A composite phase change film material based on dual-function filler enhancement and a preparation method thereof

Abstract

This invention relates to a composite phase change film material and its preparation method based on a dual-functional filler reinforcement, belonging to the field of phase change composite material technology. The method includes the following steps: The composite phase change film comprises a poly(p-phenylbenzobisoxazole) nanofiber substrate, phase change microcapsules, liquid gallium metal modified with thermally conductive boron nitride nanosheets, and thermochromic ink. The prepared liquid gallium metal modified with boron nitride nanosheets has a core-shell structure with an average particle size of 576.9 nm. The prepared composite phase change film possesses excellent thermal conductivity, high heat storage performance, outstanding mechanical properties, and flexibility. Furthermore, this composite phase change film exhibits passive thermal management and active safety warning effects, achieving a dual thermal protection function combining visual cues for heat storage and temperature control. In a small car model, it not only triggered a blue-to-yellow color transition at 50°C, providing an intuitive temperature warning, but also achieved a temperature suppression effect of 5.9°C.

Description

A composite phase change thin film material reinforced with bifunctional fillers and its preparation method Technical Field

[0001] This invention relates to the field of phase change composite materials technology, and in particular to a composite phase change thin film material and its preparation method based on bifunctional filler reinforcement. Background Technology

[0002] With the rapid development of electronic information technology and new energy transportation, electronic devices are moving towards higher integration and miniaturization, while the power batteries of new energy vehicles are developing towards higher energy density. This significant increase in power density has led to increasingly serious heat accumulation problems during operation. Under high temperature or high load conditions, power batteries are prone to localized overheating, which can cause performance degradation, shortened lifespan, and even thermal runaway, among other safety issues. Traditional passive cooling solutions are insufficient for real-time monitoring and proactive intervention of overheating risks. Therefore, developing intelligent thermal management materials that combine thermal buffering and visual early warning functions has become a key direction for solving the thermal safety problems of electronic devices and new energy electric vehicles.

[0003] Phase change materials (PCMs) have attracted much attention due to their ability to absorb and store large amounts of latent heat near their phase change temperatures, enabling active temperature control. Among them, organic solid-liquid phase change materials (OPCMs) (such as n-docosahexadecane (C22)) have become a preferred choice for researchers due to their advantages such as high phase change enthalpy, suitable phase change temperature, low undercooling, and low cost. However, the inherent problems of this material, such as easy leakage above the phase change temperature, low thermal conductivity, and solid-state brittleness, severely limit its practical applications. These problems not only reduce its heat storage capacity and thermal response speed but also increase interfacial contact thermal resistance, making it unsuitable for high-power thermal management systems and flexible electronic devices.

[0004] To overcome the aforementioned problems, researchers have explored various improvement strategies to optimize the overall performance of OPCMs. Firstly, microencapsulation technology and polymer backbone encapsulation strategies can effectively suppress leakage during the phase change process. Secondly, introducing high thermal conductivity fillers (such as metal nanoparticles, graphene (Gr), carbon nanotubes (CNTs), and hexagonal boron nitride (h-BN)) and constructing three-dimensional thermally conductive networks can enhance the thermal conductivity of OPCMs. Furthermore, loading OPCMs into polymer matrices with excellent mechanical strength and flexibility can endow composite phase change materials with good flexibility and processability. However, these single modification strategies still have significant limitations: Firstly, the introduction of a single thermally conductive filler often fails to simultaneously achieve a synergistic improvement in high thermal conductivity, strong interfacial bonding, and good mechanical properties; excessive filling can easily lead to a decrease in the flexibility and latent heat of phase change of the composite phase change material. Secondly, traditional methods are limited by the constraints of material design and structural control, making it difficult to overcome the performance balance bottleneck between high thermal conductivity, excellent mechanical strength, outstanding latent heat of phase change, and good flexibility. Therefore, developing composite phase change materials with high thermal conductivity, excellent phase change enthalpy, high mechanical strength, and excellent flexibility and stability based on a multi-element thermally conductive filler synergistic strategy remains an important challenge. Summary of the Invention

[0005] This invention aims to provide a composite phase change film material and its preparation method based on bifunctional filler reinforcement, solving the challenge of traditional passive heat dissipation materials failing to achieve real-time monitoring and active intervention of overheating risks. The composite phase change film incorporates bifunctional fillers and integrates thermochromic inks on its surface, forming an intelligent thermal management interface with dual functions of "heat storage + early warning." Furthermore, addressing the difficulty of achieving a synergistic enhancement of high thermal conductivity, strong interfacial bonding, and good mechanical properties in composite phase change films using a single thermally conductive filler, a multi-component thermally conductive filler synergistic reinforcement strategy is proposed. Simultaneously, through simulation experiments on new energy electric vehicles, an innovative thermal management material solution is provided for high-power electronic devices and new energy electric vehicle systems.

[0006] The present invention discloses a composite phase change thin film material and its preparation method based on bifunctional filler reinforcement, which specifically includes the following steps:

[0007] S1. Grind hexagonal boron nitride (h-BN), sodium hydroxide (NaOH) and potassium hydroxide (KOH) evenly, then add them to a mixed solution of isopropanol (IPA) and deionized water (H2O), and sonicate to obtain boron nitride nanosheets (BNNs).

[0008] S2. Add BNNs to NaOH solution, and obtain a suspension of boron hydroxynitride nanosheets after hydrothermal treatment. After washing, centrifugation and drying, obtain boron hydroxynitride nanosheet powder.

[0009] S3. Add boron nitride nanosheet powder and liquid gallium (Ga) to a mixed solution of anhydrous ethanol and H2O. After ultrasonic treatment, a liquid Ga nano-suspension modified with boron nitride nanosheets is obtained. After washing, centrifugation and drying, liquid Ga (BGa) powder modified with boron nitride nanosheets is obtained.

[0010] S4. Add poly(p-phenylenebenzodioxazole) (PBO) microfibers to a mixture of methanesulfonic acid (MSA) and trifluoroacetic acid (TFA), stir until homogeneous, and obtain a PBO nanofiber acid solution.

[0011] S5. Add thermally conductive filler BGa powder and MPCM to MSA, then add a certain amount of PBO nanofiber acid solution and stir evenly; then, add a certain amount of ethyl acetate (EA) and H2O mixed solution dropwise and stir to disperse evenly to form a mixed BGa / MPCM / PBO composite acid sol; pour the composite acid sol into a petri dish and gel it to obtain BGa / MPCM / PBO composite phase change acid gel; after solvent exchange of the acid gel to pH 7, a BGa / MPCM / PBO composite phase change gel is formed; after hot pressing and drying the BGa / MPCM / PBO composite phase change gel, a BGa / MPCM / PBO composite phase change film is obtained.

[0012] S6. Apply thermochromic ink to the surface of the BGa / MPCM / PBO composite phase change film to obtain the composite phase change film material.

[0013] As a further improvement of the present invention, the average size of h-BN in step S1 is 5~10 µm; the mass ratio of NaOH to KOH is 1:1; the grinding is uniform, specifically grinding in an agate mortar for 30 min; the volume ratio of IPA to H2O in the mixed solution of IPA and H2O is 55:45; the ultrasonic treatment is performed at room temperature, with an interval of 0.2~0.6 s, an ultrasonic power of 70% of 12000 W, and an ultrasonic time of 15~45 min.

[0014] As a further improvement of the present invention, the concentration of the NaOH solution in step S2 is 2~7 mol / L; the hydrothermal treatment is specifically carried out in a reaction vessel at a temperature of 150~200℃ for 5 h; the washing is specifically carried out using deionized water as the solvent, 5~7 times, until the pH reaches 7; the centrifugation is carried out at a speed of 6500~8500 rpm for 7~10 min; and the drying is specifically carried out in an oven at a temperature of 60℃~80℃ for 12~48 h.

[0015] As a further improvement of the present invention, in step S3, the mass ratio of boron hydroxynitride nanosheets to liquid metal Ga is 1:5; the mass ratio of anhydrous ethanol to H2O in the mixed solution of anhydrous ethanol and H2O is 4:1; the ultrasonic treatment is specifically performed in an ice-water bath, with an ultrasonic interval of 0.2~0.6s, an ultrasonic power of 60~90% of 12000 W, and an ultrasonic time of 30~60 min; the washing is performed 2~5 times, using deionized water as the solvent; the centrifugation is performed at a speed of 6000~9000 rpm for 5~10 min; and the drying is specifically performed as freeze drying, with a pressure of 10~20 Pa, a temperature of -55℃~-65℃, and a time of 24~48 h.

[0016] As a further improvement of the present invention, the mass ratio of MSA and TFA mixed acid in step S4 is 1:1; the stirring is carried out under the following conditions: at room temperature, at a speed of 400-600 rpm, magnetic stirring is performed for 48-96 hours; and the concentration of the PBO nanofiber acid solution is 0.5 wt%.

[0017] As a further improvement of the present invention, the mass ratio of the thermally conductive filler BGa powder, MPCM and PBO nanofibers in step S5 is (0~1):3:1; the stirring is carried out under the specific conditions of mechanical stirring at a speed of 350~450 rpm for 5~15 min; the mass ratio of EA and H2O in the EA and H2O mixed solution is 8:1.

[0018] As a further improvement of the present invention, the stirring and dispersion in step S5 is specifically carried out under the following conditions: mechanical stirring at a speed of 350-450 rpm for 5-8 min; the gelation is specifically carried out under the following conditions: standing at room temperature for 24 h; the solvent exchange is specifically carried out under the following conditions: firstly, replacement in 70 wt% MSA for 12 h, then replacement in 30 wt% MSA for 12 h, followed by solvent exchange in 50% tert-butanol (TBA) solution for 48-72 h; the hot-press drying is carried out in an oven at a temperature of 60-80°C for 24-48 h.

[0019] As a further improvement of the present invention, the thermochromic ink mentioned in step S6 changes color from blue to colorless when the temperature is higher than 50°C.

[0020] As a further improvement of the present invention, a composite phase change film material based on bifunctional filler reinforcement is provided. The composite phase change film includes a PBO nanofiber substrate, MPCM, thermally conductive filler BGa powder, and thermochromic ink. The thermally conductive filler BGa powder has an average particle size of 576.9 nm and has a core-shell structure. The MPCM is composed of melamine resin as the shell material and the organic phase change material n-dodecane (C22) as the core material, and also has a core-shell structure.

[0021] As a further improvement of the present invention, a composite phase change thin film material based on bifunctional filler reinforcement is provided, wherein the composite phase change thin film possesses excellent thermal conductivity, high heat storage performance, outstanding mechanical properties, and flexibility. Its in-plane thermal conductivity (kJ / mol) is... ∥ The thermal conductivity reaches 9.4257 W / (m·K), and the vertical thermal conductivity (kJ / K) is... ⊥ The phase transition enthalpy (ΔH) is 1.7188 W / (m·K). m The tensile strength is 124.7 J / g, the tensile strength is 14.37 MPa, and the toughness is as high as 38.26 MJ / m³.

[0022] As a further improvement of the present invention, a composite phase change film material based on dual-functional filler reinforcement is provided. This composite phase change film possesses dual thermal protection functions, combining passive thermal management (heat storage and temperature control) with active safety warning (visual cues). In a small vehicle model, it triggers a blue-to-yellow color transition at 50°C, providing an intuitive temperature warning. Simultaneously, it achieves a temperature suppression effect of 5.9°C.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) By introducing a bifunctional filler reinforcement strategy, represented by thermally conductive filler BGa powder and phase change material MPCM, the thermophysical properties of the material were significantly optimized. Among them, the three-dimensional thermally conductive network with liquid metal Ga as the thermal bridge and boron hydroxynitride nanosheets as the reinforcing skeleton significantly improved the in-plane and vertical thermal conductivity of the composite phase change film, and its surface k ∥ It is 9.4257 W / (m·K), k ⊥ The value is 1.7188 W / (m·K). The introduction of MPCM endows it with excellent heat storage capacity, with ΔH... m It is 124.7 J / g.

[0025] (2) This invention employs a simple "sol-gel-film" process to achieve uniform dispersion and controllable construction of a three-dimensional network structure of thermally conductive fillers BGa and MPCM in a PBO matrix. This composite phase change film exhibits excellent mechanical properties, with a tensile strength of 14.37 MPa and a toughness of 38.26 MJ·m. -3 It also features excellent flexibility, while further preventing the realization of efficient MPCM packaging.

[0026] (3) A composite phase change film material was successfully prepared by coating thermochromic ink onto the surface of the composite phase change film using a simple coating process. This composite phase change film has dual thermal protection functions, combining passive thermal management (heat storage and temperature control) and active safety warning (visual cues). In a car model, it was demonstrated that the blue-to-yellow transition was triggered at 50°C, providing an intuitive temperature warning. At the same time, a temperature suppression effect of 5.9°C was achieved. Attached Figure Description

[0027] Figure 1 is a flowchart of the preparation method of a composite phase change thin film material based on bifunctional filler reinforcement according to the present invention.

[0028] Figure 2(a) is a scanning electron microscope image of the original h-BN, Figure 2(b) is a scanning electron microscope image of the boron hydroxynitride nanosheets prepared in Example 1, and Figure 2(c) is a particle size distribution diagram of the boron hydroxynitride nanosheets.

[0029] Figure 3(a) shows the SEM and EDS results of the BGa powder prepared in Example 1, and Figure 3(b) shows the particle size distribution of the BGa powder prepared in Example 1.

[0030] Figure 4(a) shows the total X-ray photoelectron spectroscopy (XPS) spectrum of the BGa powder prepared in Example 1, and Figure 4(b) shows the test results of the N 1s sub-spectrum of the X-ray photoelectron spectroscopy of the BGa powder prepared in Example 1.

[0031] Figure 5(a) shows the thermal conductivity of the composite phase change films prepared in Examples 1-5 and Comparative Example 1, and Figure 5(b) shows the increase in thermal conductivity of the prepared composite phase change films compared to pure MPCM.

[0032] Figure 6(a) shows the stress-strain curves of the composite phase change film prepared in Example 1, and Figure 6(b) shows the tensile stress and toughness data of the composite phase change film prepared in Example 1.

[0033] Figure 7 is a folded physical image of the composite phase change film prepared in Example 1.

[0034] Figure 8 shows the infrared device used in the simulation experiment of the car model in Example 1.

[0035] Figure 9(a) shows the color change of the prepared composite phase change film in the simulation experiment, and Figure 9(b) shows the infrared thermal image of the surface temperature of the prepared composite phase change film over time in the simulation experiment. Detailed Implementation

[0036] This invention provides a method for preparing a composite phase change thin film material reinforced with bifunctional fillers. To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, this invention will be further described in conjunction with specific embodiments and accompanying drawings.

[0037] Example 1

[0038] As shown in Figure 1, the preparation method of the composite phase change thin film material based on bifunctional filler reinforcement according to the present invention is carried out through the following steps:

[0039] Step 1: Add 1.0 g of hexagonal boron nitride (h-BN), 5.6 g of sodium hydroxide (NaOH), and 5.6 g of potassium hydroxide (KOH) to an agate mortar and grind for 30 min. Then add to a mixed solution of 50 ml isopropanol (IPA) and deionized water (H2O) (where the volume ratio of IPA to H2O is 55:45). Under the conditions of room temperature, sonication interval of 0.4 s, and sonication power of 12000 W at 70%, sonicate for 30 min to obtain boron nitride nanosheets (BNNs).

[0040] Step 2: 1.0 g of BNNs was added to a 5 mol / L NaOH solution and subjected to a hydrothermal reaction at 180 °C for 5 h in a reaction vessel. Then, the mixture was washed with deionized water until the pH reached 7. Next, it was centrifuged at 7000 rpm for 8 min. Finally, it was dried at 80 °C for 48 h to obtain hydroxylated boron nitride nanosheet powder.

[0041] Step 3: Add 60 mg of boron hydroxynitride nanosheets and 0.3 g of liquid gallium (Ga) to a mixed solution of 50 ml of anhydrous ethanol and H2O (the volume ratio of anhydrous ethanol to H2O is 1:4). In an ice-water bath, sonicate at intervals of 0.3 s and at 70% of 12000 W for 30 min to obtain a liquid Ga nano-suspension modified with boron hydroxynitride nanosheets. Then wash three times with H2O and centrifuge at 8000 rpm for 10 min. Finally, dry in a freeze dryer at a pressure of 10 Pa and a temperature of -55℃ for 36 h to obtain liquid Ga (BGa) powder modified with thermally conductive boron hydroxynitride nanosheets.

[0042] Step 4: Add 3.0 g of poly(p-phenylenebenzodioxazole) (PBO) microfibers to a mixture of 300.0 g of methanesulfonic acid (MSA) and 300.0 g of trifluoroacetic acid (TFA), and magnetically stir at 520 rpm for 72 h at room temperature to obtain a 0.5 wt% PBO nanofiber acid solution.

[0043] Step 5: Add 0.05 g of thermally conductive filler BGa powder and 0.15 g of phase change microcapsules (MPCM) to 16 g of MSA, then add 10.0 g of PBO nanofiber acid solution and mechanically stir at 400 rpm for 10 min. Next, add 4.0 g of ethyl acetate (EA) and 0.5 g of H2O dropwise and mechanically stir at 400 rpm for 7 min to obtain a BGa / MPCM / PBO composite acid sol. Then, pour the composite acid sol into a petri dish and gel for 24 h to obtain a BGa / MPCM / PBO composite phase change acid gel. Then, displace the acid gel first in 70 wt% MSA for 12 h, then in 30 wt% MSA for 12 h, and then perform solvent exchange in 50% tert-butanol (TBA) solution for 72 h until the pH reaches 7. Finally, dry in an oven at 70°C for 36 hours. After h, a BGa / MPCM / PBO composite phase change film was obtained.

[0044] Step 6: Apply thermochromic ink, which changes color from blue to colorless at temperatures above 50°C, to the surface of the BGa / MPCM / PBO composite phase change film to obtain the composite phase change film material.

[0045] Examples 2-5

[0046] Examples 2-5 provide a method for preparing a composite phase change thin film material based on bifunctional filler reinforcement. Compared with Example 1, the difference is that in step 5, the mass of thermally conductive filler BGa powder is 0.01 g, 0.025 g, 0.1 g and 0.15 g, respectively. The rest is the same as in Example 1 and will not be repeated here. A composite phase change thin film is obtained.

[0047] Comparative Example 1

[0048] Comparative Example 1 provides a method for preparing a composite phase change thin film material based on bifunctional filler reinforcement. Compared with Example 1, the difference is that steps 1, 2, and 3 are removed, and the thermally conductive filler BGa powder is removed in step 5. The rest is the same as in Example 1 and will not be repeated here. An MPCM / PBO composite phase change thin film is obtained.

[0049] Comparative Example 2

[0050] Comparative Example 2 provides a method for preparing a composite phase change thin film material based on bifunctional filler reinforcement. Compared with Example 1, the difference is that steps 1, 2, and 3 are removed, and the thermally conductive filler BGa powder and MPCM are removed in step 5. The rest is the same as in Example 1 and will not be repeated here. A PBO thin film is obtained.

[0051] The original h-BN and the boron hydroxynitride nanosheets prepared in Example 1 were subjected to scanning electron microscopy (SEM) and particle size analysis, and the results are shown in Figures 2(a), (b) and (c), respectively.

[0052] Figure 2(a) reveals that the original h-BN is stacked in thick sheets with a size of approximately 5–10 μm. Compared to h-BN, the boron hydroxynitride nanosheets exhibit a thinner sheet structure (Figure 2(b)) with an average particle size of 467.2 nm (Figure 2(c)).

[0053] The BGa prepared in Example 1 was subjected to SEM, energy dispersive spectroscopy (EDS), particle size analysis and X-ray photoelectron spectroscopy (XPS), and the results are shown in Figures 3(a), (b), 4(a) and (b), respectively.

[0054] Figure 3(a) clearly shows that boron hydroxynitride nanosheets are coated on the surface of liquid metal Ga particles. The corresponding EDS image (inset of Figure 3(a)) shows a significant N element signal on the surface, indicating the successful coating of boron hydroxynitride nanosheets and the formation of a typical "core-shell" structure with an average particle size of 576.9 nm (Figure 3(b)). Furthermore, Figure 4 shows that a chemical bond is formed between Ga and N atoms, and the characteristic peak at 396.4 eV in the high-resolution XPS spectrum of the N 1s orbital of BGa (Figure 4(b)) can be attributed to the Ga-N coordination bond.

[0055] The composite phase change films prepared in Examples 1-5 and Comparative Examples 1-2 were tested for their thermophysical properties using a differential scanning calorimeter (DSC) from TA Instruments (USA) (heating rate 5 °C / min, temperature range 0-90 °C). The test results are shown in the table below:

[0056] Table 1. Test results of the thermophysical properties of the composite phase change film.

[0057] Sample name T m (°C)T c (°C)ΔH m (J / g)ΔH c(J / g) Comparative Example 1: 47.4 38.1 134.5 133.9 Comparative Example 2: / / / / Example 2: 47.5 37.8 132.6 132.1 Example 3: 46.9 38.7 128.5 129.2 Example 1: 46.4 38.8 124.7 124.6 Example 4: 46.9 38.4 108.4 106.4 Example 5: 45.8 39.3 72.6 74.3 surface

[0058] As shown in Table 1, with the increase of the thermally conductive filler BGa content, the melting enthalpy (ΔH) of Examples 1-5 decreased. m The ΔH value shows a decreasing trend, but still exhibits good thermal energy storage performance. Specifically, the composite phase change material prepared in Example 1 shows a decreasing ΔH value. m The energy density reaches 124.7 J / g, which is significantly higher than that of common thermal interface materials, indicating that this material has significant advantages in energy storage.

[0059] The composite phase change films prepared in Examples 1-5 and Comparative Examples 1-2 were tested for thermal conductivity using a laser thermal conductivity meter. The test results are shown in Figures 5(a) and (b). The PBO film prepared in Comparative Example 2 already possesses thermal conductivity superior to most polymers, with a vertical thermal conductivity (k... ⊥ ) and in-plane thermal conductivity (k ∥ The thermal conductivity (η) of the composite phase change film prepared in Comparative Example 1 after combining MPCM with PBO substrate reached 0.9520 W / (m·K) and 2.9483 W / (m·K), respectively. ⊥ and η ∥ Compared to pure MPCM, the thermal conductivity was significantly improved, with increases of 179.6% and 894.5%, respectively. Further introduction of the thermally conductive filler BGa resulted in a continuous increase in the thermal conductivity of the composite system with increasing BGa content. When the BGa content was 20.0 wt%, the k-value of the composite phase change film prepared in Example 1 was [missing information]. ⊥ and k ∥ The thermal conductivity reached 1.7188 W / (m·K) and 9.4257 W / (m·K), respectively. When the filler content increased to 33.3 wt%, Example 4 exhibited the best thermal conductivity. ⊥ and k ∥ The concentrations were increased to 5.1345 W / (m·K) and 16.0747 W / (m·K) respectively, representing increases of 2345.0% and 7557.1% compared to pure MPCM.

[0060] The mechanical properties of the composite phase change films prepared in Examples 1-5 and Comparative Example 1 were tested using a universal tensile testing machine, and the results are shown in Figures 6(a) and (b), respectively. The composite phase change film prepared in Example 1 exhibited the best overall mechanical properties, with a tensile strength as high as 14.37 MPa, a fracture strain of 3.85%, a Young's modulus of 921.3 MPa, and a fracture toughness of 38.26 MJ·m. -3 .

[0061] The composite phase change film prepared in Example 1 was demonstrated to have excellent flexibility through folding, as shown in Figure 7. The composite phase change film can be folded into complex shapes (such as origami cranes) without breaking, exhibiting excellent deformation resistance and flexibility.

[0062] Application example: The composite phase change film prepared in Example 1 was used as a thermal management material for electronic devices. A small-scale vehicle model simulation experiment was conducted to simulate the material's thermal buffering and early warning capabilities. The detailed experimental steps are as follows:

[0063] The composite phase change film was applied to the surface of a car model, which was then placed on a hot plate at 80°C to simulate the high-temperature environment of a new energy electric vehicle operating under heavy load or rising ambient temperature. Simultaneously, the temperature changes of the car were recorded in real time using an infrared thermal imaging device as shown in Figure 8. Experimental results show that the composite phase change film has dual thermal protection functions in a high-temperature operating environment: Firstly, when the temperature exceeds 50°C, as shown in Figure 9(a), the thermochromic ink undergoes a significant color change, changing from blue to colorless, and the composite phase change film appears yellow, providing a direct visual warning of overheating. Secondly, the composite phase change film exhibits significant thermal buffering performance. As shown in Figure 9(b), the composite phase change film prepared in Example 1 absorbs and stores a large amount of heat through a solid-liquid phase change process, effectively delaying the overall temperature rise of the vehicle body. Compared with the control group (blank) that did not use the composite phase change film, after heating on an 80°C hot plate for 120 s, the average temperature (Ta) at the center of the area covered by the film decreased by 5.9°C, directly verifying its excellent thermal regulation capability.

[0064] The above embodiments are only used to illustrate preferred embodiments of the present invention and do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, or optimizations made within the technical concept and principle framework of the present invention should be considered to fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a composite phase change thin film material reinforced with bifunctional fillers, specifically comprising the following steps: S1. Grind hexagonal boron nitride, sodium hydroxide and potassium hydroxide evenly, then add them to a mixed solution of isopropanol and deionized water, and sonicate to obtain boron nitride nanosheets, i.e. BNNs. S2. Boron nitride nanosheets are added to a sodium hydroxide solution and subjected to hydrothermal treatment to obtain a hydroxy boron nitride nanosheet suspension. After washing, centrifugation, and drying, hydroxy boron nitride nanosheet powder is obtained. S3. Hydroxy boron nitride nanosheet powder and liquid gallium metal are added to a mixed solution of anhydrous ethanol and deionized water. After ultrasonic treatment, a hydroxy boron nitride nanosheet-modified liquid Ga metal nanosheet suspension is obtained. After washing, centrifugation, and drying, a thermally conductive filler hydroxy boron nitride nanosheet-modified liquid Ga metal powder, i.e., BGa, is obtained. S4. Poly(p-phenylene benzodioxazole) microfibers are added to a mixed acid of methanesulfonic acid and trifluoroacetic acid and stirred until homogeneous to obtain a poly(p-phenylene benzodioxazole) nanofiber acid solution. S5. Thermally conductive filler BGa powder and phase change microcapsules, i.e., MPC, are added to the solution. M is added to methanesulfonic acid, followed by the addition of poly(p-phenylenebenzodioxazole) nanofiber acid solution, and stirred until homogeneous. Then, a mixture of ethyl acetate and deionized water is added dropwise, stirred until evenly dispersed, forming a mixed BGa / MPCM / PBO composite acid sol. The composite acid sol is poured into a petri dish and gelled to obtain a BGa / MPCM / PBO composite phase change acid gel. The acid gel is solvent-exchanged to pH 7 to form a BGa / MPCM / PBO composite phase change gel. The BGa / MPCM / PBO composite phase change gel is hot-pressed and dried to obtain a BGa / MPCM / PBO composite phase change film. S6. Thermochromic ink is coated onto the surface of the BGa / MPCM / PBO composite phase change film to obtain the composite phase change film.

2. The method for preparing a composite phase change thin film material based on bifunctional filler reinforcement according to claim 1, characterized in that, The average size of the hexagonal boron nitride mentioned in step S1 is 5~10. m; the mass ratio of sodium hydroxide to potassium hydroxide in step S1 is 1:1; the grinding in step S1 is uniform, specifically grinding in an agate mortar for 30 minutes; the volume ratio of isopropanol to deionized water in the mixed solution of isopropanol and deionized water in step S1 is 55:45; the ultrasonic treatment in step S1 is performed at room temperature, with an interval of 0.2~0.6s, an ultrasonic power of 70% of 12000 W, and an ultrasonic time of 15~45 minutes.

3. The method for preparing a composite phase change thin film material based on bifunctional filler reinforcement according to claim 1, characterized in that, The concentration of the sodium hydroxide solution mentioned in step S2 is 2~7 mol / L; the hydrothermal treatment mentioned in step S2 is carried out in a reaction vessel at a temperature of 150~200℃ for 5 h; the washing mentioned in step S2 is carried out in deionized water as the solvent, 5~7 times, until the pH reaches 7; the centrifugation mentioned in step S2 is carried out at a speed of 6500~8500 rpm for 7~10 min; the drying mentioned in step S2 is carried out in an oven at a temperature of 60℃~80℃ for 12~48 h.

4. The method for preparing a composite phase change thin film material based on bifunctional filler reinforcement according to claim 1, characterized in that, The mass ratio of boron hydroxynitride nanosheets to liquid Ga in step S3 is 1:5; the mass ratio of anhydrous ethanol to deionized water in the mixed solution of anhydrous ethanol and deionized water in step S3 is 4:1; the ultrasonic treatment in step S3 is specifically performed in an ice-water bath, with an interval of 0.2~0.6s, an ultrasonic power of 60~90% of 12000W, and an ultrasonic time of 30~60 min; the washing in step S3 is performed 2~5 times, using deionized water as the solvent; the centrifugation in step S3 is performed at a speed of 6000~9000 rpm for 5~10 min; the drying in step S3 is specifically performed as freeze drying, with a pressure of 10~20 Pa, a temperature of -55℃~-65℃, and a time of 24~48 h.

5. The method for preparing a composite phase change thin film material based on bifunctional filler reinforcement according to claim 1, characterized in that, The mass ratio of methanesulfonic acid and trifluoroacetic acid mixed acid in step S4 is 1:1; the stirring is carried out under the following conditions: at room temperature, at a speed of 400-600 rpm, magnetic stirring is performed for 48-96 h; the concentration of the poly(p-phenylenebenzodioxazole) nanofiber acid solution is 0.5 wt%.

6. The method for preparing a composite phase change thin film material based on bifunctional filler reinforcement according to claim 1, characterized in that, In step S5, the mass ratio of the thermally conductive filler BGa powder, MPCM, and poly(p-phenylenebenzodioxazole) nanofibers is (0~1):3:1, and the BGa powder content is not 0; the stirring in step S5 is specifically carried out under the condition of mechanical stirring at a speed of 350~450 rpm for 5~15 min; in the mixed solution of ethyl acetate and deionized water in step S5, the mass ratio of ethyl acetate to deionized water is 8:

1.

7. The method for preparing a composite phase change thin film material based on bifunctional filler reinforcement according to claim 1, characterized in that, The stirring and dispersion in step S5 is carried out under the following conditions: mechanical stirring at 350-450 rpm for 5-8 minutes; the gelation is carried out at room temperature for 24 hours; the solvent exchange is carried out under the following conditions: first, replacement in 70 wt% methanesulfonic acid for 12 hours, then replacement in 30 wt% methanesulfonic acid for 12 hours, followed by solvent exchange in 50% tert-butanol solution for 48-72 hours; the hot-press drying is carried out in an oven at 60-80°C for 24-48 hours; the thermochromic ink in step S6 changes color from blue to colorless when the temperature is above 50°C.

8. A composite phase change thin film material reinforced with bifunctional fillers, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

9. A composite phase change thin film material based on bifunctional filler reinforcement according to claim 8, characterized in that, The composite phase change film comprises a poly(p-phenylene benzodioxazole) nanofiber substrate, MPCM, thermally conductive filler BGa powder, and thermochromic ink; the thermally conductive filler BGa powder has an average particle size of 576.9 nm and has a "core-shell" structure; the MPCM is composed of melamine resin as the shell material and n-dodecane as the organic phase change material.

10. A composite phase change thin film material based on bifunctional filler reinforcement according to claim 9, characterized in that, Its in-plane thermal conductivity reaches 9.4257 W / (m·K), its vertical thermal conductivity is 1.7188 W / (m·K), its phase change enthalpy of fusion is 124.7 J / g, its tensile strength is 14.37 MPa, and its toughness is as high as 38.26 MJ / m. 3 The composite phase change film has a dual thermal protection function that combines passive thermal management, namely thermal storage and temperature control, and active safety warning, namely visual prompts. In the car model, it realizes the blue to yellow transition process triggered at 50°C, providing an intuitive temperature warning and achieving a temperature suppression effect of 5.9°C.

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