Aerogel with stable mechanical properties and preparation method thereof
阅读说明：本技术 机械性能稳健的气凝胶及其制备方法 (Aerogel with stable mechanical properties and preparation method thereof ) 是由 法蒂玛·帕沙伊·苏巴吉 于 2018-12-22 设计创作，主要内容包括：本发明披露了用于制备超韧纳米复合气凝胶的组合物和方法。该超韧纳米复合气凝胶可包括至少一种填料在气凝胶中的分散体。该方法用于通过保留气凝胶的微观结构和热特性来改善气凝胶的机械特性,因为添加填料使得机械特性提高而密度没有任何显著增加。(Compositions and methods for preparing super tough nanocomposite aerogels are disclosed. The super tough nanocomposite aerogel can include a dispersion of at least one filler in the aerogel. This method is used to improve the mechanical properties of the aerogel by preserving its microstructure and thermal properties, since the addition of fillers allows the mechanical properties to be increased without any significant increase in density.)
1. A method for preparing a super tough nanocomposite silica aerogel comprising:
preparing a pre-hydrolyzed silica precursor solution by hydrolyzing a silica precursor in a mixture of a solvent and a first acid catalyst;
obtaining a modified filler;
preparing a hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1 and 4pH levels with a second acid catalyst and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order, wherein the second acid catalyst comprises one or more of an organic acid and an inorganic acid;
preparing a silica-filler gel by adding a basic catalyst to the hydrolyzed silica-filler precursor solution; and
drying the silica-filler gel.
2. The method of claim 1, wherein the super tough nanocomposite silica aerogel is more than 600kJ/m3 tough and has a ross-rand extinction coefficient of at least 8500m "1.
3. The method of claim 1, wherein the silica precursor comprises one or more of rice hulls, aluminosilicates, silicates, alkoxysilanes, polysilylated organic molecules, silylated molecules, and water glass.
4. The method of claim 1, wherein the hydrolyzed silica-filler precursor solution comprises 0.1-60 weight percent of the modified filler of silica precursor in the silica-filler gel.
5. The method of claim 1, wherein the solvent comprises water or an alcohol-water mixture, the alcohol comprising one or more of methanol, ethanol, propanol, butanol and other alkanols.
6. The method of claim 1, wherein the first acid catalyst comprises one or more of oxalic acid, citric acid, and acetic acid.
7. The method of claim 1, wherein preparing a pre-hydrolyzed silica precursor solution by hydrolyzing a silica precursor in a mixture of a solvent and a first acid catalyst comprises preparing the pre-hydrolyzed silica precursor by stirring at 0-80 ℃ for 0.08-100 hours.
8. The method of claim 1, wherein preparing a hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1-4pH levels with a second acid catalyst and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order comprises preparing the hydrolyzed silica-filler precursor solution by stirring at 0-80 ℃ for 0.08-100 hours.
9. The method of claim 1, wherein obtaining the modified filler comprises:
obtaining a surface functionalized filler by introducing functional groups onto the filler surface, the filler comprising one or more of graphene, graphite, clay, alumina, titania, zirconia, silica, silicon carbide, metal oxides, semimetal oxides, layered double hydroxides, silicates, and aluminosilicates, wherein the functional groups comprise hydroxyl groups, hydroxyl-terminated organic molecules, hydroxyl-terminated organo-minerals;
obtaining a surface-functionalized filler suspension by adding the surface-functionalized filler to a mixture of an alcohol and an oligomer under stirring for 0.08-24 hours or sonication for 0.08-3 hours, wherein the oligomer comprises at least one of an organic polymer or an inorganic polymer having hydroxyl groups, the alcohol comprising one or more of methanol, ethanol, propanol, butanol and other alkanols; and
drying the surface-functionalized filler suspension, the drying comprising one or more of drying at ambient pressure in the range of 0.9 to 2 atmospheres, freeze drying, or supercritical drying.
10. The method of claim 1, wherein the basic catalyst comprises one or more of an alkaline earth metal hydroxide, an alkali metal hydroxide, and ammonia.
11. The method of claim 1, wherein drying the silica-filler gel comprises drying using one or more of ambient pressure drying, freeze drying, or supercritical drying at a pressure of 0.9-2 atmospheres.
12. A method for preparing a super tough nanocomposite silica aerogel comprising:
preparing a pre-hydrolyzed silica precursor solution by hydrolyzing a silica precursor in a mixture of a solvent and a first acid catalyst;
obtaining a modified filler;
preparing a hydrolyzed silica-filler precursor solution by reducing the pH level of the pre-hydrolyzed silica precursor solution to a pH level of about 0.1 to 4 with a second acid catalyst and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order;
preparing a silica-filler gel by adding a basic catalyst to the hydrolyzed silica-filler precursor solution;
preparing a modified silica-filler gel by aging the silica-filler gel under given conditions comprising a temperature ranging from 30 ℃ to 120 ℃ and a pressure ranging from 0.9 to 5 atmospheres for 1 to 1000 hours;
hydrophobizing the silica-filler gel; and
drying the modified silica-filler gel, the super tough silica aerogel having a toughness in excess of 600kJ/m3 and a Rossler extinction coefficient of at least 8500 m-1.
13. The method of claim 12, wherein hydrophobizing the silica-filler gel comprises: adding a surface hydrophobizing agent to a solvent under agitation at 25 ℃ to 60 ℃ for 1 to 100 hours, wherein the surface hydrophobizing agent comprises Hexamethyldisilazane (HDMZ), Trimethylchlorosilane (TMCS), bis (trimethylsilylacetamide) (BTSA), methyltrimethoxysilane (MTMS), Methyltriethoxysilane (MTES), Vinyltrimethoxysilane (VTMS), Phenyltrimethoxysilane (PTES), dimethyldimethoxysilane (DMDS), trimethylmethoxysilane, Trimethylchlorosilane (TMCA), bis (trimethylsilylacetamide (BTSA), and any combination thereof, wherein the solvent comprises one or more of an alkanol and an aprotic solvent.
14. A super tough nanocomposite silica aerogel comprising:
at least one silica precursor; and
at least one modified filler;
wherein the super tough nanocomposite silica aerogel has a toughness in excess of 600kJ/m3 and a Rosslend extinction coefficient of at least 8500m-1, and a porosity of greater than about 90%.
15. The super tough nanocomposite silica aerogel of claim 14, wherein the breaking strain of the super tough silica aerogel is greater than 45%.
16. The super tough nanocomposite silica aerogel of claim 14, wherein the mechanical strength of the super tough silica aerogel is greater than 3.4 MPa.
17. The super tough nanocomposite silica aerogel of claim 14, wherein the thermal conductivity of the super tough silica aerogel is less than about 23mW/(m.k) at temperatures in the range of 20-300 ℃.
18. The super tough nanocomposite silica aerogel of claim 14, wherein the super tough silica aerogel has a mass loss of less than 10% at 600 ℃.
19. The super tough nanocomposite silica aerogel of claim 14, wherein the super tough silica aerogel has a porosity of greater than about 90% and a surface area of greater than about 700m2/g。
20. The super tough nanocomposite silica aerogel of claim 14, wherein the super tough silica aerogel has a uniform and monolithic structure.
Technical Field
The present invention relates generally to aerogels, and more particularly to a super tough aerogel having high porosity, and more particularly to a super tough aerogel having enhanced thermal properties and a method of making the same.
Background
Silica aerogels are nanoporous materials with excellent properties such as low thermal conductivity, low density, and high specific surface area. The microstructure of silica aerogel comprises interconnected nanoparticles and nanometer-sized pores that open up a pearl necklace network in three dimensions (3-D). The particular characteristics of these nanomaterials make them suitable for a variety of applications such as thermal insulation, acoustic insulation, drug delivery, catalysis and adsorption.
However, the mechanical strength, elastic modulus and therefore toughness of silica aerogels are much lower than that of dense silica; therefore, silica aerogel is easily broken when subjected to an external load. This drawback hinders the widespread use of silica aerogels. There are two conventional strategies that can improve the mechanical properties of silica aerogels.
The first conventional strategy may require the addition of an organic moiety or organic filler to improve the mechanical properties of the silica aerogel. Although the use of an organic moiety or an organic filler can improve the mechanical strength of the silica aerogel, the thermal stability is reduced due to the addition of the organic moiety, which further limits the high temperature applications of the silica aerogel.
Another mechanical reinforcement strategy may require the addition of inorganic fillers as reinforcing agents for silica aerogel networks. However, the addition of inorganic fillers to the silica aerogel network increases the density of the silica aerogel by a factor of two. Furthermore, when this method is used, the brittleness of the silica aerogel is retained, which results in a composite silica aerogel having low breaking strain.
On the other hand, the transparency of silica aerogel as a high temperature insulation at infrared wavelengths results in a dramatic increase in radiative heat transfer in high temperature insulation applications. This disadvantage is a disadvantage for high temperature applications of silica aerogels.
Therefore, there is a need to develop a new method for producing an infrared opaque and high mechanical strength silica aerogel having high toughness without losing thermal stability.
Disclosure of Invention
This summary is intended to provide an overview of the subject matter of this patent, and is not intended to identify key or critical elements of the subject matter or to delineate the scope of the claimed implementations. The proper scope of the present patent can be determined from the claims set forth below in view of the following detailed description and the attached drawings.
In one general aspect, the present disclosure is directed to an exemplary method for preparing a super tough nanocomposite silica aerogel. The method may include preparing a pre-hydrolyzed silica precursor solution by hydrolyzing a silica precursor in a mixture of a solvent and a first acid catalyst; obtaining a modified filler, preparing a hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1 and 4pH levels with a second acid catalyst, which may include one or more of an organic acid and an inorganic acid, and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order; preparing a silica-filler gel by adding a basic catalyst to the hydrolyzed silica-filler precursor solution, and drying the silica-filler gel.
The general aspects described above may have one or more of the following features. In exemplary embodiments, the silica precursor may include one or more of rice hulls, aluminosilicates, silicates, alkoxysilanes, polysilylated organic molecules, silylated molecules, and water glass. In exemplary embodiments, the hydrolyzed silica-filler precursor solution may include 0.1 to 60 weight percent of the modified filler of the silica precursor in the silica-filler gel.
Further, in exemplary embodiments, the solvent may comprise water or an alcohol-water mixture, and the alcohol may comprise one or more of methanol, ethanol, propanol, butanol, and other alkanols. In an exemplary embodiment, the first acid catalyst may include one or more of oxalic acid, citric acid, and acetic acid. In addition, in an exemplary embodiment, preparing a pre-hydrolyzed silica precursor solution by hydrolyzing a silica precursor in a mixture of a solvent and a first acid catalyst may include preparing the pre-hydrolyzed silica precursor by stirring at 0 to 80 ℃ for 0.08 to 100 hours. In an exemplary embodiment, preparing a hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1 and 4pH levels with a second acid catalyst and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order may include preparing the hydrolyzed silica-filler precursor solution by stirring at 0-80 ℃ for 0.08-100 hours. In an exemplary embodiment, obtaining a modified filler comprises obtaining a surface functionalized filler by introducing functional groups to the surface of the filler, the filler comprising one or more of graphene, graphite, clay, alumina, titania, zirconia, silica, silicon carbide, metal oxides, semimetal oxides, layered double hydroxides, silicates, and aluminosilicates, wherein the functional groups comprise hydroxyl groups, hydroxyl-terminated organic molecules, hydroxyl-terminated organo-minerals, by adding the surface functionalized filler to a mixture of an alcohol comprising at least one of an organic polymer or an inorganic polymer having hydroxyl groups, or an alcohol comprising methanol, ethanol, propanol, or an aluminosilicate, with stirring for 0.08 to 24 hours or sonication for 0.08 to 3 hours, to obtain a surface functionalized filler suspension, One or more of butanol and other alkanols; drying the surface-functionalized filler suspension, and the drying includes one or more of drying at ambient pressure in the range of 0.9 to 2 atmospheres, freeze drying, or supercritical drying. In exemplary embodiments, the basic catalyst comprises one or more of an alkaline earth metal hydroxide, an alkali metal hydroxide, and ammonia. In an exemplary embodiment, drying the silica-filler gel comprises drying using one or more of ambient pressure drying, freeze drying, or supercritical drying at a pressure of 0.9 to 2 atmospheres.
In another general aspect, the present disclosure relates to a super tough nanocomposite silica aerogel comprising at least one silica precursor and at least one modified fillerThe super-tough nano composite silicon dioxide aerogel has the thickness of more than 600kJ/m3Has a toughness of at least 8500m-1Has a ross-rand extinction coefficient with a porosity greater than about 90%. The general aspects described above may have one or more of the following features. In exemplary embodiments, the breaking strain of the super tough silica aerogel may be greater than 45%. In exemplary embodiments, the super tough silica aerogel may have a mechanical strength of greater than 3.4 MPa. In exemplary embodiments, the thermal conductivity of the super tough silica aerogel at temperatures in the range of 20 ℃ to 300 ℃ can be less than about 23 mW/(m.k). Further, in exemplary embodiments, the super tough silica aerogel can have a mass loss of less than 10% at 600 ℃. In exemplary embodiments, the super tough silica aerogel can have a porosity of greater than about 90% and a surface area of greater than about 700m2(ii) in terms of/g. In exemplary embodiments, the ultra-tough silica aerogel may have a homogeneous and monolithic structure.
In another general aspect, the present disclosure is directed to an exemplary method for preparing a super tough nanocomposite silica aerogel. The method may include preparing a pre-hydrolyzed silica precursor solution by hydrolyzing a silica precursor in a mixture of a solvent and a first acid catalyst; obtaining a modified filler, preparing a hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1 and 4pH levels with a second acid catalyst, which may include one or more of an organic acid and an inorganic acid, and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order; preparing a silica-filler gel by adding a basic catalyst to the hydrolyzed silica-filler precursor solution, preparing a modified silica-filler gel by aging the silica-filler gel under given conditions including a temperature ranging from 30 ℃ to 120 ℃ and a pressure ranging from 0.9 to 5 atmospheres for 1 to 1000 hours, hydrophobizing the silica-filler gel, and drying the modified silica-filler gel.
The general aspects described above may have one or more of the following features. In exemplary embodiments, hydrophobizing the silica-filler gel may include adding a surface hydrophobizing agent including Hexamethyldisilazane (HDMZ), Trimethylchlorosilane (TMCS), bis (trimethylsilylacetamide) (BTSA), methyltrimethoxysilane (MTMS), Methyltriethoxysilane (MTES), Vinyltrimethoxysilane (VTMS), Phenyltrimethoxysilane (PTES), dimethyldimethoxysilane (DMDS) trimethylmethoxysilane, Trimethylchlorosilane (TMCA), bis (trimethylsilylacetamide (BTSA), and any combination thereof, to a solvent including one or more alkanols and aprotic solvents with stirring at 25 ℃ to 60 ℃ for 1 to 100 hours.
Drawings
The drawings depict one or more implementations in accordance with the present teachings, by way of example only, and not by way of limitation. In the drawings, like reference numerals designate identical or similar elements.
FIG. 1A
FIG. 1A illustrates a method of producing a super tough nanocomposite silica aerogel, consistent with one or more exemplary embodiments of the present invention.
FIG. 1B
Fig. 1B shows a method of obtaining a modified filler according to one or more exemplary embodiments of the invention.
FIG. 2
FIG. 2 illustrates a method of preparing a super tough nanocomposite silica aerogel, consistent with one or more exemplary embodiments of the present invention.
FIG. 3
Fig. 3 shows a Scanning Electron Microscope (SEM) image of an embodiment of a modified clay consistent with one or more exemplary embodiments of the present invention.
FIG. 4A
Fig. 4A shows a photograph of an implementation of a silica-clay gel consistent with one or more exemplary embodiments of the present invention.
FIG. 4B
Figure 4B shows a photograph of an embodiment of a nanocomposite aerogel, consistent with one or more exemplary embodiments of the present invention.
FIG. 5A
Fig. 5A shows a Scanning Electron Microscope (SEM) image of an embodiment of a pristine aerogel, consistent with one or more exemplary embodiments of the present disclosure.
FIG. 5B
Fig. 5B shows a Scanning Electron Microscope (SEM) image of an embodiment of a nanocomposite aerogel (5 wt.% modified clay) consistent with one or more exemplary embodiments of the present invention.
FIG. 6
Figure 6 shows the pore size distribution of embodiments of samples including neat aerogel and nanocomposite aerogel (containing 4, 5, and wt.% modified clay), consistent with one or more exemplary embodiments of the present invention.
FIG. 7
Figure 7 shows the ross-rand average extinction coefficients of embodiments of samples including neat and nanocomposite aerogels (containing 4, 5, and wt.% of modified clay) consistent with one or more exemplary embodiments of the present invention.
Detailed Description
In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it is understood that the present teachings may be practiced without these details. In other instances, well known methods, procedures, components, and/or circuits have been described in relatively high-level, but not in detail, to avoid unnecessarily obscuring aspects of the present teachings. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined only by the appended claims.
An object of exemplary embodiments of the present invention is to improve mechanical properties of silica aerogels, and particularly to prepare silica aerogels having high porosity and thermal stability. Exemplary methods increase the failure strain and reduce the brittleness of silica aerogels and produce the preparation of ultra-tough aerogels having a wide range of densities, particularly low-density and infrared-opaque silica aerogels. Some benefits of this exemplary method may include, but are not limited to, the preparation of super tough nanocomposite aerogels with improved thermal stability and improved radiation extinction coefficients.
The use of the exemplary method results in a highly efficient method for preparing nanocomposite aerogels based on five main steps including prehydrolysis of a silica precursor solution under acidic conditions to obtain a modified filler, dispersing the modified filler in the prehydrolysis silica precursor solution, hydrolyzing the silica filler precursor solution by lowering the pH, preparing a silica-filler gel from the silica-filler precursor solution by gelling under alkaline conditions, followed by drying under specific conditions. The primary benefit of utilizing the exemplary method may include applying two hydrolysis steps before and after the addition of the filler, respectively, to minimize disruption of the filler during hydrolysis of the silica precursor solution. Some other benefits of utilizing the exemplary method can include developing an effective method of surface functionalizing fillers using surface functional groups to improve the dispersibility of the filler in silica aerogels. In an exemplary method, the surface functionalized filler may be obtained by introducing functional groups onto the surface of the filler and mixing with a mixture of an alcohol and an oligomer, followed by drying under specific conditions. The oligomer may include one or more organic or inorganic polymers having hydroxyl groups. The alcohol may include one or more of methanol, ethanol, propanol, and other alkanols. In exemplary embodiments, the specific conditions of the drying may include one or more of drying at ambient pressure in the range of 0.9-2 atmospheres, freeze drying, or supercritical drying.
Some benefits of utilizing the exemplary method may include, but are not limited to, developing an efficient method for aerogel aging and hydrophobization.
Throughout the disclosure, the term "nanocomposite aerogel" refers to an aerogel containing fillers having one, two, or three dimensions of less than 1000 nanometers (nm). The packing may be of any shape, including plates, tubes, rods, or any combination thereof.
Throughout this disclosure, the term "toughness" refers to the energy that an aerogel can absorb per unit volume before failing. Toughness can be determined by the integrated stress-strain curve according to equation 1:
[ equation 1]
In which it is the strain that is present,fis the strain at failure and σ is the stress.
Throughout this disclosure, the term "ultra-tough" means having a tenacity greater than 300kJ/m3The tough material of (1).
In an exemplary embodiment, the bulk density of the sample can be measured using a mass to volume ratio.
In an exemplary embodiment, the term "porosity" may be calculated by:
[ equation 2]
Where ρ isaIs the density of the silica aerogel, and ρsIs the density of the bulk silica.
In an exemplary embodiment, the temperature dependence of radiative heat transfer may be calculated by the diffusion approximation equation:
[ equation 3]
Wherein sigmaBIs equal to 5.6704 × 10-8Wm-2K-4Is the Stefin Boltzmann constant, T is the temperature, paIs the density of the aerogel, n is the refractive index, and KλIs the ross extinction coefficient.
Throughout this disclosure, the term aerogel refers to a porous solid with a porosity greater than 60%, wherein greater than 30% of the pores are less than 1 micron.
In an exemplary embodiment, the average extinction coefficient of rossland depends on the inherent properties of the material, such as, but not limited to, silica and silica-filled aerogels, the electromagnetic wavelength of the incident wave, and the temperature of the material. Silica aerogels are transparent in the wavelength range below 25 μm. Thus, infrared wavelengths below 25 μm may cover the transparent region. The extinction coefficient can be calculated using equation 4:
[ equation 4]
Wherein ebλAnd ebRespectively, the total and spectral emission power of the black body.
In addition, kλIs spectral extinction, and kλRepresents the average extinction coefficient of rossland.
kλIs calculated using the light transmission for each wavelength. Equation 4 is applied in the infrared range below 25 μm.
Exemplary silica aerogels prepared using the exemplary methods can be used as thermal insulators due to their low thermal conductivity and high thermal stability. The high thermal stability of exemplary silica aerogels makes them useful in fire protection applications for refractory materials and buildings. Furthermore, exemplary nanocomposite silica aerogels exhibit high mechanical strength and can be suitable where high mechanical strength is an essential requirement. In addition, exemplary silica aerogels can be used to make aerogel blankets and can be used as sound insulation. Due to the high specific surface area, exemplary silica aerogels can also be used as absorbents, such as, but not limited to, absorbents used in air and water purification. In exemplary embodiments, exemplary silica aerogels can be used in powder, monolithic form.
Preparation of aerogels
In one exemplary embodiment, sol-gel preparation may require two different methods, including a one-step method using a basic or acidic catalyst and another method is a two-step method using an acidic catalyst followed by a basic catalyst. Since the condensation and hydrolysis reactions may be pH dependent, the pore morphology may be different for each of the above methods.
In exemplary embodiments, after the polymerization stage, an exemplary aging step may be added to the manufacturing process in order to improve the mechanical properties of the weak solid backbone of the gel and complete the polymerization stage. In some cases, after the gel is formed, the surface modification of the silica aerogel may be performed by using one of surface modifiers including a surfactant, a crosslinking developer, and an organic template.
In addition, surface modifiers may be used to minimize shrinkage of the gel and prevent breakage by reducing capillary forces.
Various exemplary methods may be utilized to dry these materials. These methods may include: supercritical drying, ambient pressure drying and freeze drying. Supercritical drying can be based on placing the sol-gel at the supercritical point of the solvent and extracting the solvent at that point. Above the supercritical point, there is no surface tension, and therefore, the solution can be extracted without breaking the solution. Therefore, in this exemplary method, solvent extraction can be performed with high quality as compared with the conventional method.
Preparation of super-tough silica aerogel nanocomposite
The preparation of nanocomposites can be used to improve the mechanical and thermal properties of many materials. However, improving the mechanical and thermal properties of nanocomposites depends to a large extent on the filler dispersion method. The filler dispersion in the nanocomposite can be adjusted by using an appropriate filler modification method. Exemplary silica aerogels can have a porous structure and a fine structure, which can result in excellent characteristics, such as high porosity and high specific surface area. Since silica aerogels have a good microstructure, any change in the sol-gel process (e.g., the addition of fillers) can negatively impact the quality of the silica aerogel. The addition of fillers can affect the sol-gel process by hindering the completion of the hydrolysis and gelling process. Thus, in some cases, the porosity and surface area of the silica aerogel may be reduced due to the addition of the filler. Therefore, there is a need to develop an improved sol-gel method to prepare silica nanocomposite aerogels by maintaining and improving the characteristics of silica aerogels in the presence of fillers.
In exemplary embodiments, fig. 1A illustrates a method of making a super tough nanocomposite silica aerogel, consistent with one or more exemplary embodiments of the present disclosure
In detail, the exemplary method 100 may include producing a pre-hydrolyzed silica precursor solution by hydrolyzing a silica precursor in a mixture of a solvent and a first acid catalyst (step 102); obtaining a modified filler (step 104), preparing a pre-hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1 and 4pH levels with a second acid catalyst and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order (step 106), preparing a silica-filler gel by adding a basic catalyst to the hydrolyzed silica-filler precursor solution (step 108), and drying the silica-filler gel (step 110).
Further to step 102, preparing the pre-hydrolyzed silica precursor solution may include stirring at 0 ℃ to 80 ℃ for 0.08 to 100 hours. In exemplary embodiments, the silica precursor may include one or more of rice hulls, aluminosilicates, silicates, alkoxysilanes, polysilylated organic molecules, silylated molecules, and water glass. Furthermore, the solvent may comprise water or an alcohol-water mixture and the alcohol may comprise one or more of methanol, ethanol, propanol, butanol and other alkanols. The first acid catalyst may include one or more of oxalic acid, citric acid, and acetic acid.
With respect to step 104, obtaining the modified filler may be performed by method 112 of FIG. 1B. Fig. 1B illustrates a method of making a modified filler consistent with one or more exemplary embodiments of the present disclosure. Exemplary method 112 may include obtaining a surface functionalized filler by introducing functional groups onto the surface of the filler (step 114), adding the surface functionalized filler to a mixture of alcohol and oligomer by stirring for 0.08-24 hours or sonication for 0.08-3 hours to obtain a surface functionalized filler suspension (step 116), and drying the surface functionalized filler suspension (step 118).
Further to step 114, introducing functional groups onto the surface of the filler may include adding at least one functional group, such as, but not limited to, hydroxyl and hydroxyl-terminated molecules, to the surface of the filler to alter its surface characteristics and facilitate its dispersion in the silica precursor solution. In exemplary embodiments, the filler comprises one or more of graphene, graphite, clay, alumina, titania, zirconia, silica, silicon carbide, metal oxides, semimetal oxides, layered double hydroxides, silicates, and aluminosilicates.
Further to step 116, the oligomer can include at least one of an organic polymer or an inorganic polymer having hydroxyl groups, and the alcohol can include one or more of methanol, ethanol, propanol, butanol, and other alkanols.
Further to step 118, drying the surface-functionalized filler suspension may include one or more of: drying at 0.9-2 atmospheric pressure, freeze drying or supercritical drying. With further reference to step 106 of fig. 1A, preparing the hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1-4pH levels with a second acid catalyst and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order includes lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1-4pH levels by adding a second acid catalyst to the pre-hydrolyzed silica precursor solution. In exemplary embodiments, the second acid catalyst may include one or more of an organic acid and an inorganic acid, and the modified filler may be in the range of 0.1 to 60 weight percent of the silica precursor in the silica-filler gel.
Further, preparing the hydrolyzed silica-filler precursor solution by lowering the pH level of the pre-hydrolyzed silica precursor solution to between 0.1 and 4pH levels with a second acid catalyst and dispersing the modified filler in the pre-hydrolyzed silica precursor solution in any order comprises stirring for 0.08 to 100 hours at 0 to 80 ℃.
Further to step 108, preparing the silica-filler gel by adding a basic catalyst to the hydrolyzed silica-filler precursor solution may include preparing the silica-filler gel by adding one or more alkaline earth metal hydroxides, alkali metal hydroxides, and ammonia.
Further, with respect to claim 110, the dry silica-filler gel may include one or more of: ambient pressure drying, freeze drying or supercritical drying is carried out under a pressure of 0.9-2 atm.
Fig. 2 illustrates a method of making a super tough nanocomposite silica aerogel, consistent with one or more exemplary embodiments of the present disclosure.
In detail, the
Further, relative to
Further to step 210, preparing the modified silica-filler gel by aging the silica-filler gel under given conditions may include maintaining the silica-filler gel at a temperature ranging from 30 ℃ to 120 ℃ and at a pressure ranging from 0.9 to 5 atmospheres for 1 to 1000 hours to achieve mechanical improvement of the polymerization process and structure of the silica-filler gel.
Further to step 212, the hydrophobizing of the silica-filler gel may include adding the surface hydrophobizing agent to the solvent at 25 ℃ to 60 ℃ for 1 to 100 hours with stirring. In exemplary embodiments, the surface hydrophobizing agent may include Hexamethyldisilazane (HDMZ), Trimethylchlorosilane (TMCS), bis (trimethylsilylacetamide) (BTSA), methyltrimethoxysilane (MTMS), Methyltriethoxysilane (MTES), Vinyltrimethoxysilane (VTMS), Phenyltrimethoxysilane (PTES), dimethyldimethoxysilane (DMDS), trimethylmethoxysilane, Trimethylchlorosilane (TMCS), bis (trimethylsilylacetamide (BTSA), and any combination thereof.
In an exemplary embodiment, the solvent of the silica precursor solution may comprise water or an alcohol-water mixture, the alcohol may comprise one or more of methanol, ethanol, propanol, butanol and other alkanols, wherein the mass ratio of water in the alcohol-water mixture is between 10% and 100%.
In exemplary embodiments, the hydrolyzed silica-filler precursor solution may include silica precursors in the range of 0.1 to 60 weight percent of the hydrolyzed silica-filler precursor solution.
In exemplary embodiments, the surface hydrophobizing agent may be in the range of 0.5-50 wt% of the solvent.
In exemplary embodiments, the solvent for supercritical drying may include carbon dioxide, water, or alcohols including methanol, ethanol, propanol, butanol, and other alkanols.
In exemplary embodiments, the filler includes one or more of graphene, graphite, clay, alumina, titania, zirconia, silica, silicon carbide, metal oxides, semimetal oxides, layered double hydroxides, silicates, aluminosilicates, and other mineral fillers.
In an exemplary embodiment, the clay may be selected from the group consisting of: montmorillonite, halloysite, kaolinite, bentonite, hectorite or any type of clay.
In exemplary embodiments, characterization methods including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), brunauer-emitt-teller (bet), Barrett-Joyner-halenda (bjh), universal tensile tester, or hot wire method may be used to assess the morphology, microstructure analysis, specific surface area, pore size distribution, mechanical properties, thermal conductivity of the nanocomposite as described in the examples below.
Examples of the invention
Example 1: preparation of modified Clay
In example 1, a modified clay was prepared consistent with the teachings of the exemplary embodiments of the present disclosure. In this example, using the exemplary method 112 of fig. 1B, a 5 wt.% suspension of Cloisite 30B in alcohol was prepared. Then, 0.25% hydroxyl-terminated poly (dimethylsiloxane) (PDMS) was added to the suspension. The suspension was kept stirring at 60 ℃ overnight and then the solvent was removed by a freeze-drying process.
Fig. 3 shows a Scanning Electron Microscope (SEM) image of an embodiment of a modified clay consistent with one or more exemplary embodiments of the present disclosure.
It can be seen that, using this exemplary method, a layered structure is formed in the modified clay. The thickness of the layers is less than 30nm and the distance between the layers is greater than 200 nm.
Example 2: preparation of neat aerogels
In example 2, a neat aerogel was prepared using the exemplary method. In this example, by being in BSol-gel polymerization of Tetraethylorthosilicate (TEOS) in an alcohol/water mixture synthesizes a pure aerogel. The amount of acidic catalyst is adjusted to reach a pH level equal to 3. Mole ratio of TEOS: ethanol (EtOH) H2O oxalic acid NH4OH fixed at 1:6.5:6:8.7*10-4:3*10-4. Hydrolysis was carried out overnight at 60 ℃ with stirring. After hydrolysis, the remaining H is2O was mixed with ethanol and basic catalyst in another beaker and the two solutions were combined and poured into a cylindrical mold where the sol was solidified into a neat aerogel. The solvent of the purified gel was exchanged with ethanol 3 times by immersing the purified gel in pure ethanol.
Thereafter, aging of the neat gel was carried out at 50 ℃ for 24 hours. The hydrophobization of the neat gel was carried out using a 3% solution of TMCS in ethanol at 60 ℃ for 24 hours. This process was repeated three times. The ratio of TEOS/TMCS was fixed at 1: 2. Finally, the sample was dried using a supercritical carbon dioxide drying chamber.
Example 3: three-step sol-gel process
In example 3, nanocomposite aerogels were prepared consistent with the teachings of the exemplary embodiments of the present disclosure. In this example, the illustrative method 120 of fig. 1C is utilized to pre-hydrolyze a mixture comprising TEOS to EtOH in a 1:3:3 ratio at 60 ℃: h2And preparing the nano composite aerogel from the solution of O and oxalic acid for 1 hour. After adding the modified clay to the solution, oxalic acid was added and the pH of the solution was adjusted to 2.5. The suspension was then hydrolyzed at 60 ℃ overnight. The amount of modified clay is selected to be 4 wt.%, 5 wt.%, or 6 wt.% based on the total silica content in the sol. The remaining ethanol, water and alkaline catalyst are then mixed and combined with the hydrolyzed suspension and poured into a cylindrical mold where the sol cures into a silica-clay gel. The solvent of the pure silica-clay gel was exchanged with ethanol 3 times by immersing the pure silica-clay gel in pure ethanol
The silica-clay gel was aged at 50 ℃ for 24 hours. Hydrophobization of the silica-clay gel was carried out using a 3 wt.% solution of TMCS in ethanol at 60 ℃ for 24 hours. This process was repeated three times. The ratio of TEOS/TMCS was fixed at 1: 2. Finally, the sample was dried using a supercritical carbon dioxide drying process.
Fig. 4A shows a photograph of an implementation of a silica-clay gel consistent with one or more exemplary embodiments of the present disclosure. Fig. 4B shows a photograph of an embodiment of a nanocomposite aerogel, consistent with one or more exemplary embodiments of the present disclosure. Fig. 4A and 4B show that exemplary nanocomposite aerogels are monolithic and homogeneous.
Example 4: material characterization
In this example, the results of certain characterization methods performed on exemplary neat aerogels and nanocomposite aerogels (as prepared in detail in connection with examples 1, 2, and 3) are presented.
Table 1 shows the physical properties of the samples, including contact angle, porosity and bulk density. The bulk densities reported herein are obtained by measuring the weight to volume ratio of the sample.
All samples had high porosity and low density. These results show that by using the exemplary method, the addition of the modified clay results in dimensional stability of the samples to be preserved. To investigate the hydrophobicity of the samples, contact angle measurements were performed. As shown in table 1, all of the neat aerogel and nanocomposite aerogel counterparts have hydrophobic properties. In addition, the hydrophobicity of the sample was not significantly changed by the addition of the modified clay as a filler. However, as shown in table 1, there is no effect on the density using the exemplary method, since the modified filler has good dispersibility in the silica aerogel and retains the well-defined and interconnected microstructure of the silica aerogel in the presence of the modified filler, and thus the density of all samples is the same.
TABLE 1 physical Properties of hydrophobic samples
Table 2 lists XRD results for cloisite 30B and nanocomposite aerogels in the 2 theta range from 2 ° to 10 °. The main characteristic peak of cloisite 30B was observed as received at 4.7 ° 2 θ degrees, while no peak was observed for the neat aerogel. The characteristic peak of Cloisite 30B had disappeared in all nanocomposite aerogels and it revealed exfoliation of Cloisite 30B in the silica aerogel matrix. As shown in table 2, the XRD results showed the disappearance of the cloisite 30B characteristic peak and the morphology of exfoliation for all nanocomposite aerogels. These results confirm the delamination of the cloisite 30B plate during the three-step sol-gel process. Thus, cloisite 30B pieces were dispersed in the prepared silica aerogel matrix.
TABLE 2 XRD results for samples in the 2 theta range of 2 ° to 10 °
Fig. 5A shows a Scanning Electron Microscope (SEM) image of an embodiment of a neat aerogel, consistent with one or more exemplary embodiments of the present disclosure. Fig. 5B shows a Scanning Electron Microscope (SEM) image of an embodiment of a nanocomposite aerogel (5 wt.% modified clay) consistent with one or more exemplary embodiments of the present disclosure. As shown in fig. 5A and 5B, it can be concluded that both pure and nanocomposite aerogels have colloidal microstructures. In addition, stacking of silicate layers was not observed in fig. 5B, which can be attributed to delamination and dispersion of the modified clay in the silica aerogel.
Fig. 6 shows pore size distributions of embodiments of samples including neat aerogel and nanocomposite aerogel (containing 4, 5, and wt.% modified clay), consistent with one or more exemplary embodiments of the present disclosure. In particular, it is clear that in the exemplary aerogel, the addition of the modified clay did not alter the pore size distribution. The total pore volume and specific surface area of the prepared aerogel are respectively higher than 2.52cm3G and 780m2/g。
TABLE 3 texture characteristics of samples obtained from BET
Furthermore, the specific surface area and pore volume are increased by the addition of the modified clay. The pore size distribution and physical adsorption isotherm of the nanocomposite aerogel was almost similar to that of the pure sample. The modified clay did not significantly alter the pore size distribution of the aerogel. These observations, together with FE-SEM results, indicate that the exemplary method can maintain the microstructural properties of silica aerogels in the presence of modified fillers. The nitrogen adsorption-desorption isotherms of selected samples, including neat aerogels and nanocomposite aerogels (containing 4, 5, and wt.% modified clay), showed type IV isotherms confirming the presence of mesoporous structure according to the IUPAC classification.
The mechanical properties of the silica aerogel and nanocomposite aerogel are shown in table 4. The reported values are the average of three tests. These results indicate that the compressive modulus increases with increasing clay loading levels. Nanocomposites containing 5 wt.% of the modified clay showed both optimum compressive strength and modulus. Furthermore, the breaking strength in the sample containing 5 wt.% of the modified clay is very high. The failure strain of this sample was higher than 40% compared to neat aerogel and this indicates that the brittleness of silica aerogel was lost by the addition of modified clay when using the exemplary method.
In one exemplary embodiment, the compressive modulus of the nanocomposite aerogel can be increased by the addition of the modified clay due to the high modulus of the clay platelets. The best results have been obtained for the samples containing 5 wt.% modified clay. However, the compressive strength of the samples showed a different trend, with respect to the neat aerogel, which seems to increase the compressive strength of the silica aerogel by the addition of the modified clay. In one aspect, the clay platelets cause enhanced load transfer. This effect is responsible for improving the mechanical properties at all load levels. On the other hand, at high loading levels, the dispersed modified clay platelets can act as a secondary network and this results in the most effective loading in the 5 wt.% modified clay nanocomposite. By further increasing the modified clay content, no other improvement was observed. This is why the modified clay loading level has a crucial effect on the mechanical properties of the silica aerogel. Improving the mechanical properties by adding modified clay [ how ] also helps to maintain high porosity in the modified clay containing samples reported in table 1. In the exemplary embodiments, the enhancement of the mechanical properties of the aerogel without any significant change in density clearly suggests a positive effect of the modified clay loading on the mechanical properties of the silica aerogel.
TABLE 4 mechanical Properties of neat and nanocomposite aerogels
Thermogravimetric analysis (TGA) is provided in table 5. Pure aerogels undergo a significant weight loss around 272 ℃. As shown in table 5, the initial decomposition temperature was increased by the loading level of the modified clay and reached 385 ℃ for an aerogel of nanocomposite containing 6 wt.% of the modified clay. The initiation corresponds to CH attached to the silica backbone3Oxidation of the radical and retention of the organic residue. The weight loss after 600 ℃ was small, so the residue at 600 ℃ is reported in table 5. The addition of the modified clay results in an increase in the residues, initial decomposition temperature and amount of residual residues due to the high thermal stability and thermal barrier properties of the clay.
TABLE 5 thermogravimetric analysis (TGA)
By determining the spectral extinction coefficient, its temperature dependence can be calculated using the ross-rand mean function and numerical integration method using equation 4. Fig. 7 shows the ross-rand average extinction coefficients of embodiments of samples including neat aerogel and nanocomposite aerogel (containing 4, 5, and wt.% of modified clay) consistent with one or more exemplary embodiments of the present disclosure.
The rosslanded average extinction coefficient of the neat aerogel is less than the average extinction coefficient of the nanocomposite aerogel. The difference arises from the inherent properties of silica and clay minerals. Moreover, the increase in clay content enhances the extinction coefficient of the nanocomposite aerogel. The change in extinction coefficient of nanocomposite aerogels of up to 6 wt.% of modified clay is monotonic and has a tendency to increase. Since smaller fillers are more efficient at higher temperatures, the increase in extinction coefficient with increasing temperature may be due to the heat carrying radiation wavelength. For the medium temperature range, higher amounts of thermal energy will be radiated in the 2-15 μm wavelength range. Generally, the wavelength of the heat carrier and the size of the nanoparticles affect the variation of the extinction coefficient with temperature.
Effective thermal conductivity of the samples measured by hot wire method at two selected temperatures. The results are shown in table 6. As shown in table 6, the addition of the modified clay at room temperature resulted in a monotonic increase in the thermal conductivity of the aerogel, while a different trend was obtained at 293 ℃. In one aspect, for modified clay loading levels below 5 wt.%, the effect of the modified clay on the extinction coefficient of the aerogel results in a decrease in the radiative thermal conductivity and thus in a decrease in the effective thermal conductivity. On the other hand, the effective thermal conductivity increased at a modified clay loading of 6 wt.%. This is due to the incremental effect of the modified clay on the solid thermal conductivity of the aerogel.
TABLE 6 effective thermal conductivity of the samples measured
INDUSTRIAL APPLICABILITY
The product can be used as sound and heat insulating material in many industries, such as construction, construction and spacecraft. Due to the high specific surface area, the product can also be used as an absorbent, for example in air and water purification. The product can also be used for preparing aerogel blankets which are widely used as heat insulating materials in the petrochemical industry.
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