Flexible phase change material with heat-conducting insulation and electromagnetic shielding performance, preparation method and application thereof

Abstract

The application belongs to the technical field of electromagnetic shielding materials, and particularly relates to a flexible phase change material with heat-conducting insulation and electromagnetic shielding performance, and a preparation method and application thereof. The method comprises the following steps: dispersing silver nanowires in ethanol, and then performing vacuum filtration to obtain a silver nanowire film; dissolving polystyrene in a mixed solution of tetrahydrofuran and water, then adding boron nitride fillers to mix, obtaining a slurry, then pouring the slurry onto the surface of the silver nanowire film, and standing to obtain a functional carrier film; and finally, immersing the functional carrier film and the phase change material in a vacuum oven to obtain the flexible phase change material. The preparation method is simple and convenient to operate, each step adopts conventional experimental equipment and process, and does not need complex special equipment, which is beneficial to reducing production cost and improving production efficiency. The prepared phase change material is integrally formed without layering, avoids layering damage caused by performance difference between layers, further guarantees application stability, and is beneficial to realizing long-term stable use.

Description

Technical Field

[0001] This application belongs to the field of electromagnetic shielding materials technology, specifically relating to a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties, as well as its preparation method and application. Background Technology

[0002] As electronic devices evolve towards higher integration and higher power density, the large amount of heat generated during operation, if not dissipated in a timely manner, will lead to decreased device performance, shortened lifespan, and even safety accidents. Phase change materials, with their ability to absorb or release large amounts of latent heat during phase transitions, have become one of the key materials for thermal management of electronic devices. Simultaneously, the operating environment of electronic devices contains complex electromagnetic interference; if materials lack electromagnetic shielding properties, it will affect the normal signal transmission and operational stability of the device. Furthermore, many electronic components are conductive, requiring thermal management materials to possess excellent insulation properties to avoid short-circuit risks.

[0003] In existing technologies, the performance optimization of phase change materials (PCMs) is mostly focused on improving a single property: for example, thermal conductivity can be improved by adding thermally conductive fillers such as graphene and carbon nanotubes, but these carbon-based materials are usually conductive, which can lead to the loss of insulation properties and limited electromagnetic shielding effect; adding ceramic insulating fillers can ensure insulation performance, but the thermal conductivity of a single ceramic filler is low and it does not have electromagnetic shielding effect; some studies have combined thermal conductivity, insulation and electromagnetic shielding properties through composite multilayer structures, but multilayer structures have problems such as weak interfacial bonding, complex processing and high cost. At the same time, multilayer structures are difficult to accommodate the load of the PCM, so they do not have heat storage capacity and cannot meet the temperature control requirements of flexible electronic devices.

[0004] Therefore, developing an integrated phase change material that combines high thermal conductivity, excellent insulation performance, efficient electromagnetic shielding performance, and good flexibility has become a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties, along with its preparation method and applications. Specifically, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties, comprising the following steps: Silver nanowires were dispersed in ethanol and then filtered under vacuum to obtain a silver nanowire film. Polystyrene was dissolved in a mixed solution of tetrahydrofuran and water, and then boron nitride composite filler was added and mixed to obtain a slurry. The slurry is poured onto the surface of the silver nanowire film and left to stand to obtain a functional carrier film. The functional carrier membrane and the phase change material are placed in a vacuum oven for impregnation and washing to obtain the flexible phase change material that has both thermal conductivity and insulation properties as well as electromagnetic shielding properties.

[0006] In the above preparation process, when the standing time is 18-24 hours / 10 mL of solution, a functional carrier membrane with a complete pore structure is obtained.

[0007] As a further preferred embodiment, the mass fraction of the silver nanowires dispersed in ethanol is 5%-15%. Most preferably, the electromagnetic shielding effect is optimal when the mass fraction of the silver nanowires is 10% and the volume of the silver nanowire solution is 15 mL. When the concentration is below 5%, the density of the silver nanowire film obtained by vacuum filtration is insufficient, and the electromagnetic shielding function is reduced; when the concentration is above 15%, on the one hand, the difficulty of ultrasonic dispersion increases, the silver nanowires are prone to agglomeration and uneven dispersion, and on the other hand, the thickness of the final silver nanowire film obtained by vacuum filtration increases, affecting the loading of the final phase change material and reducing the enthalpy value; when the mass fraction of the silver nanowires is 10%, a dense silver nanowire film can be obtained without affecting the loading of the phase change material, ensuring heat storage density while having excellent electromagnetic shielding performance.

[0008] As a further preferred embodiment, the mixed solution contains 5%-20% polystyrene by mass, 10%-25% water by mass, and 55%-85% tetrahydrofuran by mass. Most preferably, the phase change material loading is optimal when the polystyrene mass fraction is 10%, the water mass fraction is 15%, and the tetrahydrofuran mass fraction is 75%. If the polystyrene mass fraction is too low, the pore size of the formed membrane carrier is discontinuous, reducing the phase change material loading; if the polystyrene mass fraction is too high, the pore size of the formed membrane carrier is dense, similarly reducing the phase change material loading.

[0009] As a further preferred embodiment, the boron nitride composite filler is hexagonal boron nitride nanosheets and boron nitride whiskers.

[0010] As a further preferred embodiment, the mass ratio of the hexagonal boron nitride nanosheets to boron nitride whiskers is 1:0.5-5. More preferably, the mass ratio of the hexagonal boron nitride nanosheets to boron nitride whiskers is 1:1-3; and during this preparation process, the thermal conductivity is optimally improved when the composite filler ratio of hexagonal boron nitride nanosheets to boron nitride whiskers is 0.4% polystyrene and the mass ratio of hexagonal boron nitride nanosheets to boron nitride whiskers is 1:3. At this ratio, the two-dimensional sheet-like hexagonal boron nitride and the one-dimensional fibrous boron nitride whiskers form a synergistic network, jointly promoting the improvement of thermal conductivity.

[0011] As a further preferred embodiment, the phase change material is at least one of paraffin, alkanes, fatty alcohols (with 14-18 carbon atoms), and fatty acids (with 14-18 carbon atoms).

[0012] As a further preferred embodiment, the temperature of the vacuum oven is 80℃-100℃ and the vacuum degree is -0.1MPa.

[0013] Secondly, the present invention provides a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties, which is prepared by the above-described preparation method.

[0014] The flexible phase change material prepared by this invention (1) has good flexibility, and can be bent more than 180° while maintaining its shape without breaking; (2) has good mechanical strength, with an elongation at break of 180%-320% and a tensile strength of 2.8MPa-4.6MPa; (3) has excellent heat storage density, with a phase change enthalpy greater than 120J / g; (4) has excellent shape stability, and does not leak above the phase change temperature; (5) has good phase change stability, with a phase change enthalpy decay rate ≤5% after 200 thermal cycles; (6) the system can achieve a significant improvement in thermal conductivity by relying on composite boron nitride filler, with a thermal conductivity of 1.2W / (m²) at room temperature. K)-1.8W / (m K); (7) It can achieve insulation characteristics with a volume resistivity of 1.8×10 14 Ω cm-6.2×10 15 Ω cm; (8) Excellent electromagnetic shielding performance: The electromagnetic shielding efficiency is 45dB-60dB in the frequency range of 8GHz-12GHz.

[0015] Thirdly, the present invention provides the application of the above-mentioned flexible phase change material, which combines thermal conductivity, insulation and electromagnetic shielding properties, in thermal management of electronic equipment, temperature control of new energy batteries and protection of aerospace electronic components.

[0016] The beneficial effects of this invention are as follows: (1) The preparation method of the present invention is simple and convenient to operate. Each step adopts conventional experimental equipment and processes, such as filtration, phase transformation, impregnation, etc., without the need for complex special equipment, which helps to reduce production costs, improve production efficiency, and facilitate large-scale mass production.

[0017] (2) The phase change material prepared by the present invention is integrally molded without delamination, which avoids delamination damage caused by performance differences between layers, further ensuring application stability and facilitating long-term stable use.

[0018] (3) The phase change material prepared by the present invention has excellent flexibility, making the material bendable and foldable as a whole, which can fit well with the surface of the target equipment and adapt to different application scenarios, thus improving the operational feasibility and ease of use.

[0019] (4) According to the data results of this invention, the phase change material prepared by this invention integrates the phase change part and the electromagnetic shielding part, taking into account the functions of heat storage, heat conduction, insulation and electromagnetic shielding. The phase change enthalpy is greater than 120 J / g, and it has excellent shape stability. It does not leak at temperatures above the phase change temperature. After 200 thermal cycles, the phase change enthalpy decay rate is ≤5%; the thermal conductivity is 1.2 W / (m²). K)-1.8W / (m K); Volume resistivity is 1.8 × 10⁻⁶ 14 Ω cm-6.2×10 15 Ω cm; the electromagnetic shielding efficiency is 45dB-60dB in the 8GHz-12GHz frequency range. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The diagram shown is a schematic representation of the flexible phase change material prepared in Example 1, which combines thermal conductivity, insulation, and electromagnetic shielding properties. Figure 2 The figure shows the stress-strain curve of the flexible phase change material prepared in Example 1, which has both thermal conductivity and insulation properties as well as electromagnetic shielding properties. Figure 3 The figure shows the differential scanning calorimetry curve of the flexible phase change material prepared in Example 1, which has both thermal conductivity and insulation properties as well as electromagnetic shielding properties. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Example 1 A method for preparing a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties includes the following steps: (1) Disperse silver nanowires in ethanol to prepare a 10% solution (15 mL), and obtain a silver nanowire film by vacuum filtration (50 mm diameter filtration flask); dissolve 1 g of polystyrene in tetrahydrofuran / water and stir for 2 hours to obtain a mixed solution (10% polystyrene and 15% water by mass), then add 0.4 g of boron nitride composite filler (0.1 g of hexagonal boron nitride nanosheets and 0.3 g of boron nitride whiskers) and mix evenly to obtain a slurry. Cast the slurry onto the surface of the silver nanowire film and let it stand for 24 hours to obtain a functional carrier film through solvent evaporation phase transformation. (2) The above-mentioned functional carrier membrane and eicosane were placed together in a vacuum oven and immersed for 3 hours under vacuum of -0.1 MPa and temperature of 80°C. Finally, the excess phase change material on the surface was removed (by heating the material on the filter paper again, the phase change material on the surface melted and was absorbed into the filter paper, thereby removing the excess phase change material on the surface), and a flexible phase change material with thermal conductivity, insulation and electromagnetic shielding properties was obtained.

[0024] Performance testing of the flexible phase change material prepared above revealed that the flexible phase change material prepared in this embodiment, which combines thermal conductivity, insulation, and electromagnetic shielding properties, exhibits good flexibility, maintaining its shape without breaking even after bending more than 180°; its elongation at break is approximately 260%, and its tensile strength is approximately 3.6 MPa (tensile-stress curve as shown). Figure 2 The phase transition enthalpy is 150 J / g (differential scanning calorimetry curve as shown). Figure 3 Furthermore, it does not leak above the phase transition temperature (80℃); after 200 thermal cycles, the phase transition enthalpy decay rate is approximately 3%; and the thermal conductivity at room temperature is 1.8 W / (m²). K); Volume resistivity is 5.2 × 10⁻⁶. 15 Ω cm; the electromagnetic shielding coefficient is 60dB in the 8GHz-12GHz frequency range.

[0025] Example 2 A method for preparing a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties includes the following steps: (1) Disperse silver nanowires in ethanol to prepare a solution with a mass fraction of 8% (15 mL), and obtain a silver nanowire film by vacuum filtration (50 mm diameter filtration flask); dissolve 1 g of polystyrene in tetrahydrofuran / water and stir for 2 hours to obtain a mixed solution (in which the mass fraction of polystyrene is 10% and the mass fraction of water is 15%), then add 0.3 g of boron nitride composite filler (in which 0.1 g of hexagonal boron nitride nanosheets and 0.2 g of boron nitride whiskers) and mix evenly to obtain a slurry. Cast the slurry onto the surface of the silver nanowire film and let it stand for 24 hours to obtain a functional carrier film through solvent evaporation phase transformation. (2) The above-mentioned functional carrier film and paraffin are placed together in a vacuum oven and immersed for 3 hours under vacuum of -0.1MPa and temperature of 80℃. Finally, the excess phase change material on the surface is removed to obtain a flexible phase change material with thermal conductivity, insulation and electromagnetic shielding properties.

[0026] Performance testing of the prepared flexible phase change material revealed that the flexible phase change material prepared in this embodiment, which combines thermal conductivity, insulation, and electromagnetic shielding properties, exhibits excellent flexibility, maintaining its shape without cracking even after bending more than 180°; its elongation at break is approximately 220%, and its tensile strength is approximately 4.1 MPa; its phase change enthalpy is 130 J / g, and it does not leak even above the phase change temperature (80°C); after 200 thermal cycles, the phase change enthalpy decay rate is approximately 5%; and its thermal conductivity at room temperature is 1.3 W / (m²). K); Volume resistivity is 3.8 × 10⁻⁶. 15 Ω cm; the electromagnetic shielding efficiency is 45dB in the 8GHz-12GHz frequency range.

[0027] Example 3 A method for preparing a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties includes the following steps: (1) Disperse silver nanowires in ethanol to prepare a 10% solution (10 mL), and obtain a silver nanowire film by vacuum filtration (50 mm diameter filtration flask); dissolve 1 g of polystyrene in tetrahydrofuran / water and stir for 2 hours to obtain a mixed solution (10% polystyrene and 15% water by mass), then add 0.4 g of boron nitride composite filler (0.2 g of hexagonal boron nitride nanosheets and 0.2 g of boron nitride whiskers) and mix evenly to obtain a slurry. Cast the slurry onto the surface of the silver nanowire film and let it stand for 24 hours to obtain a functional carrier film through solvent evaporation phase transformation. (2) The above-mentioned functional carrier film and stearic acid were placed together in a vacuum oven and immersed for 3 hours under vacuum of -0.1MPa and temperature of 80℃. Finally, the excess phase change material on the surface was removed to obtain a flexible phase change material with thermal conductivity, insulation and electromagnetic shielding properties.

[0028] Performance testing of the prepared flexible phase change material revealed that the flexible phase change material prepared in this embodiment, which combines thermal conductivity, insulation, and electromagnetic shielding properties, exhibits excellent flexibility, maintaining its shape without cracking even after bending more than 180°; its elongation at break is approximately 280%, and its tensile strength is approximately 3.2 MPa; its phase change enthalpy is 140 J / g, and it does not leak even above the phase change temperature (80°C); after 200 thermal cycles, the phase change enthalpy decay rate is approximately 5%; and its thermal conductivity at room temperature is 1.5 W / (m²). K); Volume resistivity is 4.8 × 10⁻⁶.15 Ω cm; the electromagnetic shielding efficiency is 40dB in the 8GHz-12GHz frequency range.

[0029] Comparative Example 1 A flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties (with only a single hexagonal boron nitride nanosheet added as a filler) specifically includes the following steps: (1) Disperse silver nanowires in ethanol to prepare a 10% solution (15 mL), and obtain a silver nanowire film by vacuum filtration (50 mm diameter filtration flask); dissolve 1 g of polystyrene in tetrahydrofuran / water and stir for 2 hours to obtain a mixed solution (where polystyrene mass fraction is 10% and water mass fraction is 15%), then add 0.4 g of hexagonal boron nitride nanosheet filler and mix evenly to obtain a slurry. Cast the slurry onto the surface of the silver nanowire film and let it stand for 24 hours to obtain a functional carrier film through solvent evaporation phase inversion; (2) The above carrier and eicosane were placed together in a vacuum oven and immersed for 3 hours under vacuum of -0.1 MPa and temperature of 80°C. Finally, the excess phase change material on the surface was removed to obtain a flexible phase change material with thermal conductivity, insulation and electromagnetic shielding properties.

[0030] Performance testing of the flexible phase change material prepared above revealed that the flexible phase change material prepared in this comparative example, which combines thermal conductivity, insulation, and electromagnetic shielding properties, exhibits excellent flexibility, maintaining its shape without cracking even after bending more than 180°; its elongation at break is approximately 280%, and its tensile strength is approximately 3.4 MPa; its phase change enthalpy is 140 J / g, and it does not leak even above the phase change temperature (80°C); after 200 thermal cycles, the phase change enthalpy decay rate is approximately 5%; and its thermal conductivity at room temperature is 0.8 W / (m²). K); Volume resistivity is 5.8 × 10⁻⁶. 15 Ω cm; the electromagnetic shielding coefficient is 60dB in the 8GHz-12GHz frequency range.

[0031] Comparative Example 2 A flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties (with only a single boron nitride nanowhisker added as a filler) specifically includes the following steps: (1) Disperse silver nanowires in ethanol to prepare a 10% solution (15 mL), and obtain a silver nanowire film by vacuum filtration (50 mm diameter filtration flask); dissolve 1 g of polystyrene in tetrahydrofuran / water and stir for 2 hours to obtain a mixed solution (where polystyrene mass fraction is 10% and water mass fraction is 15%), then add 0.4 g of boron nitride whisker filler and mix evenly to obtain a slurry. Cast the slurry onto the surface of the silver nanowire film and let it stand for 24 hours to obtain a functional carrier film through solvent evaporation phase inversion; (2) The above carrier and eicosane were placed together in a vacuum oven and immersed for 3 hours under vacuum of -0.1 MPa and temperature of 80°C. Finally, the excess phase change material on the surface was removed to obtain a flexible phase change material with thermal conductivity, insulation and electromagnetic shielding properties.

[0032] Performance testing of the prepared flexible phase change material revealed that the flexible phase change material prepared in this comparative example, which combines thermal conductivity, insulation, and electromagnetic shielding properties, exhibits excellent flexibility, maintaining its shape without cracking even after bending more than 180°. Its elongation at break is approximately 250%, and its tensile strength is approximately 3.6 MPa. The phase change enthalpy is 135 J / g, and no leakage occurs above the phase change temperature (80°C). After 200 thermal cycles, the phase change enthalpy decay rate is approximately 4%. The thermal conductivity at room temperature is 0.6 W / (m²). K); Volume resistivity is 5.6 × 10⁻⁶. 15 Ω cm; the electromagnetic shielding coefficient is 60dB in the 8GHz-12GHz frequency range.

[0033] Comparative Example 3 A flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties (with only a single hexagonal boron nitride whisker added as a filler, and a silver nanowire concentration of 4%) specifically includes the following steps: (1) Disperse silver nanowires in ethanol to prepare a 4% (15 mL) solution, and obtain a silver nanowire film by vacuum filtration (50 mm diameter filtration flask); dissolve 1 g of polystyrene in tetrahydrofuran / water and stir for 2 hours to obtain a mixed solution (10% polystyrene and 15% water by mass), then add 0.4 g of hexagonal boron nitride nanosheet filler and mix evenly to obtain a slurry. Cast the slurry onto the surface of the silver nanowire film and let it stand for 24 hours to obtain a functional carrier film through solvent evaporation phase inversion; (2) The above carrier and eicosane were placed together in a vacuum oven and immersed for 3 hours under vacuum of -0.1 MPa and temperature of 80°C. Finally, the excess phase change material on the surface was removed to obtain a flexible phase change material with thermal conductivity, insulation and electromagnetic shielding properties.

[0034] Performance testing of the flexible phase change material prepared above revealed that the flexible phase change material prepared in this comparative example, which combines thermal conductivity, insulation, and electromagnetic shielding properties, exhibits excellent flexibility, maintaining its shape without cracking even after bending more than 180°; its elongation at break is approximately 260%, and its tensile strength is approximately 2.8 MPa; its phase change enthalpy is 145 J / g, and it does not leak even above the phase change temperature (80°C); after 200 thermal cycles, the phase change enthalpy decay rate is approximately 4%; and its thermal conductivity at room temperature is 0.6 W / (m²). K); Volume resistivity is 5.6 × 10⁻⁶. 15 Ω cm; the electromagnetic shielding coefficient is 20dB in the 8GHz-12GHz frequency range.

[0035] The embodiments of this application have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the core ideas of this application. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties, characterized in that, Includes the following steps: Silver nanowires were dispersed in ethanol and then filtered under vacuum to obtain a silver nanowire film. Polystyrene was dissolved in a mixed solution of tetrahydrofuran and water, and then boron nitride composite filler was added and mixed to obtain a slurry. The slurry is poured onto the surface of the silver nanowire film and left to stand to obtain a functional carrier film. The functional carrier film and the phase change material are placed in a vacuum oven for impregnation and washing to obtain the flexible phase change material that has both thermal conductivity and insulation properties as well as electromagnetic shielding properties. The silver nanowires dispersed in ethanol have a mass fraction of 5%. 15%; the boron nitride composite filler consists of hexagonal boron nitride nanosheets and boron nitride whiskers, with a mass ratio of hexagonal boron nitride nanosheets to boron nitride whiskers of 1:0.

5. 5; The mass fraction of polystyrene in the mixed solution is 5%. 20%, water by mass is 10%. 25%, tetrahydrofuran by mass fraction is 55%. 85%.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the hexagonal boron nitride nanosheets to boron nitride whiskers is 1:

1.

3.

3. The preparation method according to claim 1, characterized in that, The phase change material is at least one of paraffin, alkanes, fatty alcohols, and fatty acids.

4. The preparation method according to claim 1, characterized in that, The temperature of the vacuum oven is 80℃. 100℃, vacuum degree is 0.1MPa.

5. A flexible phase change material that combines thermal conductivity, insulation, and electromagnetic shielding properties, characterized in that, By claim 1 It is prepared by any one of the preparation methods described in item 4.

6. The application of the flexible phase change material with thermal conductivity, insulation and electromagnetic shielding properties as described in claim 5 in thermal management of electronic equipment, temperature control of new energy batteries and protection of aerospace electronic components.

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