High-thermal-conductivity flexible composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of functional composite materials, and discloses a high-thermal-conductivity and flexible composite material as well as a preparation method and application thereof. The preparation method of the composite material comprises the following steps: (1) mixing liquid metal, hydrogen peroxide and an organic solvent, and carrying out ultrasonic treatment to obtain dispersion liquid containing liquid metal microdroplets; (2) mixing the flaky heat-conducting filler with the dispersion liquid obtained in the step (1), and performing ultrasonic treatment to obtain dispersion liquid containing the flaky heat-conducting filler coated liquid metal microdroplets; and (3) mixing a polymer fiber matrix with the dispersion liquid obtained in the step (2), carrying out ultrasonic treatment, standing to generate floccules, filtering, drying, and carrying out hot pressing to obtain the composite material. The composite material prepared by the preparation method disclosed by the invention can simultaneously have high thermal conductivity and good flexibility.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional composite materials, and in particular relates to a high thermal conductivity and flexible composite material and a preparation method and application thereof. Background Art

[0002] As electronic components develop towards miniaturization, high integration and multifunctionality, the power density of equipment has increased significantly, and as a result, the heat has also increased dramatically. How to improve the heat dissipation efficiency of devices and maintain the temperature stability of chips to achieve high working efficiency and extend life has become one of the current problems that need to be solved urgently. Thermal interface materials (TIMs) play an indispensable role in heat dissipation structures due to their unique high thermal conductivity. In order to be widely used in flexible electronic and microelectronic products, ideal TIMs must have high thermal conductivity, reduce the intrinsic thermal resistance of the material, and have high flexibility and softness to adapt to various application scenarios.

[0003] Solder is a metal-based TIM with high thermal conductivity. Due to the difference in thermal expansion coefficient between the heat sink and the device, it often causes large thermal stress and eventually forms interface cracks. Another potential material is a composite thermal interface material composed of a polymer matrix and a thermally conductive filler. Due to the high softness and compliance of the polymer, this type of TIM can effectively avoid thermal stress problems and better bridge the upper and lower contact surfaces. However, in order to overcome the low thermal conductivity of the polymer itself (0.1-0.3W·m -1 ·K -1 ), various types of high thermal conductivity fillers are introduced into composite materials. For example, carbon-based thermal conductive fillers such as graphite, carbon nanotubes and carbon fibers have high thermal conductivity, usually between 600 and 2000 W·m -1 ·K -1 However, due to the large van der Waals forces and strong π-π interactions commonly found in these carbon materials, they tend to aggregate and accumulate in the matrix, making it difficult to form an effective heat conduction path. In contrast, solid particles such as copper and silver are easier to disperse between the filler and the matrix, and increasing their volume fraction can effectively enhance the heat transfer path of the material. However, copper and silver particles have high hardness and rigidity and are difficult to bend and deform, which limits the variability and flexibility of TIMs. While improving thermal conductivity, they are prone to failure due to mechanical and thermal fatigue, thus limiting their use scenarios.

[0004] Therefore, how to achieve simultaneous improvement of material flexibility and thermal conductivity remains an important issue. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a method for preparing a composite material, and the composite material prepared by the method can have both high thermal conductivity and good flexibility.

[0006] A first aspect of the present invention provides a method for preparing a composite material, comprising the following steps:

[0007] (1) mixing liquid metal, hydrogen peroxide and an organic solvent, and ultrasonicating to obtain a dispersion containing liquid metal droplets;

[0008] (2) mixing the flaky thermally conductive filler with the dispersion obtained in step (1), and subjecting the mixture to ultrasonic treatment to obtain a dispersion containing liquid metal droplets coated with the flaky thermally conductive filler;

[0009] (3) Mixing the polymer fiber matrix with the dispersion obtained in step (2), ultrasonicating, allowing to stand to form flocs, filtering, drying, and hot pressing to obtain the composite material.

[0010] Specifically, liquid metal refers to a single metal or metal alloy material that maintains a fluid-like flow state at room temperature. It has a high thermal conductivity, usually ranging from 10 to 40 W·m -1 ·K -1 Due to its unique flow and deformation properties, liquid metal can significantly improve the mechanical properties and enhance the flexibility of composite materials when mixed with polymers. Compared with rigid fillers, flowing liquid metal is more likely to form interconnected bridges, especially under stress loading, thus forming an efficient thermal conductive network.

[0011] The present invention aims to provide a method for preparing a thermal interface material by matching liquid metal with a high thermal conductivity network, so as to obtain a composite material based on liquid metal with both high thermal conductivity and flexibility. First, under the oxidation action of hydrogen peroxide, a metal oxide layer is formed on the surface of the liquid metal droplets, which improves the bonding ability of the surface of the liquid metal droplets, prevents the liquid metal droplets from repolymerizing after ultrasonic dispersion, and improves its stability. Subsequently, the flaky high thermal conductivity filler and the metal oxide layer on the surface of the liquid metal droplets undergo hydrogen bonding, so that it is coated on the surface of the liquid metal droplets, thereby reducing the surface tension of the liquid metal droplets and improving the bonding ability of the liquid metal droplets with the polymer fiber matrix. At the same time, the flaky high thermal conductivity filler coated on the surface of the liquid metal droplets is used to build a continuous thermal conductive path inside the composite material, and the liquid metal and the flaky thermal conductive filler are bridged to each other to promote efficient heat transfer, so that a composite material with both high thermal conductivity and flexibility can be obtained.

[0012] In the preparation method of the composite material of the present invention, if hydrogen peroxide is replaced by other oxidants, such as potassium permanganate, potassium permanganate will undergo an electrochemical substitution reaction with the liquid metal, and a metal oxide layer cannot be formed on the surface of the liquid metal, resulting in poor coating effect of the flaky high thermal conductive filler on the liquid metal, thereby affecting the thermal conductivity and mechanical properties of the composite material.

[0013] In some embodiments of the present invention, the average particle size of the liquid metal droplets is ≤800 nm.

[0014] In some embodiments of the present invention, the average particle size of the liquid metal droplets is 200-800 nm.

[0015] In some embodiments of the present invention, the liquid metal includes at least one of a gallium-indium alloy, a gallium-indium-tin alloy, a gallium-zinc alloy, and a bismuth-tin alloy.

[0016] In some embodiments of the present invention, the liquid metal is selected from a gallium-indium-tin alloy, and the composition of the gallium-indium-tin alloy is: 60-80wt% gallium, 15-25wt% indium, and the balance is tin.

[0017] In some embodiments of the present invention, the sheet-like thermally conductive filler includes at least one of boron nitride nanosheets, graphene nanosheets, and graphite nanosheets.

[0018] In some embodiments of the present invention, the average diameter of the flake-shaped thermal conductive filler is 1-50 μm, and the thickness is 0.2-100 nm.

[0019] In some embodiments of the present invention, the organic solvent is selected from anhydrous ethanol.

[0020] In some embodiments of the present invention, the polymer fiber matrix includes aramid fibers and / or cellulose.

[0021] In some embodiments of the present invention, the aramid fiber includes at least one of ortho-aramid fiber, para-aramid fiber, and meta-aramid fiber.

[0022] In some embodiments of the present invention, the polymer fiber matrix is ​​selected from aramid nanofibers.

[0023] In some embodiments of the present invention, the method for preparing the aramid nanofiber comprises the following steps:

[0024] Short-cut aramid fibers and potassium hydroxide are added to dimethyl sulfoxide, and the aramid fibers are deprotonated by mechanical stirring. After stirring for one to two weeks, a uniform aramid fiber dispersion is obtained; then, the dimethyl sulfoxide and excess potassium hydroxide are removed by filtering and washing with anhydrous ethanol, and the filter residue is ultrasonically treated to obtain aramid nanofibers dispersed in anhydrous ethanol; wherein the mass ratio of the dimethyl sulfoxide to the short-cut aramid fibers and potassium hydroxide is (95-112):(3.2-4.7):(3.55-4.5), the speed of mechanical stirring is 300-400 rpm, and the time for ultrasonic dispersion of the filter residue is 40-80 minutes.

[0025] In some embodiments of the present invention, the polymer fiber matrix is ​​selected from nanocellulose.

[0026] In some embodiments of the present invention, the mass ratio of the liquid metal to hydrogen peroxide is 100:(0.1-6), preferably 100:(0.5-4), and more preferably 100:(1.5-3).

[0027] In some embodiments of the present invention, the mass ratio of the liquid metal to the sheet-like thermally conductive filler is 100:(1-10), preferably 100:(4.7-7.1).

[0028] In some embodiments of the present invention, the mass ratio of the liquid metal to the polymer fiber matrix is ​​100:(1-300), preferably 100:(8.69-300).

[0029] In some embodiments of the present invention, the ultrasonic treatment is performed in an ice water bath, and the ultrasonic treatment time is 5-60 min.

[0030] In some embodiments of the present invention, the filtration is performed by vacuum filtration through an organic filter membrane.

[0031] In some embodiments of the present invention, the temperature of the hot pressing is 70-100° C.; and / or, the time of the hot pressing is 5-8 h; and / or, the pressure of the hot pressing is 12-25 MPa.

[0032] A second aspect of the present invention provides a composite material, wherein the composite material is prepared by the preparation method described in the first aspect of the present invention, and the thermal conductivity of the composite material is greater than 5 W·m -1 ·K -1 .

[0033] The third aspect of the present invention provides the preparation method described in the first aspect of the present invention, or the application of the composite material described in the second aspect of the present invention in the preparation of flexible electronics, wearable devices, thermal energy storage, thermal energy control (such as thermal smart switches), building energy saving, heat dissipation of microelectronic devices, sensing, phononic devices or phononic computers.

[0034] A fourth aspect of the present invention provides a thermal energy control device, wherein the thermal energy control device comprises the composite material described in the second aspect of the present invention.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The present invention improves the bonding ability between liquid metal and polymer fiber matrix by using flaky thermal conductive filler to cover liquid metal droplets, thereby improving the compatibility of liquid metal and fiber materials; in addition, during the preparation process, the flaky thermal conductive material on the surface of the liquid metal droplets forms a continuous thermal conductive path inside the composite material, reducing phonon scattering during heat transfer and improving the thermal conductivity of the composite material; therefore, this process can achieve simultaneous improvement of the flexibility and thermal conductivity of the composite material.

[0037] (2) The present invention improves the surface tension of liquid metal through a simple preparation process, promotes its bonding with the polymer fiber matrix, and thereby constructs a continuous heat conduction path inside the composite material, achieving good mechanical properties and thermal conductivity, simple operation and low cost.

[0038] (3) The high thermal conductivity and flexible composite material prepared by the present invention has significant thermal conductivity and excellent flexibility, and is suitable for application in various flexible thermal management systems such as flexible electronics and wearable devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a characterization result diagram of the liquid metal droplets prepared in Example 1 of the present invention;

[0040] Figure 2 This is a transmission electron microscope image of a liquid metal droplet coated with a graphene nanosheet prepared in Example 1 of the present invention;

[0041] Figure 3 These are photos of the composite material prepared in Example 1 of the present invention bent at different angles;

[0042] Figure 4 is a scanning electron microscope image of a cross section of the composite material prepared in Example 1 of the present invention;

[0043] Figure 5 It is the sedimentation diagram of different dispersions within 48 hours during the implementation of the present invention;

[0044] Figure 6 The figure is a data comparison chart of the tensile strength of the composite materials prepared in the examples of the present invention and the comparative examples;

[0045] Figure 7 The figure is a data comparison chart of Young's modulus and fracture energy of the composite materials prepared in the examples of the present invention and the comparative examples. DETAILED DESCRIPTION

[0046] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0047] Unless otherwise specified, the raw materials, reagents or devices used in the present invention can be obtained from conventional commercial channels or by existing known methods.

[0048] The liquid metal used in the embodiment of the present invention is room temperature gallium indium tin alloy purchased from Zhenjiang Fanyada Electronic Technology Co., Ltd.

[0049] The aramid nanofibers used in the embodiments of the present invention are prepared by a preparation method comprising the following steps:

[0050] Short-cut aramid fibers and potassium hydroxide are added to dimethyl sulfoxide, and the aramid fibers are deprotonated by mechanical stirring. After stirring for one week, a uniform aramid nanofiber dispersion is obtained. The dimethyl sulfoxide and excess potassium hydroxide are then removed by filtering and washing with anhydrous ethanol, and the filter residue is ultrasonically treated to obtain aramid nanofibers dispersed in anhydrous ethanol. The mass ratio of dimethyl sulfoxide to short-cut aramid fibers and potassium hydroxide is 100:4:4, the speed of mechanical stirring is 350 rpm, and the ultrasonic time is 60 minutes.

[0051] Example 1

[0052] A method for preparing a highly thermally conductive and flexible composite material comprises the following steps:

[0053] (1) adding liquid metal and hydrogen peroxide to anhydrous ethanol, and ultrasonicating for 30 minutes in an ice-water bath to obtain a dispersion containing liquid metal droplets; wherein the mass ratio of the liquid metal to the hydrogen peroxide is 100:2;

[0054] (2) adding graphene nanosheets with an average diameter of 25 μm and a thickness of 50 nm to the dispersion obtained in step (1), and ultrasonicating for 30 min in an ice-water bath to obtain a dispersion containing graphene nanosheet-coated liquid metal droplets; wherein the mass ratio of liquid metal to graphene nanosheets is 100:6;

[0055] (3) adding the aramid nanofibers dispersed in anhydrous ethanol to the dispersion obtained in step (2), ultrasonically treating for 15 minutes in an ice-water bath, standing for 30 minutes to generate flocs, and then passing through an organic filter membrane with a pore size of 0.2 μm and vacuum filtering, and naturally drying at room temperature, and then hot pressing at a temperature of 80° C. and a pressure of 20 MPa for 8 hours to obtain a high thermal conductivity and flexible composite material; wherein the mass ratio of liquid metal to aramid nanofiber is 100:150.

[0056] Example 2

[0057] A method for preparing a highly thermally conductive and flexible composite material comprises the following steps:

[0058] (1) adding liquid metal and hydrogen peroxide to anhydrous ethanol, and ultrasonicating for 30 minutes in an ice-water bath to obtain a dispersion containing liquid metal droplets; wherein the mass ratio of the liquid metal to the hydrogen peroxide is 100:2;

[0059] (2) adding graphene nanosheets with an average diameter of 25 μm and a thickness of 50 nm to the dispersion obtained in step (1), and ultrasonicating for 30 min in an ice-water bath to obtain a dispersion containing graphene nanosheet-coated liquid metal droplets; wherein the mass ratio of liquid metal to graphene nanosheets is 100:6;

[0060] (3) Adding nanocellulose to the dispersion obtained in step (2), ultrasonically treating for 15 minutes in an ice-water bath, standing for 30 minutes to generate flocs, passing through an organic filter membrane with a pore size of 0.2 μm, and vacuum filtering, drying naturally at room temperature, and then hot pressing at a temperature of 80° C. and a pressure of 20 MPa for 8 hours to obtain a high thermal conductivity and flexible composite material; wherein the mass ratio of liquid metal to nanocellulose is 100:150.

[0061] Comparative Example 1

[0062] The only difference from Example 1 is that no graphene nanosheets are added, and the other raw materials and amounts are the same as those in Example 1.

[0063] Specifically, a method for preparing a composite material comprises the following steps:

[0064] (1) adding liquid metal and hydrogen peroxide to anhydrous ethanol, and ultrasonicating for 30 minutes in an ice-water bath to obtain a dispersion containing liquid metal droplets; wherein the mass ratio of the liquid metal to the hydrogen peroxide is 100:2;

[0065] (2) adding aramid nanofibers dispersed in anhydrous ethanol to the dispersion obtained in step (1), ultrasonically treating for 15 minutes in an ice-water bath, standing for 30 minutes to generate flocs, passing through an organic filter membrane with a pore size of 0.2 μm, and vacuum filtering. After natural drying at room temperature, hot pressing at a temperature of 80° C. and a pressure of 20 MPa for 8 hours to obtain a composite material; wherein the mass ratio of liquid metal to aramid nanofiber is 100:150.

[0066] Comparative Example 2

[0067] The only difference from Example 1 is that no liquid metal is added, and the remaining raw materials and amounts are the same as those in Example 1.

[0068] Specifically, a method for preparing a composite material comprises the following steps:

[0069] (1) adding graphene nanosheets with an average diameter of 25 μm and a thickness of 50 nm into anhydrous ethanol, and ultrasonicating for 30 min in an ice-water bath to obtain a dispersion containing graphene nanosheets;

[0070] (2) Aramid nanofibers dispersed in anhydrous ethanol are added to the dispersion obtained in step (1), and ultrasonically treated for 15 minutes in an ice-water bath. After standing for 30 minutes, flocs are generated, and then passed through an organic filter membrane with a pore size of 0.2 μm and vacuum filtered. After natural drying at room temperature, the composite material is hot-pressed at a temperature of 80° C. and a pressure of 20 MPa for 8 hours to obtain the composite material.

[0071] Product Characterization

[0072] Figure 1 The characterization results of the liquid metal droplets prepared in Example 1 of the present invention are shown in FIG. Figure 1 In the figure, (a) is the electron microscope image of the liquid metal droplet; (b) is the size distribution histogram of the liquid metal droplet; (c) is the X-ray photoelectron spectrum of Ga3d in the liquid metal droplet.

[0073] From the electron microscope image of the liquid metal droplets, it can be seen that after ultrasonic dispersion, the liquid metal forms spherical droplets with diameters mainly distributed in the range of 200-800nm. The X-ray photoelectron spectroscopy image confirms that most of the gallium on the surface of the liquid metal droplets is oxidized to trivalent gallium oxide by hydrogen peroxide.

[0074] Figure 2 This is a transmission electron microscope image of the graphene nanosheet-coated liquid metal droplet prepared in Example 1 of the present invention. It can be clearly observed from the transmission electron microscope image that a liquid metal-graphene nanosheet core-shell structure (liquid metal as the core and graphene nanosheet as the shell) connected by an oxide layer is formed.

[0075] Figure 3 This is a photo of the composite material prepared in Example 1 of the present invention. It is in the form of a film and can be bent and deformed arbitrarily. It is soft and easy to deform.

[0076] Figure 4 This is an electron microscope image of the cross section of the composite material prepared in Example 1 of the present invention. Figure 4 In the figure, (a) and (b) are cross-sectional SEM images at different magnification scales, respectively. Figure 4 (b) shows that the liquid metal droplets are evenly distributed inside the composite material and are tightly connected to each other by bridging under the wrapping of graphene nanosheets, which is conducive to the formation of a good thermal conductivity path.

[0077] Figure 5 This is a graph showing the sedimentation of different dispersions within 48 hours during the implementation of the present invention. Figure 5In the figure, (a) is the sedimentation diagram of the dispersion obtained by ultrasonic treatment of liquid metal directly in anhydrous ethanol; (b) is the sedimentation diagram of the dispersion obtained by ultrasonic treatment of liquid metal under hydrogen peroxide oxidation conditions; (c) is the floccules formed by mixing the coated liquid metal dispersion with the polymer fiber matrix and ultrasonically standing. Figure 5 As can be seen from (a) and (b) in the figure, in the presence of hydrogen peroxide, the sedimentation rate is slower, which is more conducive to the formation of a stable liquid metal dispersion. Figure 5 As can be seen in (c), the coated liquid metal and the polymer fiber matrix have basically formed stable flocs (the upper layer is clear liquid and the lower layer is flocs) after ultrasonic standing for 30 minutes.

[0078] Product performance testing

[0079] The thermal conductivity test method is as follows:

[0080] The thermal conductivity of the material is measured by the transient method:

[0081] κ=α·ρ·Cp;

[0082] Among them, α is the thermal diffusion coefficient of the material surface; ρ is the material density; Cp is the specific heat capacity of the material.

[0083] Specific test standard reference: ASTM E-1461: Standard Test Method for Thermal Diffusivity of Solids by the Flash Method.

[0084] The thermal diffusion coefficient α was measured by a flash laser thermal conductivity instrument (LFA, NETZSCH LFA 467, Germany). The material density was calculated by the formula ρ = m / v. The specific heat capacity was measured by a differential scanning calorimeter (DSC, NETZSCH DSC 200F3, Switzerland) using the sapphire specific heat method.

[0085] The test results of thermal conductivity of the composite materials prepared in Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0086] Table 1

[0087]

[0088] Mechanical properties test

[0089] The mechanical properties of the composite materials prepared in Examples 1-2 and Comparative Examples 1-2 were tested by a tensile testing machine, and the test standard was based on: ASTM D3039 / D3039M Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials.

[0090] The test results are as follows Figure 6 and Figure 7 shown.

[0091] Based on the test results of the thermal conductivity and mechanical properties, it can be seen that the composite material prepared in the present invention can have both high thermal conductivity and good flexibility.

[0092] The preferred embodiments of the present invention are specifically described above, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for preparing a composite material, characterized in that: The following steps are involved: (1) mixing liquid metal, hydrogen peroxide and an organic solvent, and ultrasonicating to obtain a dispersion containing liquid metal droplets; (2) mixing the flaky thermally conductive filler with the dispersion obtained in step (1), and subjecting the mixture to ultrasonic treatment to obtain a dispersion containing liquid metal droplets coated with the flaky thermally conductive filler; (3) Mixing the polymer fiber matrix with the dispersion obtained in step (2), ultrasonicating, allowing to stand to form flocs, filtering, drying, and hot pressing to obtain the composite material.

2. The preparation method according to claim 1, characterized in that: The liquid metal includes at least one of a gallium-indium alloy, a gallium-indium-tin alloy, a gallium-zinc alloy, and a bismuth-tin alloy.

3. The preparation method according to claim 1, characterized in that: The sheet-like thermal conductive filler includes at least one of boron nitride nanosheets, graphene nanosheets, and graphite nanosheets.

4. The preparation method according to claim 1, characterized in that: The polymer fiber matrix includes aramid fiber and / or cellulose.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the liquid metal to hydrogen peroxide is 100:(0.1-6); and / or, the mass ratio of the liquid metal to the sheet-like thermal conductive filler is 100:(1-10); and / or, the mass ratio of the liquid metal to the polymer fiber matrix is ​​100:(1-300).

6. The preparation method according to claim 1, characterized in that: The ultrasonic treatment is performed in an ice water bath, and the ultrasonic treatment time is 5-60 min.

7. The preparation method according to claim 1, characterized in that: The temperature of the hot pressing is 70-100° C.; and / or, the time of the hot pressing is 5-8 hours; and / or, the pressure of the hot pressing is 12-25 MPa.

8. A composite material, characterized in that The composite material is prepared by the preparation method according to any one of claims 1 to 7, and the thermal conductivity of the composite material is greater than 5 W·m -1 ·K -1 .

9. Use of the preparation method according to any one of claims 1 to 7, or the composite material according to claim 8 in the preparation of flexible electronics, wearable devices, thermal energy storage, thermal energy control, building energy conservation, heat dissipation of microelectronic devices, sensing, phononic devices or phononic computers.

10. A thermal energy control device, characterized in that: The composite material comprises the composite material as claimed in claim 8.

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