1, characterized in that: The silane is ethyl orthosilicate or methyl orthosilicate, and the molar ratio of the silane, ethanol and deionized water is 1: (5-10): (3-5).

8. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 1, characterized in that: In step 3, the gelation reaction temperature is 40-60° C., the relative humidity is 40%-60%, and the reaction time is 20-36 hours.

9. The method for preparing super hydrophobic silica aerogel using the combined modifier according to claim 1, characterized in that: In the step 4, the organic solvent is ethanol, acetone or isopropanol, the aging temperature is 50-60° C., and the time is 30-50 h.

10. The method for preparing super-hydrophobic silica aerogel using a combined modifier according to claim 1, characterized in that: In step 5, the supercritical carbon dioxide drying temperature is 40-60° C., the pressure is 10-15 MPa, and the time is 5-10 hours.

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