A heat dissipation composite material, a preparation method and use as a chip heat dissipation material

Abstract

The application belongs to the technical field of heat dissipation materials, and particularly relates to a heat dissipation composite material, a preparation method and an application of the heat dissipation composite material as a chip heat dissipation material. The heat dissipation composite material is composed of a directional heat conduction layer and a selective infrared emission layer. The directional heat conduction layer contains a first polymer matrix material and has a through-hole channel structure extending from a heat dissipation object side to the selective infrared emission layer. The through-hole channel structure has a solid-liquid bicontinuous heat conduction medium. A connecting interface between the directional heat conduction layer and the selective infrared emission layer has a metal reflection interface formed by a liquid metal heat conduction material. The selective infrared emission layer contains a microporous structure with a pore diameter gradually decreasing from one side of the directional heat conduction layer to an outer side. The heat dissipation material has a simple and easy-to-control preparation process, does not need to design expensive new polymer materials, is suitable for industrialized mass production, and effectively utilizes the heat dissipation characteristics of the material itself, the heat dissipation and radiation characteristics of the channel and microporous structure, and the synergistic heat dissipation effect of the heat conduction layer and the infrared emission layer.

Description

Technical Field

[0001] This invention belongs to the field of heat dissipation material technology, specifically relating to a heat dissipation composite material, its preparation method, and its use as a chip heat dissipation material. Background Technology

[0002] With the rapid development of artificial intelligence computing, high-frequency and high-speed communication, lasers, power electronics, and advanced packaging technologies, the integration level and power density per unit area of ​​chips continue to increase, and the local heat flux density has increased from the traditional 10-30 W / cm². 2 Increased to 100 W / cm 2 The above figures, and even exceed 1000 W / cm² in some high-end devices, are particularly high. 2 High heat flux density causes chip junction temperature to rise rapidly, leading to performance degradation, latency drift, decreased reliability, and even thermal failure. Therefore, the development of efficient heat dissipation materials has become a key requirement for the stable operation of advanced electronic systems.

[0003] Current heat dissipation solutions mainly include metal heat sinks, heat spreaders, heat pipes, thermal pads, and high thermal conductivity polymer composites. While metal materials possess excellent thermal conductivity, their high density and low flexibility limit their application in flexible electronics and compact packaging. Phase change heat dissipation devices rely on evaporation-condensation cycles, resulting in limited dynamic response and complex, costly fabrication processes (e.g., patent document CN115910815A). Traditional thermal pads and polymer composites typically construct thermally conductive networks using granular or sheet-like fillers, with effective thermal conductivity generally not exceeding 10–20 W / m·K, making it difficult to achieve sufficient heat transfer capacity under high heat flux density conditions (e.g., patent document CN115011315A). CN119264519A discloses a heat dissipation material prepared by interfacial modification and aqueous phase blending of gallium-indium alloy and boron nitride nanosheets, which can be added to polyurethane, but its thermal conductivity does not exceed 6 W / m·K. -1 ·K -1 CN110054864A discloses a method of coating sheet-like thermally conductive materials (such as boron nitride nanosheets) onto the surface of spherical thermally conductive materials (such as alumina and silicon oxide) using surface modification technology, and then introducing polymers to form a composite thermally conductive material. However, its thermal conductivity does not exceed 3 W·m. -1 ·K -1 Although both materials utilize liquid metals and / or two-dimensional sheet-like thermally conductive fillers with good heat dissipation properties, the results still need improvement, highlighting the significant challenge in constructing effective thermally conductive networks in polymers at present.

[0004] Furthermore, in practical applications, heat dissipation of chip-type heat sinks relies not only on the longitudinal rapid heat conduction capability of the heat dissipation material but is also significantly affected by the directionality of heat flux. When the heat dissipation material has an isotropic structure or lacks a direction control mechanism, infrared radiation from the external environment (excluding atmospheric windows) may be absorbed or reflected by the material and then returned to the chip surface, generating reverse heat flux and reducing overall heat dissipation efficiency. This phenomenon is more pronounced in scenarios involving multiple chips operating in parallel or in environments with fluctuating external temperatures. Currently, there is a lack of film materials that can both achieve rapid heat dissipation from the chip and suppress the reverse inflow of external heat through spectral structure modulation. Summary of the Invention

[0005] To address the above problems, the purpose of this invention is to provide a heat dissipation composite material, its preparation method, and its application as a chip heat dissipation material. This invention includes the following technical solutions:

[0006] A heat dissipation composite material is disclosed, comprising a directional heat-conducting layer and a selective infrared emitting layer. The directional heat-conducting layer contains a first polymer matrix material, a connectivity enhancer, a solid-liquid dual continuous thermally conductive medium, and a metal reflective interface. The directional heat-conducting layer has a through-hole channel structure extending from the heat dissipation target side towards the selective infrared emitting layer. The through-hole channel structure contains a solid-liquid dual continuous thermally conductive medium composed of a liquid metal thermally conductive material and a two-dimensional sheet thermally conductive material. The metal reflective interface is located at the connection interface between the directional heat-conducting layer and the selective infrared emitting layer and is formed by the liquid metal thermally conductive material. The selective infrared emitting layer contains a second polymer matrix material and has a microporous structure, the pore size of which gradually decreases from one side of the directional heat-conducting layer outwards.

[0007] Preferably, the pore size of the through-hole structure is 0.1 μm to 10 μm.

[0008] Preferably, the vertical orientation of the through-hole channel structure is greater than or equal to 0.9. The term "vertical orientation" is a commonly used term in the art, with a range of 0 to 1 (completely horizontal to completely vertical); it refers to the vertical orientation relative to the plane of the directional heat-conducting layer.

[0009] Preferably, in the selective infrared emitting layer, the average pore size of the microporous structure on one side of the directional heat conduction layer is 7μm~15μm; and the average pore size of the microporous structure on the outer side is 0.1μm~3μm.

[0010] Preferably, the first polymer matrix material used for the directional heat-conducting layer is selected from one or more of polyimide, polyethersulfone, and polyacrylonitrile.

[0011] Preferably, the connectivity enhancer is selected from at least one of polypropylene glycol-polybutylene glycol-polypropylene glycol and polyether-polyester-polyether.

[0012] Preferably, the liquid metal thermal conductive material used in the directional thermal conductive layer is selected from gallium indium alloy or gallium indium tin alloy, and the two-dimensional sheet thermal conductive material used in the directional thermal conductive layer is one or more of MXene nanosheets, graphene nanosheets and boron nitride nanosheets.

[0013] Preferably, the second polymer matrix material used in the selective infrared emitting layer is selected from one or more of polyvinylidene fluoride-b-polyethylene, polydimethylsiloxane-b-polyoxyethylene, and polystyrene-b-polymethyl methacrylate.

[0014] A method for preparing the aforementioned heat dissipation composite material, the method comprising the following steps:

[0015] S1 Preparation of Selective Infrared Emitting Layer: The desired second polymer matrix material is prepared into a selective infrared emitting layer coating solution with a mass percentage concentration of 7%~20% using an organic solvent. The coating solution is applied to the template material surface in 3~4 layers: After the first coating, it is semi-cured in air with a relative humidity of 70%~90%, and then solvent exchange is performed in a water bath at 20℃~30℃; after the second coating, it is semi-cured in air with a relative humidity of 50%~70%, and then solvent exchange is performed in a water bath at 10℃~20℃; after the third coating, it is semi-cured in air with a relative humidity of 30%~50%, and then solvent exchange is performed in a water bath at 0℃~10℃. The relative humidity required for each semi-curing step decreases sequentially, and the water bath temperature required for each solvent exchange step decreases sequentially. The required decrease in relative humidity between adjacent semi-curing steps is 10%~25%, and the required decrease in temperature between adjacent solvent exchange steps is 5℃~20℃. After the final solvent exchange in the water bath, the product is placed horizontally above liquid nitrogen for 2~3 seconds. The selective infrared emitting layer is obtained by directional freezing at a depth of cm for 10-20 minutes and then freeze-drying until the residual moisture content is less than 5%; the 0℃ water bath is also called "ice water bath".

[0016] S2 Preparation of solid-liquid dual continuous thermal conductive medium: Take liquid metal thermal conductive material and two-dimensional sheet thermal conductive material, disperse them in an organic solvent, sonicate, and collect the sedimentation part by centrifugation to obtain solid-liquid dual continuous thermal conductive medium;

[0017] S3 Preparation of directional thermal conductive layer coating liquid and completion of heat dissipation composite material preparation: Take organic solvent, solid-liquid dual continuous thermal conductive medium, first polymer matrix material and interconnection reinforcing agent to prepare directional thermal conductive layer coating liquid, coat it on the side with larger aperture of selective infrared emitting layer to form directional thermal conductive layer coating film; immerse the bottom of directional thermal conductive layer coating film in a water bath of 30℃~70℃, expose the top to air with relative humidity of 50%~80%, and after the film surface and cross section solidify and stabilize, dry it at 60℃~80℃ to obtain composite film. Perform 1~3 transverse mechanical pressing on the obtained composite film at 50℃~70℃ with a pressure of 0.2MPa~1MPa, and perform 2~4 longitudinal mechanical pressing on the composite film at 60℃~80℃ with a pressure of 50kPa~300kPa. Apply a DC voltage of 0.6V~1.2V to the composite film for 4min~10min.

[0018] Preferably, the freeze-drying method in step S1 is as follows: the product is placed in a freeze dryer for primary drying, and the freeze-drying temperature is maintained at -40 ℃ to -20 ℃ under a vacuum of 0.1~0.5 mbar for 6~24 hours to remove most of the water by sublimation; then, secondary drying is carried out, and the temperature is gradually raised to 0~25℃ and dried under a vacuum of 0.05~0.5 mbar to make the residual water content < 5%.

[0019] Preferably, in step S2, the mass percentage concentration of the liquid metal thermal conductive material in the organic solvent is 5% to 40%, and the mass percentage concentration of the two-dimensional sheet thermal conductive material is 1% to 10%.

[0020] Preferably, in step S3, the mass percentage concentration of the solid-liquid dual continuous heat-conducting medium in the directional heat-conducting layer coating liquid is 2%~10%, the mass percentage concentration of the first polymer matrix material is 2%~20%, and the mass percentage concentration of the interconnection reinforcing agent is 0.2%~5%.

[0021] The aforementioned heat dissipation composite material is used as a heat dissipation material for chips.

[0022] The aforementioned term "semi-cured" is a commonly used term in the field of materials such as resins and gels: it refers to a state in which an object is neither fully flowing nor fully cured.

[0023] Beneficial Effects: In the heat dissipation material of this invention: the directional heat-conducting layer constructs vertically oriented channels by utilizing the temperature and humidity dependence of the polymer coating, and a solid-liquid dual continuous heat-conducting medium composed of liquid metal heat-conducting material and two-dimensional sheet heat-conducting material is set within the channels. This utilizes the material's inherent high heat dissipation and the polymer's inherent channel orientation to improve heat conduction efficiency, especially improving the longitudinal heat conduction efficiency, which is difficult to improve. Furthermore, the vertically oriented channels can have their structural characteristics and the distribution characteristics of the liquid metal controlled through physical pressing and electrical processing, thus facilitating the distribution of liquid metal at the interface between the channels and the two layers (directional heat-conducting layer and selective infrared emitting layer). The reflective interface of the liquid metal promotes heat distribution to the selective infrared emitting layer, achieving a synergistic heat dissipation effect with the selective infrared emitting layer. The unidirectional infrared radiation layer, by utilizing the temperature and humidity dependence of the polymer coating and simple process control, forms a gradient aperture microporous structure. This gradient microporous structure promotes the selective dispersion of infrared radiation, radiating the heat energy transferred by the directional heat-conducting layer in the most suitable 8~13μm atmospheric window band, while blocking specific external thermal radiation. Therefore, the heat dissipation material of the present invention has high longitudinal thermal conductivity, high infrared reflectivity and selective infrared emissivity, which can effectively reduce the temperature of precision electronic devices such as chips, and the preparation process is simple and controllable, making it suitable for large-scale production. Attached Figure Description

[0024] Figure 1 This is a diagram illustrating the unidirectional heat transfer mechanism of the present invention.

[0025] Figure 2 This is a SEM image of the hierarchical gradient porous structure of the selective infrared emitting layer of the heat dissipation material in Example 1.

[0026] Figure 3 The infrared emission spectrum of the selective infrared emitting layer of the heat dissipation material in Example 1 is shown.

[0027] Figure 4 This is an SEM image of the directional heat-conducting layer of the heat dissipation material in Example 1;

[0028] Figure 5 The infrared reflectance spectrum of the directional heat-conducting layer of the heat dissipation material in Example 1 is shown.

[0029] Figure 6 The infrared reflectance spectrum of the directional heat-conducting layer of the heat dissipation material in Comparative Example 3 is shown.

[0030] Figure 7 The image shows the broadband high infrared emission spectrum of the heat dissipation material in Comparative Example 6. Detailed Implementation

[0031] The technical solutions and effects of the present invention will be shown and explained below with reference to specific embodiments, comparative examples, and accompanying drawings. These embodiments are only for illustrating the technical solutions of the present invention and are not intended to limit the scope of protection.

[0032] The heat dissipation composite material of the present invention is composed of a directional heat-conducting layer (located near the object to be cooled during use) and a selective infrared emitting layer (located near the external environment during use). The directional heat-conducting layer is composed of a polymer containing vertically oriented micropores filled with a solid-liquid dual continuous thermally conductive medium; the selective infrared emitting layer is a hierarchical gradient porous polymer structure designed by spectral engineering.

[0033] In the directional heat conduction layer, the solid-liquid dual continuous heat conduction medium is distributed in the microchannel (the channel contains the solid-liquid dual continuous heat conduction medium) and at the interface between the two layers (the directional heat conduction layer and the selective infrared emitting layer) (the interface between the two layers contains liquid metal distribution), forming a continuous metal reflection-heat dissipation interface, which facilitates the heat flow to be conducted to the selective infrared emitting layer in the designed direction.

[0034] The selective infrared emitting layer utilizes a special graded porous design to facilitate infrared emission heat dissipation through the 8–13 μm atmospheric window band and blocks the return of mid-infrared external radiation in the 2.5–25 μm wavelength range, thereby achieving efficient unidirectional radiative heat dissipation. For an example of its operation (unidirectional heat flow transfer) in high-power-density chip devices, please refer to [link to relevant documentation]. Figure 1 The heat transfer direction in the diagram is from the high-power-density chip layer to the external environment.

[0035] In the technical solution of this invention, the thickness of the directional heat-conducting layer and the selective infrared emitting layer is not the main innovation and can be adjusted according to the specific spatial scale requirements. Therefore, the thickness of the directional heat-conducting layer and the selective infrared emitting layer is only an illustrative example and should not be considered a limitation on the scope of protection. In the technical solution of this invention, the pore structure of the directional heat-conducting layer and the internal solid-liquid dual continuous heat-conducting medium, the liquid metal distributed between the directional heat-conducting layer and the selective infrared emitting layer (metal reflection-heat dissipation interface), and the hierarchical gradient pore structure of the selective infrared emitting layer are the key to synergistically achieving directional heat conduction and interlayer reflection (directional heat-conducting layer) - unidirectional radiation heat dissipation and blocking the transmission of external heat radiation to the heat dissipation object. Among them, the pore size of the hierarchical gradient porous structure of the selective infrared emitting layer gradually decreases from the heat dissipation object side to the external environment side, and achieves the selectivity of infrared emission and the blocking of infrared radiation of specific wavelengths from the external environment by means of specific pore size and gradient method. Among them, the pore size on the inner and outer sides of the selective infrared emitting layer is a key influencing factor, and the pore size of the middle layer is between the pore sizes on the inner and outer sides and maintains the gradient trend. Unless otherwise specified, in the following examples and comparative examples, when the infrared radiation layer of the same sample is coated in multiple coats, the thickness of each coat is the same. To ensure comparability, the "semi-cured" state in the following examples and comparative examples refers to a degree of cure of 50±5%.

[0036] All materials used in the following examples and comparative examples are commercially available. Among them, PVDF-b-PE (polyvinylidene fluoride-b-polyethylene, in which the molar ratio of polyvinylidene fluoride to polyethylene is approximately 70:30, the molecular weight of PVDF is approximately 60 kDa, and the molecular weight of PE is approximately 5 kDa), PDMS-b-PEO (polydimethylsiloxane-b-polyoxyethylene, in which the molar ratio of polydimethylsiloxane to polyoxyethylene is approximately 50:50, the molecular weight of PDMS is approximately 5 kDa, the molecular weight of PEO is approximately 2 kDa), and PS-b-PMMA (polystyrene-b-polymethyl methacrylate, in which the molar ratio of polystyrene to polymethyl methacrylate is approximately 70:30, the molecular weight of PS is approximately 50 kDa, and the molecular weight of PMMA is approximately 40 kDa) were purchased from Xi'an Qiyue Biotechnology Co., Ltd. Gallium-indium alloy (75% Ga, 25% In), gallium-indium-tin alloy (68% Ga, 22% In, 10% Sn), MXene nanosheets (approximately 1–5 μm in diameter and 1–5 nm in thickness), and boron nitride nanosheets (approximately 1–3 μm in diameter and 10–50 nm in thickness) were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd. Polyimide (approximately 50 kDa), polypropylene glycol-polybutylene glycol-polypropylene glycol (approximately 5 kDa), polyethersulfone (approximately 50 kDa), and polyether-polyester-polyether (approximately 20 kDa) were purchased from Sigma-Aldrich.

[0037] In the following examples and comparative examples, the emissivity of the atmospheric window, the emissivity of the non-atmospheric window, and the longitudinal thermal conductivity (W·m) are compared. -1 ·K -1 The methods and test conditions for determining infrared reflectance, steady-state temperature (°C), and orientation degree are as follows:

[0038] (1) Atmospheric window emissivity, non-atmospheric window emissivity and infrared reflectivity

[0039] Test method: The infrared reflectance and infrared transmittance of the sample surface were measured using a Fourier transform infrared spectrometer (FTIR, Thermo Scientific Nicoleti S50) with an integrating sphere attachment. The infrared emissivity was calculated using ε = 1-RT.

[0040] (2) Longitudinal thermal conductivity (W·m) -1 ·K -1 )

[0041] Test method: The thermal conductivity of the material is measured using the transient method, k = α·ρ·C p α is the in-plane thermal diffusivity of the material, ρ is the density of the material, and C is the density of the material. pρ represents the specific heat capacity of the material. Thermal diffusivity was measured using the laser flash calorimeter (LFA, Netzsch LFA 467, Germany). Material density was calculated using the formula ρ = m / v. Specific heat capacity was measured using a differential scanning calorimeter (DSC, Netzsch DSC200F3, Switzerland) and the sapphire specific heat method.

[0042] (3) Steady-state temperature (°C)

[0043] Test method: To evaluate the heat dissipation performance of the unidirectional heat transfer film material of the present invention, the film materials prepared in the examples and comparative examples were all cut into 10×10 mm samples and attached to the surface of a heating chip model of the same size. Under the conditions of ambient temperature of 25 ℃ and natural convection, a constant power density of 50 W·cm² was applied by bottom electric heating. -2 Heat flow was input, and the chip surface temperature was measured after the system reached steady state. Steady-state determination condition: temperature change < 0.2 ℃ / 5 min.

[0044] (4) Orientation

[0045] Test method: X-ray diffraction (XRD BRUKER D8 Advance) was used with a scanning angle range of 2θ = 5 to 90° and a step size of 0.02° / s; the radiation source was Cu Kα, the current was 40 mA, and the voltage was 40 kV. The degree of orientation was calculated based on the intensity ratio of the characteristic diffraction peaks.

[0046] Example 1: A heat dissipation composite film material and its preparation method

[0047] In this embodiment, the selective infrared emitting layer of the heat dissipation composite film is prepared using a PVDF-b-PE polymer solution system; the directional heat conduction layer is prepared using a gallium-indium alloy and MXene nanosheet organic solvent mixture as a solid-liquid dual continuous heat conduction medium, and a solvent dispersion system containing polyimide (polymer matrix) and polypropylene glycol-polybutylene glycol-polypropylene glycol (connectivity enhancer). The preparation method is as follows:

[0048] (1) Prepare a 10 wt% PVDF-b-PE solution using N,N-dimethylformamide as the solvent. The solution was uniformly coated onto a glass substrate and placed in air with a relative humidity of 80 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 25 ℃ for solvent exchange for 10 h. Subsequently, another layer of the aforementioned 10 wt% PVDF-b-PE solution was coated onto the substrate and placed in air with a relative humidity of 60 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 15 ℃ for solvent exchange for 10 h. This process was repeated, followed by another layer of the aforementioned 10 wt% PVDF-b-PE solution coating. The substrate was placed in air with a relative humidity of 40 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 5 ℃ for solvent exchange for 10 h and then oriented and frozen for 15 min at a height of 2 cm directly above liquid nitrogen. Afterward, it was placed in a freeze dryer for primary drying, maintaining a freeze-drying temperature of -40 ℃ under a vacuum of 0.1 mbar for 6 h to remove most of the moisture through sublimation. Secondary drying was then performed, with the temperature gradually increased to 0 ℃ and then at 0.05 mbar. Drying under vacuum for 2 hours to reduce the residual moisture content to <5% yields a selective infrared emitting layer (approximately 53 μm thick) with a hierarchical gradient pore structure.

[0049] The SEM image of the selective infrared emitting layer in this embodiment is as follows: Figure 2 As shown. By Figure 2 As can be seen, the selective infrared emitting layer prepared by this method contains several micropores and exhibits a hierarchical gradient porous structure, which is beneficial for unidirectional infrared radiation heat dissipation. The pore size of the hierarchical gradient pore structure gradually increases from about 1.2 μm (the pores in the outermost plane, with an average pore size of 1.2 μm) to about 10.6 μm (the pores in the innermost plane, with an average pore size of 10.6 μm) along the film thickness direction from the outermost side (external environment side, upper side in the figure) to the chip side (heat dissipation target side, lower side in the figure).

[0050] The infrared reflectance spectrum of the selective infrared emitting layer in this embodiment is as follows: Figure 3 As shown. By Figure 3 It can be seen that the selective infrared emitting layer prepared by this method has an average emissivity of 0.97 in the 8-13 μm atmospheric window band and an emissivity of less than 0.34 in the non-window band, exhibiting good unidirectional infrared radiation heat dissipation characteristics.

[0051] (2) Prepare an anhydrous ethanol dispersion system containing 15 wt% gallium indium alloy and 5 wt% MXene nanosheets. Use a probe-type ultrasonic device with a power of 130 W and a pulse frequency of 2 s ON / 1 s OFF to treat it under ice bath conditions for 8 min. Then centrifuge at 1000 rpm for 10 min, collect the sediment, and obtain a uniformly mixed solid-liquid dual continuous thermal conductive medium.

[0052] (3) Prepare a mixture of N,N-dimethylformamide / water solvent containing 5 wt% solid-liquid dual continuous thermal conductive medium, 10 wt% polyimide, and 1 wt% polypropylene glycol-polybutylene glycol-polypropylene glycol (the volume ratio of N,N-dimethylformamide / water in the mixed solvent is 4:1); magnetically stir for 18 h to obtain a uniform coating liquid; uniformly coat the coating liquid onto the side of the selective infrared emitting layer with a larger aperture to form a directional thermal conductive layer coating film; immerse the bottom half of the directional thermal conductive layer coating film horizontally in a 50 ℃ water bath for 45 min, and expose the top to air (maintaining a relative humidity of 65 RH%). After the film surface and cross-section solidify and stabilize, dry at 70 ℃ for 6 h to obtain a composite film. Perform two transverse mechanical pressings (pressure 0.7 MPa) on the obtained composite film at 60 ℃, and three longitudinal mechanical pressings (pressure 200 kPa) at 70 ℃. Apply 0.6 kPa to the composite film. A DC voltage of V was applied for 8 minutes to allow the liquid metal to form a continuous directional heat conduction network within the micropores and a continuous metal reflection interface located on the film surface and the inner pore wall, resulting in a heat dissipation composite film (total thickness 110 μm).

[0053] The SEM image (scanning electron microscope image) and infrared reflectance spectrum of the directional thermal conductive layer are shown below. Figure 4 , 5 .Depend on Figure 4 It can be seen that the directional heat-conducting layer prepared by this method has a connected vertically oriented micropore structure (extending from the heat dissipation object side to the external environment side), with a micropore diameter of about 0.5~6μm and a vertical orientation degree of about 0.94.

[0054] Depend on Figure 5 It can be seen that the average infrared reflectance of this directional heat-conducting layer in the 8~13 μm atmospheric window band is 0.87, which is conducive to achieving more efficient heat conduction and heat dissipation by means of the vertically oriented microporous structure and the internal heat-conducting medium. At the same time, it reflects the radiant heat of a specific wavelength range to the selective infrared emitting layer through the continuous metal reflective interface, thereby achieving functional synergy with the selective infrared emitting layer and jointly improving the unidirectional heat dissipation efficiency.

[0055] Example 2: A heat dissipation composite film material and its preparation method

[0056] In this embodiment, the selective infrared emitting layer of the heat dissipation composite film is prepared using a PDMS-b-PEO polymer solution system; the directional heat conduction layer is prepared using a gallium indium tin alloy and boron nitride nanosheet organic solvent mixture as a solid-liquid dual continuous heat conduction medium, and a solvent dispersion system containing polyethersulfone (polymer matrix) and polyether-polyester-polyether (connectivity enhancer). The preparation method is as follows:

[0057] (1) Prepare an 8 wt% PDMS-b-PEO solution using hexafluoroisopropanol as the solvent. The solution was uniformly coated onto a glass substrate and placed in air with a relative humidity of 70 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 20 ℃ for solvent exchange for 12 h. Subsequently, another layer of the aforementioned 8 wt% PDMS-b-PEO solution was coated, and the solution was placed in air with a relative humidity of 50 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 10 ℃ for solvent exchange for 12 h. This process was repeated, followed by another layer of the aforementioned 8 wt% PDMS-b-PEO solution coating, and the solution was placed in air with a relative humidity of 30 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 0 ℃ for solvent exchange for 12 h, and then horizontally placed 2.5 cm above liquid nitrogen for directional freezing for 18 min. Afterward, it was placed in a freeze dryer for primary drying, maintaining a freeze-drying temperature of -30 ℃ under a vacuum of 0.2 mbar for 12 h to remove most of the moisture through sublimation. Secondary drying was then performed, with the temperature gradually increased to 10 ℃ and maintained at 0.25 mbar. Drying under vacuum for 6 hours to reduce the residual moisture content to <5% yields a selective infrared emitting layer (approximately 48 μm thick) with a hierarchical gradient pore structure.

[0058] Scanning electron microscopy revealed that the pore size of the selective infrared emitting layer's hierarchical gradient pore structure gradually increases along the film thickness from approximately 1.6 μm (the pores in the outermost plane, with an average pore size of 1.6 μm) to approximately 10.4 μm (the pores in the innermost plane, with an average pore size of 10.4 μm) from the external environment side to the heat dissipation target side. The average emissivity of this selective infrared emitting layer was measured to be 0.95 in the 8–13 μm atmospheric window band, and below 0.33 in the non-window band.

[0059] (2) Prepare an anhydrous ethanol dispersion system containing 10 wt% gallium indium tin alloy and 8 wt% boron nitride nanosheets. Use a probe-type ultrasonic device with a power of 120 W and a pulse frequency of 3 s ON / 2 s OFF to treat it under ice bath conditions for 10 min. Then centrifuge at 2000 rpm for 5 min, collect the sediment, and obtain a uniform solid-liquid dual continuous thermal conductive medium.

[0060] (3) Prepare a solvent mixture containing 3 wt% solid-liquid dual continuous thermal conductive medium, 20 wt% polyethersulfone, and 2 wt% polyether-polyester-polyether N,N-dimethylacetamide / ethanol (the volume ratio of N,N-dimethylacetamide to ethanol in the mixed solvent is 3:1). Stir magnetically for 24 h to obtain a uniform coating liquid. Coat the coating liquid uniformly on the side of the selective infrared emitting layer with larger aperture to form a directional thermal conductive coating film. Immerse the bottom half of the directional thermal conductive coating film horizontally in a 60 ℃ water bath for 60 min, and expose the top to air (maintain relative humidity of 60 RH%). After the film surface and cross section solidify and stabilize, dry at 60 ℃ for 8 h to obtain a composite film. Perform two transverse mechanical pressings (pressure 0.9 MPa) on the obtained composite film at 50 ℃ and four longitudinal mechanical pressings (pressure 300 kPa) at 60 ℃. Apply a DC voltage of 0.8 V to the film. The liquid metal is processed to form a continuous directional heat conduction network and a continuous metal reflection interface on the film surface and the inner pore wall, resulting in a heat dissipation composite film (total thickness 110 μm).

[0061] Scanning electron microscopy observation shows that the directional heat-conducting layer of this embodiment has a connected vertically oriented micropore structure (extending from the heat dissipation object side to the external environment side), with a micropore diameter of about 0.3~8 μm and a vertical orientation degree of about 0.92.

[0062] The directional heat-conducting layer has an average infrared reflectance of 0.86 in the 8-13 μm atmospheric window band, which is conducive to achieving more efficient heat conduction and heat dissipation by means of the vertically oriented microporous structure and the internal heat-conducting medium. At the same time, it reflects the radiant heat of a specific wavelength range to the selective infrared emitting layer through the continuous metal reflective interface, thereby achieving functional synergy with the selective infrared emitting layer and jointly improving the unidirectional heat dissipation efficiency.

[0063] Example 3: A heat dissipation composite film material and its preparation method

[0064] In this embodiment, the selective infrared emitting layer of the heat dissipation composite film is prepared using a PS-b-PMMA polymer solution system; the directional heat conduction layer is prepared using a gallium-indium alloy and graphene nanosheet organic solvent mixture as a solid-liquid dual continuous heat conduction medium, and a solvent dispersion system of polyacrylonitrile (polymer host) and polypropylene glycol-polybutylene glycol-polypropylene glycol (connectivity enhancer). The preparation method is as follows:

[0065] (1) Prepare a 15 wt% PS-b-PMMA solution using tetrahydrofuran as the solvent. The solution was uniformly coated onto a glass substrate and placed in air with a relative humidity of 90 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 30 ℃ for solvent exchange for 8 hours. Subsequently, another layer of the aforementioned 15 wt% PS-b-PMMA solution was coated, and the solution was placed in air with a relative humidity of 70 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 20 ℃ for solvent exchange for 8 hours. This process was repeated, followed by another layer of the aforementioned 15 wt% PS-b-PMMA solution coating, and the solution was placed in air with a relative humidity of 50 RH% for semi-curing at room temperature. Then, it was placed in a water bath at 10 ℃ for solvent exchange for 8 hours, and then horizontally placed 3 cm above liquid nitrogen for directional freezing for 20 minutes. Afterward, it was placed in a freeze dryer for primary drying, maintaining a freeze-drying temperature of -20 ℃ under a vacuum of 0.5 mbar for 24 hours to remove most of the moisture through sublimation. Secondary drying was then performed, with the temperature gradually increased to 25 ℃ and maintained at 0.5 mbar. Drying under vacuum for 12 hours to reduce the residual moisture content to <5% yields a selective infrared emitting layer (approximately 58 μm thick) with a hierarchical gradient pore structure.

[0066] Scanning electron microscopy revealed that the selective infrared emitting layer exhibits a hierarchical gradient pore structure, with pore sizes gradually increasing from approximately 0.8 μm (the outermost pores, with an average pore size of 0.8 μm) to approximately 9.4 μm (the innermost pores, with an average pore size of 9.4 μm) along the film thickness from the external environment side to the heat dissipation target side. The average emissivity of this selective infrared emitting layer was measured to be 0.96 in the 8–13 μm atmospheric window band, and less than 0.35 in the non-window band.

[0067] (2) Prepare an anhydrous ethanol dispersion system containing 30 wt% gallium indium alloy and 2 wt% graphene nanosheets. Use a probe-type ultrasonic device with a power of 150 W and a pulse frequency of 2 s ON / 1 s OFF to treat it under ice bath conditions for 5 min. Then centrifuge at 1500 rpm for 8 min, collect the sediment, and obtain a uniform solid-liquid dual continuous thermal conductive medium.

[0068] (3) Prepare a solvent mixture containing 8 wt% solid-liquid dual continuous thermal conductive medium, 5 wt% polyacrylonitrile, and 0.5 wt% dimethylpyrrolidone / water in polypropylene glycol-polybutylene glycol-polypropylene glycol (the volume ratio of dimethylpyrrolidone to water in the mixed solvent is 5:1). Stir magnetically for 12 h to obtain a uniform coating liquid. Coat the coating liquid uniformly on the side of the selective infrared emitting layer with a larger aperture to form a directional thermal conductive coating film. Immerse the bottom half of the directional thermal conductive coating film horizontally in a 30℃ water bath for 60 min, and expose the top to air (maintaining a relative humidity of 70 RH%). After the film surface and cross section solidify and stabilize, dry at 80℃ for 4 h to obtain a composite film. Perform one transverse mechanical pressing (pressure 0.3 MPa) on the obtained composite film at 70℃ and two longitudinal mechanical pressings (pressure 60 kPa) at 80℃. Apply 1 A DC voltage of V was applied for 5 minutes to induce the liquid metal to form a continuous directional heat conduction network within the micropores and a continuous metal reflection interface located on the film surface and the inner pore wall, resulting in a heat dissipation composite film (total thickness 110 μm).

[0069] Scanning electron microscopy observation shows that the directional heat-conducting layer of this embodiment has a connected vertically oriented micropore structure (extending from the heat dissipation object side to the external environment side), with a micropore diameter of about 0.6~9μm and a vertical orientation degree of about 0.94.

[0070] The directional heat-conducting layer has an average infrared reflectance of 0.89 in the 8-13 μm atmospheric window band, which is conducive to achieving more efficient heat conduction and heat dissipation by means of the vertically oriented microporous structure and the internal heat-conducting medium. At the same time, it reflects the radiant heat of a specific wavelength range to the selective infrared emitting layer through the continuous metal reflective interface, thereby achieving functional synergy with the selective infrared emitting layer and jointly improving the unidirectional heat dissipation efficiency.

[0071] Example 4: Performance Comparison of Different Heat Dissipation Materials

[0072] This embodiment is used to demonstrate other comparative heat dissipation materials tested in the study and to compare their performance.

[0073] Comparative Example 1: The only difference between the heat dissipation material in this comparative example and that in Experimental Example 1 is that the heat dissipation material consists only of a directional heat-conducting layer; its total thickness is 110 μm.

[0074] Comparative Example 2: The only difference between the heat dissipation material in this comparative example and that in Experimental Example 1 is that the heat dissipation material consists only of a selective infrared emitting layer; its total thickness is 110 μm.

[0075] Comparative Example 3: The only difference between the heat dissipation material in this comparative example and that in Experimental Example 1 is that longitudinal mechanical pressing was not performed in step (3), and no DC voltage was applied to the composite film; its total thickness is approximately 110 μm. The infrared reflectance spectrum of the directional heat-conducting layer of this comparative example heat dissipation material is shown in [reference needed]. Figure 6 ,Depend on Figure 6 As can be seen, the infrared reflectivity of the directional heat-conducting layer in this comparative example is only 0.44. Even if the heat dissipation material has a directional heat-conducting layer and a selective infrared emissivity layer, it still cannot block external infrared radiation, and a secondary heat rise phenomenon will occur, which is not conducive to efficient heat dissipation.

[0076] Comparative Example 4: The difference between the heat dissipation material in this comparative example and that in Experimental Example 1 is only that: in step (3), the entire coating is immersed in a 50 ℃ water bath for complete displacement (resulting in phase separation without direction, forming a porous thermally conductive layer with a vertical orientation of about 0.48); its total thickness is 110 μm.

[0077] Comparative Example 5: The difference between the heat dissipation material of this comparative example and that of Experimental Example 1 is only that: no connectivity enhancement agent was added in step (3) (resulting in the isolation of the vertical channel structure and the formation of an unconnected directional heat conduction layer); its total thickness is still 110 μm.

[0078] Comparative Example 6 The difference between the heat dissipation material of this comparative example and that of Experimental Example 1 is only that: a low concentration (5 wt%) of PVDF-b-PE solution was used in step (1) (resulting in the formation of a gradient pore structure that increases from ~0.1 μm to ~80 μm), and the average emissivity of the resulting emission layer was measured to be 0.94 in the 8-13 μm atmospheric window band and 0.93 in the non-window band, i.e., broadband infrared emission; its total thickness is 110 μm. Figure 7 The infrared emission spectrum of this comparative heat dissipation material is shown.

[0079] Table 1 below shows the performance of the embodiments and comparative examples of the present invention.

[0080] Table 1 Comparison of Heat Dissipation Material Performance

[0081] As shown in Table 1, the heat dissipation material of the embodiment has extremely high emissivity at the atmospheric window and low emissivity at the non-atmospheric window, high longitudinal thermal conductivity, high infrared reflectivity, and a steady-state temperature significantly lower than that of the comparative heat dissipation material.

[0082] Comparative Example 1 uses only a directional heat-conducting layer, which enables rapid heat conduction along the thickness direction. However, this heat-conducting layer lacks an infrared reflection structure and selective infrared emission. In actual operation, although the heat generated by the chip can be quickly conducted to the film surface, the radiative heat dissipation efficiency to the external environment is limited, especially in the non-atmospheric window band where there is significant infrared absorption and energy loss, resulting in limited overall heat dissipation performance.

[0083] In Comparative Example 2, only a selective infrared emitting layer is provided. This layer achieves high infrared emissivity in the atmospheric window band through a porous or gradient aperture structure, but this structure lacks directional heat conduction. In this case, the heat generated by the chip mainly relies on lateral or non-directional conduction to diffuse to the emitting layer. This results in inefficient heat transfer and high thermal resistance, making it difficult to meet the rapid heat dissipation requirements of high-power-density chips, thus limiting its overall heat dissipation performance.

[0084] In Comparative Example 3, the lack of a metal reflective interface between the directional heat conduction layer and the selective infrared emitting layer (lack of electrical processing steps) caused some heat to flow back to the chip side, weakening the unidirectional heat transfer effect and thus limiting the improvement of overall heat dissipation performance.

[0085] In Comparative Example 4, the vertical orientation of the microchannels in the directional thermal conductive layer is low, and no obvious directional arrangement structure is formed along the film thickness direction. In this structure, heat exhibits obvious lateral diffusion characteristics within the thermal conductive layer, leading to an increase in equivalent thermal resistance. The heat generated by the chip is difficult to transfer to the infrared emitting layer in a timely and efficient manner, thus affecting the heat dissipation response speed and steady-state heat dissipation capability.

[0086] In Comparative Example 5, the micropores in the directional thermally conductive layer are not interconnected, failing to form a continuous heat conduction pathway. Due to the lack of interconnection, heat must frequently cross the polymer matrix or interface within the thermally conductive layer, significantly increasing interfacial thermal resistance. This makes it difficult for the directional structure to fully utilize its vertical thermal conductivity advantage, resulting in a significant reduction in overall thermal conductivity.

[0087] In Comparative Example 6, the micropore gradient control in the selective infrared emitting layer was poor, resulting in a broadband infrared emitting structure rather than a selective infrared emitting structure. This broadband infrared emitting layer also exhibited high infrared emission and absorption capabilities outside the atmospheric window band, causing the radiated energy to be unable to be effectively concentrated within the atmospheric window range. This increased environmental back-absorption loss and thus reduced the effective radiative heat dissipation efficiency.

[0088] In summary, the heat dissipation material of the embodiment, through the synergistic design of a highly oriented, unidirectional heat-conducting structure with interconnected vertical microchannels, a metal reflective interface with high infrared reflectivity, and a selective infrared emitting layer, can achieve rapid unidirectional heat transfer of high power density chips, effectively suppress infrared absorption in non-atmospheric window bands, and significantly improve heat dissipation efficiency.

[0089] Although the technical solutions and effects of the present invention have been described with reference to a limited number of embodiments, based on the above description, those skilled in the art can obtain other embodiments through simple substitutions and modifications without creative effort. Therefore, such simple substitutions, modifications, and alterations are obvious without departing from the technical route of the present invention. The disclosure of the embodiments to the present invention is illustrative and not intended to limit the scope of protection of the present invention.

Claims

1. A heat-dissipating composite material, characterized in that, The heat dissipation composite material consists of a directional heat-conducting layer and a selective infrared emitting layer. The directional heat-conducting layer contains a first polymer matrix material, a connectivity enhancer, a solid-liquid dual continuous thermally conductive medium, and a metal reflective interface. The directional heat-conducting layer has a through-hole channel structure extending from the heat dissipation target side towards the selective infrared emitting layer. The through-hole channel structure contains a solid-liquid dual continuous thermally conductive medium composed of liquid metal thermally conductive material and two-dimensional sheet thermally conductive material. The metal reflective interface is located at the connection interface between the directional heat-conducting layer and the selective infrared emitting layer and is formed by the liquid metal thermally conductive material. The selective infrared emitting layer contains a second polymer matrix material and has a microporous structure, with the pore size of the microporous structure gradually decreasing from one side of the directional heat-conducting layer outwards.

2. The heat dissipation composite material according to claim 1, characterized in that, The aperture of the through-hole structure is 0.1μm~10μm.

3. The heat dissipation composite material according to claim 1, characterized in that, The vertical orientation of the through-hole channel structure is greater than or equal to 0.

9.

4. The heat dissipation composite material according to claim 1, characterized in that, In the selective infrared emitting layer, the average pore size of the microporous structure on the directional heat conduction layer side is 7μm~15μm; The average pore size of the microporous structure on the outer side is 0.1 μm to 3 μm.

5. The heat dissipation composite material according to claim 1, characterized in that, The first polymer matrix material used in the directional heat-conducting layer is selected from one or more of polyimide, polyethersulfone, and polyacrylonitrile.

6. The heat dissipation composite material according to claim 1, characterized in that, The connectivity enhancer is selected from at least one of polypropylene glycol-polybutylene glycol-polypropylene glycol and polyether-polyester-polyether.

7. The heat dissipation composite material according to claim 1, characterized in that, The liquid metal thermal conductive material used in the directional thermal conductive layer is selected from gallium indium alloy or gallium indium tin alloy, and the two-dimensional sheet thermal conductive material used in the directional thermal conductive layer is one or more of MXene nanosheets, graphene nanosheets and boron nitride nanosheets.

8. The heat dissipation composite material according to claim 1, characterized in that, The second polymer matrix material used in the selective infrared emitting layer is selected from one or more of polyvinylidene fluoride-b-polyethylene, polydimethylsiloxane-b-polyoxyethylene, and polystyrene-b-polymethyl methacrylate.

9. A method for preparing a heat-dissipating composite material according to any one of claims 1 to 8, characterized in that, The preparation method includes the following steps: S1 Preparation of Selective Infrared Emitting Layer: The desired second polymer matrix material is prepared into a selective infrared emitting layer coating solution with a mass percentage concentration of 7%~20% using an organic solvent. The coating solution is applied to the template material surface in 3~4 layers: After the first coating, it is semi-cured in air with a relative humidity of 70%~90%, and then solvent exchange is performed in a water bath at 20℃~30℃; after the second coating, it is semi-cured in air with a relative humidity of 50%~70%, and then solvent exchange is performed in a water bath at 10℃~20℃; after the third coating, it is semi-cured in air with a relative humidity of 30%~50%, and then solvent exchange is performed in a water bath at 0℃~10℃. The relative humidity required for each semi-curing step decreases sequentially, and the water bath temperature required for each solvent exchange step decreases sequentially. The required decrease in relative humidity between adjacent semi-curing steps is 10%~25%, and the required decrease in temperature between adjacent solvent exchange steps is 5℃~20℃. After the final solvent exchange in the water bath, the product is placed horizontally above liquid nitrogen for 2~3 seconds. Directional freezing at a depth of cm for 10-20 minutes, followed by freeze-drying until the residual moisture content is less than 5%, yields a selective infrared emitting layer; S2 Preparation of solid-liquid dual continuous thermal conductive medium: Take liquid metal thermal conductive material and two-dimensional sheet thermal conductive material, disperse them in an organic solvent, sonicate, and collect the sedimentation part by centrifugation to obtain solid-liquid dual continuous thermal conductive medium; S3 Preparation of directional thermal conductive layer coating liquid and completion of heat dissipation composite material preparation: Take organic solvent, solid-liquid dual continuous thermal conductive medium, first polymer matrix material and interconnection reinforcing agent to prepare directional thermal conductive layer coating liquid, coat it on the side with larger aperture of selective infrared emitting layer to form directional thermal conductive layer coating film; immerse the bottom of directional thermal conductive layer coating film in a water bath of 30℃~70℃, expose the top to air with relative humidity of 50%~80%, and after the film surface and cross section solidify and stabilize, dry it at 60℃~80℃ to obtain composite film. Perform 1~3 transverse mechanical pressing on the obtained composite film at 50℃~70℃ with a pressure of 0.2MPa~1MPa, and perform 2~4 longitudinal mechanical pressing on the composite film at 60℃~80℃ with a pressure of 50kPa~300kPa. Apply a DC voltage of 0.6V~1.2V to the composite film for 4min~10min.

10. The use of a heat dissipation composite material according to any one of claims 1 to 8 or a heat dissipation composite material prepared by the preparation method according to claim 9 as a chip heat dissipation material.

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