Preparation method of flexible and elastic composite material with high thermal conductivity

Abstract

The invention discloses a preparation method of a flexible and elastic composite material with high thermal conductivity. With the increasingly complex operating conditions of equipment, such as irregular and dynamic surfaces, thermal interface materials (TIMs) are required to have both high thermal conductivity and soft elasticity. However, it is still a challenging task to develop materials having both soft elasticity and high thermal conductivity. According to the invention, vertical oriented graphene aerogel (VGA) is used as a microcosmic heat conduction path, and an oriented and continuous liquid metal (LM) network is reasonably designed as a macroscopic heat conduction path. In combination with the advantages of low elastic modulus and high deformability of brush-like polydimethylsiloxane (BPDMS), the designed liquid metal / vertically oriented graphene aerogel / brush-like PDMS (LM-VGA / BPDMS) composite material shows high thermal conductivity, relatively high compression ratio and ultralow elastic modulus. The LM-VGA / BPDMS soft composite material shows stable heat dissipation capability on a dynamically changing interface, and has good adaptability to different irregular surfaces. The strategy has an important application prospect in the field of interface thermal management and thermal induction in an extremely complex environment.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal interface materials, and in particular relates to a method for preparing a flexible, elastic and highly thermally conductive composite material. Background Art

[0002] With the rapid development of high-performance electronic devices and smart sensors, stable and efficient heat transfer between devices is essential to keep the system running stably. For example, the reliability of a device depends exponentially on its operating temperature, and even a slight increase in temperature of 10-15°C may result in a significant reduction in device life by 50%. To overcome this problem, thermal interface materials (TIMs) such as thermal grease and thermal pads have been developed to enhance thermal conductivity between interfaces. Among them, polymers have become an important component of TTMs due to their advantages such as good mechanical properties, easy processing and molding, and cost-effectiveness. Since polymers are poor conductors of heat, phonon transmission is hindered, and their thermal conductivity is low, generally only 0.1-0.4 Wm -1 K -1 Therefore, a large amount of high thermal conductivity fillers need to be added to form an effective thermal conduction path to achieve the purpose of rapid heat transfer. According to the Newton-Laplace equation, it is difficult for thermally conductive composite materials to have both high thermal conductivity and low modulus at the same time. Therefore, the preparation of new thermal interface materials that are soft, resilient, and highly thermally conductive is still a huge challenge.

[0003] Compared with traditional cross-linked polymers, brush polymers graft long side chains into the polymer backbone, reduce the entanglement energy by increasing the diameter and length of the polymer, and thus reduce the elastic modulus of the polymer. In addition, the prefabricated thermal conductive filler network can construct a large number of thermal conductive pathways under the condition of adding only a small amount of filler, thereby improving the utilization efficiency of thermal fillers. Prefabricated thermal conductive networks can be achieved through a variety of strategies, such as self-assembly, templating, and external field induction, to generate three-dimensional continuous network structures and directional architectures during the processing stage. In addition, liquid metals (LM), such as gallium-indium alloys, are popular due to their flexibility, self-healing ability, and high κ (26.4 Wm -1 K -1 ), which is becoming increasingly popular in chemistry, materials, and biomedical research. Compared with traditional rigid metal-polymer composites, LM / polymer materials show excellent flexibility and mechanical reliability. However, the current method of preparing LM / polymer materials is usually to blend liquid metal with a matrix. The huge interfacial thermal resistance between the randomly dispersed LM particles and the matrix greatly hinders the heat transfer efficiency.

[0004] Based on this, the present invention provides a method for preparing a flexible, elastic, and highly thermally conductive composite material. A macroscopic and microscopic dual thermal conductive path is formed by utilizing vertically oriented graphene aerogel (VGA) and a directional, adjustable liquid metal (LM) network. Subsequently, we utilized the advantages of low elastic modulus and high deformation capacity of brush-like polydimethylsiloxane (BPDMS) to prepare a composite material that is both soft, resilient, and highly thermally conductive. The present invention can effectively resolve the contradiction between high thermal conductivity and low modulus, and provide a new method for preparing a flexible, elastic, and thermally conductive composite material. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that in the prior art a large amount of thermally conductive fillers are added to achieve high thermal conductivity of composite materials, which leads to serious deterioration of comprehensive properties such as mechanical properties and processing properties of the composite materials, and it is impossible to balance the comprehensive mechanical properties of the material while obtaining good thermal conductivity.

[0006] S1. Preparation of vertically oriented graphene aerogel (VGA). First, graphite nanosheets (GNPs) were added to 100 mL of carboxymethyl cellulose (SCMC) aqueous solution. SCMC / GNPs slurry was obtained by stirring the mixture for 12 hours using a ball mill. The resulting slurry was then poured into a polymethyl methacrylate (PMMA) mold and placed on a copper rod, partially immersed in liquid nitrogen. The sample was frozen and then freeze-dried for about 72 hours to obtain VGA.

[0007] Furthermore, the mass of GNPs is 0.5 g to 2 g.

[0008] The concentration of the further carboxymethyl cellulose solution is 1-2 wt.%.

[0009] Furthermore, the rotation speed of the ball mill is 100-500 rpm.

[0010] S2. Preparation of brush-shaped polydimethylsiloxane (BPDMS): a certain amount of vinyl-terminated polydimethylsiloxane (VPDMS), dodecyl acrylate, polydimethylsiloxane containing silicon hydrogen groups in the side chain (MHPDMS) and Karstedt catalyst (5 mg / L) were added into a flask, stirred at 1000 rpm for 30 minutes, and heated to react for a period of time under an argon atmosphere.

[0011] Furthermore, the Mw of VPDMS is 17000 g / mol; the Mw of MHPDMS is 60000 g / mol, wherein the content of Si-H groups is 0.87 mol / Kg.

[0012] Further, the molar ratio of MHPDMS to (VPDMS+dodecyl acrylate) was fixed at 1:(30-50).

[0013] Furthermore, the molar ratios of VPDMS and dodecyl acrylate in the experiments were (0, 10-3, 10-2 and 10-1):1, respectively.

[0014] Furthermore, the reaction temperature is 80-120° C., and the heating time is 6 h-12 h.

[0015] S3. Preparation of patterned LM-VGA / BDMS composites. VGA / BPDMS composites were prepared by repeated vacuum-assisted impregnation using VGA with different densities and the above-mentioned BPDMS precursor. The resulting composites were reacted at 80°C for 24 hours. In addition, microgrooves of different shapes were etched on the VGA / BPDMS samples using a digital laser etcher. After surface plasma treatment, an appropriate amount of LM inclusions were injected into the substrate grooves using a microinjector, and then encapsulated with the GNP / BPDMS mixture and heated for curing.

[0016] Furthermore, the content of VGA in VGA / BPDMS is 3.6±0.3wt.% to 10.9±0.3wt.%.

[0017] Furthermore, the mass function of the liquid metal is 57.5±2.7wt.% to 65.0±3.2wt.%.

[0018] Further microgrooves are shaped as dot array (D), line array (L) and network (N).

[0019] Furthermore, the model of the digital laser etching machine is CMA-4030, Han's Yueming, moving speed: 100 mm / s, laser power: 30W.

[0020] Further, the surface is plasma treated for 10s-60s.

[0021] Furthermore, the curing temperature is 80-120°C and the curing time is 8-12h. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of liquid metal patterning.

[0023] Figure 2 Scanning electron microscope images of vertical graphene aerogel VGA and its VGA / BPDMS composite material

[0024] Figure 3 The vertical thermal conductivity of the patterned LM-VGA / BPDMS composite material varies with the VGA density and liquid metal pattern.

[0025] Figure 4Actual pictures of compression, bending, and distortion of patterned LM-VGA / BPDMS. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with specific embodiments.

[0027] Embodiment 1

[0028] S1. 0.5 g of graphite nanosheets (GNPs) were added to 100 mL of 1 wt.% carboxymethyl cellulose (SCMC) aqueous solution. The SCMC / GNPs slurry was obtained by stirring the mixture for 12 hours using a ball mill (300 rpm). The resulting slurry was then poured into a polymethyl methacrylate (PMMA) mold and placed on a copper rod, partially immersed in liquid nitrogen. The sample was frozen and then freeze-dried for about 72 hours to obtain VGA.

[0029] S2. A certain amount of vinyl-terminated polydimethylsiloxane (VPDMS, 17600 g / mol), dodecyl acrylate, polydimethylsiloxane containing side silicon hydrogen groups (MHPDMS, 60000 g / mol, wherein the content of Si-H groups is 0.87 mol / Kg) and Karstedt catalyst (5 mg / L) were added into a flask, stirred at 1000 rpm for 30 minutes, and heated for a period of time under an argon atmosphere. Among them, the molar ratio of MHPDMS to (VPDMS+dodecyl acrylate) was fixed at 1: (30-50). Furthermore, the molar ratio of VPDMS to dodecyl acrylate in the experiment was 0: 1, respectively.

[0030] S3. The above-mentioned VGA and BPDMS precursors were subjected to repeated vacuum-assisted impregnation to prepare a VGA / BPDMS composite material. The resulting composite material was reacted at 80°C for 24 hours. In addition, a digital laser etcher was used to etch microgrooves of a network structure (N) on the VGA / BPDMS sample. After surface plasma treatment for 30 seconds, an appropriate amount of LM inclusions was injected into the substrate grooves using a microinjector, and then encapsulated with a GNP / BPDMS mixture and heated to cure. At this time, the content of VGA in VGA / BPDMS was 3.6±0.3wt.%, and the mass function of the liquid metal was 57.5±2.7wt.% to 65.0±3.2wt.%.

[0031] The thermal conductivity of the prepared patterned N-LM-VGA / BPDMS is: 1.47 Wm -1 K -1 The maximum compression rate is 60%, the stress is, and the elastic modulus is 10.13 kPa.

[0032] Embodiment 2

[0033] S1. 1 g of graphite nanosheets (GNPs) was added to 100 mL of 1 wt.% carboxymethyl cellulose (SCMC) aqueous solution. The SCMC / GNPs slurry was obtained by stirring the mixture for 12 hours using a ball mill (300 rpm). The resulting slurry was then poured into a polymethyl methacrylate (PMMA) mold and placed on a copper rod, partially immersed in liquid nitrogen. The sample was frozen and then freeze-dried for about 72 hours to obtain VGA.

[0034] S2. A certain amount of vinyl terminated polydimethylsiloxane (VPDMS, 17600 g / mol), dodecyl acrylate, polydimethylsiloxane containing side silane groups (MHPDMS, 60000 g / mol, wherein the content of Si-H groups is 0.87 mol / Kg) and Karstedt catalyst (5 mg / L) were added to a flask, stirred at 1000 rpm for 30 minutes, and heated for a period of time under an argon atmosphere. Among them, the molar ratio of MHPDMS to (VPDMS+dodecyl acrylate) was fixed at 1:50. Furthermore, the molar ratio of VPDMS to dodecyl acrylate in the experiment was 0:1, respectively.

[0035] S3. The above-mentioned VGA and BPDMS precursors were subjected to repeated vacuum-assisted impregnation to prepare a VGA / BPDMS composite material. The resulting composite material was reacted at 80°C for 24 hours. In addition, a digital laser etcher was used to etch network-shaped (N) microgrooves on the VGA / BPDMS sample. After surface plasma treatment for 30 seconds, an appropriate amount of LM inclusions was injected into the substrate grooves using a microinjector, and then encapsulated with a GNP / BPDMS mixture and heated to cure. At this time, the content of VGA in VGA / BPDMS was 6.7±0.3wt.%, and the mass function of the liquid metal was 57.5±2.7wt.%~65.0±3.2wt.%.

[0036] The thermal conductivity of the prepared patterned N-LM-VGA / BPDMS is: 4.46 Wm -1 K -1 ; The maximum compression rate is 40%; the elastic modulus is 20.13kPa.

[0037] Embodiment 3

[0038] S1. 2 g of graphite nanosheets (GNPs) were added to 100 mL of 1 wt.% carboxymethyl cellulose (SCMC) aqueous solution. The SCMC / GNPs slurry was obtained by stirring the mixture for 12 hours using a ball mill (300 rpm). The resulting slurry was then poured into a polymethyl methacrylate (PMMA) mold and placed on a copper rod, partially immersed in liquid nitrogen. The sample was frozen and then freeze-dried for about 72 hours to obtain VGA.

[0039] S2. A certain amount of vinyl terminated polydimethylsiloxane (VPDMS, 17600 g / mol), dodecyl acrylate, polydimethylsiloxane containing side silane groups (MHPDMS, 60000 g / mol, wherein the content of Si-H groups is 0.87 mol / Kg) and Karstedt catalyst (5 mg / L) were added to a flask, stirred at 1000 rpm for 30 minutes, and heated for a period of time under an argon atmosphere. Among them, the molar ratio of MHPDMS to (VPDMS+dodecyl acrylate) was fixed at 1:50. Furthermore, the molar ratio of VPDMS to dodecyl acrylate in the experiment was 0:1, respectively.

[0040] S3. The above-mentioned VGA and BPDMS precursors were subjected to repeated vacuum-assisted impregnation to prepare a VGA / BPDMS composite material. The resulting composite material was reacted at 80°C for 24 hours. In addition, a digital laser etcher was used to etch microgrooves in a dot array shape (D) on the VGA / BPDMS sample. After surface plasma treatment for 30 seconds, an appropriate amount of LM inclusions was injected into the substrate grooves using a microinjector, and then encapsulated with a GNP / BPDMS mixture and heated to cure. At this time, the content of VGA in VGA / BPDMS was 10.9±0.3wt.%, and the mass function of the liquid metal was 65.0±3.2wt.%.

[0041] The thermal conductivity of the prepared patterned D-LM-VGA / BPDMS is: 7.11 Wm -1 K -1 The maximum compression rate is 20%, the stress is, and the elastic modulus is 741kPa.

Claims

1. A method for preparing a flexible, elastic and highly thermally conductive composite material, characterized in that: S1. The method adds 0.5-2g of graphite nanosheets (GNPs) to 100mL of 1wt.-2wt.% carboxymethyl cellulose (SCMC) aqueous solution. The SCMC / GNPs slurry is obtained by stirring the mixture for 12 hours using a ball mill (300rpm). The resulting slurry is then poured into a polymethyl methacrylate (PMMA) mold and placed on a copper column, partially immersed in liquid nitrogen. The sample is frozen and then freeze-dried for about 72h to obtain VGA. S2. A certain amount of vinyl-terminated polydimethylsiloxane (, dodecyl acrylate, polydimethylsiloxane containing silicon hydrogen groups in the side chain and Karstedt catalyst (5 mg / L) were added to a flask, stirred at 1000 rpm for 30 minutes, and heated for a period of time under an argon atmosphere. The Mw of VPDMS was 17000 g / mol; the Mw of MHPDMS was 60000 g / mol. The content of Si-H groups was 0.87 mol / Kg. S3. The above VGA and BPDMS precursors were subjected to repeated vacuum-assisted impregnation to prepare VGA / BPDMS composites. The resulting composites were reacted at 80°C for 24 hours. After surface plasma treatment, an appropriate amount of LM inclusions were injected into the substrate grooves using a microinjector, and then encapsulated with the GNP / BPDMS mixture and heated for curing.

2. The method according to claim 1, characterized in that The molar ratio of MHPDMS to (VPDMS + dodecyl acrylate) was fixed at 1:

50. The molar ratios of VPDMS and dodecyl acrylate were (0, 10 -3 , 10 -2 and 10 -1 )∶1. The heating temperature is 80-120°C and the reaction time is 6-8h.

3. The method according to claim 1, characterized in that The shapes of the microgrooves engraved on the surface of the VGA / BPDMS composite material are dot array (D), line array (L) and network (N).

4. The method according to claim 1, characterized in that The surface of the VGA / BPDMS composite material was treated with plasma for 10s-60s.

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