LOW THERMAL CONDUCTIVITY AND LOW-K DIELECTRIC AEROGEL MATERIAL AND PREPARATION METHOD THEREFOR

Abstract

The present invention discloses the an aerogel material featuring of low thermal conductivity, low dielectric constant (low-D.sub.K) and low dielectric-loss (low-D.sub.F) and a preparation method therefor. The method comprises steps of: (1) mix and hydrolysis, (2) dispersion and condensation, (3) molding, and (4) drying. The prepared pure aerogel or fiber/aerogel composite is further processed by steps of: (5) polymer solution impregnating, (6) solvent drying and (7) crosslinking-solidifying to obtain a polymer/aerogel composite or a polymer/fiber/aerogel composite featuring of high strength, low thermal conductivity, low-D.sub.K and low-D.sub.F. The method provided by the present invention does not involve highly conductive solvents or additives, and a highly porous structure is formed so that the dielectric constant and dielectric loss of the aerogel material are significantly reduced, suitable for 5G communications, microwave circuits, protection and insulation for electric vehicle lithium battery modules.

Claims

1. A method for making a low thermal conductivity and low-k dielectric aerogel material, wherein the aerogel material comprises a pure aerogel or a fiber/aerogel composite, and the method comprising steps of: mixing and hydrolysis step: adding a siloxane precursor to an ethanol water solution to form a mixed solution and then adding an acid catalyst to the mixed solution to perform a hydrolysis reaction, wherein the siloxane precursor comprises a hydrophobic siloxane compound, a siloxane compound or a combination thereof; dispersion and condensation step: adding a dispersing solution to the mixed solution and then using an emulsifier or a stirring equipment to disperse the siloxane precursor to form a homogeneous sol, wherein the dispersing solution comprises a base catalyst; molding step: injecting the sol to a mold so as to promote the sol to further condense into a solid-like aerogel wet-gel structure, wherein the mold comprises a molding mold or a molding mold comprising a fiber; and drying step: at atmospheric pressure, drying the solid-like aerogel wet-gel structure at a drying temperature so as to obtain a low thermal conductivity and low-k dielectric aerogel material with a homogeneous structure, wherein the drying temperature ranges from 60 to 150° C.

2. The method as claimed in claim 1, wherein the drying step comprises steps of: solvent vaporizing step: placing the solid-like aerogel structure at an azeotropic vaporizing temperature so that ethanol water solution in the solid-like aerogel wet-gel structure accomplishes azeotropic vaporization rapidly, and then distilling and drying the ethanol water solution to obtain a half-dried aerogel structure, wherein the azeotropic vaporizing temperature ranges from 60 to 110° C.; and solvent bumping step: adjusting temperature of the half-dried aerogel structure to a bumping temperature so that trace amount of solvent in the half-dried aerogel structure bumps rapidly with water molecules to produce a positive vapor pressure, and the positive vapor pressure produces a large amount of micropores in the half-dried aerogel structure, wherein the bumping temperature ranges from 110 to 150° C.

3. The method as claimed in claim 1, wherein the siloxane compound comprises tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) or the combination thereof; the hydrophobic siloxane compound comprises methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES) or the combination thereof, wherein in the siloxane precursor, a molar ratio of the siloxane compound to the hydrophobic siloxane compound ranges from 0:100 to 40:60.

4. The method as claimed in claim 1, wherein the ethanol water solution comprises (1) ethanol, and (2) deionized water, distilled water or secondary distilled water.

5. The method as claimed in claim 1, wherein the fiber comprises glass fiber, ceramic fiber, rock wool fiber, polypropylene fiber, nylon fiber or polyester fiber; wherein the fiber comprises multi-porous glyph, multi-porous paper, multi-porous blanket, multi-porous rope, multi-porous plate or a combination thereof.

6. The method as claimed in claim 1, wherein the low thermal conductivity and low-k dielectric aerogel material is a multi-porous structure with porosity ranging from 40.0 to 95%, density ranging from 0.180 to 0.600 g/cm.sup.3; thermal conduction k ranging from 0.013 to 0.018 W/mk, dielectric constant ranging from 1.20 to 1.87 and dielectric loss ranging from 0.0026 to 0.0078.

7. The method as claimed in claim 1, wherein the aerogel material further comprises a polymer/aerogel composite or a polymer/fiber/aerogel composite, and the method further comprising steps of: polymer solution impregnating step: preparing a polymer solution and injecting the polymer solution into the low thermal conductivity and low-k dielectric aerogel material so that polymeric chain penetrates homogeneously into interior of the low thermal conductivity and low-k dielectric aerogel material to form a polymer solution-containing pure aerogel composite or a polymer solution-containing fiber/aerogel composite, wherein the polymer solution comprises a polymer and a mixing solvent, and the polymer comprises a thermosetting polymer, a thermoplastic polymer, a liquid crystalline polymer or a combination thereof; and solvent drying step: placing the polymer solution-containing pure aerogel composite or the polymer solution-containing fiber/aerogel composite at a solvent drying temperature so as to vaporize the mixing solvent of the polymer solution, so that the polymer coats a network structure surface inside the pure aerogel or a fiber surface inside the pure aerogel or the fiber/aerogel composite to form a polymer/aerogel composite or a polymer/fiber/aerogel composite, wherein the solvent drying temperature ranges from 60 to 115° C.; wherein the polymer concentration in the polymer solution ranges from 0.01 wt % to 80.0 wt %.

8. The method as claimed in claim 7, wherein the thermoplastic polymer comprises polyethylene, polypropylene, PTFE, polycarbonate, polyamide, polyamide, polyester or a combination thereof.

9. The method as claimed in claim 8, wherein the polymer concentration in the polymer solution ranges from 5.0 wt % to 30.0 wt %.

10. The method as claimed in claim 7, wherein the polymer is a thermosetting polymer, and the method further comprising a step of: crosslinking-solidifying step: placing the polymer/aerogel composite or the polymer/fiber/aerogel composite at a specific crosslinking-solidifying temperature, and crosslinking molecular chain of the polymer coating the network structure surface and silica-based aerogel molecule to obtain a thermosetting polymer/aerogel composite or a thermosetting polymer/fiber/aerogel composite, wherein the thermosetting polymer/aerogel composite or the thermosetting polymer/fiber/aerogel composite features low thermal conductivity, low-k dielectric, high thermal resistance, high intensity and light weight.

11. The method as claimed in claim 10, wherein the polymer concentration in the polymer solution ranges from 5.0 wt % to 30.0 wt %.

12. The method as claimed in claim 10, wherein the thermosetting polymer comprises epoxy, polyimide, polyetherimide, polyphenylene ether, polyphenylene sulfide, polyether ketone, phenolic plastic ester, polymelamine-formaldehyde plastic ester or a combination thereof.

13. The method as claimed in claim 11, wherein when the thermosetting polymer is epoxy, the crosslinking-solidifying temperature ranges from 150 to 180° C.

14. The method as claimed in claim 11, wherein when the thermosetting polymer is polyimide, the crosslinking-solidifying temperature ranges from 120 to 325° C.

15. A low thermal conductivity and low-K dielectric aerogel material, being made by a method as claimed in claim 1.

16. The low thermal conductivity and low-K dielectric aerogel material as claimed in claim 15, wherein the method further comprises steps of: polymer solution impregnating step: preparing a polymer solution and injecting the polymer solution into the low thermal conductivity and low-k dielectric aerogel material so that polymeric chain penetrates homogeneously into interior of the low thermal conductivity and low-k dielectric aerogel material to form a p polymer solution-containing pure aerogel composite or a polymer solution-containing fiber/aerogel composite, wherein the polymer solution comprises a polymer and a mixed solvent, and the polymer comprises a thermosetting polymer, a thermoplastic polymer, a liquid crystalline polymer or a combination thereof; and solvent drying step: placing the polymer solution-containing pure aerogel composite or the polymer solution-containing fiber/aerogel composite at a solvent drying temperature so as to vaporize the mixed solvent of the polymer solution, so that the polymer coats a network structure surface inside the pure aerogel so as to form a polymer/aerogel composite or the polymer coats a network structure surface and a fiber surface inside the fiber/aerogel composite so as to form a polymer/fiber/aerogel composite, wherein the solvent drying temperature ranges from 60 to 115° C.; wherein the polymer concentration in the polymer solution ranges from 0.01 wt % to 80.0 wt %.

17. The low thermal conductivity and low-K dielectric aerogel material as claimed in claim 16, wherein the thermoplastic polymer comprising polyethylene, polypropylene, PTFE, polycarbonate, polyamide, polyamide, polyester or a combination thereof; wherein the polymer concentration in the polymer solution ranges from 5.0 wt % to 30.0 wt %.

18. The low thermal conductivity and low-K dielectric aerogel material as claimed in claim 16, wherein polymer is a thermosetting polymer, and the method further comprises a step of: crosslinking-solidifying step: placing the polymer/aerogel composite or the polymer/fiber/aerogel composite at a specific crosslinking-solidifying temperature, and crosslinking molecular chain of the polymer coating the network structure surface and silica-based aerogel molecule to obtain a thermosetting polymer/aerogel composite or a thermosetting polymer/fiber/aerogel composite, wherein the thermosetting polymer/aerogel composite or the thermosetting polymer/fiber/aerogel composite features of low thermal conductivity, low-k dielectric, high thermal resistance, high intensity and light weight.

19. The low thermal conductivity and low-K dielectric aerogel material as claimed in claim 18, wherein the thermosetting polymer comprises epoxy resin, polyimide, polyetherimide, polyphenylene ether, polyphenylene sulfide, polyether ketone, phenolic plastic ester, polymelamine-formaldehyde plastic ester or a combination thereof; wherein the polymer concentration in the polymer solution ranges from 5.0 wt % to 30.0 wt %.

20. The low thermal conductivity and low-K dielectric aerogel material as claimed in claim 19, wherein when the thermosetting polymer is epoxy, the crosslinking-solidifying temperature is a serial crosslinking-solidifying temperature ranging from 150 to 180° C.; wherein when the thermosetting polymer is polyimide, the crosslinking-solidifying temperature is a serial crosslinking-solidifying temperature ranging from 120 to 325° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The present invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as following:

[0057] FIG. 1 is a flowchart illustrating a workflow for preparing a low thermal conductivity and low-K dielectric aerogel material in the first embodiment of the present invention.

[0058] FIG. 2 is a photo demonstrating appearances of the low thermal conductivity and low-K dielectric aerogel material.

[0059] FIG. 3 is a 3000× scanning electron microscopy (SEM) photo showing cross section of the pure aerogel pad in the first embodiment.

[0060] FIG. 4 is a 250×SEM photo showing cross section of the fiber/aerogel composite in the first embodiment.

[0061] FIG. 5 is a flowchart illustrating a workflow of the second embodiment.

[0062] FIG. 6 is a photo demonstrating appearances of a low thermal conductivity and low-K dielectric aerogel material in the second embodiment.

[0063] FIG. 7 is a 250×SEM photo showing cross section of the low thermal conductivity and low-K dielectric aerogel material in the second embodiment.

[0064] FIG. 8 is a 1000×SEM photo showing cross section of the low thermal conductivity and low-K dielectric aerogel material in the second embodiment.

DETAILED DESCRIPTION

[0065] Please refer to FIG. 1 illustrating a method for making a low thermal conductivity and low-K aerogel material in a first embodiment of the present invention, wherein the aerogel material comprises a pure aerogel or a fiber/aerogel composite, and the method comprises steps of: mix and hydrolysis step (S1), dispersion and condensation step (S2), molding step (S3) and drying step (S4), wherein:

[0066] Mix and hydrolysis step (S1): adding a siloxane precursor to an ethanol water solution to form a mixed solution and then an acid catalyst is added to the mixed solution to perform a hydrolysis reaction, wherein the siloxane precursor comprises a hydrophobic siloxane compound, a siloxane compound or a combination thereof, a; in some embodiments, the siloxane compound comprises tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) or the combination thereof; the hydrophobic siloxane compound comprises methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES) or the combination thereof. The purpose of adding the hydrophobic siloxane compound is to attenuate the risk of aerogel structural cracking during drying process, and adding siloxane compound aims to regulate microstructures inside aerogel and to increase porosity. In some embodiments, based on the mixed solution, a content molar ratio of the siloxane compound or the hydrophobic siloxane compound ranges from 0.5 mol % to 40.0 mol %, and a molar ratio of the ethanol water solution ranges from 99.5 mol % to 60.0 mol %.

[0067] In some embodiments, the molar ratio of the siloxane compound to the hydrophobic siloxane compound ranges from 0:100 to 40:60; in preferred embodiments, the molar ratio of the siloxane compound to the hydrophobic siloxane compound is 5:95; in the ethanol water solution, a molar ratio of ethanol to water ranges from 0:100 to 50:50; in preferred embodiments, a molar ratio of ethanol to water is 15:85.

[0068] When the siloxane compound or the hydrophobic siloxane compound thoroughly mixes with the ethanol water solution containing trace amount of acidic catalyst, hydrolysis is performed simultaneously; wherein the ethanol water solution containing acidic catalyst comprises (1) ethanol, and (2) deionized water, treated water, secondary treated water or a combination of one or more, and a molar ratio of the siloxane compound or the hydrophobic siloxane compound to the acidic catalyst is 1:0.01 to 1:0.00005. When the molar ratio of the siloxane compound or the hydrophobic siloxane compound to the acidic catalyst is higher, the hydrolysis rate is higher. In other words, while content ratio of the acidic catalyst is higher, the entire aerogel structure contains more ions, which results in larger dielectric loss; in preferred embodiments, the molar ratio of the siloxane compound or the hydrophobic siloxane compound to the acidic catalyst is 1:0.00014.

[0069] Dispersion and condensation step (S2): a dispersing solution is added to the mixed solution and then an emulsifier or a stirring equipment is used to disperse the siloxane precursor to form a homogeneous sol, and the dispersing solution comprises a base catalyst. To be more specific, during condensation, reaction rate of condensation can be adjusted through controlling condensation temperature, water contents as well as stirring rate so as to regulate aerogel microstructure in the sol. A volume ratio of the dispersing solution to the ethanol water solution is 75:25 to 30:70. In preferred embodiments, the volume ratio of the dispersing solution to the ethanol water solution is 50:50.

[0070] During condensation, rising of temperature critically shortens condensation reaction time. In brief, gelling time of the aerogel at dispersion and condensation step (S2) can be shortened effectively. When an equivalent ratio of the basic catalyst to the acidic catalyst is 1.0:1.0, the condensation temperature ranges from 20° C. to 55° C. and the condensation time ranges from 20 to 250 minutes. In preferred embodiments, when the condensation temperature is 25° C., the condensation time is 220 minutes; when the condensation temperature is 50° C., the condensation time is 15 minutes.

[0071] In other embodiments, increasing of the basic catalyst contents also critically shortens condensation reaction time, wherein the equivalent ratio of 1.0M basic catalyst to 1.0M acidic catalyst ranges from 0.8:1.0 to 2.0:1.0, and condensation reaction time is 360 minutes to 3 minutes. In one or more embodiments, the equivalent ratio is 0.8:1.0 and the condensation reaction time is 360 minutes. In preferred embodiments, the equivalent ratio is 1.6:1.0 and the condensation reaction time is 10 minutes. In particular, when the equivalent ratio is lower than 1.0:1.0, the condensation reaction time increases gradually, and dielectric loss of the prepared aerogel is reduced significantly. When the equivalent ratio is larger than 1.0:1.0, the condensation reaction time decreases gradually, and dielectric loss of the prepared aerogel rises significantly due to increased ion contents. In one preferred embodiment, the equivalent ratio is 1.2:1.0.

[0072] Molding step (S3): the sol is injected to a mold so as to promote the sol to further condense into a solid-like aerogel wet-gel structure, and the mold comprises a molding mold or a molding mold comprising fibers. At the molding step, homogeneously dispersed siloxane molecules and hydrophobic siloxane molecules forms a 3D siloxane network into an aerogel molecular cluster under water repulsion. The initial structural size of siloxane aerogel molecules can be controlled between 5 to 10 nanometers. The initial structure further clusters to an aerogel wet-gel molecule sized of 50 to 100 nanometers. The aerogel wet-gel molecule further clusters into a larger cluster and interconnects with each other to form a 3D network structure, and a half-solidified aerogel wet gel structure containing abundant alcohols-water solutions is stabilized and formed.

[0073] In some other embodiments, the sol is injected into a mold containing a large amount of fibers. The fibers comprises inorganic fibers or organic fibers, wherein the fiber is glyph-shaped, paper-shaped, blanket-shaped, pad-shaped or a combination thereof. Specifically, siloxane aerogel molecule attaches to fiber surface and condense upon the fiber surface. The siloxane aerogel molecule clusters into aerogel wet-gel molecules sized of 50 to 100 nanometers. The aerogel wet-gel molecule further clusters into a larger cluster and interconnects with each other to form a 3D network structure, and a half-solidified aerogel wet gel structure containing abundant alcohols-water solutions is stabilized and formed. At the molding step, the sol can be compounded with the fibers by immersion, suction, spraying, pouring or vacuum suction.

[0074] In some embodiments, the fiber comprises glass fiber, ceramic fiber, rock wool fiber, polypropylene fiber, nylon fiber or polyester fiber; wherein the fiber is multi-porous glyph, multi-porous paper, multi-porous blanket, multi-porous rope, multi-porous plate or a combination thereof.

[0075] Drying step (S4): at atmospheric pressure, the solid-like aerogel wet-gel structure is dried at a drying temperature so as to obtain a low thermal conductivity and low-K dielectric aerogel material with an homogeneous structure; preferably, the drying temperature ranges from 60 to 150° C.

[0076] Preferably, the drying step comprises solvent vaporizing step (S4-1) and solvent bumping step (S4-2).

[0077] Solvent vaporizing step (S4-1): the solid-like aerogel structure is placed at an azeotropic vaporizing temperature so that ethanol water solution in the solid-like aerogel wet-gel structure accomplishes azeotropic vaporization rapidly and distilling-dries the ethanol water solution; preferably, the azeotropic vaporizing temperature ranges from 60 to 110° C.

[0078] Solvent bumping step (S4-2): temperature of the half-dried aerogel structure is adjusted to a bumping temperature so that trace amount of solvent in the half-dried aerogel structure bumps rapidly with water molecules to produce a positive vapor pressure, and drying and shrinking of the aerogel structure is inhibited, and a large amount of nano-scale to submicron-scale micropores is produced in the aerogel structure, wherein the bumping temperature ranges from 110 to 150° C. Particularly, at the bumping temperature, trace amount of alcohol molecules and water molecules inside the aerogel structure approach to bumping and create a positive pressure. The positive pressure further prevent the aerogel structure from shrinking or crushing during drying process. Meanwhile, the positive pressure drives the aerogel network structure to swell and produce porosity. Therefore, the pure aerogel or the fiber/aerogel composite of low density and high porosity can be made by the method provided in the present invention, wherein thermal conductivity of the pure aerogel composite is 0.013 W/mk to 0.018 W/mk, and thermal conductivity of the aerogel/fiber composite is 0.022 W/mk to 0.032 W/mk.

[0079] In addition, solvents other than ethanol, such as alkanes, aromatics or ammonia, are not introduced to the process. Surfactants and organic/inorganic binding agents are not introduced either. Therefore, the drying process is safer and aerogel product with high purity can be made. The aerogel material does not contain impurity and features of low thermal conductivity, low dielectric constant and low dielectric loss.

[0080] Please refer to FIG. 2. Shown in FIG. 2 is a photo of appearances of the low thermal conductivity and low-K dielectric aerogel material. The appearances are white boards or thin pads.

[0081] Please refer to FIG. 3 which is a 3000× scanning electron microscopy (SEM) photo showing cross section of a pure aerogel pad. Under electron microscopy, the microstructure demonstrates a 3D network cluster of spheric aerogel of size ranging from submicron to micron. Moreover, there are tandem structures in addition to aerogel cluster inside the low thermal conductivity and low-K aerogel material. The tandem structures connect in a serial manner and form a porous structure, which endows the aerogel material low thermal conductivity and low-K properties.

[0082] Please refer to FIG. 4 which is a 250× scanning electron microscopy (SEM) photo showing cross section of a fiber/aerogel composite. As shown in FIG. 4, the fiber/aerogel composite is a 3D aerogel network structure formed by clustering of a large amount sub-micron aerogel molecules attaching to fiber surface. There is a large amount of porosity inside entire clustering structure, which provides low thermal conductivity and low-K dielectric property, while fibers enhance intensity of the fiber/aerogel composite.

[0083] Please refer to FIG. 5. A workflow of the second embodiment in the present invention is illustrated in FIG. 5. In the second embodiment, a large amount of polymer solution is used for immersing or injecting into the aforementioned low thermal conductivity and low-K dielectric aerogel material so that a polymer/aerogel composite or a polymer/fiber/aerogel composite featuring of high intensity, low conductivity and low-K dielectric property is prepared. In the second embodiment, the method further comprises steps of: mix and hydrolysis step (S1″), dispersion and condensation step (S2″), molding step (S3″), drying step (S4″), polymer solution impregnating step (S5″), solvent drying step (S6″) and crosslinking-solidifying step (S7″), wherein:

[0084] Mix and hydrolysis step (S1″): a siloxane precursor is added to an ethanol water solution to form a mixed solution and then an acid catalyst is added to the mixed solution to perform a hydrolysis reaction, wherein the siloxane precursor comprises a hydrophobic siloxane compound, a siloxane compound or a combination thereof; wherein the siloxane compound comprises tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) or the combination thereof; the hydrophobic siloxane compound comprises methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES) or the combination thereof. Based on the entire mixed solution, a content molar percentage of the siloxane compound or the hydrophobic siloxane compound is 0.5 mol % to 40.0 mol %, and the content molar percentage of the ethanol water solution is 99.5 mol % to 60.0 mol %.

[0085] In some embodiments, a molar ratio of the siloxane compound to the hydrophobic siloxane compound is 0:100 to 40:60; in one preferred embodiment, the molar ratio of the siloxane compound to the hydrophobic siloxane compound is 5:95; in the ethanol water solution, a molar ratio of ethanol to water is 0.01:100 to 50:50; in one preferred embodiment, the molar ratio of ethanol to water is 15:85.

[0086] When the siloxane compound or the hydrophobic siloxane compound thoroughly mixes with the ethanol water solution containing trace amount of acidic catalyst, hydrolysis is performed simultaneously; wherein the ethanol water solution containing acidic catalyst comprises (1) ethanol, and (2) deionized water, treated water, secondary treated water or a combination of one or more, and a molar ratio of the siloxane compound or the hydrophobic siloxane compound to the acidic catalyst is 1:0.01 to 1:0.00005. When the molar ratio of the siloxane compound or the hydrophobic siloxane compound to the acidic catalyst is higher, the hydrolysis rate is higher. In other words, while content ratio of the acidic catalyst is higher, the entire aerogel structure contains more ions, which results in higher dielectric loss; in preferred embodiments, the molar ratio of the siloxane compound or the hydrophobic siloxane compound to the acidic catalyst is 1:0.00014.

[0087] Dispersion and condensation step (S2″): a dispersing solution is added to the mixed solution and then an emulsifier or a stirring equipment is used to disperse the siloxane precursor to form a homogeneous sol, and the dispersing solution comprises a base catalyst. A volume ratio of the dispersing solution to the ethanol water solution is 75:25 to 30:70. In preferred embodiments, the volume ratio of the dispersing solution to the ethanol water solution is 50:50.

[0088] During condensation, rising of temperature critically shortens condensation reaction time. In brief, gelling time of the aerogel at dispersion and condensation step (S2″) can be reduced effectively. When an equivalent ratio of the basic catalyst to the acidic catalyst is 1.0:1.0, the condensation temperature ranges from 20° C. to 55° C. and the condensation time ranges 20 to 250 minutes. In preferred embodiments, when the condensation temperature is 25° C., the condensation time is 220 minutes; when the condensation temperature is 50° C., the condensation time is 25 minutes.

[0089] In other embodiments, increasing of the basic catalyst contents also critically shorten condensation reaction time, wherein the equivalent ratio of 1.0M basic catalyst to 1.0M acidic catalyst is 0.8:1.0 to 2.0:1.0, and condensation reaction time is 3 minutes to 360 minutes. In one or more embodiments, the equivalent ratio is 0.8:1.0 and the condensation reaction time is 360 minutes. In preferred embodiments, the equivalent ratio is 1.6:1.0 and the condensation reaction time is 10 minutes. In one preferred embodiment, the equivalent ratio is 1.2:1.0.

[0090] Molding step (S3″): the sol is injected to a mold so as to promote the sol to further condense into a solid-like aerogel wet-gel structure, and the mold comprises a molding mold or a molding mold comprising fibers. At the molding step, homogeneously dispersed siloxane molecules and hydrophobic siloxane molecules forms a 3D siloxane network into an aerogel molecular cluster under water repulsion. The initial structural size of siloxane aerogel molecules can be controlled between 5 to 10 nanometers. The initial structure further clusters to an aerogel wet-gel molecule sized of 50 to 100 nanometers. The aerogel wet-gel molecule further clusters into a larger cluster and interconnects with each other to form a 3D network structure, and a half-solidified aerogel wet gel structure containing abundant alcohols-water solutions is stabilized and formed.

[0091] In some other embodiments, the sol is injected into a mold containing abundant fibers. The fibers comprises inorganic fibers or organic fibers, wherein the fiber is glyph-shaped, paper-shaped, blanket-shaped, pad-shaped or a combination thereof. Specifically, siloxane aerogel molecules attach to fiber surface and condense upon the fiber surface. The siloxane aerogel molecules cluster into aerogel wet-gel molecular drops sized of 50 to 100 nanometers. The aerogel wet-gel molecular drops further clusters into a larger cluster and interconnects with each other to form a 3D network structure, and a half-solidified aerogel wet-gel structure containing abundant alcohols-water solutions is stabilized and formed. At the molding step, the sol can be compounded with the fibers via immersion, suction, spraying, pouring or vacuum suction.

[0092] In one or various embodiments, the fiber comprises glass fiber, ceramic fiber, rock wool fiber, polypropylene fiber, nylon fiber or polyester fiber; wherein the fiber is multi-porous glyph, multi-porous paper, multi-porous blanket, multi-porous rope, multi-porous plate or a combination thereof.

[0093] Drying step (S4″): at atmospheric pressure, the solid-like aerogel wet-gel structure is dried at a drying temperature so as to obtain a low thermal conductivity and low-K dielectric aerogel material with an homogeneous structure; preferably, the drying temperature ranges from 60 to 150° C.

[0094] Preferably, the drying step comprises solvent vaporizing step (S4-1″) and solvent bumping step (S4-2″), wherein:

[0095] Solvent vaporizing step (S4-1″): the solid-like aerogel structure is placed at an azeotropic vaporizing temperature so that ethanol water solution in the solid-like aerogel wet-gel structure accomplishes azeotropic vaporization rapidly and then the ethanol water solution is distilled and dried; preferably, the azeotropic vaporizing temperature ranges from 60 to 110° C.

[0096] Solvent bumping step (S4-2″): temperature of the half-dried aerogel structure is adjusted to a bumping temperature so that trace amount of solvent in the half-dried aerogel structure bumps rapidly with water molecules to produce a positive vapor pressure, and the positive vapor pressure produces a large amount of micropores in the half-dried aerogel structure, wherein the bumping temperature ranges from 110 to 150° C. Particularly, at the bumping temperature, trace amount of alcohol molecules and water molecules inside the aerogel structure approach to bumping and create a positive pressure. The positive pressure further prevent the aerogel structure from shrinking or crushing during drying process. Meanwhile, the positive pressure drives the aerogel network structure to swell and produce porosity. Therefore, aerogel material featuring of low density and high porosity can be made by the method provided in the present invention, wherein thermal conductivity of the pure aerogel thin film or the pure aerogel thin film pad ranges from 0.013 W/mk to 0.018 W/mk, and thermal conductivity of the aerogel/fiber thin film or the pure aerogel thin film pad ranges from 0.022 W/mk to 0.032 W/mk.

[0097] Polymer solution impregnating step (S5″): a polymer solution is prepared and the polymer solution is injected into the low thermal conductivity and low-K dielectric aerogel material so that polymeric chain penetrates homogeneously into interior of the low thermal conductivity and low-K dielectric aerogel material to form a polymer solution-containing pure aerogel composite or a polymer solution-containing fiber/aerogel composite, wherein the polymer solution comprises a polymer and a mixing solvent, and the polymer comprises a thermosetting polymer, a thermoplastic polymer, a liquid crystalline polymer or a combination thereof.

[0098] Drying step (S6″): the polymer solution-containing pure aerogel composite or the polymer solution-containing fiber/aerogel composite is placed at a temperature higher than boiling point of the mixing solvent so that the mixing solvent vaporizes and attachment of the polymer to surfaces of aerogel network or the fibers is promoted, wherein the drying temperature ranges from 60 to 115° C.

[0099] In particular, when the polymer solution is a thermoplastic polymer, the polymer/aerogel composite or the polymer/fiber/aerogel composite is obtained by solidification after the solvent drying step. When the polymer solution is a thermosetting polymer, the polymer/aerogel composite or the polymer/fiber/aerogel composite is molded at a crosslinking or solidification temperature after the solvent drying step. By technologies as mentioned above, the aerogel material featuring of high intensity, low thermal conductivity and low-K dielectric property is obtained, wherein the aerogel material is a thermosetting polymer/aerogel composite, a thermosetting polymer/fiber/aerogel composite, a thermoplastic polymer/aerogel composite or a thermoplastic polymer/fiber/aerogel composite.

[0100] Preferably, at the polymer solution impregnating step (S5″), when the pure aerogel or the fiber/aerogel composite is dried and molded, the pure aerogel or the fiber/aerogel composite is instantly immersed in the polymer solution or the polymer solution is sprayed onto the pure aerogel or the fiber/aerogel composite so that the polymer solution homogeneously seeps into interior pores of the pure aerogel or the fiber/aerogel composite and a polymer solution-containing pure aerogel composite is formed. The polymer solution-containing pure aerogel composite comprises a polymer solution-containing pure aerogel composite or a polymer solution-containing fiber/aerogel composite.

[0101] Preferably, based on entire volume of the polymer solution, the polymer concentration in the polymer solution ranges from 0.01 wt % to 80.0 wt %; in preferred embodiments, the polymer concentration in the polymer solution ranges from 5.0 wt % to 30.0 wt %; wherein the lower the polymer concentration is, the more efficiently the polymer seeps into pores inside the aerogel structure, and the low thermal conductivity and low-K dielectric polymer/aerogel composite or the polymer/fiber/aerogel composite contains higher porosity. Therefore, low thermal and low-K dielectric properties of the polymer/aerogel composite or the polymer/fiber/aerogel composite are more superior. On the contrary, the polymer concentration is the higher, and content ratio the polymer coating inside the silicon-based aerogel is higher, and the intensity of end-product is better. Therefore, adjusting concentration of the polymer solution allows controlling dielectric property and intensity of the low thermal conductivity and low-K polymer/aerogel composite or the polymer/fiber/aerogel composite. More preferably, the polymer concentration in the polymer solution ranges from 5.0 wt % to 30.0 wt %.

[0102] In the aforementioned method, when the polymer is a thermoplastic polymer, a thermoplastic polymer/aerogel composite or polymer/fiber/aerogel composite featuring of high intensity, high tensile strength, light-weighted and low-K dielectric property can be formed after solvent drying step (S6″) is accomplished. In particular, the thermoplastic polymer comprises polyethylene (PE), polypropylene (PP), polycarbonate (PC), polyamide (PA), polyesteramide (PEA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) or a combination thereof.

[0103] In some embodiments, the pure aerogel or the fiber/aerogel composite can be compounded with the polymer solution by techniques comprising injection, immersion, suction, spraying, impregnation or vacuum suction. In another aspect, when the polymer is a thermosetting polymer, a crosslinking-solidifying step (S7″) follows the solvent drying step (S6″), and a thermosetting polymer/aerogel composite or a thermosetting polymer/fiber/aerogel composite is obtained. Preferably, the thermosetting polymer comprises epoxy, polyimide (PI), polyetherimine (PEI), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyetherketone (PEK), polyetheretherketone (PEEK) or a combination thereof.

[0104] Preferably, in the aerogel material, when content of aerogel molecules is higher or concentration of the polymer solution is thinner, the interior porosity is higher. Therefore, the aerogel material demonstrates low thermal conductivity, low dielectric constant and low dielectric loss, and transforming electric field energy into heat on a high-frequency condition is rendered difficult. On the other hand, physical properties such as intensity, tensile strength or rigidity of the aerogel material is lower. On the contrary, when content of aerogel molecules is lower or concentration of the polymer solution is higher, physical properties such as intensity, tensile strength or rigidity of the aerogel material is higher, but thermal conductivity, dielectric constant and dielectric loss are also higher. The method disclosed in the present invention realizes adjustment of thermal conductivity and dielectric properties through controlling contents of aerogel and concentration of the polymer solution.

[0105] At the solvent drying step (S6″), organic solvents in the polymer solution-containing pure aerogel composite or the polymer solution-containing fiber/aerogel composite is vaporized in an ambient environment at a solvent drying temperature. During the solvent drying process, the polymer solution inside the polymer solution-containing pure aerogel composite or the polymer solution-containing fiber/aerogel composite undergoes a liquid-solid phase separation. A solvent-rich phase and a polymer-rich phase are formed and during phase separation solvent of the solvent-rich phase is vaporized gradually. On the other hand, polymer chains of the polymer-rich phase coat on aerogel framework or fiber surface, and a polymer membrane layer is formed on a aerogel framework or a fiber structure. In some embodiments, the mixing solvent is ethanol and the solvent drying temperature ranges from 60° C. to 75° C. In other embodiments, the mixing solvent is butanone and the solvent drying temperature ranges from 80° C. to 90° C.; the mixing solvent is toluene and the solvent drying temperature ranges from 100° C. to 110° C. The aerogel material is not deformed when there is no large amount of bubbles produced as the solvent drying temperature is too high.

[0106] In some embodiments, when the polymer is a thermosetting polymer, the method further comprises a crosslinking-solidifying step (S7″): at a crosslinking-solidifying temperature, the thermosetting polymer is crosslinked with aerogel molecules so as to be solidified. When the thermosetting polymer is epoxy, the crosslinking-solidifying temperature ranges from 150° C. to 180° C., and 150° C. or 180° C. is preferred. When the thermosetting polymer is a polyimide, the crosslinking-solidifying temperature ranges from 120° C. to 325° C., and 120° C., 180° C., 260° C. or 325° C. is preferred. At the crosslinking-solidifying step (S7″), at a specific crosslinking-solidifying temperature, molecular chains of the thermosetting polymer coating on aerogel framework are crosslinked with silicon-based aerogel molecule. A crosslinking reaction occurs between polymer chains of the polymers coating on the aerogel framework, and bonding between polymers or between polymers and aerogel molecules is created so that a thermosetting polymer/aerogel composite or a thermosetting polymer/fiber/aerogel composite featuring of high heat resistance, high intensity, light weight and low-K dielectric property is obtained.

[0107] Please refer to FIG. 6. Appearance of a low thermal conductivity and low-K dielectric aerogel material pad in a preferred embodiment is demonstrated in FIG. 6, wherein the aerogel material pad is a polyimide/aerogel composite or a polyimide/ceramic fiber/aerogel composite pad.

[0108] FIG. 7 is a 250×SEM photo showing cross section of the low thermal conductivity and low-K dielectric aerogel material in a preferred embodiment, which shows a microstructure of a multi-porous polyimide/aerogel composite pad. Polyimide coating on aerogel network structure forms a multi-porous polyimide/aerogel composite pad with a homogeneous appearance.

[0109] Please refer to FIG. 8 which is a 1000×SEM photo showing cross section of the low thermal conductivity and low-K dielectric aerogel material in one preferred embodiment. As shown in FIG. 8, polyimide coats on ceramic fiber surface and aerogel network structure surface in a polyimide/ceramic fiber/aerogel composite pad. Through adhesive property provided by polyimide, the ceramic fiber can be firmly adhered to the aerogel clustering structure, and a polyimide/ceramic fiber/aerogel composite pad featuring of high intensity, high heat resistance and low-K dielectric property is prepared.

[0110] Please refer to TABLE 1. Physical properties of the ceramic fiber/aerogel composite pads impregnated by polymer solutions at various concentrations are listed in TABLE 1. In this example, the polyimide/ceramic fiber/aerogel composites are prepared by impregnating ceramic fiber/aerogel composites in 80 wt %, 50 wt %, 30 wt %, 20 wt % or 15 wt % polyimide solutions. Each polyimide/ceramic fiber/aerogel composite is designated as PI-80/CF/AC, PI-50/CF/AC, PI-30/CF/AC, PI-20/CF/AC, PI-15/CF/AC, respectively. In addition, a pure aerogel is designated as PA and a ceramic fiber/aerogel composite without polymer solution impregnation is designated as CF/AC.

TABLE-US-00001 TABLE 1 Density Thermal conductivity Test frequency (g/cm.sup.3) coefficient (W/mk) (GHz) D.sub.K D.sub.F PA 0.123 0.0249 2 1.326 0.0025 0.123 0.0249 3 1.320 0.0024 0.123 0.0249 5 1.314 0.0026 0.123 0.0249 10 1.315 0.0026 CF/AC 0.204 0.0271 2 1.372 0.0034 0.204 0.0271 3 1.370 0.0034 0.204 0.0271 5 1.351 0.0032 0.204 0.0271 10 1.346 0.0026 PI-15/ 0.366 0.0472 2 1.403 0.0037 CF/AC 0.366 0.0472 3 1.394 0.0037 0.366 0.0472 5 1.380 0.0036 0.366 0.0472 10 1.350 0.0033 PI-20/ 0.461 0.0631 2 1.567 0.0047 CF/AC 0.461 0.0631 3 1.563 0.0046 0.461 0.0631 5 1.548 0.0044 0.461 0.0631 10 1.521 0.0041 PI-30/ 0.538 0.1125 2 1.678 0.0078 CF/AC 0.538 0.1125 3 1.661 0.0077 0.538 0.1125 5 1.655 0.0074 0.538 0.1125 10 1.654 0.0073 PI-50/ 0.678 0.1632 2 1.846 0.0125 CF/AC 0.678 0.1632 3 1.838 0.0121 0.678 0.1632 5 1.812 0.0120 0.678 0.1632 10 1.804 0.0114 PI-80/ N/A N/A N/A N/A N/A CF/AC N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A

[0111] As indicated in TABLE 1, density of the pure aerogel composite is 0.123 g/cm.sup.3, while density of the ceramic fiber/aerogel composite (CF/AC) is 0.204 g/cm.sup.3. Density of the polyimide/ceramic fiber/aerogel composite (PI/CF/AC) increases as concentration of the polyimide solution increases. Densities of PI-15/CF/AC, PI-20/CF/AC, PI-30/CF/AC and PI-50/CF/AC are 0.366 g/cm.sup.3, 0.461 g/cm.sup.3, 0.575 g/cm.sup.3 and 0.678 g/cm.sup.3, respectively. However, when concentration of polyimide solution rises up to 80 wt %, seepage of the polymer solution into aerogel becomes inhomogeneous. In addition, viscosity of polyimide solution increases critically such that during the process the aerogel material tends to crack or to dissociate into aerogel powder, and the aerogel material eventually becomes unable to form.

[0112] Moreover, thermal conductivity coefficient of the pure aerogel is 0.0249 W/mk and that of the ceramic fiber/aerogel composite is 0.0271 W/mk. The thermal conductivity coefficient increases as concentration of the polymer solution rises, and thermal conductivity coefficients of PI-15/CF/AC, PI-20/CF/AC, PI-30/CF/AC and PI-50/CF/AC are 0.0472 W/mk, 0.0631 W/mk, 0.1125 W/mk and 0.1632 W/mk, respectively. PI-80/CF/AC is unable to form during the manufacturing process and thus no thermal conductivity coefficient is measured.

[0113] Furthermore, the dielectric properties including D.sub.K and D.sub.F both decrease as test frequency decreases. However, when test frequency increases from 2 GHz to 10 GHz, D.sub.K of the pure aerogel decreases from 1.326 to 1.315 while D.sub.F of the pure aerogel increases from 0.025 to 0.026. As for CF/AC without polymer solution treatment, D.sub.K decreases from 1.372 to 1.346 and D.sub.F decreases from 0.0034 to 0.0026. As measured at test frequency of 10 GHz, D.sub.K and D.sub.F of the polyimide/ceramic fiber/aerogels both increase as concentration of the polymer solution increases. D.sub.K values of PI-15/CF/AC, PI-20/CF/AC, PI-30/CF/AC and PI-50/CF/AC are 1.350, 1.521, 1.654 and 1.804, respectively. D.sub.F values of PI-15/CF/AC, PI-20/CF/AC, PI-30/CF/AC and PI-50/CF/AC are 0.0033, 0.0041, 0.0072 and 0.0144, respectively. The ceramic fiber/aerogel composite and polymer/ceramic fiber/aerogel composite both present excellent dielectric properties, and the dielectric properties change as concentration of the polymer solution variates. Thus, physical properties of the aerogel material can be adjusted through manipulation of the polymer solution concentrations.

[0114] As illustrated in the embodiments and examples mentioned above, the method provided in the present invention realizes rapid preparation of a low thermal conductivity and low dielectric aerogel material at atmospheric pressure. The aerogel material can be in a form of a membrane, a pad, a chunk or a sheet, but not limited hereto. Moreover, the method provided in the present invention does not require a large amount of organic solvents such as alkanes, aromatics or benzenes, and thus time-consuming solvent displacement is omitted and supercritical drying equipment is not necessary, which simplifies the process and makes it safer and more cost-effective.

[0115] As is understood by a person skilled in the art, the aforementioned preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. In view of the foregoing, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims. Thus, the scope of which should be accorded the broadest interpretation in order to encompass all such modifications and similar structures.