Heat insulation-heat dissipation integrated phase change composite material and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of heat insulation materials, and relates to a heat insulation-heat dissipation integrated phase change composite material and a preparation method thereof. The method comprises the following steps: preparing a thermal insulation layer precursor solution; preparing a heat dissipation layer precursor solution; respectively preparing the heat insulation layer precursor solution and the heat dissipation layer precursor solution to obtain a heat insulation layer aerogel green body and a heat dissipation layer aerogel green body which are not imidized; the preparation method comprises the following steps: uniformly coating a PAA solution on to-be-bonded interfaces of two layers of green bodies, folding the two layers of green bodies, applying pressure on the folding interfaces, carrying out thermal imidization treatment to form integrated polyimide aerogel, immersing a heat dissipation layer into a phase change material, carrying out vacuum impregnation, and cooling to room temperature to obtain the heat insulation-heat dissipation integrated phase change composite material. Through the design of a homogeneous material system and a compact bonding layer, excellent heat insulation and heat dissipation performance is achieved, and the problem of PCM leakage is thoroughly solved. The preparation method is controllable in process, and firm and compact combination between the two layers can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat insulation material preparation, and relates to a heat insulation-heat dissipation integrated phase change composite material and a preparation method thereof. BACKGROUND

[0002] Current traditional commercial aerogels (such as silica and polyimide systems) have become high-efficiency heat insulation materials due to their ultra-low thermal conductivity and ultra-high porosity. However, their single heat insulation property exposes their fundamental defects when dealing with high-power dynamic heat load scenarios (such as power battery packs and 5G base station chips), which often require the material to block the internal and external heat conduction while quickly dissipating the internal local hot spots (lithium battery working temperature difference > 15℃). Especially when dealing with transient thermal shock, the material lacks the buffering mechanism of phase change latent heat, thereby significantly increasing the risk of thermal runaway.

[0003] To improve the dynamic heat regulation performance, researchers attempt to load phase change materials (PCMs) in the aerogel framework, relying on the property of absorbing / releasing a large amount of latent heat during the phase change process to maintain a relatively constant temperature, so that the material has heat energy storage and temperature regulation characteristics. However, this also causes new contradictions, especially in its molten liquid state, which is prone to leakage and precipitation from the porous network. This not only leads to a sharp decline in heat management efficiency with the increase in use cycle number, but also may contaminate surrounding precision components, causing safety problems such as short circuits, which seriously restricts its practical application.

[0004] Recently, researchers have proposed a multi-layer design idea of "functional decoupling". For example, Chinese patent CN119978538A discloses a preparation method of a heat insulation-heat conduction integrated phase change composite material, which uses the "bridge" effect of calcium ions to simultaneously connect the polymer chain segments in the heat insulation layer and the sodium alginate forming the heat conduction layer framework, and then partially impregnates the phase change material after directional freezing and regulation of the pore size direction, finally realizing the integrated preparation of the heat insulation layer and the heat conduction layer. Although this method can theoretically solve the problem of bidirectional heat management, it actually faces serious interface bonding challenges. The "bridge effect" of ionic bonds cannot meet the requirements of interface strength in practical applications, and the compatibility and physical and chemical properties (such as thermal expansion coefficient and modulus) of heterogeneous materials differ greatly, resulting in weak interface bonding strength. Under thermal stress or mechanical stress, delamination or layering between layers is prone to occur. The sodium alginate matrix has poor high-temperature resistance and high moisture absorption rate, and the limitations of the material system make it more prone to failure in high-temperature and high-humidity environments. More importantly, the bonding interface between the two layers is naturally the weakest link and the preferred channel for PCM leakage, and the leakage of PCM will lead to the failure of the heat management system. However, existing bonding techniques cannot form a continuous, dense and defect-free perfect barrier between the interfaces to block the migration of PCM molecules.

[0005] It is extremely challenging to achieve firm and dense interfacial bonding on such ultra-lightweight and high-porosity materials as aerogels. Conventional solvent-based adhesives can destroy the pore structure of aerogels during the infiltration process, resulting in a decrease in strength or deterioration in thermal insulation performance. Solvent residues or curing shrinkage can also introduce defects at the interface. For systems involving PCM, the bonding layer must also have extremely low permeability to effectively block PCM molecules, which poses almost stringent requirements for the density and compatibility of the bonding layer with the substrate.

[0006] In summary, the prior art cannot truly achieve seamless integration of thermal insulation and heat dissipation performance, and the core bottleneck is that there is a lack of an interlayer connection technology that can simultaneously satisfy ultra-strong interfacial bonding and completely block PCM leakage. Therefore, developing a new type of structural design and preparation method to fundamentally solve the interface problem and PCM leakage problem is the key to promoting the development of this field. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art and provide a thermal insulation-heat dissipation integrated phase change composite material and a preparation method thereof. By using a homogeneous material system and a dense bonding layer design, excellent thermal insulation, heat dissipation / heat storage performance is achieved, and the PCM leakage problem is completely solved. The preparation method is process controllable and can achieve firm and dense bonding between the two layers.

[0008] The technical scheme adopted by the present application to solve the technical problems is: The present application provides a preparation method of a thermal insulation-heat dissipation integrated phase change composite material, comprising: (1) preparing a thermal insulation layer precursor solution: dissolving polyamide acid (PAA) powder in deionized water, then adding a salting agent, stirring and reacting at room temperature for 2-4 hours to obtain a uniform thermal insulation layer precursor solution with a PAA concentration of 15-130 mg / mL; (2) preparing a heat dissipation layer precursor solution: dissolving PAA powder in deionized water, sequentially adding a salting agent and high-thermal-conductivity nano-filler, and stirring vigorously at room temperature for 2-4 hours to obtain a uniform heat dissipation layer precursor solution with a PAA concentration of 30-130 mg / mL; (3) pouring the thermal insulation layer precursor solution and the heat dissipation layer precursor solution into a directional freezing mold and freezing, after complete freezing, quickly transferring the sample to a freeze dryer, and freeze-drying at a temperature below -50°C and a vacuum degree of 5-10 Pa for 40-50 hours to obtain an un-imidized thermal insulation layer aerogel blank and a heat dissipation layer aerogel blank, respectively; (4) A PAA solution with a solid content of 25-35 wt% is uniformly coated on the interface to be bonded of the thermal insulation layer aerogel blank and the heat dissipation layer aerogel blank respectively, the two blanks are matched, pressure is applied on the matched interface to obtain a double-layer blank, and then the integrated double-layer blank is subjected to thermal imidization treatment under programmed temperature rising in nitrogen atmosphere to form an integrated polyimide aerogel; (5) The heat dissipation layer of the integrated polyimide aerogel is immersed in a phase change material, vacuum impregnation is performed at 50-70℃ for 20-40 minutes, cooled to room temperature, and the residual phase change material on the surface is wiped off to obtain a thermal insulation-heat dissipation integrated phase change composite material.

[0009] Further, the preparation method of the PAA solution and the PAA powder is as follows: under the condition of ice water bath at 0-5℃ and nitrogen protection, aromatic diamine is added to a reactor containing an organic solvent, and mechanically stirred until completely dissolved, then aromatic dianhydride (PMDA) is slowly added in batches, the molar ratio of aromatic diamine to aromatic dianhydride is 1:1.01, the feeding speed is controlled to avoid sudden temperature rise of the system, after the feeding is completed, the reaction is stirred in the ice water bath for 6 hours, the stirring speed is 400-600 rpm, a yellow, viscous PAA solution with a solid content of 15-30 wt% is obtained, the PAA solution is poured into excess deionized water for precipitation, and the precipitate is washed repeatedly with deionized water for 3-5 times, finally, the obtained light yellow flocculent precipitate is dried in a vacuum drying oven at 50-70℃ for 20-30 hours to obtain light yellow PAA powder.

[0010] Further, the aromatic diamine is one and more than two of 4,4'-diamino diphenyl ether (ODA), p-phenylenediamine (p-PDA), 4,4'-diamino diphenyl methane (MDA), m-phenylenediamine (m-PDA), and is further preferably 4,4'-diamino diphenyl ether. The aromatic dianhydride is one and more than two of pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), and is further preferably pyromellitic dianhydride. The organic solvent is one or more than two of N,N-dimethylacetamide (DMAc), N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and is further preferably N,N-dimethylacetamide.

[0011] Further, the aromatic dianhydride is added in 6 times, the mass of each addition is halved, and the addition time is 20 minutes for the first 4 times and 30 minutes for the last 2 times.

[0012] Furthermore, the salt-forming agent is one or more of triethylamine (TEA), trimethylamine, N,N-diisopropylethylamine, and pyridine, with triethylamine being more preferred, and is used to convert water-insoluble polyamic acid (PAA) into water-soluble polyamic acid salt, thereby realizing the water-based processing of the precursor.

[0013] Furthermore, the PAA concentration in the precursor solution of the insulation layer is 15-130 mg / mL, and the viscosity is between 100-3000 mPa·s. This parameter range is optimized based on the balance between the shrinkage resistance, thermal conductivity, and mechanical strength of the insulation layer aerogel. When the amount of PAA added in the precursor solution of the insulation layer is below the lower limit, the polyimide aerogel exhibits significant shrinkage during freeze-drying and thermal imidization due to insufficient PAA content, and its mechanical strength is also reduced. When the amount added exceeds the upper limit, although excessive PAA can enhance the mechanical strength of the polyimide aerogel, the increased solid content leads to a decrease in material porosity and an increase in thermal conductivity, thus adversely affecting the insulation performance of the aerogel.

[0014] Furthermore, the highly thermally conductive nanofiller is used to construct efficient heat transfer pathways within the polymer matrix. The highly thermally conductive nanofiller is one or more of the following: reduced graphene oxide (rGO), graphene oxide (GO), carbon nanotubes (CNTs), boron nitride nanosheets (BNNS), aluminum nitride (AlN), and aluminum oxide (Al2O3).

[0015] Furthermore, in steps (1) and (2), the mass ratio of PAA powder to salt-forming agent is 1:0.5.

[0016] Furthermore, in step (2), the mass ratio of PAA powder to high thermal conductivity nanofiller is 1:0.05-5. When the addition ratio is lower than the lower limit of the parameter, the filler content is insufficient, and a continuous and efficient thermally conductive network cannot be formed in the polymer matrix. This results in an insignificant improvement in the thermal conductivity of the heat dissipation layer, failing to meet the application requirements for rapid heat conduction. When the addition ratio is higher than the upper limit of the parameter, the excessive filler content will significantly increase the viscosity of the precursor solution, leading to difficulties in filler dispersion, easy agglomeration and sedimentation, and deterioration of processability. At the same time, excessive filler will destroy the directional porous structure formed during freezing, causing the aerogel preform to easily crack, increase in density, and deteriorate in mechanical properties during drying.

[0017] Furthermore, before using the PAA solution described in step (4), it is cast onto a plate and treated in a forced-air oven at 50-60°C for 20-40 minutes to remove some of the solvent and significantly increase its viscosity.

[0018] Furthermore, the programmed temperature rise specifically involves heating to 100℃, 200℃, and 300℃ at a rate of 2-5℃ / min, holding at each temperature for 60 minutes, and then naturally cooling to room temperature. During this process, PAA undergoes an intramolecular cyclization and dehydration reaction, transforming into polyimide (PI), thereby achieving a strong chemical bond between the two aerogel layers and forming an integrated bilayer aerogel.

[0019] Further, polyethylene glycol (PEG) is placed in a container and heated to melt at 60-70°C. Further, the solid content of the PAA solution for the adhesive layer is controlled at 25-35 wt%. If the parameter is below the lower limit, excessive solvent will erode the aerogel preform structure, and the imidized interfacial layer will be loose and mismatched with the shrinkage stress of the aerogel preform, easily leading to performance degradation and cracking / peeling. If the parameter is above the upper limit, the solution viscosity will be too high, making coating difficult. The high-viscosity solution cannot effectively wet the surface of the aerogel preform, resulting in poor interfacial contact. Furthermore, the excessively high solid content will lead to poor solution stability and easy gelation.

[0020] Furthermore, in step (4), the bonding process of the heat insulation layer aerogel preform and the heat dissipation layer aerogel preform is strictly controlled so that the directional pore directions of the heat dissipation layer and the heat insulation layer aerogel preform are perpendicular to each other. Specifically, the pore direction of the heat insulation layer is parallel to the working surface, and the pore direction of the heat dissipation layer is perpendicular to the working surface, forming an asymmetric and anisotropic structure. The heat insulation layer greatly extends the heat conduction path and inhibits convective heat transfer, thereby providing extremely high thermal resistance in the thickness direction and achieving excellent heat insulation. The heat dissipation layer uses highly thermally conductive pore walls and highly thermally conductive nanofillers oriented along the pore walls to construct an axially rapid heat conduction channel from the heat source outward, achieving efficient heat dissipation.

[0021] Further, in step (5), the phase change material is selected from polyethylene glycol, paraffin wax, fatty acids, hydrated salts, or low-melting-point alloys. The fatty acids are lauric acid, palmitic acid, or stearic acid; the hydrated salts are sodium sulfate decahydrate, calcium chloride hexahydrate, or sodium acetate trihydrate; and the low-melting-point alloys are Wood's alloy or gallium indium tin alloy.

[0022] The selection of the phase change material (PCM) can be optimized according to the target operating temperature. It should be understood that the PCM is not limited to a specific substance, but encompasses a range of latent heat storage materials with different phase change temperatures. The selection principle is to choose a PCM with a phase change temperature matching the target temperature range to be maintained or controlled, ensuring effective solid-liquid phase change at the target operating temperature, thereby maximizing its heat storage and dissipation efficiency. For example, for low-temperature protection of electronic equipment (~45-60℃), polyethylene glycol (PEG) or specific paraffin waxes can be selected; for medium-temperature applications (~50-80℃), fatty acids (such as lauric acid, palmitic acid) or their eutectic mixtures can be selected; and for higher-temperature applications (>80℃), hydrated salts (such as sodium sulfate decahydrate) or low-melting-point alloys can be selected.

[0023] The second aspect of the present invention provides an integrated heat insulation and heat dissipation phase change composite material, which is prepared by the preparation method described above and is composed of a heat insulation layer, an interface bonding layer and a heat dissipation layer bonded together in sequence.

[0024] Furthermore, the heat dissipation layer is composed of polyimide-based composite aerogel, in which highly thermally conductive nanofillers are dispersed and impregnated with phase change material, and its pore direction is perpendicular to the working surface; the heat insulation layer is composed of polyimide aerogel, which has an oriented pore structure with the pore direction parallel to the working surface; the interface bonding layer is composed of polyimide, which forms chemical bonds and molecular chain entanglements with the heat insulation layer and the heat dissipation layer through a co-imidization reaction, thereby achieving a dense bond between the two layers and preventing leakage of phase change material.

[0025] The advantages and positive effects of this invention are: (1) Functional integration: The pure polyimide oriented pore aerogel of the insulation layer provides ultimate thermal insulation, and the polyimide-thermal conductive functional filler-PCM composite layer of the heat dissipation layer provides a high thermal conductivity path and latent heat storage of phase change, realizing the synergy and optimization of thermal insulation and heat dissipation functions in a single lightweight structure.

[0026] (2) Strong interfacial bonding: The adhesive layer achieves a triple strengthening effect: 1) Homogeneous thermal compatibility: The adhesive layer and the aerogel layer have the same polyimide nature, avoiding thermal mismatch at the interface of heterogeneous materials. The expansion coefficients of the same material are similar, so it can still maintain high interfacial performance under repeated thermal shock (such as the switching on and off of electronic devices). 2) Molecular-level co-imidization reaction: The PAA molecular chain of the interface layer and the polyimide (PI) matrix of the heat dissipation layer and the heat insulation layer form a cross-linked network during high-temperature curing through hydrogen bonding and interpenetrating entanglement of molecular chains after co-imidization, eliminating the weak boundary layer of traditional physical bonding. 3) Mechanical interlocking: The PAA of the interface layer generates a dense structure in situ on the surface of the aerogel, forming a topological lock with the micropores of the aerogel, which improves the interfacial peel strength, and at the same time constructs a dense barrier layer to completely block the penetration of molten PCM into the lower layer; (3) Eliminating PCM leakage: Through the key process of gradient temperature curing of high solid content PAA solution, a dense polyimide adhesive layer is formed at the interface. This dense layer physically blocks any possible path of the upper PCM to migrate downward or leak outward, ensuring the long-term reliability and safety of the product. Attached Figure Description

[0027] Figure 1 The interface-completely filled SEM image of the bilayer phase change composite material (PI / PG@PCM) prepared in Example 1.

[0028] Figure 2 The image shows the interface morphology of the final aerogel after thermal imidization in Example 1. The left side shows the dense structure of the interface layer, and the right side shows the porous structure of the aerogel.

[0029] Figure 3 This is a planar pore structure diagram of the thermal insulation layer of the phase change composite material in Example 1; Figure 4 This is a cross-sectional pore structure diagram of the thermal insulation layer of the phase change composite material in Example 1; Figure 5 The heat dissipation layer of the phase change composite material in Example 1 has a pore structure with high thermal conductivity nanofiller loaded on it. Figure 6 The diagram shows the interface defects that appeared after using a low-concentration PAA solution for bonding in Comparative Example 4. Figure 7 The simulated battery temperature rise curves of the phase change composite materials of Example 1 and Comparative Example 7 are shown.

[0030] Figure 8 The stress-strain curves are shown for the interfacial tensile properties of the phase change composite material in Example 1. Detailed Implementation

[0031] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0032] Example 1 A method for preparing an integrated heat insulation and heat dissipation phase change composite material, comprising: (1) Synthesizing polyamic acid (PAA) powder: Under ice-water bath conditions of 0-5℃ and nitrogen protection, aromatic diamine 4,4'-diaminodiphenyl ether (ODA) was added to a reactor containing the organic solvent N,N-dimethylacetamide (DMAc), and mechanically stirred until completely dissolved. Then, aromatic dianhydride pyromellitic dianhydride (PMDA) was slowly added in six portions (each addition was halved, with the first four additions spaced 20 minutes apart and the last two 30 minutes apart), at a molar ratio of ODA to PMDA of 1:1.01. The addition rate was controlled to avoid a sudden rise in system temperature. After the addition was complete, the reaction was vigorously stirred (500 rpm) in an ice-water bath for 6 hours to obtain a pale yellow, viscous PAA solution with a solid content of 15 wt%. The PAA solution was poured into excess deionized water to precipitate, and the precipitate was washed repeatedly with deionized water five times. Finally, the resulting pale yellow flocculent precipitate was dried in a vacuum drying oven at 60℃ for 24 hours to obtain a pale yellow PAA powder.

[0033] (2) Preparation of heat insulation layer precursor solution: Dissolve PAA powder from step (1) in deionized water, then add triethylamine (TEA) at a mass ratio of 1:0.5 between PAA powder and triethylamine. Stir vigorously at room temperature (500 rpm) for 3 hours to completely convert PAA powder into water-soluble polyamide salt, and obtain a uniform and transparent heat insulation layer precursor solution with a PAA concentration of 50 mg / mL and a viscosity of 700 mPa·s.

[0034] (3) Preparation of heat dissipation layer precursor solution: Dissolve PAA powder from step (1) in deionized water, and add triethylamine (TEA) and graphene oxide (GO) powder in sequence. The mass ratio of PAA powder, triethylamine, and graphene oxide is 1:0.5:1. Stir vigorously at room temperature (500 rpm) for 3 hours to form a salt of PAA powder and ensure uniform dispersion of graphene oxide, to obtain a homogeneous, black heat dissipation layer precursor solution with a PAA concentration of 50 mg / mL.

[0035] (4) Preparation of thermal insulation layer aerogel preform and heat dissipation layer aerogel preform: The thermal insulation layer precursor solution and the heat dissipation layer precursor solution were poured into a polytetrafluoroethylene (PTFE) directional freezing mold. The copper sheet of the mold was contacted with liquid nitrogen for unidirectional freezing. After complete freezing, the sample was quickly transferred to a freeze dryer and freeze-dried at -50℃ and vacuum degree 9 Pa for 48 hours to obtain the non-imide-treated thermal insulation layer aerogel preform and heat dissipation layer aerogel preform.

[0036] (5) Integrated bonding and thermal imidization: Using the same preparation method as in step (1), a yellow, viscous PAA solution with a solid content of 30 wt% was prepared. The yellow, viscous PAA solution with a solid content of 30 wt% was cast onto a plate and placed in a 60°C forced-air oven for 30 minutes to remove some of the solvent and further increase its viscosity significantly. This PAA solution was uniformly coated onto the interface to be bonded between the heat insulation layer aerogel preform and the heat dissipation layer aerogel preform. The two preforms were precisely aligned and a slight pressure was applied to ensure close contact. The assembled integrated preform was placed in an oven and thermal imidization was performed under nitrogen protection: the temperature was increased to 100°C, 200°C, and 300°C at a rate of 5°C / min, and held at each temperature for 60 minutes, and then naturally cooled to room temperature. During this process, PAA undergoes an intramolecular cyclization and dehydration reaction, transforming into polyimide (PI), thereby achieving a strong chemical bond between the two aerogel layers and forming an integrated polyimide aerogel.

[0037] (6) Place polyethylene glycol (PEG) in a container and heat it to melt it into a liquid at 70°C. Immerse the heat dissipation layer of the integrated polyimide aerogel into the molten PEG, and transfer the entire system to a vacuum drying oven and keep it at 60°C for 30 minutes to ensure that the PEG fully penetrates into the pores of the heat dissipation layer aerogel. Remove the sample, cool it to room temperature, and wipe off the residual PEG on the surface to obtain the heat insulation-heat dissipation integrated phase change composite material (PI / PG@PCM).

[0038] The bonding interface of the PI / PG@PCM prepared in Example 1 was tested by scanning electron microscopy, and the results are as follows: Figure 1 As shown, a complete and dense interface layer can be seen, demonstrating the composite structure in which high-viscosity PAA successfully penetrates and fills the pores of the underlying aerogel, and is tightly bonded to the framework after thermal imidization. Figure 2 The interfacial morphology of the final aerogel after thermal imidization is shown. A clear and continuous interface was observed at low magnification. No cracks, pores, or obvious separation gaps were observed. Figure 3 This is a planar pore structure diagram of the thermal insulation layer of the phase change composite material in Example 1. Figure 4 The diagram shows the cross-sectional pore structure of the thermal insulation layer of the phase change composite material in Example 1. It can be seen that the thermal insulation layer has a directional pore structure with the pore direction parallel to the working surface. Figure 5 The heat dissipation layer of the phase change composite material in Example 1 has a pore structure with high thermal conductivity nanofiller. The heat dissipation layer contains high thermal conductivity nanofiller and is impregnated with phase change material. The pore direction is perpendicular to the working surface.

[0039] Example 2 A method for preparing an integrated heat insulation and heat dissipation phase change composite material, comprising: (1) Synthesis of polyamic acid (PAA) powder: The preparation method is the same as in Example 1; (2) Preparation of heat insulation layer precursor solution: Dissolve PAA powder from step (1) in deionized water, then add triethylamine (TEA) at a mass ratio of 1:0.5 between PAA powder and triethylamine. Stir vigorously at room temperature (500 rpm) for 3 hours to completely convert PAA powder into water-soluble polyamide salt, and obtain a uniform and transparent heat insulation layer precursor solution with a PAA concentration of 15 mg / mL and a viscosity of 200 mPa·s.

[0040] (3) Preparation of heat dissipation layer precursor solution: Dissolve the PAA powder from step (1) in deionized water, and add triethylamine (TEA) and graphene oxide (GO) powder in sequence. The mass ratio of PAA powder, triethylamine, and graphene oxide is 1:0.5:3. Stir vigorously at room temperature (500 rpm) for 3 hours to form a salt of PAA powder and ensure uniform dispersion of graphene oxide, to obtain a homogeneous, black heat dissipation layer precursor solution with a PAA concentration of 30 mg / mL.

[0041] (4) Preparation of thermal insulation layer aerogel preform and heat dissipation layer aerogel preform: The thermal insulation layer precursor solution and the heat dissipation layer precursor solution were poured into a polytetrafluoroethylene (PTFE) directional freezing mold. The copper sheet of the mold was contacted with liquid nitrogen for unidirectional freezing. After complete freezing, the sample was quickly transferred to a freeze dryer and freeze-dried at -60℃ and vacuum degree 9 Pa for 48 hours to obtain the non-imide thermal insulation layer aerogel preform and the heat dissipation layer aerogel preform, respectively.

[0042] (5) Integrated bonding and thermal imidization: Using the same preparation method as in Example 1, a yellow, viscous PAA solution with a solid content of 35 wt% was prepared. The yellow, viscous PAA solution with a solid content of 35 wt% was cast onto a plate and placed in a 60°C forced-air oven for 30 minutes to remove some of the solvent and further significantly increase its viscosity. This PAA solution was uniformly coated onto the interface to be bonded between the heat insulation layer aerogel preform and the heat dissipation layer aerogel preform. The two preforms were precisely aligned and a slight pressure was applied to ensure close contact. The assembled integrated preform was placed in an oven and thermal imidization was performed under nitrogen protection: the temperature was increased to 100°C, 200°C, and 300°C at a rate of 5°C / min, and held at each temperature for 60 minutes, followed by natural cooling to room temperature. During this process, PAA undergoes an intramolecular cyclization and dehydration reaction, transforming into polyimide (PI), thereby achieving a strong chemical bond between the two aerogel layers and forming an integrated polyimide aerogel.

[0043] (6) Place polyethylene glycol (PEG) in a container and heat it to melt it into a liquid at 60°C. Immerse the heat dissipation layer of the integrated polyimide aerogel into the molten PEG, and transfer the entire system to a vacuum drying oven. Keep it at 60°C for 30 minutes to ensure that the PEG fully penetrates into the pores of the heat dissipation layer aerogel. Remove the sample, cool it to room temperature, and wipe off the residual PEG on the surface to obtain the heat insulation-heat dissipation integrated phase change composite material.

[0044] Example 3 A method for preparing an integrated heat insulation and heat dissipation phase change composite material, comprising: (1) Synthesis of polyamic acid (PAA) powder: The preparation method is the same as in Example 1; (2) Preparation of heat insulation layer precursor solution: Dissolve PAA powder from step (1) in deionized water, then add triethylamine (TEA) at a mass ratio of 1:0.5 between PAA powder and triethylamine. Stir vigorously at room temperature (500 rpm) for 3 hours to completely convert PAA powder into water-soluble polyamide salt, and obtain a uniform and transparent heat insulation layer precursor solution with a PAA concentration of 120 mg / mL and a viscosity of 1700 mPa·s.

[0045] (3) Preparation of heat dissipation layer precursor solution: Dissolve PAA powder from step (1) in deionized water, and add triethylamine (TEA) and graphene oxide (GO) powder in sequence. The mass ratio of PAA powder, triethylamine, and graphene oxide is 1:0.5:5. Stir vigorously at room temperature (500 rpm) for 3 hours to form a salt of PAA powder and ensure uniform dispersion of graphene oxide, to obtain a homogeneous, black heat dissipation layer precursor solution with a PAA concentration of 120 mg / mL.

[0046] (4) Preparation of thermal insulation layer aerogel preform and heat dissipation layer aerogel preform: The thermal insulation layer precursor solution and the heat dissipation layer precursor solution were poured into a polytetrafluoroethylene (PTFE) directional freezing mold. The copper sheet of the mold was contacted with liquid nitrogen for unidirectional freezing. After complete freezing, the sample was quickly transferred to a freeze dryer and freeze-dried at -60℃ and vacuum degree 9 Pa for 48 hours to obtain the non-imide thermal insulation layer aerogel preform and the heat dissipation layer aerogel preform, respectively.

[0047] (5) Integrated bonding and thermal imidization: Using the same preparation method as in Example 1, a yellow, viscous PAA solution with a solid content of 35 wt% was prepared. The yellow, viscous PAA solution with a solid content of 35 wt% was cast onto a plate and placed in a 60°C forced-air oven for 30 minutes to remove some of the solvent and further significantly increase its viscosity. This PAA solution was uniformly coated onto the interface to be bonded between the heat insulation layer aerogel preform and the heat dissipation layer aerogel preform. The two preforms were precisely aligned and a slight pressure was applied to ensure close contact. The assembled integrated preform was placed in an oven and thermal imidization was performed under nitrogen protection: the temperature was increased to 100°C, 200°C, and 300°C at a rate of 5°C / min, and held at each temperature for 60 minutes, followed by natural cooling to room temperature. During this process, PAA undergoes an intramolecular cyclization and dehydration reaction, transforming into polyimide (PI), thereby achieving a strong chemical bond between the two aerogel layers and forming an integrated polyimide aerogel.

[0048] (6) Place polyethylene glycol (PEG) in a container and heat it to melt it into a liquid at 60°C. Immerse the heat dissipation layer of the integrated polyimide aerogel into the molten PEG, and transfer the entire system to a vacuum drying oven. Keep it at 60°C for 30 minutes to ensure that the PEG fully penetrates into the pores of the heat dissipation layer aerogel. Remove the sample, cool it to room temperature, and wipe off the residual PEG on the surface to obtain the heat insulation-heat dissipation integrated phase change composite material.

[0049] Comparative Example 1 The only difference from Example 1 is that step (5) in Example 1 is omitted, and instead commercially available paste-like epoxy resin structural adhesive (Guangdong Kuaijingda Technology Co., Ltd., high-strength building structural adhesive) is used to conduct a lamination experiment. After applying the adhesive, it is cured at room temperature and pressure. Then, the two aerogel blanks are put together and a slight pressure is applied to effectively bond them together to obtain a phase change composite material blank.

[0050] Comparative Example 2 The only difference from Example 1 is that step (5) in Example 1 is omitted. Instead, commercially available cyanoacrylate adhesive (instant adhesive, low viscosity) (Guangdong Aibida Adhesive Co., Ltd., 20280) is used for the lamination experiment. After applying the adhesive, the curing process (curing at room temperature and pressure) is performed. Then, the two aerogel blanks are put together and a slight pressure is applied to effectively bond them together to obtain the phase change composite material blank.

[0051] Comparative Example 3 The only difference from Example 1 is that step (5) in Example 1 is omitted, and instead, a commercially available anaerobic adhesive (Changsha Jianxiang Adhesive Co., Ltd., HJJ-003) is used for the lamination experiment. After applying the adhesive, a curing process (curing at room temperature and pressure) is performed, and then the two aerogel blanks are put together and a slight pressure is applied to effectively bond them together to obtain a phase change composite material blank.

[0052] Comparative Examples 1-3 involved removing the "homologous coimide bonding layer" and bonding with three commercially available adhesives. The experiments showed that the epoxy structural adhesive, due to its paste-like properties, was easy to apply and exhibited acceptable initial bond strength. The cyanoacrylate and anaerobic adhesives, due to their low viscosity, rapidly penetrated the capillaries of the aerogel surface after application, achieving initial fixation of the preform, but clearly failing to form a continuous and complete filling layer at the interface. After a thermal shock test at 200℃, all three adhesive systems experienced devastating interfacial failure, resulting in complete separation of the two aerogel layers.

[0053] Despite the use of different types of commercial adhesives, none could meet the stringent interfacial bonding requirements of the phase change composite material system of this invention. The selected adhesives and the polyimide (PI) aerogel matrix are heterogeneous materials with significant differences in their coefficients of thermal expansion (CTE), modulus, and other physical properties. Under severe temperature cycling, the thermal stress accumulated at the interface cannot be effectively released or offset, ultimately leading to cracking. The maximum temperature of the integrated thermal imidization process of this invention is 300°C. The selected commercial adhesives (epoxy resins typically have a thermal decomposition temperature <300°C, cyanoacrylates have a heat resistance of approximately 80-120°C, and anaerobic adhesives typically have a heat resistance <150°C) undergo severe chemical degradation, carbonization, or loss of tackiness under this high-temperature environment, resulting in complete loss of bonding function. This is a key factor in their failure during thermal shock testing. Commercial adhesives only provide physical bonding. Low-viscosity adhesives (such as cyanoacrylates) exhibit capillary penetration that locally disrupts the porous structure of the aerogel and cannot form a dense layer to block the PCM. None of them possess the dense barrier function of the adhesive layer of this invention to block PCM.

[0054] Comparative Example 4 The only difference from Example 1 is that the yellow, viscous PAA solution with a solid content of 30 wt% (viscosity of 9000 mPa·s after partial solvent evaporation) in step (5) of Example 1 is replaced with a PAA solution with a solid content of 15 wt% (viscosity of approximately 2000 mPa·s).

[0055] Comparative Example 4 involved removing the "high-solids-content dense leak-proof layer" and using a low-solids-content interfacial adhesive layer. The low-viscosity (2000 mPa·s) PAA solution, after being applied to the aerogel preform surface, failed to maintain a uniform prepolymer layer at the interface. Instead, it rapidly penetrated into the macroscopic and microscopic pores of the aerogel surface through capillary action. After thermal imidization treatment, obvious shrinkage cracks were visually observed in the interfacial area, indicating insufficient bonding and structural defects. A scanning electron microscope image of the interfacial adhesive layer is shown below. Figure 6 As shown, observation of its cross-sectional morphology reveals that the supposedly continuous adhesive layer is incomplete, with some areas missing due to excessive solution penetration. Furthermore, through-cracks caused by stress concentration during curing shrinkage are observed at the interface, indicating that the rheological properties (such as viscosity) of the adhesive layer precursor solution are crucial for its function in forming a dense and complete barrier layer. The low viscosity (2000 mPa·s) causes the surface tension of the PAA solution to dominate, making it unable to resist the strong capillary forces of the porous aerogel structure, leading to its preferential penetration into the pores rather than spreading at the interface. This consumes materials that could be used to construct a continuous and dense interface layer, resulting in a discontinuous PI interface layer. Low solids content implies a high solvent content in the system. During thermal imidization, the evaporation of a large amount of solvent and the cyclization shrinkage of the molecular chains during the conversion of PAA to PI generate significant volumetric shrinkage stress. This stress is concentrated and released at the interface, which has become fragile due to penetration, triggering cracking. The high-solids content solution (9000 mPa·s) of the present invention has a high initial polymer content and low solvent content, resulting in a significantly reduced curing shrinkage rate. Furthermore, its high viscosity helps to form a gel state with better toughness, which can effectively buffer and disperse stress and prevent cracking.

[0056] Comparative Example 5 The only difference from Example 1 is that step (3) in Example 1 is omitted, and the heat dissipation layer is replaced with a piece of commercial polyurethane (PU) flexible foam material. First, the commercial PU foam is vacuum impregnated with PEG to simulate the heat storage function of its upper layer. It is then physically superimposed with the lower polyimide aerogel material prepared by the method of the present invention and a slight pressure (0.1 MPa) is applied to simulate interfacial contact to evaluate its thermal insulation capability as the lower layer.

[0057] Comparative Example 6 This comparative example verifies the necessity of forming a strong bond through co-imidization reaction of the interface layer. The only difference from Example 1 is that step (5) in Example 1 is omitted. The heat insulation layer aerogel preform and the heat dissipation layer aerogel preform obtained in step (4) are directly physically stacked and cold-pressed at a pressure of 0.1 MPa.

[0058] Comparative Example 7 The only difference from Example 1 is that (3) no graphene oxide (GO) filler is added when preparing the heat dissipation layer precursor solution, that is, the heat dissipation layer is also a pure polyimide (PI) aerogel. A pure PI / PCM composite material is prepared.

[0059] Performance and Testing Differential scanning calorimetry (DSC) was used to test the enthalpy values ​​of Examples 1-3 and Comparative Examples 1-7, and the results are shown in Table 1.

[0060] Cyclic heating tests were conducted on the polyethylene glycol-loaded heat dissipation layer sample, subjecting it to 100 heating-cooling cycles. Specifically, the sample was placed in a 60°C oven and heated for 10 minutes, then removed and cooled to room temperature until the polyethylene glycol underwent a phase transition and crystallized. This process was repeated 100 times, and the DSC enthalpy value was compared to evaluate the thermal cycling stability of the sample. The results are shown in Table 1.

[0061] The thermal conductivity of the insulation layers in the examples and comparative examples was tested using a thermal conductivity meter, and the results are shown in Table 1.

[0062] A heating plate was used to simulate battery heating. The examples and comparative examples simulated real application scenarios. A constant power (12V 1A) aluminum heating element was used to simulate battery heating. The simulated temperature rise equilibrium temperature is shown in Table 1.

[0063] Table 1

[0064] As shown in Table 1, the phase change composite materials prepared in Examples 1-3 of this invention possess excellent latent heat storage performance and cycling stability. The material exhibits a phase change enthalpy exceeding 171 J / g, providing excellent heat storage capacity. Simultaneously, the thermal conductivity of the insulation layer is as low as 0.032–0.035 W / m·K, ensuring effective thermal barrier properties, while the heat dissipation layer, due to the introduction of graphene, achieves rapid heat diffusion. In simulated dynamic thermal management applications, this material can significantly suppress the heat source equilibrium temperature within a lower range of 62–67℃, and maintains an extremely high phase change enthalpy even after hundreds of thermal cycles, demonstrating its robust interfacial bonding, reliable PCM encapsulation, and excellent long-term stability.

[0065] Comparative Examples 1-3 were bonded using three commercially available adhesives. When the homogeneous PAA adhesive layer of this invention was replaced with commercially available high-performance adhesives such as epoxy resin and cyanoacrylate, the resulting phase change composite material underwent complete interfacial failure under thermal shock at 200°C, and the two aerogel layers completely separated. This demonstrates that traditional heterogeneous adhesives cannot withstand the high-temperature environment during the preparation and use of polyimide aerogels. Their insufficient heat resistance and thermal expansion mismatch are the root causes of the complete breakdown of the interfacial bond, making them completely unsuitable for thermal insulation applications.

[0066] Comparative Example 5, after impregnation with commercial PU foam, exhibited a phase transition enthalpy of only 55.37 J / g (fusion enthalpy) and 46.42 J / g (crystallization enthalpy), compared to 181 J / g for pure PEG, indicating a PEG loading rate of only 25.6%. This demonstrates an inherent deficiency in the adsorption and retention capacity of commercial porous framework materials for PCM, failing to meet the required heat storage density for efficient thermal management. After subjecting the physically laminated bilayer structure to 100 thermal cycles (60℃-20℃), significant volume shrinkage (approximately 25%) and deformation were observed in the PU foam layer.

[0067] Comparative Example 5 reveals the fundamental reason for the inevitable failure of heterogeneous systems from both material and interface perspectives. The porous structure and surface chemistry of commercial PU foam are not designed for stable PCM loading, resulting in poor compatibility with PEG, extremely low loading rate, and easy PCM precipitation during long-term use. In contrast, the polyimide skeleton of this invention forms controllable pores through directional freezing and has good wettability with PEG, achieving high loading rate and long-term stability. The chemical structures and physical properties of the two polymers are drastically different; PU undergoes chain segment movement at relatively low temperatures (low... T g), whose modulus changes significantly with temperature, and whose coefficient of thermal expansion (CTE) is much higher than that of PI. During thermal cycling, this huge [modulus]... T The difference between g and CTE leads to uncoordinated thermal stress at the interface, which is the driving force for interfacial delamination. The softening and shrinkage of PU after heating further exacerbates the instability of the interface. In contrast, the homogeneous PI system of this invention forms a strong and continuous polymer network at the interface, making the two layers act as a whole, fundamentally eliminating interfacial failure caused by material differences.

[0068] The material prepared in Comparative Example 6 does not contain a co-imide interface layer, and the interlayer bonding is extremely weak; the two layers can be easily torn apart with a finger. After cyclic heating testing of the Comparative Example 6 sample, the phase transition enthalpy of its upper layer decreased from the initial melting enthalpy of 173.5 J / g to 142.5 J / g, and the crystallization enthalpy decreased from 164.6 J / g to 134.7 J / g. This significant performance degradation indicates that a large amount of PCM was lost from the system during the test. During slight heating and cooling, interlayer separation occurred due to the phase transition volume change of PCM and the failure of the weak interlayer bonding.

[0069] This demonstrates that cold pressing provides only negligible physical contact, with a bonding energy far lower than the destructive energy generated by thermal stress or volume changes during PCM phase transitions in practical applications. This is vastly different from the robust interface formed by covalent bonds, hydrogen bonds, and molecular chain entanglement through co-iminolation in this invention. Without a dense chemically bonded layer, the microscopic interface between the two aerogel preforms naturally becomes a pathway for PCM molecular migration. Driven by capillary forces and concentration gradients, molten PCM rapidly diffuses and leaks along this weak interface, leading to a significant decrease in its DSC enthalpy and contamination of the underlying insulation material, thus rendering it ineffective.

[0070] After vacuum impregnating the fillerless heat dissipation layer prepared in Comparative Example 7 with PEG, differential scanning calorimetry (DSC) testing showed that its phase transition enthalpy was 151.5 J / g (fusion enthalpy) and 144 J / g (crystallization enthalpy). These values ​​are significantly lower than those of the PI-GO / PCM composite material in Example 1 (173.5 J / g and 164.6 J / g). Compared to the 95.8% loading rate in Example 1, its loading rate was only 83%. This indicates that the introduction of GO filler improves the PCM loading capacity of the material and increases its heat storage density.

[0071] The temperature rise curves of Example 1 and Comparative Example 7 are as follows: Figure 7As shown, the test results indicate that without any thermal management material (blank control): the heat source temperature rises to 100°C within 450 seconds. The final equilibrium temperature of the heat source for Comparative Example 7 (pure PI / PCM) is 76°C, while the final equilibrium temperature of the heat source for the PI-GO / PCM in Example 1 is only 66°C. After removing the upper GO thermally conductive filler, although the polyimide aerogel skeleton maintains high porosity and a high loading of phase change material (PCM), its intrinsic thermal insulation properties result in a significant blockage of heat transfer within the system. Under dynamic thermal shock, heat flow in the pure PI skeleton can only be conducted slowly, and its extremely low thermal diffusion rate cannot timely transport and disperse local heat energy to the entire PCM heat storage body. This causes the PCM at the heat source interface to undergo phase change first, thus forming a saturation zone near the heat source, forcing the temperature in this region to rise sharply and exhibit an equilibrium temperature as high as 76°C. In contrast, in this invention, the thermally conductive filler GO constructs a continuous thermally conductive network within the channels formed by directional freezing ( Figure 5 Its function goes far beyond simply increasing the thermal conductivity of the system; it essentially creates preferential heat conduction paths within the adiabatic PI matrix. This network can divert and radially diffuse heat generated by the heat source, thereby simultaneously activating the latent heat of phase change in the PCM region far from the heat source. This heat flow distribution capability achieved by the packing network is the core physical mechanism by which this invention effectively suppresses the heat source temperature at 66°C.

[0072] Peeling or tensile tests were performed on the integrated bilayer phase change composite material of Example 1, and the failure mode was observed to be typical bulk fracture, meaning the fracture occurred within the aerogel rather than at the bonding interface. (Macroscopic photograph) Figure 8 The fracture surface is clearly uneven, with residual aerogel fragments adhering to both sides, while the interface remains intact and continuous, showing no signs of delamination or separation. This phenomenon directly indicates that the interfacial bonding strength has exceeded the mechanical strength of the aerogel matrix itself. The stress-strain curve further corroborates this phenomenon, showing a sharp drop after reaching the maximum stress, a typical fracture characteristic of porous and brittle materials. Crucially, throughout the entire test, the curve did not exhibit the "steps" or "stress drops followed by rebounds" characteristic of gradual interfacial failure; the fracture occurred in a single event, proving that the failure was due to the matrix material reaching its strength limit, rather than interfacial delamination.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing an integrated heat insulation and heat dissipation phase change composite material, characterized in that, include: (1) Preparation of heat insulation layer precursor solution: Dissolve PAA powder in deionized water, then add salting agent, stir and react at room temperature for 2-4 hours to obtain a homogeneous heat insulation layer precursor solution with PAA concentration of 15-130 mg / mL; (2) Preparation of heat dissipation layer precursor solution: Dissolve PAA powder in deionized water, add salting agent and high thermal conductivity nanofiller in sequence, stir vigorously at room temperature for 2-4 hours to obtain a uniform heat dissipation layer precursor solution with PAA concentration of 30-130 mg / mL. (3) Pour the heat insulation layer precursor solution and the heat dissipation layer precursor solution into the directional freezing mold and freeze them. After they are completely frozen, quickly transfer the samples to the freeze dryer and freeze dry for 40-50 hours to obtain the non-imide-treated heat insulation layer aerogel preform and the heat dissipation layer aerogel preform, respectively. (4) A PAA solution with a solid content of 25-35 wt% is uniformly coated on the interface to be bonded between the heat insulation layer aerogel preform and the heat dissipation layer aerogel preform. The two preforms are put together and pressure is applied at the bonding interface to obtain an integrated double-layer preform. Then, the integrated double-layer preform is heated under nitrogen protection to perform thermal imidization treatment to form an integrated polyimide aerogel. (5) Immerse the heat dissipation layer of the integrated polyimide aerogel into the phase change material, vacuum impregnate it at 50-70℃ for 20-40 minutes, and cool it to room temperature to obtain the heat insulation-heat dissipation integrated phase change composite material.

2. The preparation method according to claim 1, characterized in that, The preparation method of the PAA solution and PAA powder is as follows: under ice-water bath conditions of 0-5℃ and nitrogen protection, aromatic diamine is added to a reactor containing organic solvent and stirred to dissolve. Then, aromatic dianhydride is slowly added in batches, with a molar ratio of aromatic diamine to aromatic dianhydride of 1:1.

01. The feeding rate is controlled. After the feeding is completed, the reaction is stirred in an ice-water bath to obtain a PAA solution with a solid content of 15-30 wt%. The PAA solution is poured into excess deionized water to precipitate, and the precipitate is washed repeatedly with deionized water 3-5 times. Finally, the obtained flocculent precipitate is dried in a vacuum drying oven at 50-70℃ for 20-30 hours to obtain PAA powder.

3. The preparation method according to claim 2, characterized in that, The aromatic diamine is one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 4,4'-diaminodiphenylmethane, and m-phenylenediamine; the aromatic dianhydride is one or more of pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride; and the organic solvent is an aprotic polar solvent selected from one or more of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

4. The preparation method according to claim 1, characterized in that, The salt-forming agent is one or more of triethylamine, trimethylamine, N,N-diisopropylethylamine, and pyridine.

5. The preparation method according to claim 1, characterized in that, The high thermal conductivity nanofiller is one or more of the following: reduced graphene oxide, graphene oxide, carbon nanotubes, boron nitride nanosheets, aluminum nitride, and aluminum oxide.

6. The preparation method according to claim 1, characterized in that, In steps (1) and (2), the mass ratio of PAA powder to salt-forming agent is 1:0.

5.

7. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of PAA powder to high thermal conductivity nanofiller is 1:0.05-5.

8. The preparation method according to claim 1, characterized in that, The phase change material is selected from one of polyethylene glycol, paraffin wax, fatty acids, hydrated salts, or low-melting-point alloys.

9. A phase change composite material integrating heat insulation and heat dissipation, characterized in that, It is prepared by the preparation method according to any one of claims 1-8, and is composed of a heat insulation layer, an interface adhesive layer and a heat dissipation layer bonded together in sequence.

10. The integrated heat insulation and heat dissipation phase change composite material according to claim 9, characterized in that, The heat dissipation layer is composed of polyimide-based composite aerogel, in which highly thermally conductive nanofillers are dispersed and impregnated with phase change material. It has an oriented pore structure with the pore direction perpendicular to the working surface. The heat insulation layer is composed of polyimide aerogel, which has an oriented pore structure with the pore direction parallel to the working surface. The interface bonding layer is composed of polyimide, which forms chemical bonds and molecular chain entanglements with the heat insulation layer and the heat dissipation layer through a co-imidization reaction, achieving a dense bond between the two layers and preventing leakage of the phase change material.

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