CN111170323A

CN111170323A - Silica aerogel microsphere wrapping/releasing oily substances and preparation method thereof

Info

Publication number: CN111170323A
Application number: CN202010114072.4A
Authority: CN
Inventors: 赵永亮; 朱晓敏
Original assignee: Shanghai Teli Material Technology Co ltd
Current assignee: Ningbo Te Li Science and Technology Ltd.
Priority date: 2020-02-26
Filing date: 2020-02-26
Publication date: 2020-05-19
Anticipated expiration: 2040-02-26
Also published as: CN111170323B

Abstract

The invention discloses a silicon dioxide aerogel microsphere for wrapping/releasing oily substances and a preparation method thereof, wherein the aerogel is spherical and has a unique composite structure: the spherical shell is compact, the interior is porous, and the barrier property exceeds that of the microcapsule with a core-shell structure. Can wrap oily substances, and the oily substances can be released through micropores and mesopores on the spherical shell under the external stimulation. The preparation method comprises the following steps: 1 synthesizing a polyalkoxy siloxane prepolymer; 2, uniformly mixing the prepolymer, the oily substance and water, and then adding alkali to obtain white emulsion; and 3, separating, washing, concentrating or drying the white emulsion to obtain aerogel microsphere dispersion liquid or aerogel microsphere powder. The preparation of the aerogel and the wrapping of the oily substance are synchronously finished, the method is simple and efficient, the cost is low, the wrapping efficiency is close to 100%, and the wrapping amount can reach 95%. The aerogel microspheres have strong mechanical properties, and the surface and internal hydrophilicity and hydrophobicity can be adjusted. The aerogel microspheres can be widely used in the industries of construction, textile, cosmetics, biomedicine and the like.

Description

Silica aerogel microsphere wrapping/releasing oily substances and preparation method thereof

Technical Field

The invention relates to a silicon dioxide aerogel microsphere for wrapping/releasing an oily substance and a preparation method thereof, in particular to a high-porosity aerogel microsphere for wrapping an oily substance, which is prepared under the conditions of not using a stabilizer or a surfactant and not using supercritical drying or solvent replacement, and a preparation method and application thereof.

Background

Aerogel is because of its ultra-low density (0.003-0.6 g/cm)³) And has ultrahigh specific surface area (400-1500 m)²The material has the advantages of high porosity (80-99.8%) and low thermal conductivity (0.013-0.038W/mK), and is the lightest solid material with the best thermal insulation performance. The aperture of the aerogel is generally less than 50 nanometers and is lower than the mean free path (70 nanometers) of air molecules at normal temperature and normal pressure, so that the collision probability among the air molecules is reduced, the heat conduction is avoided, and the aerogel becomes a super heat-insulating material.

However, silica aerogels have not been used on a large scale because of their special preparation process. The preparation of silica aerogels is generally carried out in two steps, first of all by hydrolysis of a silica precursor (organosiliconate, water glass or silicon tetrachloride) in an alcoholic solvent to give an alcosol of silicon, and by adjusting the pH to neutrality, to give a wet gel, the so-called sol-gel process. The solvent is then removed from the wet gel to yield a dried silica aerogel. This step is usually carried out by supercritical drying or atmospheric drying. Supercritical drying is carried out in a high-pressure vessel, and the temperature and pressure inside the vessel are adjusted to exceed the critical point of the drying medium, so that the gas/liquid interface existing before disappears, the surface tension does not exist, and the drying medium replaces the alcohol solvent in the wet gel. Therefore, the supercritical drying process can effectively avoid the shrinkage and collapse of the aerogel framework in the drying process, and obtain the aerogel with high porosity and high mechanical property. However, supercritical drying equipment is expensive, the drying conditions are harsh, the risk is high, and the production cost is high. The drying medium disclosed in Chinese patent CN103706342A is CO₂The supercritical pressure is 8-12 MPa, and the supercritical drying temperature of the ethanol disclosed in Chinese patent CN101973558A is 250-275^oC, the pressure is 9-13 MPa. Based on this, researchers began to explore methods for preparing aerogels by atmospheric drying, but the method is limited to the first step of sol-gel preparation process, and the atmospheric drying requires replacing the solvent (mostly alcohol or water) in the aerogel pore channels with a solvent with low surface tension (such as n-hexane, cyclohexane, etc.), sometimes even the inner surface of the pore channels needs to be subjected to hydrophobic treatment, so as to ensure that the aerogel framework does not shrink or collapse during the solvent volatilization process. For example, chinese patents CN101503195, CN102020285A and CN103043673A disclose methods for preparing silica aerogel by atmospheric drying respectively, but the production cycle is long, the amount of solvent used is large, the environmental protection pressure is large, and the operation is tedious.

Currently produced silica aerogel is mainly used for development of heat insulation materials such as heat insulation felt and heat insulation coating, but there is a fresh report that silica aerogel is used in the field of wrapping/slow release. The inventors believe that possible causes arise from the aerogel preparation process and the structure of the aerogel itself. As mentioned above, the solvent is removed by supercritical or other drying methods during the aerogel preparation process to obtain the desired porosity, so that the coating of the functional material (which is removed together with the solvent during drying) cannot be achieved during the aerogel preparation process, and even if the coating is achieved by other auxiliary means, the coating can only occur after the aerogel preparation process is completed. On the other hand, the aerogel that makes is mostly block structure, will realize the high-efficient complex with other materials, if compound with engineering plastics, compound with the emulsion, all need smash into ideal size, except can destroying the gluey hole of aerogel, still can make the aerogel possess more open structure, if be used for wrapping up functional material, hardly realize long-term encapsulation, more can not realize later stage controllable release. Moreover, the aerogel has a hydrophobic surface and low density, and is difficult to disperse in an aqueous system, and the traditional silica encapsulation technology needs to combine a sol-gel method and an oil-water emulsion (refer to Chinese patents CN105797659A and CN108699427A and U.S. Pat. No. 3, 6303149B 1) and use a large amount of surfactant to stabilize the emulsion. Therefore, the application of silica aerogel with high porosity for the encapsulation and release of functional substances is difficult to achieve in the prior art.

Disclosure of Invention

In order to overcome the disadvantages of the prior art, it is an object of the present invention to provide silica aerogel microspheres that encapsulate/release an oily substance.

The silica aerogel microspheres for wrapping/releasing oily substances provided by the invention comprise a silica framework or an organic group modified silica framework and an oily substance filled in the silica framework. The silica framework has a composite structure, the outer layer is a silica shell layer containing 1-50 nanometer micropores and mesopores, and the inner part is a porous structure containing a combination of 1-500 nanometer micropores, mesopores and macropores. The oily substance is a substance which is not soluble with water or slightly soluble in water, is mainly filled in micropores, mesopores and macropores of 1-500 nanometers formed in the silica aerogel microspheres, and can be controlled and released through the micropores and the mesopores on the silica shell layer under the external stimulation.

The silica aerogel microspheres for wrapping/releasing oily substances provided by the invention have the size of 0.5-100 microns, can be subjected to size design according to different application fields, and are preferably 1-50 microns, and more preferably 1-20 microns. The microspherical shape is spherical or approximately spherical, so that the aerogel microspheres are favorably and uniformly compounded with other materials, the mechanical property of the composite material is not damaged while the processing difficulty is reduced, and in the field of cosmetics, spherical particles are considered to be capable of effectively improving the smooth effect of the surface of the coating.

According to the silica aerogel microspheres for wrapping/releasing the oily substances, if the silica accounts for 5-99% of the total mass of the microspheres and the oily substances account for 1-95% of the total mass of the microspheres in mass ratio, the ratio of the silica to the oily substances can be flexibly adjusted, and the requirements of an application end on the ratio of the silica aerogel microspheres to the oily substances are met. In general, the higher the oily material fraction, the higher the porosity and lower the density of the silica aerogel microspheres are required.

Another object of the present invention is to provide a method for preparing the silica aerogel microspheres for encapsulating/releasing oily substances.

The preparation method of the silica aerogel microspheres for wrapping/releasing oily substances, provided by the invention, comprises the following steps of:

s1: fully mixing silane, a hydrophilic compound containing hydroxyl, a solvent and water with the aid of dispersing equipment, adding a catalyst solution, heating to react completely, and removing the solvent to obtain a polyalkoxy siloxane prepolymer with certain viscosity;

s2: fully mixing the polyalkoxysiloxane prepolymer obtained in the step S1, an oily substance and water to obtain a white emulsion, adding alkali, adjusting the pH to 7-11, and continuously reacting for a certain time to obtain a silicon dioxide aerogel microsphere dispersion liquid wrapping the oily substance;

s3: and (4) separating and washing the silica aerogel microsphere dispersion solution coated with the oily substance obtained in the step (S2) through a separation device, or concentrating to obtain the silica aerogel microsphere dispersion solution coated with the oily substance, or drying to obtain silica aerogel microsphere powder coated with the oily substance.

The silane used in step S1 can be understood as any precursor that can finally form silica through hydrolysis and condensation, and can be a monomer compound or a low molecular polymer, which is a main source for forming the silica skeleton of the aerogel microspheres. Preferably, the silane may be a monomer having the formula R¹ _4-n-Si-(OR²)_nWherein n = 2-4, R¹A non-hydrolyzable group selected from a halogenated alkyl group such as an alkyl group, a vinyl alkyl group, an epoxyalkyl group, a styrylalkyl group, a methacryloxyalkyl group, an acryloxyalkyl group, an aminoalkyl group, a ureido alkyl group, a chloropropylalkyl group OR a sulfanyl group, an isocyanate alkyl group OR a hydroxyalkyl group, OR²Is a hydrolyzable group, R²Is an alkyl group having 1 to 6 carbon atoms, having a plurality of R¹When each R is¹May be the same OR different from each other, and have a plurality of ORs²When each OR is²The silane may be the same or different from each other, and may be a commercially available poly having a silica content of 60% or lessThe alkoxy siloxane prepolymer includes one or more of silicon 40, silicon 48, silicon 53, etc.

The main function of the hydrophilic compound containing hydroxyl group added in step S1 is to endow the synthesized polyalkoxysiloxane prepolymer with certain hydrophilicity, which facilitates the emulsification of oily substances into emulsion droplets with certain size in the water phase. Preferably at least one of all hydroxyl-containing hydrophilic substances such as polyethylene glycol, polyethylene glycol monoethers, copolymers of ethylene glycol and propylene glycol, polyvinyl alcohol, and polyglycerol. The molecular weight is preferably 200 to 10000, more preferably 300 to 5000, and even more preferably 500 to 2500. The mass ratio thereof to silane is preferably (0.01-1): 1, more preferably (0.03-0.7): 1, even more preferably (0.05-0.5): 1.

the solvent in step S1 can be understood as any organic solvent that can help the silane and the hydroxyl-containing hydrophilic compound to be mutually soluble, and is at least one of methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, acetone, butanone and the like, preferably at least one of methanol, ethanol, isopropanol, propylene glycol methyl ether, and more preferably at least one of ethanol or propylene glycol methyl ether. The mass ratio of the silane to the silane is (0.1-10): 1.

the water is added in step S1 for the purpose of hydrolyzing and condensing the silane, preferably in a weight ratio of water to silane of (0.01-1): 1, more preferably (0.05-0.5): 1, even more preferably (0.1-0.3): 1.

the catalyst added in step S1 is to promote hydrolysis and condensation of alkoxy groups in silane, thereby improving the reaction efficiency. Preferably, protonic acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, solid acid such as acidic cation exchange resin, or Lewis acid such as one of aluminum trichloride, boron trifluoride, titanium alkoxide and the like, but not limited thereto, and the molar concentration of the catalyst is 0.01 to 10mol/L and the mass ratio thereof to silane is (0.001 to 0.2): 1.

preferably, the temperature of the heating reaction of step S1 is 30-100 deg.C, more preferably 50-90 deg.C, and even more preferably 70-80 deg.C.

Preferably, the heating reaction time of step S1 is 1 to 24 hours, more preferably 5 to 15 hours, and even more preferably 8 to 10 hours.

The solvent removal in step S1 is intended to purify the resulting polyalkoxysiloxane prepolymer, otherwise too much solvent remaining would interfere with the formation of the aerogel microspheres in step S2. Preferably, the method for removing the solvent is one of atmospheric distillation, vacuum distillation, thin film evaporation or rotary evaporation, and more preferably one of vacuum distillation or thin film evaporation.

The oily substance described in step S2 can be understood as any liquid or solid that is immiscible with or slightly soluble in water, preferably at least one of hydrophobic solvents, nanoparticles, fragrances, drugs, pigments, dyes. In some special cases, it may be necessary to coat the solid by dispersing it in a specific solvent, which can be achieved by the technical solution of the present invention. The mass ratio of the oily substance to the polyalkoxysiloxane prepolymer is (0.001-20): 1, and if the weight of the oily substance exceeds that of the polyalkoxysiloxane prepolymer too much, the wrapping efficiency may not reach 100%.

The manner of mixing the polyalkoxysiloxane prepolymer, the oily substance and the water in step S2 can be understood as any manner known to those skilled in the art, including magnetic stirring, mechanical stirring, ultrasonic dispersion, emulsification with an emulsifier, and the like. The purpose of adding the base in step S2 is to further promote hydrolysis and condensation of the polyalkoxysiloxane, and to quickly form a silica structure having a certain mechanical strength, and the base is preferably at least one of sodium hydroxide, potassium hydroxide, and ammonia water. After the alkali is added, the reaction needs to be continued for a period of time, so that the hydrolysis and the condensation are fully completed, the mechanical strength of the silicon dioxide is further increased, and the reaction time is prolonged, which proves that various performances of the finally obtained silicon dioxide aerogel microspheres cannot be damaged.

The purpose of the separation and washing in step S3 is to remove the alkali added in step S2, preferably washing to neutral from the viewpoint of the use of the final product, but it is not excluded that some special application scenarios do not require the removal of alkali from the silica aerogel microsphere dispersion. The aerogel microsphere dispersion liquid or the aerogel microsphere powder is finally obtained, and the skilled person can flexibly master the method depending on the subsequent use scene. The separation and washing equipment is all equipment known to those skilled in the art, and is preferably at least one of a centrifuge, a funnel filtration device, an ultrafiltration device and a dialysis equipment, and the drying method is preferably oven drying, freeze drying, spray drying and the like.

Compared with the prior art, the invention has the beneficial effects that:

1) the silica aerogel microspheres provided by the invention have high porosity and low density, can be used for the traditional heat insulation field, can be widely used for wrapping various oily substances, has the wrapping efficiency of up to 100 percent, and has strong barrier property, and simultaneously, as the spherical shells of the aerogel microspheres contain micropores and mesopores, the wrapped oily substances can be controllably released through the micropores and the mesopores;

2) the size of the silicon dioxide aerogel microspheres is micron-sized, the silicon dioxide aerogel microspheres are different from the traditional massive aerogel, crushing is not needed before use, so that the pore structure of the aerogel can be retained to the maximum extent, and meanwhile, the spherical structure can be uniformly filled when being compounded with other materials, so that the mechanical property of the composite material is not influenced, and the smoothness degree of a coating can be increased;

3) the silica aerogel microspheres provided by the invention have a unique composite structure, the interior of the silica aerogel microspheres is of a porous structure similar to the traditional aerogel, and the outer layer of the silica aerogel microspheres is of a compact silica shell layer, so that on one hand, oily substances can be effectively encapsulated in pores in the microspheres, and on the other hand, when the silica aerogel microspheres are compounded with other materials, external substances can be prevented from permeating into the microspheres to fill the pores, and the advantages of high porosity and low density of aerogel materials are lost;

4) the silicon dioxide aerogel microspheres provided by the invention are prepared in a water phase, the surface of the silicon dioxide aerogel microspheres is rich in hydroxyl, and the silicon dioxide aerogel microspheres can be directly used in a water-based system and can also be subjected to hydrophobic treatment on the surface of the silicon dioxide aerogel microspheres to be used in an oily system;

5) according to the preparation method of the silica aerogel microspheres coated with the oily substance, other stabilizing agents or surfactants are not required to be added, the amphiphilic polyalkoxysiloxane prepolymer promotes the oily substance to be emulsified in water to form a microsphere structure, other byproducts are not generated, and the preparation efficiency is high;

6) the preparation method of the silica aerogel microspheres wrapped with the oily substance provided by the invention does not need a supercritical drying method or a plurality of solvent replacement processes, conventional drying can be realized, and the preparation of the aerogel microspheres and the wrapping of the oily substance are synchronously completed, so that the production cost is reduced, and the production efficiency is improved;

7) the preparation method of the silica aerogel microspheres provided by the invention can realize the wrapping of most oily substances, so that the application fields of the aerogel microspheres, such as cosmetics, coatings, biological medicines and the like, are greatly expanded, and the preparation method is not limited to the current heat insulation field.

Drawings

FIG. 1 is a scanning electron micrograph of the silica aerogel microspheres coated with hexane obtained in example 1;

FIG. 2 is a TEM image of silica aerogel microspheres coated with hexane obtained in example 1;

FIG. 3 is a BET adsorption-desorption curve and a pore size distribution diagram of the hexane-coated silica aerogel microsphere powder obtained in example 1;

FIG. 4 is a Thermogram (TGA) of hexane coated silica aerogel microspheres obtained in example 1;

FIG. 5 shows the hexane coated silica aerogel microspheres obtained in example 1 at 800^oC, scanning electron microscope photo after calcination;

FIG. 6 is a scanning electron micrograph of silica aerogel microspheres coated with octyl acetate obtained in example 2;

FIG. 7 is a transmission electron micrograph of silica aerogel microspheres coated with octyl acetate obtained in example 2;

FIG. 8 is a BET adsorption-desorption curve and a pore size distribution diagram of silica aerogel microsphere powder coated with octyl acetate obtained in example 2;

FIG. 9 is a thermal weight loss plot (TGA) of octyl acetate coated silica aerogel microspheres obtained in example 2;

FIG. 10 shows silica aerogel microspheres coated with octyl acetate obtained in example 2 at 800^oC, scanning electron microscope photo after calcination;

FIG. 11 is a scanning electron micrograph of the silica aerogel microspheres coated with toluene obtained in example 3;

FIG. 12 is a TEM image of silica aerogel microspheres coated with limonene obtained in example 4;

FIG. 13 is a TEM image of the PDMS-coated silica aerogel microspheres obtained in example 5.

Detailed Description

The present invention will be further illustrated with reference to the accompanying drawings and specific examples, which are not intended to limit the scope of the invention in any way and, unless otherwise indicated, the reagents used in the specific examples may be obtained by commercially available means or by routine experimentation.

Example 1

1) 208 g of tetraethyl orthosilicate, 50 g of ethanol and 10 g of polyethylene glycol (average molecular weight is 500) are uniformly mixed until the mixture is transparent, then 7.5 g of concentrated hydrochloric acid (mass fraction is 37%) and 5 g of deionized water are respectively added and uniformly mixed, after stirring for 5 minutes, the temperature is raised to 70 ℃ for continuous reaction for 4 hours, and the solvent in the system is quickly removed by reduced pressure distillation, so that the transparent polyalkoxysiloxane prepolymer with certain viscosity and fluidity is obtained. 2) Adding 50 g of polyalkoxysiloxane prepolymer and 25 g of hexane into 200 g of deionized water, rapidly stirring to obtain uniform white emulsion, adding 25 g of ammonia water (mass concentration is 25%), and continuously stirring for 5 hours to obtain milky white silica aerogel microsphere dispersion liquid coated with hexane; 3) centrifuging the aerogel microsphere dispersion liquid to remove supernatant, washing the white solid at the lower layer, repeating the process until the dispersion liquid is neutral or nearly neutral, continuously centrifuging, and freeze-drying the solid at the lower layer to obtain the silica aerogel microsphere powder wrapped with hexane.

The scanning electron micrograph of the obtained silica aerogel microspheres wrapped with hexane is shown in FIG. 1The average size is about 10 microns, the size distribution is uniform, the spherical structure is complete, and the surface is closed. The transmission electron micrograph is shown in FIG. 2, which shows that the silica skeleton (dark color part) and the porous structure (light color part) inside the microspheres are clearly observed, the porosity is high, and the bulk density is 0.05 g/cm³. The specific surface area of the aerogel microspheres is 550 m calculated from the BET adsorption-desorption curve of FIG. 3²The pore diameter is distributed in the range of 2-100 nanometers and is concentrated at about 10 nanometers. According to the invention, the wrapping amount and the wrapping efficiency of the silica aerogel microspheres wrapped with hexane can be evaluated through thermal weight loss curves (TGA) of the silica aerogel microspheres wrapped with hexane at different temperatures, wherein the wrapping amount refers to the mass percentage of oily substances in the whole aerogel microspheres, and the wrapping efficiency refers to the wrapping ratio of the oily substances which are initially input to the aerogel microspheres. As shown in fig. 4, the weight loss of the whole aerogel microspheres is about 54%, which indicates that the coating amount of the aerogel to hexane is 54%, and the coating efficiency of the aerogel to hexane is close to 100% by calculating the feed ratio. From the descending trend of the TGA curve, it can be further determined that the hexane is slowly released through the micropores and mesopores on the spherical shell of the aerogel microsphere. Mixing silica aerogel microsphere coated with hexane at 800^oAs shown in fig. 5, it can be seen that after the aerogel microspheres are subjected to such a high temperature treatment, the aerogel microspheres still maintain their complete spherical structures, and no significant damage is observed on the surfaces of the aerogel microspheres, which indicates that the aerogel microspheres obtained in this embodiment have excellent thermal stability and higher mechanical properties, and further indicates that the release of hexane is achieved through micropores or mesopores on the surfaces of the microspheres, rather than through the crushing of the microspheres.

Example 2

Example 2 differs from example 1 in that polyethylene glycol (average molecular weight 500) was replaced with polyvinyl alcohol (average molecular weight 750) in step 1), the amounts of concentrated hydrochloric acid and deionized water were increased to 15 g and 10 g, respectively, hexane was replaced with octyl acetate in step 2), and the centrifugation-water washing operation in step 3) was replaced with funnel filtration.

The obtained coated acetogeninThe scanning electron micrograph of the ester silica aerogel microspheres is shown in fig. 6, the size of the ester silica aerogel microspheres is in the range of 1-4 microns, the size distribution is uniform, the spherical structure is complete, and the surface is closed. The transmission electron micrograph is shown in FIG. 7, which shows that the silica skeleton (dark color part) and the porous structure (light color part) inside the microspheres are clearly observed, the porosity is high, and the bulk density is 0.06 g/cm³. The specific surface area of the aerogel microspheres calculated from the BET adsorption-desorption curve of FIG. 8 was 500 m²The pore diameter is distributed in the range of 2-100 nanometers, and is concentrated on about 10 nanometers and 100 nanometers. The thermal weight loss (TGA) curve is shown in fig. 9, the weight loss is about 60%, which indicates that the wrapping amount of the aerogel to the octyl acetate is 60%, and the wrapping efficiency of the aerogel to the octyl acetate is calculated to be close to 100%. From the descending trend of the TGA curve, it can also be judged that the octyl acetate is slowly released through the micropores and mesopores on the spherical shell of the aerogel microsphere. Coating silica aerogel microspheres coated with octyl acetate in 800 parts^oThe scanning electron microscope photograph of the calcined aerogel microspheres is shown in fig. 10, the spherical structure of the aerogel microspheres is complete, and no obvious damage is observed on the surface, which indicates that the aerogel microspheres obtained in this embodiment have excellent thermal stability and high mechanical properties, and further indicates that octyl acetate is slowly released through micropores or mesopores on the surfaces of the microspheres.

Example 3

Example 3 differs from example 1 in that 208 g of tetraethyl orthosilicate in step 1) were replaced by 152 g of tetramethyl orthosilicate, ethanol by isopropanol, polyethylene glycol by polyethylene glycol monomethyl ether (molecular weight 500), 7.5 g of concentrated hydrochloric acid (mass fraction 37%) by 7 g of concentrated nitric acid (mass fraction 68%), 25 g of hexane in step 2) by 35 g of toluene and 25 g of aqueous ammonia by 25 g of aqueous sodium hydroxide (0.1M).

The scanning electron micrograph of the obtained toluene-coated silica aerogel microspheres is shown in fig. 11, the spherical structures of the microspheres are complete, and the size of the microspheres is about 10 microns. Bulk density 0.065 g/cm³Specific surface area 480 m²The pore diameter is distributed in the range of 2-100 nanometers, and is concentrated in 10 nanometers, namely, the para-formazanThe coating amount of benzene is 60%, the coating efficiency is 100%, the release is slow, and the spherical structure is still complete after high-temperature calcination.

Example 4

Example 4 differs from example 1 in that 208 grams of tetraethyl orthosilicate in step 1) was replaced with 146 grams of silicon 40 commonly used in the silicone industry, 10 grams of polyethylene glycol (average molecular weight 500) was replaced with 12 grams of polyethylene glycol monoethyl ether (average molecular weight 400), 7.5 grams of concentrated hydrochloric acid (mass fraction 37%) and 5 grams of deionized water were replaced with 10 grams of concentrated hydrochloric acid (mass fraction 37%) and 7.5 grams of deionized water, respectively, the reduced pressure distillation was replaced with thin film evaporation, the mass of polyalkoxysiloxane in step 2) was reduced to 42 grams, 25 grams of hexane was replaced with 36 grams of limonene, and the lyophilization in step 3) was replaced with spray drying.

The transmission electron micrograph of the obtained limonene-coated silica aerogel microspheres is shown in FIG. 12, the spherical structures of the microspheres are complete, the size of the microspheres is about 4 micrometers, the internal porosity of the microspheres is high, and the bulk density is 0.08 g/cm³Specific surface area 450 m²The pore size is distributed in the range of 2-100 nanometers, the pore size is concentrated in 10 nanometers, the coating amount of limonene is 70%, the coating efficiency is 100%, the release is slow, and the spherical structure is still complete after high-temperature calcination.

Example 5

Example 5 differs from example 1 in that 208 grams of tetraethyl orthosilicate in step 1) was replaced with a combination of 104 grams of tetraethyl orthosilicate and 104 grams of methyltriethoxysilane, ethanol was replaced with propylene glycol methyl ether, concentrated hydrochloric acid was replaced with 20 grams of a macroporous strong acid cation exchange resin, and the reaction temperature was increased to 80 deg.f^oC, reducing the amount of the polyalkylsiloxane prepolymer in the step 2) to 15 g, replacing 25 g of hexane with 60 g of polydimethylsilane (PDMS, molecular weight 500), and replacing the freeze-drying in the step 3) with oven drying.

The transmission electron micrograph of the obtained PDMS-coated silica aerogel microspheres is shown in FIG. 13, the spherical structures of the microspheres are complete, the size of the microspheres is about 1 micron, the internal porosity of the microspheres is very high (light-colored part), and three-dimensional net-shaped silica aerogel microspheres can be obviously observedSilica skeleton of structure (dark part), bulk density 0.08 g/cm³Specific surface area 400 m²The pore diameter is distributed in the range of 2-100 nanometers, the pore diameter is concentrated and distributed in 10 nanometers, the coating amount of PDMS is 80%, the coating efficiency is 100%, the release is slow, and the spherical structure is still complete after high-temperature calcination.

Other corresponding changes and modifications will occur to those skilled in the art from the foregoing description and the accompanying drawings, and all such changes and modifications are intended to be included within the scope of the appended claims.

Claims

1. The silica aerogel microspheres for wrapping/releasing oily substances are characterized by comprising a silica framework or an organic group modified silica framework and oily substances filled in the silica framework.

2. The silica aerogel microspheres for wrapping/releasing oily substances according to claim 1, wherein the silica skeleton has a composite structure, the outer layer is a silica shell layer containing 1-50 nm micropores and mesopores, and the inner part is a porous structure containing a combination of 1-500 nm micropores, mesopores and macropores; the oily substance is insoluble or slightly soluble in water, and the coated oily substance can be released through micropores and mesopores on the silica shell layer.

3. Silica aerogel microspheres encapsulating/releasing oily substances, according to claims 1-2, characterized in that said aerogel microspheres have a size comprised between 0.5 and 100 microns and are spherical or approximately spherical in shape; in the aerogel microspheres, silicon dioxide accounts for 5-99% and oily substances account for 1-95% in mass ratio.

4. A preparation method of silica aerogel microspheres for wrapping/releasing oily substances is characterized by comprising the following steps:

s1, fully mixing silane, a hydrophilic compound containing hydroxyl, a solvent and water with the aid of dispersing equipment, adding a catalyst solution, heating to react completely, and removing the solvent to obtain a polyalkoxysiloxane prepolymer with certain viscosity;

s2, fully mixing the polyalkoxysiloxane prepolymer obtained in the step S1, an oily substance and water to obtain a white emulsion, adding alkali, adjusting the pH value to 7-12, and continuously reacting for a certain time to obtain a silicon dioxide aerogel microsphere dispersion liquid wrapping the oily substance;

and S3, separating and washing the silica aerogel microsphere dispersion liquid coated with the oily substance obtained in the step S2 by using a separation device, or concentrating to obtain the silica aerogel microsphere dispersion liquid coated with the oily substance, or drying to obtain silica aerogel microsphere powder coated with the oily substance.

5. The method of claim 4, wherein the silane of step S1 is a monomer of the formula R¹ _4-n-Si-(OR²)_nWherein n = 2-4, R¹A non-hydrolyzable group selected from a halogenated alkyl group such as an alkyl group, a vinyl alkyl group, an epoxyalkyl group, a styrylalkyl group, a methacryloxyalkyl group, an acryloxyalkyl group, an aminoalkyl group, a ureido alkyl group, a chloropropylalkyl group OR a sulfanyl group, an isocyanate alkyl group OR a hydroxyalkyl group, OR²Is a hydrolyzable group, R²Is an alkyl group having 1 to 6 carbon atoms, having a plurality of R¹When each R is¹May be the same OR different from each other, and have a plurality of ORs²When each OR is²The silane may be the same or different from each other, and may be a commercially available polyalkoxysiloxane prepolymer having a silica content of 60% or less, including at least one of silicon 40, silicon 48, silicon 53, and the like.

6. The method according to claim 4, wherein the hydroxyl-containing hydrophilic compound in step S1 is one of polyethylene glycol, polyethylene glycol monoether, copolymer of ethylene glycol and propylene glycol, polyvinyl alcohol, polyglycerol, etc., and has a molecular weight of 200 to 10000, and the mass ratio of the hydroxyl-containing hydrophilic compound to the silane is (0.01-1): 1; in step S1, the solvent is at least one of methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, acetone, butanone and the like, and the mass ratio of the solvent to the silane is (0.1-10): 1; the catalyst in step S1 is one of protonic acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, solid acid such as acidic cation exchange resin, or lewis acid such as aluminum trichloride, boron trifluoride, titanium alkoxide, etc., but not limited thereto, and the molar concentration of the catalyst is 0.01 to 10mol/L, and the mass ratio thereof to silane is (0.001 to 0.2): 1.

7. the method according to claim 4, wherein the heating reaction in step S1 is carried out at 30-100 ℃ for 1-24 hours, and the solvent removal method comprises one or a combination of atmospheric distillation, vacuum distillation, thin film evaporation or rotary evaporation.

8. The method according to claim 4, wherein the oily substance in step S2 is at least one of hydrophobic solvent, nanoparticles, perfume, drug, pigment and dye, and the mass ratio of the oily substance to the polyalkoxysiloxane prepolymer is (0.001-20): 1; in step S2, the alkali is sodium hydroxide, potassium hydroxide, ammonia water, or the like.

9. The method according to claim 4, wherein the separation apparatus in step S3 is a centrifuge, a funnel filter device, an ultrafiltration device, a dialysis apparatus, and the drying method is oven drying, freeze drying, spray drying, or the like.

10. The silica aerogel microspheres coated with the oily substance are used in the building industry, the textile industry, the cosmetic industry and the biomedical industry.