Silicon oxide aerogel with asymmetric wettability and preparation method thereof

Abstract

The invention provides a silicon oxide aerogel with asymmetric wettability and a preparation method thereof. The silicon oxide aerogel with asymmetric wettability has the characteristics that the outer surface is hydrophilic and the inner surface is hydrophobic. The method for preparing the silicon oxide aerogel with asymmetric wettability comprises the following steps: providing hydrophobic silicon oxide aerogel, wherein the outer surface of the hydrophobic silicon oxide aerogel and the inner surfaces of pore channels are hydrophobic; the outer surface of the hydrophobic silicon oxide aerogel is subjected to plasma treatment, the plasma treatment atmosphere is oxygen or air, hydrophobic groups on the outer surface of the hydrophobic silicon oxide aerogel are oxidized and converted into hydrophilic groups such as hydroxyl groups and carboxyl groups, the hydrophilicity of the outer surface is achieved, and the hydrophobicity of the inner surface of the hydrophobic silicon oxide aerogel is reserved; in order to further improve the hydrophilicity of the outer surface of the silicon oxide aerogel subjected to plasma treatment, the silicon oxide aerogel subjected to plasma treatment is modified with hydroxysilane in a gas phase environment, and the type and content of hydrophilic groups on the outer surface of the silicon oxide aerogel are increased.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, specifically to an asymmetric wettable silica aerogel and its preparation method. Background Technology

[0002] Aerogels are porous materials with a three-dimensional nanonetwork structure, high porosity, high specific surface area, and low density, showing great application potential in fields such as thermal insulation, adsorption, catalysis, drug delivery, and energy storage. Among them, silica aerogels have become one of the most widely researched and applied aerogel varieties due to their good chemical stability and relatively mature preparation processes.

[0003] In many fields such as coatings, pharmaceuticals, and catalysis, aerogel materials require both a hydrophilic outer surface to ensure good biocompatibility or dispersion in aqueous phase, and a hydrophobic internal pore surface to prevent water from entering and disrupting the aerogel's pore structure. The hydrophobicity of the internal pores also ensures effective loading and protection of organic molecules or drugs. However, current surface modification of aerogels is mostly uniform, either making them completely hydrophilic or completely hydrophobic, lacking effective methods for differentiated and precise modification of the internal and external surfaces. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related art. Therefore, one object of this invention is to provide an asymmetric wettability silica aerogel that can achieve different wettability requirements for inner and outer surfaces.

[0005] In one aspect of the invention, a method for preparing asymmetric wettable silica aerogel is provided. According to an embodiment of the invention, the method for preparing asymmetric wettable silica aerogel includes: providing a hydrophobic silica aerogel, wherein both the outer surface and the inner surface of the pores of the hydrophobic silica aerogel are hydrophobic; and subjecting the outer surface of the hydrophobic silica aerogel to plasma treatment, wherein the plasma treatment atmosphere is oxygen or air, thereby converting the hydrophobic groups on the outer surface of the hydrophobic silica aerogel into hydrophilic groups. Thus, by subjecting the outer surface of the hydrophobic silica aerogel to plasma treatment, the hydrophobic groups on the outer surface of the hydrophobic silica aerogel are oxidized and transformed into oxygen-containing hydrophilic groups such as hydroxyl and carboxyl groups, achieving hydrophilicity of the outer surface. However, the plasma treatment has no effect on the hydrophobic groups on the inner surface of the pores in the hydrophobic silica aerogel, so the inner surface of the pores in the silica aerogel remains hydrophobic. Thus, the wettability of the inner and outer surfaces of the prepared silica aerogel is different, with the outer surface being hydrophilic and the inner surface of the pores being hydrophobic. Moreover, the plasma treatment method described above is simple and efficient, and has a high uniformity of action on the hydrophobic groups on the outer surface of the silica aerogel, which can effectively improve the hydrophilicity of the outer surface of the silica aerogel.

[0006] According to an embodiment of the present invention, the method for preparing asymmetric wettable silica aerogel further includes: placing the silica aerogel after plasma treatment in a gaseous environment for surface modification, wherein the gaseous environment contains hydroxysilane. This further improves the hydrophilicity of the outer surface of the silica aerogel.

[0007] According to an embodiment of the present invention, the power of the plasma treatment is 15~240W, and the treatment time is 1~15 minutes.

[0008] According to an embodiment of the present invention, the surface modification method includes: placing the plasma-treated aerogel and the hydroxysilane in a container and heating the container.

[0009] According to an embodiment of the present invention, the surface modification time is 1 to 12 hours, the heating temperature is 60 to 90°C, / or, in the container, the volume ratio of the hydroxysilane to the aerogel is (1 to 10): 1.

[0010] According to embodiments of the present invention, the hydroxysilane includes at least one of 3-aminopropyltrihydroxysilane and vinyltrihydroxysilane.

[0011] According to embodiments of the present invention, the hydrophobic silica aerogel includes at least one of the following morphologies: microspheres, powder, and bulk.

[0012] In another aspect, the present invention provides an asymmetric wettable silica aerogel. According to an embodiment of the invention, the asymmetric wettable silica aerogel is prepared by the method described above, wherein the outer surface of the silica aerogel has hydrophilic groups, and the surface of the inner pores of the silica aerogel has hydrophobic groups. Thus, the wettability of the inner and outer surfaces of the silica aerogel differs, effectively achieving the requirement of a hydrophilic outer surface and a hydrophobic inner surface for a single-material silica aerogel.

[0013] According to embodiments of the present invention, the hydrophilic group includes at least one of hydroxyl, carboxyl, and amino groups, and the hydrophobic group includes silanylmethyl.

[0014] According to an embodiment of the present invention, the water contact angle of the outer surface of the silica aerogel is 40°. -70 The water contact angle of the inner surface of the pores in the silica aerogel is greater than or equal to 110°. .

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of a method for preparing asymmetric wettable silica aerogel in one embodiment of the present invention; Figure 2 This is a flowchart of a method for preparing asymmetric wettable silica aerogel in another embodiment of the present invention; Figure 3 These are test diagrams of the water contact angle of the relevant products in some embodiments; Figure 4 This is a schematic diagram showing the relationship between the water contact angle of the outer surface of the silica aerogel in Examples 1-6 and the power and time of plasma treatment; Figure 5 This is a schematic diagram of the hydrophobic silica aerogel microspheres in water and a schematic diagram of the silica aerogel that has undergone plasma treatment and surface modification in Example 13 in water. Detailed Implementation

[0017] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0018] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0019] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0020] In one aspect of the invention, a method for preparing asymmetric wettable silica aerogels is provided. According to an embodiment of the invention, referring to… Figure 1 Methods for preparing asymmetric wettable silica aerogels include: S100: Provides hydrophobic silica aerogel, the outer surface of which and the inner surface of which are hydrophobic.

[0021] In some embodiments of the present invention, the outer surface of the hydrophobic silica aerogel and the inner surface of the pores are both covered by hydrophobic groups, i.e., they exhibit hydrophobicity, wherein the hydrophobic groups include silyl groups.

[0022] In some embodiments of the present invention, the hydrophobic silica aerogel includes at least one of the following morphologies: microspheres, powder, and bulk. Therefore, the preparation method of the present invention is applicable to various morphologies of hydrophobic silica aerogels, thus enabling the preparation of silica aerogels with different morphologies of asymmetric wetting properties. That is, using microsphere-shaped hydrophobic silica aerogels, asymmetric wetting silica aerogels in microsphere form can be prepared; using powder-shaped hydrophobic silica aerogels, asymmetric wetting silica aerogels in powder form can be prepared; and using bulk-shaped hydrophobic silica aerogels, asymmetric wetting silica aerogels in bulk form can be prepared.

[0023] In some embodiments of the present invention, there are no special requirements for the preparation method of hydrophobic silica aerogel. Those skilled in the art can use conventional techniques in the prior art to prepare hydrophobic silica aerogel.

[0024] In some specific embodiments, hydrophobic silica aerogel microspheres can be prepared using microfluidic technology.

[0025] S200: Plasma treatment is applied to the outer surface of the hydrophobic silica aerogel. The plasma treatment atmosphere is oxygen or air, which transforms the hydrophobic groups on the outer surface of the hydrophobic silica aerogel into hydrophilic groups. By plasma treatment of the outer surface of the hydrophobic silica aerogel, the hydrophobic groups are oxidized and transformed into oxygen-containing hydrophilic groups such as hydroxyl and carboxyl groups, achieving hydrophilicity on the outer surface. However, the plasma treatment has no effect on the hydrophobic groups on the inner surface of the pores in the hydrophobic silica aerogel, so the inner surface of the pores in the silica aerogel remains hydrophobic. Thus, a silica aerogel with different wettability on its inner and outer surfaces can be obtained, with the outer surface being hydrophilic and the inner surface of the pores being hydrophobic. Moreover, the above plasma treatment method is simple, efficient, and has a high uniformity of action on the hydrophobic groups on the outer surface of the silica aerogel, which can effectively improve the wettability of the outer surface of the silica aerogel.

[0026] In some embodiments of the present invention, the plasma treatment power is 15~240W (e.g., 15W, 20W, 50W, 80W, 100W, 120W, 150W, 180W, 210W, 240W, etc.), and the treatment time is 1~15 minutes (e.g., 1 minute, 5 minutes, 10 minutes, 15 minutes, etc.). Under the above conditions, the hydrophobic groups on the outer surface of the hydrophobic silica aerogel can be efficiently oxidized into oxygen-containing hydrophilic groups such as hydroxyl and carboxyl groups, achieving hydrophilicity of the outer surface without negatively affecting the silica aerogel itself or changing the hydrophobicity of the inner surface of the pores in the hydrophobic silica aerogel. If the power is too low or the time is too short, the hydrophilicity of the outer surface of the hydrophobic silica aerogel may not be well improved; if the power is too high or the time is too long, the hydrophilicity of the outer surface of the silica aerogel cannot be further improved, and it may instead lead to energy waste or excessively prolong the process time.

[0027] According to some embodiments of the present invention, with reference to Figure 2 The method for preparing asymmetric wettable silica aerogel further includes step S300: placing the plasma-treated aerogel in a gaseous environment for surface modification, wherein the gaseous environment contains hydroxysilanes. Thus, by using a gaseous environment containing hydroxysilanes, hydroxysilanes can be grafted onto the outer surface of the plasma-treated silica aerogel. Specifically, hydroxysilanes are grafted onto oxygen-containing groups such as hydroxyl and carboxyl groups formed on the outer surface of the silica aerogel. Since hydroxysilanes have hydrophilic groups such as hydroxyl and amino groups, a greater number of hydrophilic groups such as hydroxyl and amino groups can be grafted onto the outer surface of the silica aerogel, thereby further improving the hydrophilicity of the outer surface of the silica aerogel, i.e., reducing the water contact angle of the outer surface.

[0028] In some embodiments of the present invention, the surface modification method includes placing plasma-treated aerogel and hydroxysilane in a container and heating the container. During the heating process, a small amount of liquid hydroxysilane vaporizes, thus obtaining a gaseous environment containing hydroxysilane, which can effectively modify the outer surface of the silica aerogel. In some embodiments, the container can be a sealed container, in which the aerogel and hydroxysilane are placed separately. Preferably, the hydroxysilane can be placed at the bottom of the container, and the aerogel can be placed above the hydroxysilane, so that the vaporized hydroxysilane can more comprehensively act on the aerogel surface.

[0029] In some embodiments of the present invention, the surface modification time is 1 to 12 hours (e.g., 1 hour, 2 hours, 5 hours, 8 hours, 10 hours, 12 hours, etc.), and the temperature is 60 to 90°C (e.g., 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.). Under the above conditions, the gas phase contains hydroxysilane, which allows the hydroxysilane to be effectively grafted onto the outer surface of the silica aerogel.

[0030] In some embodiments of the present invention, the volume ratio of hydroxysilane to aerogel in the container is (1~10):1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc. This allows for sufficient modification of the outer surface of the aerogel by the hydroxysilane.

[0031] In some embodiments of the present invention, the hydroxysilane includes at least one of 3-aminopropyltrihydroxysilane and vinyltrihydroxysilane. Therefore, the aforementioned hydroxysilane has a greater number of hydroxyl and / or amino groups, which can increase the number of hydrophilic groups such as carboxyl and hydroxyl groups grafted onto the outer surface of the plasma-treated silica aerogel, thereby further enhancing the hydrophilicity of the silica aerogel's outer surface. Moreover, the aforementioned hydroxysilane exhibits relatively high activity under the aforementioned surface modification conditions, enabling it to be efficiently grafted onto the outer surface of the silica aerogel.

[0032] In summary, the asymmetric wettable silica aerogel prepared by the above method has hydrophilic groups including at least one of hydroxyl, carboxyl, and amino groups on its outer surface, and hydrophobic groups including silanyl groups on the inner surface of its pores, which makes the outer surface of the silica aerogel have excellent hydrophilicity, while the inner surface of its internal pores has good hydrophobicity.

[0033] In another aspect, the present invention provides an asymmetric wettable silica aerogel. According to an embodiment of the invention, the asymmetric wettable silica aerogel is prepared by the method described above, wherein the outer surface of the silica aerogel has hydrophilic groups, and the surface of the inner pores of the silica aerogel has hydrophobic groups. Thus, the wettability of the inner and outer surfaces of the silica aerogel differs, effectively achieving the requirement of a hydrophilic outer surface and a hydrophobic inner surface for a single-material silica aerogel.

[0034] In some embodiments of the present invention, the hydrophilic group includes at least one of hydroxyl, carboxyl, and amino groups, and the hydrophobic group includes silanylmethyl.

[0035] In some embodiments of the present invention, the water contact angle of the outer surface of the silica aerogel is 40°~70° (e.g., 40°, 45°, 50°, 55°, 60°, 65°, 70°, etc.), and the water contact angle of the inner surface of the pores in the silica aerogel is greater than or equal to 110°. Therefore, the outer surface of this asymmetric wettable silica aerogel exhibits excellent hydrophilicity, while the surface of its internal pores exhibits good hydrophobicity.

[0036] Example Example 1 Step 1: Preparation of hydrophobic silica aerogel microspheres (microfluidic technology preparation method) (1) Weigh 0.72 g of water glass with a modulus of 2.1 and dissolve it in 9.5 g of deionized water to prepare a water glass solution with a mass fraction of 7 wt%. Stir at 600 rpm for 20 minutes to mix it evenly. Then, add the pretreated H-type cation exchange resin (IR120) to the water glass solution and continue stirring until the pH value of the solution drops to 3.6 to remove sodium ions and obtain acidic silica sol. After filtering to remove the resin, add glacial acetic acid dropwise to the silica sol at a volume ratio of 90:1 and stir evenly to obtain a stable silica sol with a pH of 3 for later use. (2) The silica sol obtained in step (1) is used as the dispersed phase, and liquid paraffin containing 2.5% (v / v) sorbitan trioleate (Span 85) is used as the continuous phase. A stepped T-type microchannel chip is used, and the flow rate of the continuous phase is controlled at 20 mL / h and the flow rate of the dispersed phase is 0.9 mL / h. Under the shearing action of the microchannel, silica sol microdroplets with good monodispersity and high sphericity are generated.

[0037] (3) The silica sol microdroplets were introduced into a gel bath. The gel bath was composed of liquid paraffin, triethylamine and Span 85 in a volume ratio of 400:1:10. Under the action of the alkaline catalyst triethylamine, the silica sol microdroplets gelled to form solid silica gel microspheres.

[0038] (4) The formed silica gel microspheres were allowed to stand in a gel bath for 4 hours for aging. After aging, the gel microspheres were collected and washed twice with a 3:1 volume ratio of ethanol / n-hexane mixed solution to remove the surface oil phase and prevent microsphere aggregation.

[0039] (5) The washed gel microspheres were first immersed in anhydrous ethanol, with the ethanol being replaced twice to complete the solvent replacement from water to ethanol. Subsequently, the ethanol was replaced with n-hexane. Next, the microspheres were transferred to a mixed solution of hexamethyldisilazane (HMDS) and n-hexane (volume ratio 1:5) and subjected to surface hydrophobic modification at 50°C for 12 hours. After the reaction was completed, the microspheres were washed twice with clean n-hexane to remove residual HMDS.

[0040] (6) The surface-modified wet gel microspheres were immersed in n-hexane, and then the container was placed in an oven at 200°C for rapid atmospheric pressure drying to obtain hydrophobic silica aerogel microspheres (i.e., the inner and outer surfaces of the aerogel are hydrophobic), with a water contact angle of 126.9°, which is strongly hydrophobic.

[0041] Step 2: Plasma treatment The hydrophobic silica aerogel microspheres obtained in step 1 were placed in the reaction chamber of a plasma treatment instrument, and air was introduced for plasma treatment at a power of 15W for 4 minutes.

[0042] The plasma-treated silica aerogel microspheres were laid flat into a thin plane, and the water contact angle of the outer surface of the silica aerogel microspheres was tested. The silica aerogel microspheres were then thoroughly ground to expose the inner surface of the pores of the silica aerogel microspheres, and the water contact angle of the inner surface of the silica aerogel microspheres was tested. The test results are shown in Table 1.

[0043] Examples 2 to 10 The only difference from Example 1 is the power and time of the plasma treatment, as detailed in Table 1. The test results of the water contact angles of the inner and outer surfaces of the obtained silica aerogel microspheres are shown in Table 1.

[0044] Example 11 Step 1: Preparation of hydrophobic silica aerogel microspheres The method steps are consistent with those in step 1 of Example 1 for preparing hydrophobic silica aerogel microspheres.

[0045] Step 2: Plasma treatment The hydrophobic silica aerogel microspheres obtained in step 1 were placed in the reaction chamber of a plasma treatment instrument, and air was introduced for plasma treatment at a power of 180W for 6 minutes.

[0046] Step 3: Surface finishing The plasma-treated aerogel from step 2 and 3-aminopropyltrihydroxysilane were placed in a sealed container with a volume ratio of 5:1. The 3-aminopropyltrihydroxysilane was placed at the bottom of the container, and the aerogel was placed on a screen above the 3-aminopropyltrihydroxysilane. The container was heated to 90°C for 1 hour.

[0047] The surface-modified silica aerogel microspheres were laid flat into a thin plane, and the water contact angle of the outer surface of the silica aerogel microspheres was tested. The surface-modified silica aerogel microspheres were then thoroughly ground to expose the inner surface of the pores of the silica aerogel microspheres, and the water contact angle of the inner surface of the silica aerogel microspheres was tested. The test results are shown in Table 1.

[0048] Examples 12-14 The only difference from Example 11 is the surface modification time, as detailed in Table 1. The test results for the water contact angles of the inner and outer surfaces of the obtained silica aerogel microspheres are shown in Table 1.

[0049] Example 15 Step 1: Take a small piece (approximately 3mm x 3mm) of hydrophobic silica aerogel with a contact angle greater than 120°. .

[0050] Step 2: The hydrophobic silica aerogel from step (1) was placed in the reaction chamber of a plasma treatment instrument, and air was introduced for reaction. The power was 180W, and the treatment time was 6 minutes. The water contact angle measured on the outer surface of the bulk silica aerogel was 61.4°. It is hydrophilic.

[0051] Step 3: The block of silica aerogel was cut and crushed, spread into a thin layer, and the water contact angle was measured to be 120.3°. This indicates that the inner surface of the bulk silica aerogel is hydrophobic.

[0052] Example 16 Step 1: Take 5 mg of hydrophobic silica aerogel powder (size between 125-150 μm).

[0053] Step 2: Spread the hydrophobic silica aerogel powder into a thin layer, and measure the water contact angle of the thin layer. The contact angle is 127.7°, indicating strong hydrophobicity.

[0054] Step 3: Place the hydrophobic silica aerogel from Step 1 into the reaction chamber of the plasma treatment instrument, introduce air for reaction, use 180W power, and process for 6 minutes. Spread the plasma-treated silica aerogel powder into a thin layer, and measure the water contact angle of the outer surface of the silica aerogel to be 58.8°. .

[0055] Step 4: After the plasma treatment described above, surface modification is performed for 4 hours at a temperature of 90°C, following step 3 in Example 11. The water contact angle of the outer surface of the silica aerogel powder was measured to be 45.6°.

[0056] Step 5: The silica aerogel obtained in Step 4 was pulverized using a grinding bowl and spread into a thin layer. The water contact angle was measured to be 118.3°. This indicates that the inner surface of the silica aerogel is hydrophobic.

[0057] Table 1

[0058] in, Figure 3 (a) in the figure is a test diagram of the water contact angle on the outer surface of the hydrophobic silica aerogel microspheres in Example 1; Figure 3 (b) in Example 13 is a test diagram of the water contact angle on the inner surface of the silica aerogel microspheres after plasma treatment and surface modification. Figure 3 (c) in Example 9 is a test diagram of the water contact angle on the outer surface of the silica aerogel microspheres after plasma treatment; Figure 3 (d) in Example 13 is a test diagram of the water contact angle on the outer surface of the silica aerogel microspheres after plasma treatment and surface modification. Figure 3 (e) in Example 16 is a test graph of the water contact angle of the hydrophobic silica aerogel powder when it was untreated; Figure 3 (f) in Example 15 is a test diagram of the water contact angle of the outer surface of the hydrophobic silica aerogel block after plasma treatment; Figure 3 (g) in Example 16 is a test diagram of the water contact angle of the outer surface of the hydrophobic silica aerogel powder after plasma treatment; Figure 3 (h) in Example 16 is a test diagram of the water contact angle of the outer surface of the hydrophobic silica aerogel powder after plasma treatment and surface modification.

[0059] As can be seen from the data in Table 1, plasma treatment of hydrophobic silica aerogels in microsphere, bulk, or powder form can effectively reduce the water contact angle of their outer surface, thus improving their hydrophilicity, while not negatively affecting the hydrophobicity of the inner surface of the silica aerogel, meaning that the good hydrophobicity of the inner surface of the silica aerogel can still be maintained.

[0060] Based on the data from Examples 1-6 and Figure 4 It is evident that as the power of plasma treatment increases, the water contact angle on the outer surface of silica aerogel gradually decreases, indicating a gradual improvement in the hydrophilicity of the silica aerogel's outer surface. In Example 1, due to the lower power, the hydrophilication effect was not significant, suggesting insufficient energy input, making it difficult to effectively destroy the silanyl methyl hydrophobic groups on the outer surface of the silica aerogel and introduce hydrophilic groups.

[0061] Based on the data from Examples 7-10 and Figure 4 It can be seen that with the plasma treatment time (corresponding to...) Figure 4 As the x-axis (the angle between the x and y axes) increases, the water contact angle on the outer surface of the silica aerogel gradually decreases, indicating a gradual improvement in the hydrophilicity of the silica aerogel's outer surface. In Example 7, the hydrophilication effect was insufficient due to the short treatment time. Comparing Examples 9 and 10 reveals that, compared to Example 9, the change in the water contact angle on the outer surface of the silica aerogel in Example 10 is very small, indicating that the plasma modification in Example 9 was sufficient.

[0062] As can be seen from Examples 9 and 11-14, further surface modification based on plasma treatment can significantly reduce the water contact angle of the outer surface of silica aerogel, that is, further improve the hydrophilicity of the outer surface, but at the same time, it will not negatively affect the hydrophobicity of the inner surface of silica aerogel, that is, it can still maintain the good hydrophobicity of the inner surface of silica aerogel.

[0063] As can be seen from Examples 11-14, with the increase of surface modification time, the water contact angle of the outer surface of the silica aerogel gradually decreases, that is, the effect of improving the hydrophilicity of the outer surface of the silica aerogel gradually increases. Among them, by comparing Examples 13 and 14, it can be found that compared with Example 13, the change in the water contact angle of the outer surface of the silica aerogel in Example 14 is very small, indicating that the modification in Example 13 is sufficient.

[0064] A certain amount of hydrophobic silica aerogel microspheres (i.e., hydrophobic silica aerogel microspheres without plasma and surface modification treatment) prepared in step 1 of Example 1 were placed on the water surface. It was found that the hydrophobic silica aerogel microspheres aggregated due to hydrophobic interactions, such as... Figure 5 (a) and (b) in Example 13. In contrast, the plasma-treated and surface-modified silica aerogel from Example 13, when placed in water, was able to spread stably on the water surface due to its good hydrophilicity, as shown in (a) and (b). Figure 5 (c) and (d) in the text. This directly demonstrates that the technical solution of the present invention can successfully achieve the transformation of the outer surface of silica aerogel from hydrophobic to hydrophilic.

[0065] The hydrophobic silica aerogel in Example 13, the silica aerogel after plasma treatment, and the silica aerogel after plasma treatment and surface modification were quantitatively analyzed by an elemental analyzer, as shown in Table 2.

[0066] Table 2

[0067] As shown in Table 2, after air plasma treatment, the methyl groups on the outer surface of the hydrophobic silica aerogel are oxidized to generate oxygen-containing groups such as hydroxyl and carboxyl groups, resulting in a significant decrease in carbon content and an increase in oxygen content. Further surface modification with 3-aminopropyltrihydroxysilane after air plasma treatment increases the number of oxygen-containing groups on the aerogel's outer surface, further reducing carbon content and increasing oxygen content. Simultaneously, surface modification introduces amino groups onto the aerogel's outer surface, significantly increasing the nitrogen content. This indirectly confirms that air plasma treatment can successfully transform the outer surface of silica aerogel from hydrophobic to hydrophilic, and further gas-phase modification with hydroxysilane can further enhance the hydrophilicity of the silica aerogel's outer surface.

[0068] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0069] 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. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing asymmetric wettable silica aerogel, characterized in that, include: A hydrophobic silica aerogel is provided, wherein the outer surface and the inner surface of the pores of the hydrophobic silica aerogel are both hydrophobic; The outer surface of the hydrophobic silica aerogel is subjected to plasma treatment in an oxygen or air atmosphere, which transforms the hydrophobic groups on the outer surface of the hydrophobic silica aerogel into hydrophilic groups.

2. The method according to claim 1, characterized in that, Also includes: The silica aerogel, after plasma treatment, is placed in a gaseous environment for surface modification, wherein the gaseous environment contains hydroxysilane.

3. The method according to claim 1, characterized in that, The plasma treatment power is 15~240W, and the treatment time is 1~15 minutes.

4. The method according to claim 2, characterized in that, The surface modification method includes placing the plasma-treated aerogel and the hydroxysilane in a container and heating the container.

5. The method according to claim 4, characterized in that, The surface modification process takes 1 to 12 hours, and the heating temperature is 60 to 90°C. And / or, in the container, the volume ratio of the hydroxysilane to the aerogel is (1~10):

1.

6. The method according to claim 2, 4 or 5, characterized in that, The hydroxysilane includes at least one of 3-aminopropyltrihydroxysilane and vinyltrihydroxysilane.

7. The method according to any one of claims 1 to 4, characterized in that, The hydrophobic silica aerogel includes at least one of the following morphologies: microspheres, powder, and bulk.

8. A silica aerogel with asymmetric wetting properties, characterized in that, It is prepared by the method of any one of claims 1 to 7, wherein the outer surface of the silica aerogel has hydrophilic groups and the surface of the internal pores of the silica aerogel has hydrophobic groups.

9. The asymmetric wettable silica aerogel according to claim 8, characterized in that, The hydrophilic group includes at least one of hydroxyl, carboxyl, and amino groups, and the hydrophobic group includes silanylmethyl.

10. The asymmetric wettability silica aerogel according to claim 8 or 9, characterized in that, The water contact angle of the outer surface of the silica aerogel is 40°. -70 The water contact angle of the inner surface of the pores in the silica aerogel is greater than or equal to 110°. .

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