A method for preparing an anisotropic graphene aerogel by atmospheric pressure drying and its thermally conductive composite material

Abstract

The present invention relates to a method for preparing an anisotropic graphene aerogel by atmospheric pressure drying and a thermal conductive composite material thereof. The graphene aerogel is prepared by chemically reducing or hydrothermally reducing a mixed suspension of graphene oxide (GO) and graphene nanosheets / graphite microflakes (GNP) to make it into a hydrogel state, and then through steps such as directional freezing, atmospheric pressure drying, and post-heat treatment. The thermal conductive composite material is obtained by filling a polymer or a phase change material into the graphene aerogel. The graphene aerogel has an oriented structure, and at the same time, its composite material has high thermal conductivity in both the horizontal and vertical directions.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and particularly relates to a method for preparing an anisotropic graphene aerogel by atmospheric pressure drying and a thermal conductive composite material thereof. A reduced graphene oxide (RGO) / GNP hydrogel is formed by pre-reducing a mixed suspension of graphene oxide (GO) and graphene nanoplatelets (GNP), and then a graphene aerogel with vertically oriented anisotropy is obtained through directional freezing, atmospheric pressure drying, and heat treatment. A thermal conductive composite material with excellent thermal conductivity in the vertical direction is obtained by compounding with epoxy resin, silicone rubber, silicone resin precursor, or phase change material. Background Art

[0002] With the miniaturization and integration of electronic devices, the heat accumulation generated during use seriously affects the performance and lifespan of electronic devices. Therefore, the heat dissipation problem of electronic devices is a huge challenge. Among various thermal conductive materials, polymer composites have significant advantages due to their light weight, easy processing, low cost, and good stability.

[0003] Currently, thermal conductive polymer composites are mainly prepared by blending polymers with thermal conductive fillers, including metal particles such as Ag and Cu, carbon materials such as carbon nanotubes and graphene, and ceramic materials such as boron nitride and silicon carbide. Among them, graphene has an extremely high intrinsic thermal conductivity (~5300 W m -1 K -1 ). However, the thermal conductivity of graphene / polymer composites is far from the theoretical prediction, which is related to the random distribution of graphene sheets in the matrix and the contact thermal resistance and interfacial thermal resistance between graphene sheets and at the graphene / polymer interface.

[0004] Compared with the random dispersion method, highly oriented graphene sheets can give full play to the advantage of their high in-plane thermal conductivity. The sheets overlap with each other to form a high-quality thermal conductive network, reducing the contact thermal resistance and further improving the thermal conductivity of polymer composites in the graphene orientation direction.

[0005] Preparing anisotropic graphene aerogels is one of the effective ways to construct highly oriented graphene networks. However, graphene aerogels prepared by vacuum freeze-drying or supercritical drying often consume a large amount of energy and have relatively complex equipment, which limits their large-scale preparation. Natural drying under atmospheric pressure conditions, as an economical and simple method, can achieve the large-scale preparation of graphene aerogels. Summary of the Invention

[0006] To solve the above problems existing in the prior art, the present invention provides a method for preparing an anisotropic graphene aerogel by atmospheric pressure drying and its thermally conductive composite material. By using a reducing agent or hydrothermal method to preliminarily reduce GO in the GO / GNP mixed suspension to form an RGO / GNP hydrogel, and then endowing the hydrogel with a vertical pore structure through directional freezing technology. During the atmospheric pressure drying process, GNP effectively inhibits the excessive shrinkage of the aerogel and retains the vertical pore structure, thereby obtaining an anisotropic graphene aerogel with high density and excellent mechanical properties.

[0007] To achieve the object of the invention, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing an anisotropic graphene aerogel by atmospheric pressure drying, which preliminarily reduces the GO / GNP mixed suspension to form an RGO / GNP hydrogel, and then prepares the anisotropic graphene aerogel through directional freezing, atmospheric pressure drying, and heat treatment.

[0009] Furthermore, the preparation method includes the following steps:

[0010] (1) Preparation of the GO / GNP mixed suspension and the RGO / GNP hydrogel;

[0011] (2) Directionally freezing, drying at atmospheric pressure, and heat-treating the RGO / GNP hydrogel obtained in step (1) to prepare the anisotropic graphene aerogel.

[0012] In a preferred embodiment of the present invention, in step (1), the total concentration of the GO / GNP mixed suspension is 1 - 200 mg / mL, preferably 10 - 100 mg / mL, and more preferably 30 mg / mL; the mass ratio of GO to GNP is 1:0.01 - 1:100, preferably 1:1 - 1:10.

[0013] In a preferred embodiment of the present invention, in step (1), a reducing agent or hydrothermal method is used to reduce GO in the GO / GNP mixed suspension to obtain the RGO / GNP hydrogel; preferably, the reducing agent is selected from ascorbic acid, HI, etc.

[0014] In a preferred embodiment of the present invention, in step (2), the RGO / GNP hydrogel is directionally frozen and dried under atmospheric pressure conditions, and then heat-treated at 100 - 3000 °C, and the heat treatment is carried out in an inert gas atmosphere.

[0015] The present invention also protects the anisotropic graphene aerogel prepared by the above preparation method.

[0016] The present invention also protects a method for preparing a thermally conductive composite material, which is obtained by filling a polymer or a phase change material into the anisotropic graphene aerogel prepared as described above through an impregnation method.

[0017] In a preferred embodiment of the present invention, the graphene aerogel is immersed in a polymer precursor or a phase change material, and the polymer precursor or the phase change material is fully allowed to enter the graphene network system under normal pressure or vacuum conditions; the polymer precursor is selected from epoxy resins, silicone rubbers, silicone resins, etc., and the phase change material is selected from phase change materials such as polyethylene glycol and paraffin.

[0018] The present invention also protects the thermally conductive composite material prepared by the above preparation method.

[0019] Compared with the prior art, the excellent effects of the present invention are as follows:

[0020] (1) In the present invention, GO in the GO / GNP mixed suspension is chemically pre-reduced to form an RGO / GNP hydrogel, and then through directional freezing and atmospheric drying, an anisotropic graphene three-dimensional thermal conduction network with vertical orientation, high density, and excellent mechanical properties can be finally obtained, which can effectively reduce the contact thermal resistance between graphene sheets and improve the thermal conductivity of the composite material.

[0021] (2) The present invention uses an RGO / GNP hydrogel and combines directional freezing and atmospheric drying to prepare a three-dimensional thermal conduction network of high-density anisotropic graphene, effectively solving the problems of large energy consumption in vacuum freeze-drying and supercritical drying of graphene aerogels and limited large-scale preparation. In addition, the density of the graphene aerogel can be controlled by adjusting the ratio of graphene oxide and GNP.

[0022] (3) For the thermally conductive composite material prepared in the present invention, the graphene aerogel is filled with a polymer or a phase change material through an impregnation method. The graphene aerogel prepared in the present invention has an oriented structure, and at the same time, its composite material has high thermal conductivity in both the horizontal and vertical directions. Description of the Drawings

[0023] The present invention will be further described below with reference to the accompanying drawings:

[0024] Figure 1 SEM image obtained by observing the anisotropic graphene aerogel obtained in Example 1 in the direction parallel to the directional freezing direction.

[0025] Figure 2 SEM image obtained by observing the anisotropic graphene aerogel obtained in Example 1 in the direction perpendicular to the directional freezing direction.

[0026] Figure 3 Morphology comparison of the RGO / GNP hydrogel obtained in Examples 1-3 before and after natural drying at room temperature.

[0027] Figure 4 Comparison chart of the thermal conductivities of the graphene / epoxy resin composites and pure epoxy resin obtained in Examples 1-3. Detailed implementation manners

[0028] The method of the present invention will be described below through specific examples, but the present invention is not limited thereto.

[0029] In the following examples, the experimental methods are all conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0030] Example 1: GO was dispersed in deionized water by ultrasonic fragmentation to form a 10 mg / mL GO dispersion. 2.5 g of GNP was dispersed in 50 mL of deionized water to form a 50 mg / mL GNP dispersion. 50 mL of the GO dispersion and 50 mL of the GNP dispersion were mixed, and then 0.5 g of ascorbic acid (VC) was added, and homogenized with a homogenizer for 30 min. The above solution was poured into a glass mold and heated in an oven at 65 °C for 3 h, and then heated at 75 °C for 1 h to obtain an RGO / GNP hydrogel. The RGO / GNP hydrogel was then directionally frozen and dried at room temperature in air to obtain an RGO / GNP aerogel. It was treated at 1000 °C for 2 h under argon protection to further remove the oxygen-containing functional groups on the GO sheets, and then graphitized at 2800 °C for 2 h under argon protection to obtain a high-density, vertically oriented graphene aerogel. The above graphene aerogel was immersed in a proportionally prepared epoxy resin system, and fully impregnated under vacuum conditions, and then heated at 80 °C for 4 h and at 120 °C for 2 h to obtain a high-thermal-conductivity graphene / epoxy resin composite.

[0031] Example 2: GO was dispersed in deionized water by ultrasonic fragmentation to form a 10 mg / mL GO dispersion. 4.0 g of GNP was dispersed in 50 mL of deionized water to form an 80 mg / mL GNP dispersion. 50 mL of the GO dispersion and 50 mL of the GNP dispersion were mixed, and then 0.5 g of ascorbic acid (VC) was added. The mixture was homogenized for 30 min using a homogenizer. The above solution was poured into a glass mold and heated in an oven at 65 °C for 3 h, and then heated at 75 °C for 1 h to obtain an RGO / GNP hydrogel. The RGO / GNP hydrogel was then directionally frozen and dried at room temperature and atmospheric pressure in air to obtain an RGO / GNP aerogel. It was treated at 1000 °C for 2 h under argon protection to further remove the oxygen-containing functional groups on the GO sheets, and then graphitized at 2800 °C for 2 h under argon protection to obtain a high-density, vertically oriented graphene aerogel. The above graphene aerogel was immersed in a proportionally prepared epoxy resin system and fully impregnated under vacuum conditions, and then heated at 80 °C for 4 h and at 120 °C for 2 h to obtain a highly thermally conductive graphene / epoxy composite material.

[0032] Example 3: GO was dispersed in deionized water by ultrasonic fragmentation to form a 10 mg / mL GO dispersion. 5.0 g of GNP was dispersed in 50 mL of deionized water to form a 100 mg / mL GNP dispersion. 50 mL of the GO dispersion and 50 mL of the GNP dispersion were mixed, and then 0.5 g of ascorbic acid (VC) was added. The mixture was homogenized for 30 min using a homogenizer. The above solution was poured into a glass mold and heated in an oven at 65 °C for 3 h, and then heated at 75 °C for 1 h to obtain an RGO / GNP hydrogel. The RGO / GNP hydrogel was then directionally frozen and dried at room temperature and atmospheric pressure in air to obtain an RGO / GNP aerogel. It was treated at 1000 °C for 2 h under argon protection to further remove the oxygen-containing functional groups on the GO sheets, and then graphitized at 2800 °C for 2 h under argon protection to obtain a high-density, vertically oriented graphene aerogel. The above graphene aerogel was immersed in a proportionally prepared epoxy resin system and fully impregnated under vacuum conditions, and then heated at 80 °C for 4 h and at 120 °C for 2 h to obtain a highly thermally conductive graphene / epoxy composite material.

[0033] Figure 1 Figure 7 shows the SEM image of the anisotropic graphene aerogel obtained in Example 1 observed in the direction parallel to the direction of directional freezing. From Figure 1 it can be seen that the graphene aerogel prepared by the directional freezing method has a rich pore structure.

[0034] Figure 2 Figure 13 shows the SEM image of the anisotropic graphene aerogel obtained in Example 1 observed in the direction perpendicular to the direction of directional freezing. From Figure 2It can be seen that the vertically oriented structure of the graphene aerogel prepared by the directional freezing method is relatively obvious.

[0035] Figure 3 Figure 4 shows the morphological comparison of the RGO / GNP hydrogels obtained in Examples 1-3 before and after natural drying at room temperature. Figure 3 It can be seen that GNP significantly inhibits the excessive shrinkage of the RGO / GNP hydrogel during drying at room temperature, and the higher the GNP content, the smaller the shrinkage of the aerogel after drying at room temperature.

[0036] Figure 4 Figure 5 is a comparison chart of the thermal conductivities of the graphene / epoxy resin composites and pure epoxy resin obtained in Examples 1-3. Figure 4 It can be seen that the thermal conductivity of the graphene / epoxy resin composite prepared by the present invention can reach 35.5 W m -1 K -1 .

[0037] Although the present invention has been described in detail above with general descriptions, specific embodiments and experiments, on the basis of the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A method for preparing an anisotropic graphene aerogel by atmospheric pressure drying, characterized in that, a reduced graphene oxide / graphene nanoplatelets (RGO / GNP) hydrogel is formed by pre-reducing a GO / GNP mixed suspension, and then the anisotropic graphene aerogel is prepared by directional freezing, atmospheric pressure drying, and heat treatment, including the following steps: (1) Preparation of the GO / GNP mixed suspension and the RGO / GNP hydrogel; (2) Directionally freezing, drying at atmospheric pressure, and heat treating the RGO / GNP hydrogel obtained in step (1) to prepare the anisotropic graphene aerogel; In step (1), the total concentration of the GO / GNP mixed suspension is 1 - 200 mg / mL; the mass ratio of GO to GNP is 1:0.01 - 1:100; a reducing agent or hydrothermal method is selected to reduce GO in the GO / GNP mixed suspension to obtain the RGO / GNP hydrogel; In step (2), the RGO / GNP hydrogel is directionally frozen and dried under atmospheric pressure conditions, and then heat treated at 100 - 3000 °C, and the heat treatment is carried out in an inert gas atmosphere.

2. The preparation method according to claim 1, characterized in that, in step (1), the total concentration of the GO / GNP mixed suspension is 10 - 100 mg / mL; the mass ratio of GO to GNP is 1:1 - 1:

10.

3. The preparation method according to claim 2, characterized in that, in step (1), the total concentration of the GO / GNP mixed suspension is 30 mg / mL.

4. The preparation method according to claim 3, characterized in that, in step (1), the reducing agent is selected from ascorbic acid and HI.

5. The anisotropic graphene aerogel prepared by the preparation method according to any one of claims 1 - 4.

6. A method for preparing a thermal conductive composite material, characterized in that, the anisotropic graphene aerogel according to claim 5 is filled with a polymer or a phase change material by an impregnation method.

7. The preparation method according to claim 6, characterized in that, the anisotropic graphene aerogel is immersed in a polymer precursor or a phase change material, and the polymer precursor or the phase change material is allowed to fully enter the graphene network system under atmospheric pressure or vacuum conditions.

8. The preparation method according to claim 7, characterized in that, the polymer precursor is selected from epoxy resin, silicone rubber or silicone resin, and the phase change material is selected from polyethylene glycol or paraffin.

9. The thermal conductive composite material prepared by the preparation method according to any one of claims 6 - 8.

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