CN111908478B

CN111908478B - Preparation method of flexible silica aerogel

Info

Publication number: CN111908478B
Application number: CN202010794789.8A
Authority: CN
Inventors: 张瑜; 聂朝胤; 谢红梅
Original assignee: Southwest University
Current assignee: Southwest University
Priority date: 2020-08-10
Filing date: 2020-08-10
Publication date: 2023-01-17
Anticipated expiration: 2040-08-10
Also published as: CN111908478A

Abstract

The invention discloses a preparation method of flexible silica aerogel, which comprises the following steps: s1, dissolving CTAB in a mixed solvent to obtain a mixed solution, wherein the mixed solvent comprises ethanol, water and hydrochloric acid; s2, sequentially adding TEOS, MTES and DEDMS into the mixed solution under the stirring condition, and mixing and stirring to obtain silica sol; s3, dropwise adding ammonia water with the concentration of 2-3 mol/L into the silica sol under the stirring condition, and mixing and stirring to obtain silica gel; the molar ratio of the ammonia to the DEDMS added in the S2 is 0.008-0.012: 0.015 to 0.025; and S4, carrying out aging treatment, cleaning and drying on the silicon dioxide gel to obtain the flexible silicon dioxide aerogel. The method can improve the connection strength of the aerogel framework, shorten the preparation time and improve the preparation efficiency.

Description

Preparation method of flexible silica aerogel

Technical Field

The invention relates to preparation of an aerogel, in particular to a preparation method of a flexible silicon dioxide aerogel.

Background

Aerogels are considered the lightest solid materials in the world. Because of its ultra-high porosity and unique pore structure, aerogels have a number of important applications in thermal insulation, adsorptive separation, catalysts and catalyst carriers, optical devices, electrical devices, and the like. Aerogels mainly include oxide aerogels such as silica, carbon aerogels, cellulose aerogels and the like, and these aerogels are usually prepared by preparing a wet gel by a sol-gel process and then replacing the solvent in the wet gel with air to obtain the aerogel. The displacement drying process usually requires supercritical carbon dioxide drying or freeze drying, otherwise, the pores in the material collapse due to the action of capillary force, so that the skeleton structure is damaged. The supercritical carbon dioxide drying and freeze-drying technology has the problems of high price, insecurity, environmental pollution and the like, so that the production cost of the aerogel is high, and the large-scale production preparation and industrial application of the aerogel are not facilitated.

The preparation of the silicon dioxide aerogel generally takes organosilicon precursors (tetraethoxysilane and methyl orthosilicate) as raw materials, and is the aerogel which is the most mature in preparation technology and application at present. The preparation process generally comprises the steps of forming a wet gel with a dendritic and three-dimensional network structure by using a sol-gel method, and removing a solution in the gel by combining a proper drying process to obtain the aerogel, but the method has the problems of long time (usually more than 2 days), low connection strength of a product skeleton structure and the like.

Disclosure of Invention

The invention aims to provide a preparation method of a flexible silica aerogel, which can improve the connection strength of an aerogel framework, shorten the preparation time and improve the preparation efficiency.

The preparation method of the flexible silica aerogel comprises the following steps:

s1, dissolving CTAB in a mixed solvent at the temperature of 30-50 ℃ to obtain a mixed solution, wherein the mixed solvent comprises ethanol, water and hydrochloric acid, and the molar ratio of CTAB, ethanol, water and hydrochloric acid is 0.00024-0.0003: 1.6-1.7: 3.6-3.7: 0.0001 to 0.00015;

s2, sequentially adding TEOS, MTES and DEDMS into the mixed solution under the stirring condition, and mixing and stirring to obtain silica sol, wherein the molar ratio of TEOS, MTES, DEDMS to hydrochloric acid in the mixed solution is 0.04-0.05: 0.235 to 0.245: 0.015-0.025: 0.0001 to 0.00015;

s3, dropwise adding ammonia water with the concentration of 2-3 mol/L into the silica sol under the stirring condition, and mixing and stirring to obtain silica gel;

the molar ratio of the ammonia to the DEDMS added in the S2 is 0.008-0.012: 0.015 to 0.025;

and S4, carrying out aging treatment, cleaning and drying on the silicon dioxide gel to obtain the flexible silicon dioxide aerogel.

Furthermore, the concentration of the hydrochloric acid in the S1 is 0.08-0.15 mol/L.

Further, the aging temperature of the aging treatment in the S4 is 30-50 ℃, and the aging time is 3-6 h.

Further, the drying in S4 is specifically: firstly drying for 1-2 h at the temperature of 40-50 ℃, and then drying for 1-3 h at the temperature of 60-80 ℃.

Further, the ammonia water concentration in the S3 is 2.5mol/L.

Further, the molar ratio of ammonia in the S3 and the DEDMS added by the S2 is 0.01:0.021.

CTAB is the abbreviation for cetyl trimethyl ammonium bromide, TEOS is the abbreviation for tetraethoxysilane, MTES is the abbreviation for methyltriethoxysilane, DEDMS is the abbreviation for dimethyldiethoxysilane.

Compared with the prior art, the invention has the following beneficial effects.

1. According to the invention, the crosslinking degree of the aerogel framework is controlled by controlling the addition amount of DEDMS, the particle size of the aerogel framework is controlled by utilizing the concentration and the addition amount of ammonia water of an alkali catalyst, and a coarsened aerogel framework is obtained by combining the limitation of other components. And the time of the whole process flow can be shortened to 8-12h, the preparation time of the flexible silicon dioxide aerogel is greatly shortened, and the preparation efficiency is improved.

2. The invention controls and optimizes the adding proportion of each component, namely the molar ratio of TEOS, MTES, DEDMS, ethanol, water, CTAB, hydrochloric acid and ammonia water is 0.04-0.05: 0.235 to 0.245: 0.015-0.025: 1.6-1.7: 3.6-3.7: 0.00024 to 0.0003:0.0001 to 0.00015: 0.008-0.012. Particularly, DEDMS and ammonia water are controlled, wherein if the addition amount of DEDMS is too small, effective connection cannot be formed among silica clusters, the aerogel framework is formed by stacking a large number of fragmented silica clusters, the connection among the silica clusters is loose, a large number of gaps exist, and the connection strength is weak. If the addition amount of DEDMS is too large, the silicon dioxide clusters further react to form smooth secondary spherical particles, and the interfaces among the spherical particles are sunken, so that the connection effect of the aerogel framework is weakened. If the addition of ammonia water is too little, the polycondensation reaction of the system is insufficient, so that a complete three-dimensional network structure cannot be formed, namely a firm aerogel skeleton structure cannot be formed, and the flexibility is poor. If ammonia water addition is too much, promoted condensation polymerization rate for the aerogel skeleton has not yet been ready to form complete structure and just become the gel state, so that there are more gaps between the secondary particle, and then the connection is comparatively loose.

3. The invention adopts sectional drying, firstly, the sample is dried for a period of time at a lower temperature, the solvent on the surface of part of the sample is evaporated, and meanwhile, the temperature of the surface and the temperature of the interior of the sample tend to be consistent, and the cracking caused by the overlarge temperature difference between the surface and the interior of the sample is avoided. And then the temperature is raised for drying, and the residual solvent in the aerogel is quickly removed, so that the sample preparation time is shortened.

Drawings

FIG. 1 is an SEM image of a flexible silica aerogel prepared according to a first embodiment of the present invention;

FIG. 2 is an SEM image of a silica aerogel of comparative example one;

FIG. 3 is an SEM image of a silica aerogel of comparative example two;

FIG. 4 is an SEM image of a silica aerogel of comparative example III;

FIG. 5 is an SEM image of a silica aerogel of comparative example No. four;

FIG. 6 is an SEM image of a silica aerogel of comparative example five;

fig. 7 is an SEM image of a silica aerogel of comparative example six;

FIG. 8 is an SEM image of a silica aerogel of comparative example seven;

FIG. 9 is a stress-strain plot of silica aerogels obtained with varying amounts of DEDMS added;

FIG. 10 is a graph showing the stress-strain curves of silica aerogels obtained by adding ammonia water of different concentrations.

Detailed Description

The invention is described in detail below with reference to the figures and the specific embodiments.

In one embodiment, a method for preparing a flexible silica aerogel comprises the following steps: weighing raw materials, wherein the molar ratio of TEOS, MTES, DEDMS, ethanol, water, CTAB, hydrochloric acid and ammonia water is 0.045:0.242:0.021:1.65:3.67:0.00027:0.00012:0.01, ethanol is absolute ethanol, water is deionized water, the concentration of hydrochloric acid is 0.12mol/L, and the concentration of ammonia water is 2.5mol/L.

S1, dissolving CTAB in a mixed solvent at the temperature of 40 ℃ to obtain a mixed solution, wherein the mixed solvent comprises ethanol, water and hydrochloric acid.

And S2, sequentially adding TEOS, MTES and DEDMS into the mixed solution under the stirring condition, carrying out hydrolysis reaction, and mixing and stirring to obtain the silica sol.

And S3, dropwise adding ammonia water into the silica sol under the stirring condition, carrying out polycondensation reaction, and mixing and stirring to obtain the silica gel.

And S4, aging the silicon dioxide gel at the aging temperature of 40 ℃ for 4h, washing the silicon dioxide gel with absolute ethyl alcohol for three times, then drying the silicon dioxide gel in sections, firstly drying the silicon dioxide gel for 1h at the temperature of 50 ℃, and then drying the silicon dioxide gel for 2h at the temperature of 70 ℃ to obtain the flexible silicon dioxide aerogel.

The obtained flexible silica aerogel is observed by a scanning electron microscope, and as a result, referring to fig. 1, the obtained aerogel has a coarsened skeleton, the silica clusters are very tightly connected, and gaps are hardly seen.

The second embodiment is a preparation method of the flexible silica aerogel, the raw material component ratio, the hydrolysis reaction and the polycondensation reaction are the same as those in the first embodiment, except that the aging treatment and the drying treatment are carried out, the aging temperature of the aging treatment is 30 ℃, the aging time is 6 hours, and the drying treatment specifically comprises the following steps: drying is carried out firstly at a temperature of 40 ℃ for 2h and then at a temperature of 60 ℃ for 3h. And observing the obtained flexible silicon dioxide aerogel by using a scanning electron microscope, wherein the aerogel framework is of a coarsened structure.

Embodiment three, a preparation method of a flexible silica aerogel, the raw material component ratio, hydrolysis reaction, and polycondensation reaction operations are the same as those of embodiment one, except for aging treatment and drying treatment, the aging temperature of the aging treatment is 50 ℃, the aging time is 3 hours, and the drying treatment specifically comprises: drying is carried out firstly at a temperature of 45 ℃ for 1.5h and then at a temperature of 80 ℃ for 1h. And observing the obtained flexible silica aerogel by adopting a scanning electron microscope, wherein the aerogel framework is of a coarsening structure.

Example four, a method for preparing a flexible silica aerogel, hydrolysis, polycondensation, aging, and drying are the same as in example one, except for the raw material ratios, the molar ratio of TEOS, MTES, DEDMS, ethanol, water, CTAB, hydrochloric acid, and ammonia is 0.04:0.245:0.025:1.6:3.6:0.0003:0.0001:0.008, and the concentration of ammonia water is 3mol/L. And observing the obtained flexible silica aerogel by adopting a scanning electron microscope, wherein the aerogel framework is of a coarsening structure.

Example five, a preparation method of a flexible silica aerogel, hydrolysis reaction, polycondensation reaction, aging treatment and drying treatment are the same as in example one, except that the raw material ratio is that the molar ratio of TEOS, MTES, dedims, ethanol, water, CTAB, hydrochloric acid and ammonia water is 0.05:0.238:0.016:1.63:3.67:0.00028:0.00013:0.012 and the ammonia concentration was 2mol/L. And observing the obtained flexible silica aerogel by adopting a scanning electron microscope, wherein the aerogel framework is of a coarsening structure.

The sixth embodiment is a method for preparing a flexible silica aerogel, in which the hydrolysis reaction, the polycondensation reaction, the aging treatment, and the drying treatment are the same as those of the first embodiment, except that the raw material ratio is that the molar ratio of TEOS, MTES, DEDMS, ethanol, water, CTAB, hydrochloric acid, and ammonia water is 0.042:0.245:0.024:1.65:3.68:0.00026:0.00012:0.011, and the concentration of ammonia water is 2.1mol/L. And observing the obtained flexible silica aerogel by adopting a scanning electron microscope, wherein the aerogel framework is of a coarsening structure.

Example seven, the effect of the amount of DEDMS added on the flexible silica aerogel structure was analyzed.

DEDMS with different contents is added according to the mixture ratio in the table 1, and the rest conditions are the same as the first embodiment.

TABLE 1 silica aerogels with different DEDMS contents

	TEOS	MTES	DEDMS	Ethanol	Water (I)	CTAB	Hydrochloric acid	Ammonia water
									Example one	0.045	0.242	0.021	1.65	3.67	0.00027	0.00012	0.01
Comparative example 1	0.045	0.251	0.012	1.65	3.67	0.00027	0.00012	0.01
									Comparative example No. two	0.045	0.233	0.03	1.65	3.67	0.00027	0.00012	0.01
Comparative example No. three	0.045	0.224	0.039	1.65	3.67	0.00027	0.00012	0.01

The silica aerogel structures of comparative example one, comparative example two, and comparative example three were observed with a scanning electron microscope, respectively, and the results are shown in fig. 2 to 4. As can be seen from fig. 2, when the amount of the DEDMS is too small, effective connection between the silica clusters cannot be formed, the aerogel framework is formed by stacking a large amount of fragmented silica clusters, the connection between the silica clusters is loose, and a large number of gaps exist, so that a coarsened aerogel framework structure cannot be formed. As shown in fig. 3, when the amount of DEDMS is too large, the silica clusters further react to form smooth secondary spherical particles, and the interface between the spherical particles is recessed, which weakens the connection function of the aerogel skeleton. As the amount of DEDMS added is further increased, the depressions between the secondary spherical particles in fig. 4 are further deepened as compared with fig. 3, indicating that the connection of the aerogel skeleton is further weakened.

Mechanical property tests were performed on the first example, the first comparative example, the second comparative example, and the third comparative example, respectively, to obtain corresponding stress-strain curves, and the results are shown in fig. 9. As can be seen from fig. 9, as the addition ratio of the dms increases, the compressible content of the silica aerogel increases and then decreases, and when the molar ratio of the dms addition is 0.021, the compressible content reaches 78.2%, which is far higher than that corresponding to other ratios. In addition, the young's moduli of the four groups of samples were 45kPa, 14kPa, 17kPa, and 20kPa, respectively, as the addition ratio was increased, and when the molar ratio of the addition amount of DEDMS was 0.021, the young's modulus was the smallest, indicating that the flexibility of the silica aerogel reached a high level at this time.

Example eight, the effect of ammonia addition on the flexible silica aerogel structure was analyzed.

Ammonia water with different contents and different concentrations is added according to the mixture ratio in the table 2, and the other conditions are the same as the first embodiment.

TABLE 2 silica aerogels with different contents and concentrations of ammonia

	MTES	Aqueous ammonia	Concentration of ammonia
				Example one	0.242	0.01	2.5mol/L
Comparative example No. four	0.242	0.002	0.5mol/L
				Comparative example five	0.242	0.018	4.5mol/L
Comparative example six	0.242	0.026	6.5mol/L
				Comparative example seven	0.242	0.034	8.5mol/L

The other component ratios not listed in table 2 were the same as in example one.

The silica aerogel structures of comparative examples four to seven were observed with a scanning electron microscope, respectively, and the results are shown in fig. 5 to 8. As can be seen from fig. 5, when the amount of ammonia added is too small and the concentration is low, the polycondensation reaction of the system is insufficient due to the too small amount of ammonia, so that a complete three-dimensional network structure cannot be formed, i.e., a firm aerogel skeleton structure cannot be formed. As can be seen from fig. 6, when the amount of ammonia added is too large and the concentration is high, the aerogel skeleton becomes significantly thinner and the secondary particles become significantly smaller compared to fig. 5. The higher concentration ammonia water promotes the condensation polymerization reaction rate, so that the aerogel framework has not yet formed a complete structure and becomes a gel state, and more gaps exist among secondary particles. As can be seen from fig. 7, with further increase of the ammonia water, the polycondensation reaction of the system is further accelerated, so that the secondary particles do not grow sufficiently to form a gel, and the aerogel skeleton is formed by aggregation of fine secondary particles. As can be seen from fig. 8, the silica skeleton was formed by aggregating finer particles as the amount of ammonia water was further increased.

And respectively carrying out mechanical property tests on the comparative example four, the comparative example five and the comparative example six of ammonia water with different concentrations to obtain corresponding stress-strain curves, and obtaining the results shown in the figure 10. As can be seen from FIG. 10, the compressible amount of the sample was the largest, i.e., 78.2%, when the ammonia water concentration was 2.5mol/L. Along with the increase of the ammonia water concentration, the corresponding Young modulus is respectively 38kPa, 14kPa, 32kPa and 79kPa, which shows that the flexibility of the silicon dioxide aerogel reaches a higher level when the ammonia water concentration is 2.5mol/L.

The above description is only for the preferred embodiment of the present invention and is not intended to limit the present invention, but all equivalent variations and modifications made according to the present invention should be included in the protection scope of the present invention.

Claims

1. The preparation method of the flexible silica aerogel is characterized by comprising the following steps of:

s1, dissolving CTAB in a mixed solvent at the temperature of 30-50 ℃ to obtain a mixed solution, wherein the mixed solvent comprises ethanol, water and hydrochloric acid, and the molar ratio of CTAB, ethanol, water and hydrochloric acid is 0.00024-0.0003: 1.6 to 1.7:3.6 to 3.7:0.0001 to 0.00015;

s2, sequentially adding TEOS, MTES and DEDMS into the mixed solution under the stirring condition, and mixing and stirring to obtain silica sol, wherein the molar ratio of TEOS, MTES, DEDMS to hydrochloric acid in the mixed solution is 0.04 to 0.05:0.235 to 0.245:0.015 to 0.025:0.0001 to 0.00015;

s3, dropwise adding ammonia water with the concentration of 2-3mol/L into the silica sol under the stirring condition to obtain silica gel;

the molar ratio of the ammonia to the DEDMS added in the S2 is 0.008 to 0.012:0.015 to 0.025;

2. The method for preparing a flexible silica aerogel according to claim 1, characterized in that: the concentration of hydrochloric acid in the S1 is 0.08 to 0.15mol/L.

3. The method for preparing a flexible silica aerogel according to claim 1 or 2, characterized in that: the aging temperature of the aging treatment in the S4 is 30 to 50 ℃, and the aging time is 3 to 6h.

4. The method for preparing a flexible silica aerogel according to claim 1 or 2, wherein the drying in S4 is specifically: drying for 1 to 2h under the temperature of 40 to 50 ℃, and then drying for 1 to 3h under the temperature of 60 to 80 ℃.

5. The method for preparing a flexible silica aerogel according to claim 1 or 2, characterized in that: the ammonia water concentration in the S3 is 2.5mol/L.

6. The method for preparing a flexible silica aerogel according to claim 1 or 2, characterized in that: the molar ratio of ammonia in the S3 and DEDMS added by the S2 is 0.01:0.021.