A flexible composite film with high out-of-plane thermal conductivity and its preparation method and application

Abstract

The present application relates to the technical field of heat-conducting materials, in particular to a flexible composite film with high out-of-plane thermal conductivity, a preparation method and application thereof.The flexible composite film is composed of aramid nanofiber as a reinforcing framework and graphene@silicon carbide (GS) heterostructure as a heat-conducting reinforcing phase; in the GS heterostructure, SiC nanoparticles are randomly attached to the surface and edges of the graphene sheet, forming a vertical phonon transmission channel.The present application solves the bottleneck of low out-of-plane thermal conductivity of graphene, enabling the composite film to have high out-of-plane thermal conductivity, excellent flame retardant performance and flexibility.The multifunctional synergistic design of the present application provides a key technical path for flexible electronic devices, 5G communication base stations and aerospace thermal interface materials.The high-thermal-conductivity flexible composite film prepared by filler hybridization has the advantages of batch production, strong implementation and low cost, and has good application prospects in the field of thermal management.

Description

Technical Field

[0001] This invention relates to the field of thermal conductive materials technology, specifically to a flexible composite film with high out-of-plane thermal conductivity, its preparation method, and its application. Background Technology

[0002] The evolution of high-performance chips, high-power LEDs, and portable flexible electronic devices towards "small size, high power consumption" inevitably brings heat dissipation challenges. The large amount of heat generated by electronic components during operation, if not quickly dissipated, can cause a sudden spike in localized temperature. This not only affects processing speed but can also lead to equipment meltdown or even fires. Therefore, developing high-performance thermal management materials has become an urgent need for the modern microelectronics industry.

[0003] Among numerous thermally conductive materials, graphene (Gr) is highly anticipated due to its excellent intrinsic thermal conductivity. However, in the actual film fabrication process, Gr sheets often tend to align horizontally. While this allows for extremely rapid heat dissipation in the in-plane direction, its thermal conductivity is poor in the direction perpendicular to the film (out-of-plane direction). This severe anisotropy creates a significant bottleneck for heat transfer in the out-of-plane direction, making it impossible to effectively dissipate heat from the chip to the external environment. Simply increasing the thickness or content of graphene not only fails to fundamentally solve the problem of vertical thermal conductivity but also leads to increased brittleness and loss of flexibility in the material.

[0004] To break this deadlock, the scientific and industrial communities have been exploring how to build "thermal bridges" between graphene layers. Introducing ceramic particles with good thermal conductivity and stable physical properties, and "pinning" them between graphene layers to construct a vertical phonon transport network, would fundamentally improve the material's out-of-plane thermal conductivity. Silicon carbide (SiC), as a high-performance semiconductor material, possesses excellent thermal stability, chemical resistance, and outstanding thermal conductivity, making it an ideal material for constructing such vertical "thermal bridges."

[0005] Furthermore, real-world application environments place stringent demands on the safety and mechanical stability of materials. Traditional metal heat sinks are bulky and inflexible, failing to meet the needs of flexible screens or foldable devices. Ordinary plastic-based thermal conductive films, on the other hand, have poor heat resistance and are highly susceptible to ignition when exposed to fire. Aramid nanofibers (ANF), as a high-performance polymer fiber material with extremely high mechanical strength, excellent heat resistance, and intrinsic flame-retardant properties, provide an ideal three-dimensional network framework for thermally conductive fillers.

[0006] Based on this, the research on a flexible composite film with high out-of-plane thermal conductivity is significant not only for overcoming the technical challenge of graphene's anisotropic thermal conductivity, but also for integrating efficient heat dissipation, strong flame retardancy, and ultra-high toughness into a single unit through multi-scale and multi-dimensional material design, achieving a unified structural and functional design. The emergence of this novel composite film material will help drive the advancement of high-performance electronic components towards miniaturization, safety, and durability. Summary of the Invention

[0007] The primary objective of this invention is to provide a flexible composite film with high out-of-plane thermal conductivity. This is achieved by constructing a vertical thermal conduction pathway using a zero-dimensional / two-dimensional nano-heterogeneous structure and building a flexible framework with flexible nanofibers.

[0008] A second objective of this invention is to provide a method for preparing the aforementioned flexible composite film with high out-of-plane thermal conductivity. Zero-dimensional silicon carbide nanoparticles are anchored onto the surface of two-dimensional graphene using a planetary ball milling strategy to prepare a heterostructure with out-of-plane thermal bridging functionality. This heterostructure is then incorporated into an aramid nanofiber matrix obtained through deprotonation exfoliation, and a flexible composite film with a three-dimensional phonon transport network is constructed using vacuum-assisted self-assembly technology and hot-pressing densification.

[0009] A third objective of the present invention is to provide the use of the above-mentioned flexible composite film with high out-of-plane thermal conductivity.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A flexible composite film with high out-of-plane thermal conductivity is composed of an aramid nanofiber (ANF) as a reinforcing skeleton and a graphene (Gr)@silicon carbide (SiC) (GS) heterostructure as a thermally conductive reinforcing phase; in the GS heterostructure, SiC nanoparticles are randomly attached to the surface and edges of the graphene sheets to form vertical phonon transport channels.

[0011] The mass ratio of graphene to silicon carbide nanoparticles is 90:10 to 50:50.

[0012] The mass percentage of the GS heterostructure in the composite film is 10 wt% to 50 wt%.

[0013] The out-of-plane thermal conductivity of the flexible composite film is not less than 0.449 W / (m·K).

[0014] The flexible composite film has a dense layered cross-linked structure with a thickness of 40 μm to 100 μm and is flexible enough to withstand 180° folding without breaking.

[0015] A method for preparing a flexible composite thin film with high out-of-plane thermal conductivity, the process principle of which is as follows: (1) Precise construction of heterostructures: Using the strong shear force and collision energy generated by a planetary ball mill, SiC nanoparticles with different ratios are mixed with Gr. The ball milling process creates tiny structural defects on the edges of Gr, which provide active sites for the adhesion of SiC particles. The SiC particles are interspersed between the Gr sheets, like tiny pillars, which prevent the excessive horizontal orientation of the graphene sheets, thereby opening up the vertical heat transfer pathway.

[0016] (2) Deprotonation exfoliation of the three-dimensional network matrix: Poly(p-phenylene terephthalamide) fibers were placed in a dimethyl sulfoxide / potassium hydroxide system (DMSO / KOH). Under the action of the alkaline environment, the hydrogen bond network between the fibers was gradually broken down, thereby exfoliating ANF fiber slurry with a diameter of only tens of nanometers and a highly active surface. These ANF fibers have a huge specific surface area and can form a strong π-π stacking effect with thermally conductive fillers.

[0017] (3) Self-assembly induction of the composite system: The thermally conductive composite GS heterostructure is mixed with ANF fiber slurry, and the two are fully mixed and interwoven by high-intensity ultrasonic-assisted mixing. Then, the ANF / GS layer-by-layer stacked structure is formed by vacuum filtration, water washing and ethanol washing. This "layer-to-layer" structure ensures the mechanical continuity of the material, while the SiC particles interspersed between the Gr layers ensure the effective scattering and transmission of phonons in the vertical direction of the film.

[0018] (4) Densification by hot pressing: The initially formed ANF / GS wet film contains a large number of solvent molecules and tiny pores. By hot pressing at a specific temperature, the interlayer spacing is further compressed, eliminating interfacial bubbles. This process greatly reduces the interfacial thermal resistance, allowing phonons to shuttle more smoothly between different components, ultimately forming a thermally conductive film with excellent performance.

[0019] Furthermore, the specific steps include: (1) Gr and SiC particles were mixed in proportion and then subjected to planetary ball milling in an anhydrous ethanol system to prepare GS suspension; (2) An ANF slurry solution was prepared by deprotonation reaction of poly(p-phenylene terephthalamide) fiber in a dimethyl sulfoxide / potassium hydroxide system; (3) Mix the GS suspension with the ANF slurry and use high-speed stirring to form a uniform ANF / GS composite slurry; (4) The solvent is washed with water and ethanol multiple times by vacuum filtration to allow the solvent to pass through the microporous filter membrane, and the solute self-assembles layer by layer to form a wet membrane. (5) The wet film is hot-pressed and dried under a certain pressure to prepare an ANF / GS composite film.

[0020] In step (1), Gr and SiC particles are mixed in a ethanol solution system with a mass fraction of 85% and then subjected to planetary ball milling. The ball milling speed is set to 200-300 rpm and the continuous ball milling time is 3-5 h to ensure that the SiC particles form a strong physical bond on the graphene surface.

[0021] In step (3), the high-speed stirring speed is 1000-1800 rpm and the time is 4-12 h, so as to stabilize the interface between GS and ANF by utilizing π-π interaction.

[0022] In step (4), during the vacuum filtration process, water washing and ethanol washing are alternated and repeated 4 times to ensure that the solution color changes from dark yellow to single yellow.

[0023] In step (5), the hot pressing temperature is 50 ℃~70 ℃, the pressure range is 0.05 MPa~0.3 MPa, and the hot pressing time is 7 h~12 h. The residual solvent is discharged and the stacking density between components is increased by driving the pressure.

[0024] The flexible composite film prepared by this invention can be used to prepare high-performance LED heat sinks, flexible circuit board substrates, or electromagnetic shielding and heat dissipation components.

[0025] Compared with the prior art, the beneficial effects of the present invention are: (1) The flexible composite film of the present invention effectively solves the bottleneck of low out-of-plane thermal conductivity of graphene, enabling the composite film to achieve high out-of-plane thermal conductivity while also possessing excellent flame retardant properties and flexibility. This multifunctional synergistic design provides a key technical path for flexible electronic devices, 5G communication base stations, and aerospace thermal interface materials.

[0026] (2) The invention utilizes the filler hybridization synergy to prepare a high thermal conductivity flexible composite membrane, which has the advantages of mass production, strong implementation and low cost, and has good application prospects in the field of thermal management. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the fabrication process for a flexible composite film with high out-of-plane thermal conductivity.

[0028] Figure 2 This is a comparison diagram of the out-of-plane thermal conductivity of the embodiment and the comparative example.

[0029] Figure 3 This is a comparison chart of the thermal conductivity of ANF / GS30 thin film and pure ANF film.

[0030] Figure 4This is a comparison chart of the flame retardant properties of ANF / GS30 film and pure ANF film.

[0031] Figure 5 This is a comparison chart of the heat release rates of ANF / GS30 film and pure ANF film.

[0032] Figure 6 This is a cross-sectional morphology diagram of the ANF / GS30 thin film.

[0033] Figure 7 This is a diagram showing the flexibility of the ANF / GS30 film.

[0034] Figure 8 This is a comparison chart of the tensile strength of ANF / GS30 film and pure ANF film. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1: Balanced Proportion Optimization Group (ANF / GS30) like Figure 1 As shown, a method for preparing a flexible composite film with high out-of-plane thermal conductivity includes the following steps: (1) Weigh 70 mg of graphene powder and 30 mg of SiC particles with an average particle size of 40 nm (mass ratio Gr:SiC=7:3, abbreviated as GS30). Add 30 mL of anhydrous ethanol and ball mill in a planetary ball mill at 250 rpm for 3 h to obtain GS30 dispersion.

[0037] (2) Take 1 g of PPTA fiber and 1.5 g of KOH and add them to 500 mL of DMSO. Seal and stir for 4 hours until the solution turns dark red.

[0038] (3) Mix a certain amount of GS30 dispersion with a certain amount of ANF slurry (total filler content 30wt%) and sonicate for 40 min.

[0039] (4) Using vacuum filtration technology, the ANF / GS mixed slurry obtained in step (3) is washed with water and ethanol multiple times to obtain ANF / GS30 wet film.

[0040] (5) At 70 °C, the thin-layer composite thermally conductive film ANF / GS30 was obtained by hot pressing and drying at 0.1 MPa pressure.

[0041] At this ratio, SiC is most evenly distributed, forming the best vertical phonon channels and exhibiting the best overall thermal conductivity.

[0042] Example 2: Low particle size ratio group (ANF / GS10) like Figure 1 As shown, a method for preparing a flexible composite film includes the following steps: (1) Weigh 90 mg of graphene powder and 10 mg of SiC particles with an average particle size of 40 nm (mass ratio Gr:SiC=9:1, abbreviated as GS10). Add 30 mL of anhydrous ethanol and ball mill in a planetary ball mill at 200 rpm for 3 h to obtain GS10 dispersion.

[0043] (2) Take 1 g of PPTA fiber and 1.5 g of KOH and add them to 500 mL of DMSO. Seal and stir for 4 h until the solution turns dark red.

[0044] (3) Mix a certain amount of GS10 dispersion with a certain amount of ANF slurry (total filler percentage 30 wt%) and sonicate for 40 min.

[0045] (4) Using vacuum filtration technology, the ANF / GS mixed slurry obtained in step (3) is washed with water and ethanol multiple times to obtain ANF / GS10 wet film.

[0046] (5) At 70 °C, the thin-layer composite thermally conductive film ANF / GS10 was obtained by hot pressing and drying at 0.1 MPa pressure.

[0047] At this ratio, due to the smaller number of SiC particles and insufficient vertical thermal conductivity pathways, the out-of-plane thermal conductivity is only slightly improved, but the in-plane thermal conductivity is excellent.

[0048] Example 3: High particle size ratio group (ANF / GS50) like Figure 1 As shown, a method for preparing a flexible composite film includes the following steps: (1) Weigh 50 mg of graphene powder and 50 mg of SiC particles with an average particle size of 40 nm (mass ratio Gr:SiC=5:5, abbreviated as GS50). Add 30 mL of anhydrous ethanol and ball mill in a planetary ball mill at 300 rpm for 5 h to enhance the binding force of the high-content powder. GS50 dispersion is obtained.

[0049] (2) Take 1 g of PPTA fiber and 1.5 g of KOH and add them to 500 mL of DMSO. Seal and stir for 4 h until the solution turns dark red.

[0050] (3) Mix a certain amount of GS50 dispersion with a certain amount of ANF slurry (total filler percentage 30 wt%) and sonicate for 40 min.

[0051] (4) Using vacuum filtration technology, the ANF / GS mixed slurry obtained in step (3) is washed with water and ethanol multiple times to obtain ANF / GS50 wet film.

[0052] (5) At 70 °C, the thin-layer composite thermally conductive film ANF / GS50 was obtained by hot pressing and drying at 0.1 MPa pressure.

[0053] In this embodiment, the large number of SiC particles significantly increases the vertical thermal conductivity of the composite film, and the out-of-plane thermal conductivity reaches its peak. However, the film brittleness increases and the mechanical tensile strength decreases slightly, making it difficult to apply in practice.

[0054] Example 4 High-pressure densification process assembly (ANF / GS30) like Figure 1 As shown, a method for preparing a flexible composite film includes the following steps: (1) Weigh 70 mg of graphene powder and 30 mg of SiC particles with an average particle size of 40 nm (mass ratio Gr:SiC=7:3, abbreviated as GS30). Add 30 mL of anhydrous ethanol and ball mill in a planetary ball mill at 250 rpm for 3 h to obtain GS30 dispersion.

[0055] (2) Take 1 g of PPTA fiber and 1.5 g of KOH and add them to 500 mL of DMSO. Seal and stir for 4 h until the solution turns dark red.

[0056] (3) Mix a certain amount of GS30 dispersion with a certain amount of ANF slurry (total filler percentage 30 wt%) and sonicate for 40 min.

[0057] (4) Using vacuum filtration technology, the ANF / GS mixed slurry obtained in step (3) is washed with water and ethanol multiple times to obtain ANF / GS30 wet film.

[0058] (5) At 70 °C, hot-pressed at 0.3 MPa for 10 h and dried to obtain a thin-layer composite thermally conductive film ANF / GS30.

[0059] In this experiment, increasing the hot pressing pressure and time did not cause significant changes in the film; therefore, a pressure of 0.1 MPa was sufficient for hot pressing.

[0060] To highlight the beneficial effects of the present invention, the following comparative experiments are provided. Comparative example: Pure ANF thin film (1) Take 1 g of PPTA fiber and 1.5 g of KOH and add them to 500 mL of DMSO. Seal and stir for 4 h until the solution turns dark red.

[0061] (2) Using vacuum filtration technology, the ANF mixed slurry obtained in step (1) is washed with water and ethanol multiple times to obtain an ANF wet film.

[0062] (3) At 70 °C, the thin-layer composite thermally conductive film ANF was obtained by hot pressing and drying at 0.1 MPa pressure.

[0063] Example 5 Performance Testing (1) Thermal conductivity test The thermal conductivity of the composite film was tested using an LFA 467 thermal conductivity meter. The test results show that ( Figure 2 Example 1 (ANF / GS30 film) has an out-of-plane thermal conductivity of 0.45 W / (m·K), which is nearly 3.5 times higher than that of the comparative pure ANF film without filler (0.13 W / (m·K)). The in-plane thermal conductivity is even higher at 4.94 W / (m·K), showing typical bidirectional high thermal conductivity characteristics.

[0064] (2) Flame retardant properties The flame retardant performance of Example 1 and the comparative example was compared using a micro-combustion calorimetry test. The experimental results showed that ( Figure 5 Example 1: The heat release rate of the ANF / GS30 film was 83.92 W / g, while that of the comparative pure ANF film was 182.7 W / g. Furthermore, in the open flame ablation test ( Figure 4 The ANF / GS30 film in Example 1 only turned slightly black after being exposed to a flame for 5 seconds, without violent combustion or dripping of molten droplets, demonstrating significant flame-retardant safety compared to the comparative pure ANF film.

[0065] (3) Mechanical property testing Tensile strength test results show that ( Figure 8 The ANF / GS30 film in Example 1 has a tensile strength of 41.08 MPa. Furthermore, no cracks were observed after 1000 cycles of bending, demonstrating the high reliability of the ANF / GS30 film in flexible devices.

[0066] (4) Actual thermal conductivity test The actual thermal conductivity of the composite film was monitored using a thermal infrared imager. The ANF / GS30 film from Example 1 and the pure ANF film were simultaneously placed on an 80°C heating plate. The surface temperature of the ANF / GS30 film from Example 1 increased significantly faster than that of the comparative example. Figure 3Furthermore, the heat distribution is uniform with no localized hot spots, further demonstrating the efficient thermal equilibrium capability of the ANF / GS30 thin film.

[0067] (5) Cross-sectional morphology of the composite film: The SEM cross-sectional image is clearly displayed. Figure 6 The Gr sheets and ANF layers are stacked one after another, and SiC nanoparticles are cleverly embedded between these layers, which confirms the scientific nature of the "vertical thermal bridge" microstructure proposed in this invention.

[0068] In summary, this invention provides a method for preparing a flexible composite film with high out-of-plane thermal conductivity. It innovatively introduces high-thermal-conductivity zero-dimensional SiC nanoparticles between two-dimensional Gr sheets to construct thermally conductive pathways on the vertical planes of the Gr sheets. Flexible nanofibers (ANF fibers) are used as a framework material to stably anchor the high-thermal-conductivity GS heterostructure to the surface, endowing the composite film with flexibility and good mechanical properties. This allows for wide application on chip substrate surfaces requiring high thermal conductivity. Performance testing shows that this flexible composite film exhibits good flame retardancy (heat release rate of 83.92 W / g), excellent out-of-plane thermal conductivity (out-of-plane thermal conductivity of 0.45 W / (m·K)), and stable mechanical properties (tensile strength up to 41.08 MPa, with no cracks observed after 1000 cycles of bending). Figure 7 (As shown).

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. 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 some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A flexible composite film with high out-of-plane thermal conductivity, characterized in that: It is composed of aramid nanofibers as a reinforcing skeleton and graphene@silicon carbide (GS) heterostructure as a thermally conductive reinforcing phase; in the GS heterostructure, SiC nanoparticles are randomly attached to the surface and edges of the graphene sheets to form vertical phonon transport channels.

2. The flexible composite film according to claim 1, characterized in that: The mass ratio of graphene to silicon carbide nanoparticles is 90:10 to 50:

50.

3. The flexible composite film according to claim 1, characterized in that: The mass percentage of the GS heterostructure in the composite film is 10 wt% to 50 wt%.

4. The flexible composite film according to claim 1, characterized in that: The out-of-plane thermal conductivity of the flexible composite film is not less than 0.449 W / (m·K).

5. The flexible composite film according to claim 1, characterized in that: The flexible composite film has a dense layered cross-linked structure with a thickness of 40 μm to 100 μm, and is flexible enough to withstand 180° folding without breaking.

6. A method for preparing a flexible composite film with high out-of-plane thermal conductivity as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Gr and SiC particles were mixed in proportion and then subjected to planetary ball milling in an anhydrous ethanol system to prepare GS suspension; (2) An ANF slurry solution was prepared by deprotonation reaction of poly(p-phenylene terephthalamide) fiber in a dimethyl sulfoxide / potassium hydroxide system; (3) Mix the GS suspension with the ANF slurry and use high-speed stirring to form a uniform ANF / GS composite slurry; (4) The solvent is washed with water and ethanol multiple times by vacuum filtration to allow the solvent to pass through the microporous filter membrane, and the solute self-assembles layer by layer to form a wet membrane. (5) The wet film is hot-pressed and dried under a certain pressure to prepare an ANF / GS composite film.

7. The method for preparing the flexible composite film according to claim 6, characterized in that: In step (1), the ball milling speed is set to 200-300 rpm, and the continuous ball milling time is 3-5 h, so as to ensure that SiC particles form a strong physical bond on the graphene surface.

8. The method for preparing the flexible composite film according to claim 6, characterized in that: In step (3), the high-speed stirring speed is 1000-1800 rpm and the time is 4-12 h, so as to stabilize the interface between GS and ANF by utilizing π-π interaction.

9. The method for preparing the flexible composite film according to claim 6, characterized in that: In step (5), the hot pressing temperature is 50 ℃~70 ℃, the pressure range is 0.05 MPa~0.3 MPa, and the hot pressing time is 7 h~12 h. The residual solvent is discharged and the stacking density between components is increased by driving the pressure.

10. The application of the flexible composite film according to any one of claims 1-5 in the preparation of high-performance LED heat sinks, flexible circuit board substrates, or electromagnetic shielding and heat dissipation components.

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