A method for preparing tunable hydrophobic aerogel particles

Abstract

The application discloses a preparation method of adjustable hydrophobic aerogel particles, and steps are as follows: S1. mixing and stirring solvent, silicon source, deionized water and catalyst in proportion; S2. performing acid hydrolysis reaction under stirring condition, adding acid to adjust the pH of solution to 3-5, and hydrolyzing to obtain silica sol; S3. adding alkali adjusting solution to the silica sol to adjust the pH to 6-8, and obtaining SiO2 wet gel; S4. sequentially performing solvent exchange with ethanol, dichloromethane and deionized water, then, soaking the wet gel in a silane coupling agent solution, modifying at room temperature for 8 hours, and aging at a constant temperature of 20-60 DEG C for 12-48 hours; S5. soaking the hydrophobically modified wet gel in ethanol, curing, then feeding into a supercritical drying kettle for supercritical drying treatment, and drying for 2-10 hours to obtain hydrophobic aerogel particles. Through the synergistic effect of solvent regulation and surface modification, the precise regulation of hydrophobic performance is realized, and the process is simplified and the cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of aerogel particle preparation technology, and specifically to a method for preparing tunable hydrophobic aerogel particles. Background Technology

[0002] Aerogels, as materials with a nanoporous network structure, have broad application prospects in energy, environmental protection, aerospace, and other fields due to their low density, high porosity, and excellent thermal insulation properties. However, the abundance of hydroxyl groups (-OH) on the aerogel surface leads to strong hydrophilicity, making it prone to adsorbing moisture from the air, thereby reducing its thermal insulation performance and affecting its long-term stability. Therefore, hydrophobic modification is a key step in improving the application performance of aerogels.

[0003] In existing technologies, hydrophobic modification methods for aerogels mainly include chemical vapor deposition (CVD), surface coating with silane coupling agents, and cold plasma treatment. For example, CVD modification of aerogels using methyltrichlorosilane (MTCS) can achieve a water contact angle of over 130°. However, these methods typically have the following problems: (1) limited range of hydrophobic properties, making it difficult to achieve customized solutions; (2) complex processes and high costs; and (3) some modifiers are environmentally unfriendly. Furthermore, aerogels prepared by traditional methods exhibit uniform hydrophobicity, failing to meet the differentiated hydrophobic requirements of specific scenarios. Summary of the Invention

[0004] Therefore, this invention provides a method for preparing tunable hydrophobic aerogel particles, which achieves precise control of hydrophobic properties through the synergistic effect of solvent control and surface modification, while simplifying the process and reducing costs.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing tunable hydrophobic aerogel particles, comprising the following steps: S1. Mix and stir the solvent, silicon source, deionized water, and catalyst in a molar ratio of 5-20:1-10:1-5:0.01-0.9; S2. Under stirring conditions, carry out the acid hydrolysis reaction, add acid to adjust the pH of the solution to 3-5, so as to hydrolyze it and obtain silica sol; S3. Add an alkaline solution to the silica sol to adjust the pH to 6-8, so that polymerization occurs and the sol-gel transition is promoted to obtain SiO2 wet gel; S4. Using in-situ two-stage extraction technology, solvent exchange was performed sequentially with ethanol, dichloromethane, and deionized water to rapidly replace the solvent in the wet gel; subsequently, the wet gel was immersed in a silane coupling agent solution and modified by reacting at room temperature for 8 hours. The silane coupling agent reacted with the hydroxyl groups on the surface of the aerogel to form a hydrophobic layer, and then aged at a constant temperature of 20-60℃ for 12-48 hours. S5. The hydrophobically modified wet gel is immersed in ethanol for curing, and then sent to a supercritical drying autoclave for supercritical drying treatment. After drying for 2-10 hours, hydrophobic aerogel particles are obtained.

[0006] Preferably, in step S1, the solvent is one of methanol, ethanol, or ethylene glycol; the silicon source is one of polyethyl silicate 28, tetraethyl orthosilicate, or tetraethoxysilane; and the catalyst is one or more of hydrofluoric acid, hydrogen fluoride, ammonium fluoride, ammonium fluoroborate, or ammonium fluorosilicate.

[0007] Preferably, in step S2, the acid adjustment solution is one or more of hydrochloric acid, sulfuric acid, oxalic acid, acetic acid, or phosphoric acid.

[0008] Preferably, in step S3, the alkali adjustment solution is one of sodium hydroxide and ammonium hydroxide.

[0009] Preferably, in step S4, the silane coupling agent is a methyltrimethoxysilane / alcohol solvent mixture solution, and the concentration of the silane coupling agent is 0.5-4.0 wt%.

[0010] Preferably, in step S5, the supercritical material is supercritical carbon dioxide, and the supercritical drying parameters are: drying temperature 60-120℃, drying pressure 4-10MPa, and drying time 5-12h.

[0011] In other embodiments, in step S4, an energy input is introduced to modify the wet gel.

[0012] Preferably, the energy input is laser irradiation or heat treatment.

[0013] Preferably, the specific processing method is as follows: the laser processing parameters are power 5-10 W and scanning speed 10-20 mm / s, which can increase the contact angle of a specific area from 130° to more than 150°.

[0014] The above technical solution has the following beneficial effects: This invention achieves precise control of the hydrophobic properties of aerogel particles through the synergistic effect of solvent regulation and surface modification. The preparation process is simple, low-cost, and environmentally friendly. The obtained aerogel particles have broad application prospects in oil-water separation, thermal insulation, and other fields. Specifically: (1) Solvent regulation mechanism: Through the miscibility-immiscibility of ethanol-dichloromethane-water, rapid solvent exchange is achieved, which significantly shortens the preparation time and reduces the amount of solvent used.

[0015] (2) Adjustable hydrophobic properties: By adjusting the concentration of silane coupling agent or energy input, the contact angle can be precisely controlled within the range of 130°-155° to meet the needs of different application scenarios.

[0016] (3) Environmental friendliness: Non-toxic or low-toxic silane coupling agents (such as MTMS) are used to avoid the corrosive problems of traditional modifiers (such as TMCS). Attached Figure Description

[0017] Figure 1 This is a physical image of a type of tunable hydrophobic aerogel particle.

[0018] Figure 2 This is a schematic diagram illustrating the principle of solvent-controlled hydrophobic properties of aerogels, showing the effect of ethanol / water exchange on interfacial groups (Si-OH / Si-OEt).

[0019] Figure 3 SEM images of the aerogel surface before and after laser treatment show the effect of energy input on the microstructure. Detailed Implementation

[0020] To illustrate the technical content, structural features, objectives, and effects of the technical solution in detail, the following description is provided in conjunction with specific embodiments and accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0021] Example 1 S1. Ethanol, tetraethoxysilane, deionized water, and hydrogen fluoride are mixed in a molar ratio of 20:10:2:0.1 and stirred for 30 min to obtain a silica mixed solution; S2. Add hydrochloric acid to the obtained silica mixed sol solution and stir for 5 minutes to adjust the pH of the solution to 4, so as to fully hydrolyze it; S3. Add ammonium hydroxide and stir for 5 minutes to adjust the pH of the solution to 7, so that polymerization can occur and SiO2 wet gel is obtained; S4. The SiO2 wet gel was immersed in a solution of ethanol, dichloromethane and deionized water in a mass ratio of 2:3:2 for solvent exchange for 6 hours to rapidly replace the solvent in the wet gel. Subsequently, the wet gel was immersed in a 3.0% silane coupling agent solution, which was a methyltrimethoxysilane / alcohol solvent mixture, and reacted at room temperature for 8 hours to allow the silane coupling agent to react with the hydroxyl groups on the surface of the aerogel to form a hydrophobic layer. The gel was then aged at a constant temperature of 40°C for 24 hours. S5. The hydrophobically modified SiO2 wet gel was immersed in ethanol and then placed in a supercritical drying vessel for supercritical drying. The parameters were set at 60℃ and 8MPa, and dried for 5.5h to obtain hydrophobic SiO2 aerogel particles. The hydrophobic SiO2 aerogel particles (25℃) have a thermal conductivity of 0.017W / (m·K), a hydrophobicity of 97%, and a hydrophobic angle of 142°.

[0022] Example 2 S1. Mix methanol, tetraethyl orthosilicate, deionized water, and ammonium fluoroborate in a molar ratio of 5:2:2:0.02 and stir for 30 minutes to obtain a silica mixed solution; S2. Add hydrochloric acid to the obtained silica mixed sol solution and stir for 5 minutes to adjust the pH of the solution to 4, so as to fully hydrolyze it; S3. Add ammonium hydroxide and stir for 5 minutes to adjust the pH of the solution to 7, so that polymerization can occur and SiO2 wet gel is obtained; S4. The SiO2 wet gel was immersed in a solution of ethanol, dichloromethane and deionized water in a mass ratio of 2:3:2 for solvent exchange for 6 hours to rapidly replace the solvent in the wet gel. Subsequently, the wet gel was immersed in a 4.0% silane coupling agent solution and reacted at room temperature for 8 hours to allow the silane coupling agent to react with the hydroxyl groups on the surface of the aerogel to form a hydrophobic layer. The gel was then aged at a constant temperature of 40°C for 24 hours. S5. The hydrophobically modified SiO2 wet gel was immersed in ethanol and then placed in a supercritical drying reactor for supercritical drying treatment. The parameters were set at 60℃ and 8MPa, and dried for 5.5h to obtain hydrophobic SiO2 aerogel particles. The hydrophobic SiO2 aerogel particles (25℃) have a thermal conductivity of 0.017W / (m·K), a hydrophobicity of 99%, and a hydrophobic angle of 152°.

[0023] Example 3 S1. Ethylene glycol, polyethyl silicate 28, deionized water, and hydrofluoric acid are mixed and stirred for 30 minutes in a molar ratio of 15:6:3:0.6 to obtain a silica mixed solution; S2. Add hydrochloric acid to the obtained silica mixed sol solution and stir for 5 minutes to adjust the pH of the solution to 4, so as to fully hydrolyze it; S3. Add ammonium hydroxide and stir for 5 minutes to adjust the pH of the solution to 7, so that polymerization can occur and SiO2 wet gel is obtained; S4. The SiO2 wet gel was immersed in a solution of ethanol, dichloromethane, and deionized water in a mass ratio of 2:3:2 for solvent exchange for 6 hours to rapidly displace the solvent in the wet gel. Subsequently, the wet gel was immersed in a 2.0% silane coupling agent solution and reacted at room temperature for 8 hours to allow the silane coupling agent to react with the hydroxyl groups on the aerogel surface to form a hydrophobic layer. The gel was then aged at a constant temperature of 40°C for 24 hours. S5. The hydrophobically modified SiO2 wet gel was immersed in ethanol and then placed in a supercritical drying vessel for supercritical drying treatment. The parameters were set at 60℃ and 8MPa, and dried for 5.5h to obtain hydrophobic SiO2 aerogel particles. The hydrophobic SiO2 aerogel particles (25℃) have a thermal conductivity of 0.018W / (m·K), a hydrophobicity of 95%, and a hydrophobic angle of 140°.

[0024] Example 4 S1. Ethanol, tetraethoxysilane, deionized water, and hydrogen fluoride are mixed in a molar ratio of 20:10:2:0.1 and stirred for 30 min to obtain a silica mixed solution; S2. Add hydrochloric acid to the obtained silica mixed sol solution and stir for 5 minutes to adjust the pH of the solution to 4, so as to fully hydrolyze it; S3. Add ammonium hydroxide and stir for 5 minutes to adjust the pH of the solution to 7, so that polymerization can occur and SiO2 wet gel is obtained; S4. The SiO2 wet gel was immersed in a solution of ethanol, dichloromethane, and deionized water in a mass ratio of 2:3:2 for solvent exchange for 6 hours to rapidly displace the solvent in the wet gel. Subsequently, the wet gel was placed in a laser processing device and its surface was irradiated at a power of 8 W and a scanning speed of 15 mm / s.

[0025] S5. The irradiated SiO2 wet gel was immersed in ethanol and then placed in a supercritical drying vessel for supercritical drying. The parameters were set at 60℃ and 8MPa, and dried for 5.5h to obtain hydrophobic SiO2 aerogel particles. The hydrophobic SiO2 aerogel particles (25℃) have a thermal conductivity of 0.017W / (m·K), a hydrophobicity of 99%, a hydrophobic angle of 152°, and exhibit superhydrophobicity throughout.

[0026] Example 5 S1. Ethanol, tetraethoxysilane, deionized water, and hydrogen fluoride are mixed in a molar ratio of 20:10:2:0.1 and stirred for 30 min to obtain a silica mixed solution; S2. Add hydrochloric acid to the obtained silica mixed sol solution and stir for 5 minutes to adjust the pH of the solution to 4, so as to fully hydrolyze it; S3. Add ammonium hydroxide and stir for 5 minutes to adjust the pH of the solution to 7, so that polymerization can occur and SiO2 wet gel is obtained; S4. The SiO2 wet gel was immersed in a solution of ethanol, dichloromethane, and deionized water in a mass ratio of 2:3:2 for solvent exchange for 6 hours to rapidly displace the solvent in the wet gel. Subsequently, the wet gel was placed in a laser processing device and its surface was irradiated at a power of 6 W and a scanning speed of 20 mm / s.

[0027] S5. The irradiated SiO2 wet gel was immersed in ethanol and then placed in a supercritical drying vessel for supercritical drying. The parameters were set at 60℃ and 8MPa, and dried for 5.5h to obtain hydrophobic SiO2 aerogel particles. The hydrophobic SiO2 aerogel particles (25℃) have a thermal conductivity of 0.017W / (m·K), a hydrophobicity of 98%, a hydrophobic angle of 147°, and exhibit superhydrophobicity in specific regions.

[0028] Comparative Example 1: No in-situ two-stage extraction technology (single solvent exchange) was used. Unlike Example 1, step S4 involved a single solvent exchange using only ethanol (without dichloromethane and deionized water), extending the soaking time to 18 hours (the time required for traditional single solvent exchange). Results: Insufficient solvent exchange resulted in significant residual original solvent (e.g., methanol) in the wet gel; after drying, the aerogel particles exhibited a hydrophobic angle of 125°, a hydrophobicity of 88%, and a thermal conductivity of 0.021 W / (m·K). Conclusion: In-situ two-stage extraction significantly shortens the solvent exchange time (from 18 hours to 6 hours) and reduces the interference of residual solvent on the formation of the hydrophobic layer, thereby improving hydrophobic properties and thermal insulation.

[0029] Comparative Example 2: No hydrophobic modification (no silane coupling agent treatment) Unlike Example 1, the silane coupling agent soaking and aging process in step S4 was omitted, and the wet gel after solvent exchange was directly subjected to supercritical drying. Results: The aerogel surface retained a large number of hydroxyl groups (-OH), exhibiting strong hydrophilicity, with a water contact angle of only 65°, a hydrophobicity of less than 10%, and a thermal conductivity increase to 0.035 W / (m·K) after water absorption. Conclusion: Silane coupling agent treatment is key to achieving hydrophobic properties; this invention significantly improves hydrophobicity and long-term stability through surface modification.

[0030] Comparative Example 3: Modification using conventional CVD (methyltrichlorosilane) Unlike Example 1, step S4 uses methyltrichlorosilane (MTCS) for chemical vapor deposition modification (vacuum environment, reaction at 80°C for 4 hours), omitting the silane coupling agent solution soaking; step E is the same as in Example 1. Results: The hydrophobic angle can reach 132°, but the modification process requires vacuum equipment, making the process complex and costly; methyltrichlorosilane is highly corrosive and has poor environmental friendliness; and the hydrophobic angle cannot be controlled by adjusting the concentration (maximum only 135°). Comparative conclusion: This invention uses the silane coupling agent solution soaking method, which is simple (no vacuum equipment required), uses a low-toxicity modifier, and has a wider range of hydrophobic properties control (above 130°-150°).

[0031] Comparative Example 4: Using freeze drying instead of supercritical drying Unlike Example 1, step S5 was replaced with freeze drying (-50°C, vacuum 10 Pa, drying for 24 h). Results: During drying, the gel network shrank due to ice crystal growth, and the porosity decreased from 90% in Example 1 to 75%; the hydrophobic angle decreased to 128°, and the thermal conductivity increased to 0.028 W / (m·K). Conclusion: Supercritical drying can avoid gel structure shrinkage, retain high porosity, and ensure the integrity of the hydrophobic layer and low thermal conductivity.

[0032] Comparative Example 5: The concentration of silane coupling agent exceeded the control range (4.5 wt%). Unlike Example 1, the silane coupling agent solution in step S4 has a mass fraction of 4.5 wt% (exceeding the 0.5-4.0 wt% range of this invention). Results: Excessive silane coupling agent leads to an excessively thick hydrophobic layer on the surface, forming a brittle structure, making the aerogel particles easily breakable; although the hydrophobic angle reaches 155°, the mechanical strength decreases by 40%, and the thermal conductivity increases to 0.020 W / (m·K). Comparative conclusion: The silane coupling agent concentration range (0.5-4.0 wt%) defined in this invention can ensure high hydrophobicity while avoiding structural embrittlement, balancing mechanical properties and thermal insulation.

[0033] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Unless otherwise specified, an element defined by the phrase "comprising..." or "including..." does not exclude the presence of additional elements in the process, method, article, or terminal device that includes said element. Additionally, in this document, "greater than," "less than," "exceeding," etc., are understood to exclude the stated number; "above," "below," "within," etc., are understood to include the stated number.

[0034] Although the above embodiments have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the above descriptions are merely embodiments of the present invention and do not limit the scope of patent protection of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing tunable hydrophobic aerogel particles, characterized in that, The steps are as follows: S1. Mix and stir the solvent, silicon source, deionized water, and catalyst in a molar ratio of 5-20:1-10:1-5:0.01-0.9; the solvent is one of methanol, ethanol, or ethylene glycol; the silicon source is one of polyethyl silicate 28 or tetraethoxysilane; the catalyst is one or more of hydrofluoric acid, ammonium fluoride, ammonium fluoroborate, or ammonium fluorosilicate. S2. Under stirring conditions, carry out the acid hydrolysis reaction, add acid to adjust the pH of the solution to 3-5, so as to hydrolyze it and obtain silica sol; S3. Add an alkaline solution to the silica sol to adjust the pH to 6-8, so that polymerization occurs and the sol-gel transition is promoted to obtain SiO2 wet gel; S4. In-situ two-stage extraction technology was used to rapidly replace the solvent in the wet gel by sequential solvent exchange with ethanol, dichloromethane, and deionized water. Subsequently, the wet gel was immersed in a silane coupling agent solution, which was a methyltrimethoxysilane / alcohol solvent mixture with a concentration of 0.5-4.0 wt%. The gel was modified by reacting at room temperature for 8 hours and then aged at a constant temperature of 20-60℃ for 12-48 hours. S5. The hydrophobically modified wet gel is immersed in ethanol for curing, and then sent to a supercritical drying autoclave for supercritical drying treatment. After drying for 2-10 hours, hydrophobic aerogel particles are obtained.

2. The preparation method according to claim 1, characterized in that, In step S2, the acid adjustment solution is one or more of hydrochloric acid, sulfuric acid, oxalic acid, acetic acid, or phosphoric acid.

3. The preparation method according to claim 1, characterized in that, In step S3, the alkali adjustment solution is either sodium hydroxide or ammonium hydroxide.

4. The preparation method according to claim 1, characterized in that, In step S5, the supercritical material is supercritical carbon dioxide, and the supercritical drying parameters are: drying temperature 60-120℃, drying pressure 4-10MPa, and drying time 5-12h.

5. The preparation method according to any one of claims 1-4, characterized in that, In step S4, energy input is introduced to modify the wet gel.

6. The preparation method according to claim 5, characterized in that, Energy input is introduced through laser irradiation and heat treatment.

7. The preparation method according to claim 6, characterized in that, The specific processing method is as follows: the laser processing parameters are power 5-10 W and scanning speed 10-20 mm / s.

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