Aerogel particles and method of making the same

Abstract

A method includes the steps of (a) adding an organosilicon compound containing methyl groups and a surfactant into water, mixing well and carrying out hydrolysis to get a mixed aqueous solution; (b) mixing the mixed aqueous solution with 0.1-0.2M ammonium hydroxide and a remaining percentage of an organic solvent, and stirring the mixture under nitrogen atmosphere for emulsion polymerization to get a water-in-oil (w/o) emulsion; and (c) removing the organic solvent and drying the w/o emulsion to get aerogel particles. Thereby the aerogel particles are produced by the present method without hydrophobic treatment and solvent exchange. Therefore the cost and time used for preparing the aerogel particles are saved.

Claims

1. A method for making aerogel particles, comprising: adding at least one organosilicon compound containing methyl groups and at least one surfactant into water to produce an aqueous solution containing 50-70 percentage by volume (vol. %) of the organosilicon compound and 0.1-0.3 vol. % of the surfactant; mixing the aqueous solution evenly and carrying out hydrolysis to produce a mixed aqueous solution; mixing the mixed aqueous solution with 0.1-0.2M ammonium hydroxide (NH.sub.4OH) and an organic solvent to produce a mixture containing 12-16 vol. % of the mixed aqueous solution, 5-6 vol. % of the 0.1-0.2M ammonium hydroxide (NH.sub.4OH), and a remaining percentage of the organic solvent; stirring the mixture under nitrogen atmosphere for emulsion polymerization to produce a water-in-oil (w/o) emulsion; and removing the organic solvent and drying the w/o emulsion to produce aerogel particles.

2. The method as claimed in claim 1, wherein: the organosilicon compound containing methyl groups is selected from the group consisting of methyltrimethoxysilane, methyltriethoxysilane, dimethoxydimethylsilane, and dimethyldiethoxylsilane; the organic solvent is selected from the group consisting of alkanes, alcohols, ethers, and ketones; and the surfactant is selected from the group consisting of hexadecyl-trimethyl-ammonium bromide, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, and n-hexadecyltrimethylammonium chloride.

3. The method as claimed in claim 1, wherein: the mixture is stirred at 1,000-5,000 rpm; and the w/o emulsion is dried at 80 C.-150 C. in a normal atmosphere for 2-6 hours.

4. The method as claimed in claim 3, further comprising carrying out heat treatment of the aerogel particles at 400 C.-500 C. under normal atmosphere for 2-8 hours to produce hydrophilic aerogel particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein:

(2) FIG. 1 is a flow chart showing steps of an embodiment according to the present invention;

(3) FIG. 2 is a flow chart showing steps of another embodiment according to the present invention;

(4) FIG. 3 is a scanning electron micrograph of aerogel particles magnified 3000 of an embodiment according to the present invention;

(5) FIG. 4 is a scanning electron micrograph of aerogel particles magnified 40000 of an embodiment according to the present invention;

(6) FIG. 5 is a photo showing a contact angle of hydrophobic aerogel particles of an embodiment according to the present invention;

(7) FIG. 6 is a photo showing a contact angle of hydrophilic aerogel particles of an embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(8) Refer to FIG. 1, a method for making aerogel particles according to the present invention includes the following steps. (a) adding a 50-70 vol. % organosilicon compound containing methyl groups and a 0.1-0.3 vol. % surfactant into water, mixing evenly and carrying out hydrolysis to get a mixed aqueous solution. (b) mixing the 12-16 vol. % mixed aqueous solution with 5-6 vol. %, 0.1-0.2M ammonium hydroxide (NH.sub.4OH) and a remaining percentage of an organic solvent according to the percentage by volume (vol %) and stirring the mixture at 1,000-5,000 rpm under nitrogen atmosphere for emulsion polymerization to get a water-in-oil (w/o) emulsion. (c) removing the organic solvent and drying the w/o emulsion at 80 C.-150 C. in a normal atmosphere for 2-6 hours to get aerogel particles. In a preferred embodiment, the organosilicon compound containing methyl groups includes methyltrimethoxysilane, methyltriethoxysilane, dimethoxydimethylsilane, dimethyldiethoxylsilane, and polydimethylsiloxane while the organic solvent can be alkanes, alcohols, ethers, or ketones such as hexane, ethanol, dimethyl ether, and acetone. The surfactant is selected from hexadecyl-trimethyl-ammonium bromide, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, and n-hexadecyltrimethylammonium chloride.

(9) As shown in FIG. 2, the method further includes a step (d) of carrying out heat treatment of aerogel particles at 400 C.-500 C. under normal atmosphere for 2-8 hours to get hydrophilic aerogel particles.

(10) In this embodiment, the organosilicon compound containing methyl groups is used as precursor. After hydrolysis, condensation polymerization of the organosilicon compound is carried out in the w/o emulsion. Then the w/o emulsion is dried to get the hydrophobic aerogel particles directly and the particle diameter of the aerogel is 75-330 M. Once the hydrophobic aerogel particles are processed by high temperature heat treatment, the hydrophilicity of the aerogel particles is increased.

Embodiment One

(11) Add 30 ml dimethoxydimethylsilane (as precursor) and 0.1 g hexadecyl-trimethyl-ammonium bromide (as surfactant) into 15 ml water and stir well for 20 minutes. Then add 20 ml 0.2M ammonia water into the above aqueous solution as a catalyst for condensation polymerization and stir the solution constantly for several minutes. Next 300 ml ethanol is poured into the aqueous solution and stirred at 2,500 rpm for emulsion polymerization to form a water-in-oil (w/o) emulsion. The dispersed phase gradually changes into aerogel particles owing to condensation polymerization after about 10 minutes. Next, after removal of ethanol, the w/o emulsion is dried at 80 C. in a normal atmosphere for 2 hours (also can be dried at room temperature for a long time) and then dried again at 150 C. for 4 hours to get hydrophobic aerogel particles. A scanning electron microscope (SEM) is used to capture images showing appearance and distribution of the aerogel particles at different magnifications, as shown in FIG. 3 and FIG. 4.

Embodiment Two

(12) Add 30 ml methyltrimethoxysilane (as precursor) and 0.15 g sodium dodecyl benzene sulfonate (as surfactant) into 30 ml water and stir well for 20 minutes. Then add 20 ml 0.2M ammonia water into the above aqueous solution as a catalyst for condensation polymerization and stir the aqueous solution constantly for several minutes. Next 300 ml acetone is poured into the aqueous solution and stirred at 2,500 rpm for emulsion polymerization to obtain a water-in-oil (w/o) emulsion. The dispersed phase gradually changes into aerogel particles owing to condensation polymerization after about 10 minutes. Next after removal of acetone, the w/o emulsion is dried at 80 C. in a normal atmosphere for 2 hours (also can be dried at room temperature for a long time) and then dried again at 150 C. for 4 hours to get hydrophobic aerogel particles.

Embodiment Three

(13) Add 30 ml polydimethylsiloxane (as precursor) and 0.1 g n-hexadecyltrimethylammonium chloride (as surfactant) into 20 ml water and stir well for 20 minutes. Then add 20 ml 0.1M ammonia water into the above aqueous solution as a catalyst for condensation polymerization and stir the solution constantly for several minutes. Next 300 ml n-hexane is poured into the aqueous solution and stirred at 2,500 rpm for emulsion polymerization to get a water-in-oil (w/o) emulsion. The dispersed phase gradually changes into aerogel particles by condensation polymerization after about 10 minutes. Next after removal of n-hexane, the w/o emulsion is dried at 80 C. in a normal atmosphere for 2 hours (also can be dried at room temperature for a long time) and then dried again at 150 C. for 4 hours to get hydrophobic aerogel particles.

Embodiment Four

(14) Add 30 ml dimethyldiethoxylsilane (as precursor) and 0.15 g sodium dodecyl sulfate (as surfactant) into 25 ml water and stir well for 20 minutes. Then add 20 ml 0.2M ammonia water into the above aqueous solution as a catalyst for condensation polymerization and stir the solution constantly for several minutes. Next 300 ml dimethyl ether is poured into the aqueous solution and stirred at 2,500 rpm for emulsion polymerization to get a water-in-oil (w/o) emulsion. The dispersed phase gradually changes into aerogel particles by condensation polymerization after about 10 minutes. Next after removal of dimethyl ether, the w/o emulsion is dried at 80 C. in a normal atmosphere for 2 hours (also can be dried at room temperature for a long time) and then dried again at 150 C. for 4 hours to get hydrophobic aerogel particles.

(15) A plurality of tests is done for analysis of the hydrophobic aerogel particles, including data obtained by contact angle measurement with a contact angle meter. The test results are shown in FIG. 5 and Table 1. The bulk density, the specific surface area (SSA), the porosity, the particle diameter, the thermal conductivity and the contact angle of the hydrophobic aerogel particle are 0.037 g/cm.sup.3, 546.83 m.sup.2/g, 90.56%, 75-330 m, 0.035 W/m.Math.K, and 145 degrees, respectively.

(16) TABLE-US-00001 TABLE 1 property data bulk density (g/cm.sup.3 ) 0.037 specific surface area (m.sup.2/g) 546.83 porosity (%) 90.56 particle diameter (m) 75-330 thermal conductivity (W/m .Math. K) 0.035 contact angle 145

Embodiment Five

(17) Aerogel particles with different hydrophilicity are obtained after heat treatment of the hydrophobic aerogel particles produced by the method in the embodiment one at 400 C. and 450 C. for 2 hours, respectively. Refer to FIG. 6, measure the contact angle of the hydrophilic aerogel particles obtained after 400 C. heat treatment for 2 hours. The result shows that the contact angle is 26.08 degrees.

(18) In summary, compared with the technique available now, the present invention has the following advantages:

(19) 1. In the present invention, the hydrolyzed organosilicon compound is mixed with an organic solvent to get a water-in-oil (w/o) emulsion after emulsion polymerization. No surface treatment (such as surface hydroxylation) or hydrophobic dispersion medium is required for modifying the surface into the hydrophobic one. The emulsion is dried directly to get hydrophobic aerogel particles. Thus the method of the present invention shortens the production process and reduces the production cost.
2. No acid catalysts and chloro-acetylated organic molecules are used for hydrolysis and modification. Thus the shortcoming of the conventional method such as generation of highly acidic waste solutions can be overcome.
3. The hydrophilicity of the aerogel particles can be adjusted by heat treatment for production of aerogel particles with different properties that are more widely used in industrial applications.

(20) Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalent.