A bidirectional high-thermal-conductivity polymer-based nanocomposite film, a preparation method and applications thereof

Abstract

The application discloses a bidirectional high-thermal-conductivity polymer-based nanocomposite film and a preparation method and application thereof, and belongs to the technical field of polymer composites. The application preliminarily disperses carbon nanotube powder by using a specific solvent, adds boron nitride to obtain a boron nitride / carbon nanotube dispersion liquid, then gradually adds the dispersion liquid into a graphene oxide aqueous solution, stirs, washes with water and centrifugates to obtain a graphene oxide / boron nitride / carbon nanotube composite. Then, the graphene oxide / boron nitride / carbon nanotube composite is dispersed in water to form a composite aqueous solution; the composite aqueous solution and a polyvinyl alcohol aqueous solution are compounded, hydrazine hydrate is added dropwise for reduction to obtain a partially reduced solution; and finally, the partially reduced solution is coated on the surface of a substrate and gradient drying is carried out to obtain the bidirectional high-thermal-conductivity polymer-based nanocomposite film. The bidirectional high-thermal-conductivity polymer-based nanocomposite film prepared by the application has a good application prospect in the fields of thermal interface materials, heat dissipation coatings and the like.

Description

Technical Field

[0001] This invention relates to a bidirectional high thermal conductivity polymer-based nanocomposite film, its preparation method and application, belonging to the field of polymer composite material technology. Background Technology

[0002] The continuous miniaturization and integration of electronic devices places higher demands on their heat dissipation performance. Traditional anisotropic thermally conductive materials can achieve rapid lateral heat diffusion in the parallel direction (in-plane), but the high interfacial thermal resistance in the perpendicular direction (through-plane) reduces the overall heat dissipation efficiency of the material, limiting its application in the electronics industry. Therefore, developing materials with high thermal conductivity in both the parallel and perpendicular directions is an effective way to solve the above problems.

[0003] Hexagonal boron nitride (h-BN) possesses a graphite-like layered structure, good chemical stability, and high thermal conductivity (400 W / (m·K)), making it an important filler for preparing high thermal conductivity polymer composites. However, BN tends to agglomerate in polymer matrices, is difficult to disperse, and has poor interfacial compatibility with the matrix, significantly increasing interfacial thermal resistance. Common methods include ball milling, ultrasonic dispersion, and surface modification to control the dispersibility and directional alignment of BN in polymers, thereby improving the parallel-direction thermal conductivity of the material. Furthermore, techniques such as ice template methods and bidirectional freeze-assembly combined with vacuum impregnation can disperse and align BN in the vertical direction to achieve higher vertical thermal conductivity.

[0004] For bidirectional thermal conductivity, current methods mainly involve combining two-dimensional sheet-like boron nanotubes (BN) with one-dimensional nanofillers (such as carbon nanotubes and silicon carbide nanowires) via chemical vapor deposition (Li Yun, Tian Xiaojuan, Yang Wang, et al. Dielectric composite reinforced by in-situ growth of carbon nanotubes on boron nitridenanosheets with high thermal conductivity and mechanical strength[J]. Chemical Engineering Journal, 2019, 358: 718-724.), template-assisted in-situ growth (Yang Wang, Wang Yifan, Li Yun, et al. Three-dimensional skeleton assembled by carbon nanotubes / boron nitride as filler in epoxy for thermal management materials with high thermal conductivity and electrical insulation[J]. Composites Part B: Engineering, 2021, 224: 109168.), and electrospinning (Yang Liu, Zhang Ling, Li Chunzhong. Bridging boron nitride nanosheets with oriented carbon nanotubes by electrospinning for the fabrication of thermal...). Three-dimensional thermally conductive structures can be constructed using methods such as conductivity-enhanced flexible nanocomposites[J]. Composites Science and Technology, 2020, 200: 108429., providing pathways for phonon conduction in multiple dimensions. However, these methods are costly and complex, making large-scale fabrication difficult.

[0005] In recent years, nanomaterials such as graphene, carbon nanotubes, and boron nitride have shown great promise in fields such as thermal interface materials, heat dissipation coatings, and thermal management of high-power devices. However, no graphene / carbon nanotube / boron nitride composite system has yet been discovered. Moreover, the main challenge in the preparation of aqueous ternary composite slurries lies in the uniform dispersion of graphene, carbon nanotubes, and boron nitride in the aqueous phase and the effective thermally conductive network assembly among the three. Currently, an economically feasible approach is to improve the water dispersibility of various nanomaterials through covalent functionalization, but this method often severely damages the intrinsic high thermal conductivity of boron nitride. Alternatively, the good water dispersibility of graphene oxide and its non-covalent interactions with carbon nanotubes and boron nitride can be used to directly disperse the latter two. However, this mixed system often requires prolonged ultrasonic treatment, which can easily lead to damage to the graphene oxide structure, severing of carbon nanotubes, and fragmentation of boron nitride sheets. Furthermore, multiple centrifugations and washings are usually required afterward to remove agglomerates, resulting in problems such as low yield, high energy consumption, and complex processes in the preparation process.

[0006] Therefore, developing bidirectional, highly thermally conductive, waterborne graphene / carbon nanotube / boron nitride ternary polymer-based nanocomposite films that can maintain the intrinsic thermal conductivity of materials, have simple processes, and are suitable for large-scale preparation for high-performance thermal management applications remains an important and challenging task. Summary of the Invention

[0007] [Technical Issues] Graphene, carbon nanotubes and boron nitride are difficult to disperse uniformly in an aqueous phase; Conventional polymer-based nanocomposite films cannot achieve bidirectional thermal conductivity; The preparation method of bidirectional thermal conductive materials is complex and costly, making it difficult to achieve industrial production.

[0008] [Technical Solution] To address the aforementioned problems, this invention provides a bidirectional high thermal conductivity polymer-based nanocomposite film, its preparation method, and its applications. Specifically, this invention uses a specific solvent to initially disperse carbon nanotube powder, then adds boron nitride to obtain a boron nitride / carbon nanotube dispersion; subsequently, it is gradually added to an aqueous graphene oxide solution, stirred, washed with water, and centrifuged to obtain a graphene oxide / boron nitride / carbon nanotube composite. Then, the graphene oxide / boron nitride / carbon nanotube composite is dispersed in water to form a composite aqueous solution; next, the composite aqueous solution is combined with an aqueous polyvinyl alcohol solution, and hydrazine hydrate is added dropwise for reduction to obtain a partially reduced solution; finally, the partially reduced solution is coated onto a substrate surface and subjected to gradient drying to obtain a bidirectional high thermal conductivity polymer-based nanocomposite film. The bidirectional high thermal conductivity polymer-based nanocomposite film prepared by this invention has promising application prospects in thermal interface materials, heat dissipation coatings, and thermal management of high-power devices.

[0009] The first objective of this invention is to provide a method for preparing a bidirectional high thermal conductivity polymer-based nanocomposite film, comprising the following steps: (1) Add boron nitride to the carbon nanotube dispersion, stir and homogenize to obtain boron nitride / carbon nanotube dispersion; (2) Add boron nitride / carbon nanotube dispersion dropwise to graphene oxide solution, stir, wash with water and centrifuge to obtain graphene oxide / boron nitride / carbon nanotube composite. (3) The graphene oxide / boron nitride / carbon nanotube composite was dispersed in water to obtain an aqueous solution of the composite; (4) Combine the aqueous solution of the complex and the aqueous solution of polyvinyl alcohol, and reduce them by adding hydrazine hydrate solution dropwise to obtain a partially reduced solution; (5) The partially reduced solution is coated on the surface of the substrate and then subjected to gradient drying to obtain a bidirectional high thermal conductivity polymer-based nanocomposite film.

[0010] In one embodiment of the present invention, the solvent of the carbon nanotube dispersion in step (1) is any one or more of m-cresol, o-cresol, p-cresol, resorcinol, etc.; or the above solvent is mixed with any one or more of n-hexane, 1,4-dioxane, toluene, anisole, chloroform, etc. in any proportion.

[0011] In one embodiment of the present invention, the mass ratio of carbon nanotubes to solvent in the carbon nanotube dispersion in step (1) is 0.1-0.5:100.

[0012] In one embodiment of the present invention, the mass ratio of carbon nanotubes to boron nitride in step (1) is 0.1-0.5:1.

[0013] In one embodiment of the present invention, the stirring in step (1) is water bath ultrasound, specifically ultrasound at 20-30℃ and 40-50W for 20-40 min.

[0014] In one embodiment of the present invention, the homogenization in step (1) is to homogenize and disperse at 8000-10000 r / min for 10-20 min.

[0015] In one embodiment of the present invention, the solvent for the graphene oxide solution in step (2) is water.

[0016] In one embodiment of the present invention, the concentration of the graphene oxide solution in step (2) is 5-15 mg / mL.

[0017] In one embodiment of the present invention, the volume ratio of graphene oxide solution and boron nitride / carbon nanotube dispersion in step (2) is 200:50-150.

[0018] In one embodiment of the present invention, the rate of dropwise addition in step (2) is 5-10 mL / min.

[0019] In one embodiment of the present invention, the stirring in step (2) is carried out at 10-35℃ (room temperature) and 3000-5000 rpm for 20-40 min.

[0020] In one embodiment of the present invention, the water washing centrifugation in step (2) is centrifugation at 8000-12000 rpm for 10-20 min, followed by water washing 2-4 times.

[0021] In one embodiment of the present invention, the concentration of the complex aqueous solution in step (3) is 0.5-50 mg / mL.

[0022] In one embodiment of the present invention, the dispersion in step (3) is ultrasonic dispersion.

[0023] In one embodiment of the present invention, the mass concentration of the polyvinyl alcohol aqueous solution in step (4) is 1-20%.

[0024] In one embodiment of the present invention, the volume ratio of the complex aqueous solution, the polyvinyl alcohol aqueous solution, and the hydrazine hydrate solution in step (4) is 5-25:1:0.002-0.1.

[0025] In one embodiment of the present invention, the hydrazine hydrate solution is added at a rate of 1-5 mL / min in step (4).

[0026] In one embodiment of the present invention, the solvent of the hydrazine hydrate solution in step (4) is water, and the solid content is 85%.

[0027] In one embodiment of the present invention, the reduction in step (4) is carried out by stirring at 65-75°C and 100-500 rpm for 30-60 min.

[0028] In one embodiment of the present invention, the coating thickness in step (5) can be selected as needed, ranging from 100 to 1000 μm.

[0029] In one embodiment of the present invention, the substrate in step (5) can be selected as needed, including PET film, tetrafluoroethylene film, etc.

[0030] In one embodiment of the present invention, the gradient temperature rise in step (5) is 0.5-5 MPa pressure, drying at 45-55℃ for 10-20 min, drying at 75-85℃ for 10-20 min, drying at 95-105℃ for 10-20 min, and drying at 115-125℃ for 50-70 min.

[0031] The second objective of this invention is to prepare a bidirectional high thermal conductivity polymer-based nanocomposite film using the method described herein.

[0032] The third objective of this invention is the application of the bidirectional high thermal conductivity polymer-based nanocomposite film described herein in the preparation of thermal interface materials, heat dissipation coatings, or high-power devices.

[0033] The fourth objective of this invention is to provide a method for improving the bidirectional thermal conductivity of polyvinyl alcohol, which employs the bidirectional high thermal conductivity polymer-based nanocomposite film described in this invention.

[0034] The fifth objective of this invention is to provide a method for improving the dispersion performance of graphene, carbon nanotubes and boron nitride in an aqueous phase, which employs the bidirectional high thermal conductivity polymer-based nanocomposite film described in this invention.

[0035] [Beneficial Effects] (1) In the process of preparing the graphene oxide / boron nitride / carbon nanotube composite of the present invention, the solvent is removed by washing with water and the dispersion medium is deionized water, which greatly reduces the pollution to the environment.

[0036] (2) In this invention, graphene oxide aqueous solution and boron nitride / carbon nanotube dispersion are mixed and stirred evenly to prepare a uniform and stable graphene oxide / boron nitride / carbon nanotube composite (oil-in-water emulsion). Thousands of small oil droplets are surrounded by graphene oxide as an emulsifier for stability, which facilitates the subsequent interfacial assembly between graphene oxide, boron nitride and carbon nanotubes. This greatly increases the interaction efficiency between graphene oxide, boron nitride and carbon nanotubes, so as to achieve the preparation of a highly dispersed graphene / boron nitride / carbon nanotube composite.

[0037] (3) In this invention, graphene oxide, boron nitride and carbon nanotubes interact with each other. After efficient dispersion and structural assembly, graphene oxide avoids the self-aggregation and entanglement of boron nitride and carbon nanotubes in the aqueous medium due to van der Waals forces to a certain extent. The interlayer insertion of boron nitride and carbon nanotubes also effectively prevents the stacking of graphene oxide sheets, so as to achieve a highly dispersed graphene oxide / boron nitride / carbon nanotube composite.

[0038] (4) This invention utilizes the interaction between graphene oxide, boron nitride, and carbon nanotubes, which are stabilized in polyvinyl alcohol. The oxygen-containing functional groups, such as hydroxyl, epoxy, and carboxyl groups, abundant on the graphene oxide sheets can form a dense hydrogen bond network and strong physical adsorption with the hydroxyl groups on the polyvinyl alcohol molecular chain. This characteristic allows graphene oxide to not only be uniformly dispersed in the polyvinyl alcohol aqueous solution, but also to act as a highly efficient "interfacial compatibilizer" and "structural stabilizer": on the one hand, graphene oxide generates non-covalent interactions with boron nitride and carbon nanotubes through its surface functional groups, promoting their uniform dispersion in the polyvinyl alcohol precursor solution; on the other hand, the strong molecular-level interaction between graphene oxide and the polyvinyl alcohol chain can effectively "anchor" and lock fillers such as boron nitride and carbon nanotubes in the three-dimensional network of polyvinyl alcohol, significantly inhibiting the sedimentation and phase separation of fillers during processing and use, thereby forming a structurally stable composite system.

[0039] (5) In this invention, hydrazine hydrate is used to reduce the graphene oxide / boron nitride / carbon nanotube composite solution. The presence of boron nitride and carbon nanotubes effectively avoids the stacking of the reduced graphene oxide. During the reduction process, the reduction product of hydrazine hydrate maintains a certain water dispersion stability of graphene / boron nitride / carbon nanotubes, resulting in a water-based highly dispersed graphene / boron nitride / carbon nanotube composite. The reduction product of hydrazine hydrate also retains some functional groups to maintain the stability of the system and improve the thermal conductivity of the material while restoring its sp² conjugated structure and high intrinsic thermal conductivity to the greatest extent.

[0040] (6) The bidirectional high thermal conductivity polymer-based nanocomposite film prepared by the present invention has excellent thermal conductivity and has good application prospects in the fields of thermal interface materials, heat dissipation coatings and thermal management of high power devices. Attached Figure Description

[0041] Figure 1 Digital photographs of the aqueous solutions of boron nitride and the aqueous solution of the graphene oxide / boron nitride / carbon nanotube composite in Example 1 diluted to 1 mg / mL.

[0042] Figure 2 Here are SEM cross-sectional images of the membranes; where (a) PVA; (b) PVA / BN; (c) PVA / rGO-BN; (d) 5% PVA / rGO-BN-SWCNT; (e) 15% PVA / rGO-BN-SWCNT; and (f) 25% PVA / rGO-BN-SWCNT.

[0043] Figure 3 This is a physical image of the composite membrane in Comparative Example 5. Detailed Implementation

[0044] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0045] Test method: 1. Scanning electron microscopy (SEM) analysis: The composite material sample was quenched with liquid nitrogen, and the fracture surface was sprayed with gold. The microstructure of the sample fracture surface was observed using a field emission scanning electron microscope (S-4800, Hitachi Limitcd) with the working voltage set to 5 kV.

[0046] 2. Mechanical property testing: The test was conducted using an electronic universal testing machine (AI-7000SU1, China High Speed ​​Rail Technology Co., Ltd.) according to the GB / T 2567-2021 standard. The dumbbell-shaped spline dimensions were 20 mm × 4 mm, and the tensile rate was 2 mm / min.

[0047] 3. Thermal conductivity test: The thermal conductivity of the composite film was tested using a laser thermal conductivity meter (LFA467, NETZSCH). The thermal diffusivity in the parallel and perpendicular directions at 20°C was measured. Conductive graphite was sprayed onto both sides of the sample. The sample size was a circular specimen with a diameter of 30 mm and a thickness of 0.01 mm. The thermal diffusivity of each sample was measured three times, and the average value was taken.

[0048] Thermal conductivity ( k ) Calculated using formula (1): (1) In the formula, k , α These represent the thermal conductivity and thermal diffusivity of the composite film, respectively. β —Density, calculated using the displacement method; C p —Specific heat capacity, determined by DSC, using sapphire as the standard sample.

[0049] 4. Thermogravimetric analysis (TG) test: A thermogravimetric analyzer (TGA2, Mettler Toledo) was used with nitrogen as the protective gas at a flow rate of 50 mL / min. The sample was heated from 40 °C to 800 °C at a heating rate of 20 °C / min.

[0050] Raw materials used in the examples: Boron nitride (BN): Shanghai Maclean Biochemical Technology Co., Ltd.; particle size 1-2 μm; Single-walled carbon nanotubes (SWCNTs): AOCHI Airmo (Shenzhen) Co., Ltd.; diameter 1-2.5 nm; Graphene oxide: Graphene oxide filter cake was dispersed in water to form an aqueous dispersion of 10 mg / mL; ultrasonic cleaning was performed in a water bath for 30 min, triethylamine was added to adjust the pH to 5, and then centrifuged (2000 rpm, 15 min) 3 times to obtain graphene oxide at pH 5; Graphene oxide filter cake (GO, solid content: 44.84%): Changzhou Sixth Element. Polyvinyl alcohol: 117, Kuraray Corporation, Japan; Hydrazine hydrate and sodium hydroxide: analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0051] The normal temperature is 10-35℃.

[0052] Example 1 A method for preparing a bidirectional high thermal conductivity polymer-based nanocomposite film includes the following steps: (1) 0.3g of carbon nanotubes were dispersed in 100g of m-cresol and sonicated in a water bath at 25℃ and 45 W for 30min to obtain a carbon nanotube dispersion. Then, while sonicating in a water bath and stirring (100 rpm), 1g of boron nitride was added to the carbon nanotube dispersion and stirred for another 30min. Then, the dispersion was obtained by homogenizing at 8000 r / min for 15min to obtain a boron nitride / carbon nanotube dispersion. (2) Add graphene oxide to water to obtain a graphene oxide aqueous dispersion with a concentration of 10 mg / mL; Take 200 mL of graphene oxide aqueous dispersion into a 500 mL three-necked flask, start stirring at room temperature at 3500 rpm, then add 100 mL of boron nitride / carbon nanotube dispersion dropwise (5 mL / min), stir at room temperature and 3500 rpm for 30 min; stop stirring, add water and centrifuge twice (10000 rpm, 15 min) to obtain graphene oxide / boron nitride / carbon nanotube composite. (3) The graphene oxide / boron nitride / carbon nanotube composite was ultrasonically dispersed (45 W for 1 h) in water to obtain an aqueous solution of the composite with a concentration of 1 mg / mL. (4) Stir and disperse 10g of polyvinyl alcohol and 90g of water to form a 10% (w / w) polyvinyl alcohol aqueous solution; Mix 1500 mL of the complex aqueous solution and 100 mL of the polyvinyl alcohol aqueous solution evenly, and add 0.45 mL of hydrazine hydrate solution (solid content of 85%, solvent of water) dropwise (5 mL / min). Stir and reduce at 70℃ and 200 rpm for 60 min to obtain a partially reduced solution. (5) Using a 750μm four-sided preparation tool, the partially reduced solution was scraped onto a PET film. In a press, at 2MPa, 50℃ for 15 min, 80℃ for 15 min, 100℃ for 15 min, and 120℃ for 60 min, a polyvinyl alcohol / graphene / boron nitride / carbon nanotube composite film was obtained, labeled as 15%PVA / rGO-BN-SWCNT (the sum of the masses of polyvinyl alcohol / graphene / boron nitride / carbon nanotube (7:3:1) accounts for 15% of the mass of polyvinyl alcohol).

[0053] Comparative Example 1 A method for preparing a polyvinyl alcohol / boron nitride composite film includes the following steps: Mix 10g of polyvinyl alcohol and 90g of water, and ultrasonically stir in a water bath at 25℃, 45 W and 200 rpm for 60 min to obtain a 10% (w / w) polyvinyl alcohol aqueous solution. Add 1.5 g boron nitride powder to 100 g polyvinyl alcohol aqueous solution, and ultrasonically stir in a water bath at 25 °C, 45 W, and 200 rpm for 60 min to obtain an aqueous polyvinyl alcohol / boron nitride slurry. The same drying process as in step (5) of Example 1 was performed to obtain an aqueous polyvinyl alcohol / boron nitride composite film, denoted as PVA / BN.

[0054] Comparative Example 2 The carbon nanotubes in Example 1 were omitted, and everything else remained the same as in Example 1, resulting in a polyvinyl alcohol / graphene / boron nitride composite film, denoted as PVA / rGO-BN.

[0055] Comparative Example 3 A method for preparing a polyvinyl alcohol film includes the following steps: Mix 10g of polyvinyl alcohol and 90g of water, and ultrasonically stir in a water bath at 25℃, 45 W and 200 rpm for 60 min to obtain a 10% (w / w) polyvinyl alcohol aqueous solution. The same steps (5) of Example 1 were followed for drying to obtain an aqueous polyvinyl alcohol film, denoted as PVA.

[0056] The obtained composite membrane was subjected to performance testing, and the test results are as follows: Figure 1 Digital photographs of the aqueous solutions of boron nitride and the graphene oxide / boron nitride / carbon nanotube composite in Example 1 diluted to 1 mg / mL. Figure 1It can be seen that boron nitride is hydrophobic, and the solution is white and opaque after dispersion in water. The diluted aqueous dispersion of graphene oxide / boron nitride / carbon nanotubes turns significantly black and becomes transparent and free of particles, confirming that graphene oxide successfully stabilizes boron nitride and carbon nanotubes in the aqueous phase. Furthermore, the prepared aqueous graphene / boron nitride / carbon nanotube dilute dispersion exhibits a significant Tyndall effect, indicating that the aqueous dispersion of graphene / boron nitride / carbon nanotubes has good colloidal stability.

[0057] Example 2 The amount of the composite aqueous solution added in step (4) of Example 1 was adjusted to 500 mL and 2500 mL; other steps remained the same as in Example 1, and polyvinyl alcohol / graphene / boron nitride / carbon nanotube composite films were obtained, labeled as 5%PVA / rGO-BN-SWCNT and 25%PVA / rGO-BN-SWCNT.

[0058] The obtained composite membrane was subjected to performance testing, and the test results are as follows: Figure 2 Here are SEM cross-sectional images of the membranes; where (a) PVA; (b) PVA / BN; (c) PVA / rGO-BN; (d) 5% PVA / rGO-BN-SWCNT; (e) 15% PVA / rGO-BN-SWCNT; and (f) 25% PVA / rGO-BN-SWCNT. Figure 2 It can be seen that the BN sheets in the PVA / BN composite film are relatively thick and severely agglomerated; in contrast, the rGO-BN sheets in the PVA / rGO-BN composite film are thinner, more uniformly dispersed, and have larger lateral dimensions. The rGO-BN sheets are interconnected at the edges, forming extended planes, and exhibit a certain horizontal orientation in the PVA. In the PVA / rGO-BN-SWCNT composite film, SWCNTs untangle and intercalate between the rGO-BN sheets, jointly constructing a three-dimensional structure. SWCNTs exhibit a certain orientation in the vertical direction, and as the rGO-BN-SWCNT content increases from 5% to 15%, the SWCNTs remain well untangled and the orientation becomes increasingly obvious. However, when the rGO-BN-SWCNT content increases to 25%, the SWCNTs become entangled due to excessive filler addition.

[0059] Table 1. Test results of the mechanical properties of the membrane

[0060] Table 2 Thermal conductivity of the membrane in the parallel and perpendicular directions

[0061] Example 3 The amount of boron nitride added in step (1) of Example 1 was adjusted to 0.22 g, 1 g, and 1.3 g, respectively. Carbon nanotubes were not added, and other steps remained the same as in Example 1, resulting in a graphene oxide / boron nitride composite dispersion.

[0062] The results showed that when the boron nitride addition was 1.3 g, black particles appeared in the graphene oxide / boron nitride composite dispersion, indicating instability. After standing, grayish-white particles appeared. At the same time, the BN sheets were relatively thick. The stability of the graphene oxide / boron nitride composite dispersion was also observed when the boron nitride addition was 0.22 g and 1 g.

[0063] Comparative Example 4 In step (1) of Example 1, the boron nitride was adjusted to 1g and the carbon nanotubes to 0.67g; all other steps remained the same as in Example 1, resulting in a carbon nanotube / boron nitride composite dispersion.

[0064] The results showed that the carbon nanotube / boron nitride composite dispersion was unstable, with black particles appearing, and the carbon nanotubes became entangled.

[0065] Comparative Example 5 Adjust step (5) of Example 1 as follows: The partially reduced solution was coated onto a PET film using a 750 μm four-sided preparation tool and dried in a press at 2 MPa and 120 °C for 60 min. Everything else remained the same as in Example 1, resulting in a composite membrane.

[0066] The results showed that the composite film surface was uneven, and the composite film had poor thermal conductivity (e.g., ...). Figure 3 ).

[0067] Comparative Example 6 Adjust step (5) of Example 1 as follows: The partially reduced solution was coated onto a PET film using a 750 μm four-sided preparation tool and dried in a press at 2 MPa and 100 °C for 60 min. Everything else remained the same as in Example 1, resulting in a composite membrane.

[0068] The results showed that the composite film surface was uneven and the reduction was incomplete, resulting in poor thermal conductivity.

[0069] Comparative Example 7 Adjust step (5) of Example 1 as follows: The partially reduced solution was coated onto a PET film using a 750 μm four-sided preparation tool and dried in a press at 2 MPa and 80 °C for 60 min. Everything else remained the same as in Example 1, resulting in a composite membrane.

[0070] The results showed that the composite membrane surface was uneven and the reduction was incomplete, resulting in poor thermal conductivity.

[0071] Comparative Example 8 The hydrazine hydrate solution in step (4) of Example 1 is omitted, and everything else is kept the same as in Example 1 to obtain a composite membrane.

[0072] The results showed that the composite membrane was not fully reduced, resulting in poor thermal conductivity for the same mass fraction of composite membrane.

[0073] Comparative Example 9 The reduction time of the hydrazine hydrate solution in step (4) of Example 1 was adjusted to 90 min, while other steps remained the same as in Example 1, to obtain a composite membrane.

[0074] The results showed that the composite membrane was over-reduced during the chemical reduction stage, resulting in black particles in the composite dispersion and instability of the dispersion.

[0075] Comparative Example 10 0.3g carbon nanotubes and 1g boron nitride were dispersed in 100g m-cresol, sonicated in a water bath at 25℃ and 45 W for 60 min, and then dispersed in a homogenizer at 8000 r / min for 15 min to obtain a boron nitride / carbon nanotube dispersion.

[0076] The results showed that particles appeared in the boron nitride / carbon nanotube composite dispersion during dispersion.

[0077] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a bidirectional high thermal conductivity polymer-based nanocomposite film, characterized in that, Includes the following steps: (1) Add boron nitride to the carbon nanotube dispersion, stir and homogenize to obtain boron nitride / carbon nanotube dispersion; (2) Add boron nitride / carbon nanotube dispersion dropwise to graphene oxide solution, stir, wash with water and centrifuge to obtain graphene oxide / boron nitride / carbon nanotube composite. (3) The graphene oxide / boron nitride / carbon nanotube composite was dispersed in water to obtain an aqueous solution of the composite; (4) Combine the aqueous solution of the complex and the aqueous solution of polyvinyl alcohol, and reduce them by adding hydrazine hydrate solution dropwise to obtain a partially reduced solution; (5) The partially reduced solution is coated on the surface of the substrate and then subjected to gradient drying to obtain a bidirectional high thermal conductivity polymer-based nanocomposite film.

2. The method according to claim 1, characterized in that, In step (1), the mass ratio of carbon nanotubes to solvent in the carbon nanotube dispersion is 0.1-0.5:

100.

3. The method according to claim 1, characterized in that, In step (1), the mass ratio of carbon nanotubes to boron nitride is 0.1-0.5:

1.

4. The method according to claim 1, characterized in that, In step (2), the concentration of the graphene oxide solution is 5-15 mg / mL; the volume ratio of the graphene oxide solution to the boron nitride / carbon nanotube dispersion is 200:50-150.

5. The method according to claim 1, characterized in that, In step (4), the volume ratio of the complex aqueous solution, polyvinyl alcohol aqueous solution, and hydrazine hydrate solution is 5-25:1:0.002-0.

1.

6. The method according to claim 1, characterized in that, In step (5), the gradient temperature is 0.5-5 MPa pressure, drying at 45-55℃ for 10-20 min, drying at 75-85℃ for 10-20 min, drying at 95-105℃ for 10-20 min, and drying at 115-125℃ for 50-70 min.

7. The bidirectional high thermal conductivity polymer-based nanocomposite film prepared by the method according to any one of claims 1-6.

8. The application of the bidirectional high thermal conductivity polymer-based nanocomposite film according to claim 7 in the preparation of thermal interface materials, heat dissipation coatings or high-power devices.

9. A method for improving the bidirectional thermal conductivity of polyvinyl alcohol, characterized in that, The bidirectional high thermal conductivity polymer-based nanocomposite film described in claim 7 was used.

10. A method for improving the dispersion performance of graphene, carbon nanotubes, and boron nitride in an aqueous phase, characterized in that, The bidirectional high thermal conductivity polymer-based nanocomposite film described in claim 7 was used.

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