Phase change microcapsule heat conducting composite material, preparation method and application thereof

Abstract

The present application belongs to the technical field of polymer-based phase change heat-conducting composite material, and particularly relates to a phase change microcapsule heat-conducting composite material, a preparation method and application thereof. The present application aims at the defects of existing phase change composite material, such as heat-conducting filler agglomeration, poor interface compatibility, discontinuous heat-conducting network, and easy leakage of phase change material. The surface of the phase change microcapsule is aminated by microfluidic technology, the heat-conducting filler is modified by epoxy group, and the composite material is prepared by synergistic dispersion and dynamic force field hot pressing. The aminated phase change microcapsule filling amount is 10-50wt% of the mass of PDMS, and the modified heat-conducting filler addition amount is 5-10wt%. The material has excellent heat storage, heat conduction and mechanical flexibility, the phase change enthalpy value can be up to 156J / g, and the heat conductivity coefficient can be up to 2.5W / (mK), which can be applied to the fields of flexible electronics, intelligent wear, spacecraft thermal management and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer-based phase change thermally conductive composite materials technology, specifically relating to a phase change microcapsule thermally conductive composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electronic devices towards miniaturization, flexibility, and high power, the heat flux density during device operation is increasing dramatically. This places increasingly higher demands on the comprehensive performance of thermal management materials, including heat storage and temperature control, heat conduction and dissipation, and flexible adaptation. Phase change materials (PCMs) are one of the core functional materials in the field of thermal management because they can reversibly store and release a large amount of latent heat through a solid-liquid phase change process, effectively mitigating temperature fluctuations in electronic devices.

[0003] To address the shortcomings of pure organic phase change materials (such as hexadecane) in their molten state, such as easy leakage and phase separation, the industry typically employs microencapsulation technology. This involves encapsulating the phase change core material within a polymer or inorganic shell to create phase change microcapsules. Phase change microcapsules not only solve the leakage problem of phase change materials but also significantly increase their specific surface area and accelerate heat transfer efficiency. They have been widely applied in fields such as flexible electronics, smart wearables, and spacecraft thermal management.

[0004] However, phase change microcapsules inherently suffer from insufficient thermal conductivity. Their polymer shell further hinders heat transfer between the core material and the external environment, resulting in a slow thermal response rate that cannot meet the rapid heat dissipation requirements of high-power electronic devices. Therefore, the industry commonly employs a technique of combining phase change microcapsules with highly thermally conductive fillers and then filling them into a polymer matrix. This involves constructing a continuous and efficient thermally conductive network using the highly thermally conductive fillers to compensate for the thermal conductivity shortcomings of phase change microcapsules, thus producing composite thermal management materials that combine heat storage and temperature control with thermal conductivity and heat dissipation.

[0005] Polydimethylsiloxane (PDMS) is a preferred matrix for flexible phase change thermally conductive composites due to its excellent flexibility, resistance to high and low temperatures, electrical insulation, and biocompatibility. Commonly used high thermal conductivity fillers include silver powder, copper powder, silicon nitride, boron nitride, alumina, diamond, flake graphite, graphene, and short carbon fibers. By synergistically filling these fillers with phase change microcapsules, continuous thermal conductivity pathways can be constructed within the matrix, thereby improving the thermal conductivity of the composite system. Meanwhile, with the mature development of microfluidic technology, the industry can now prepare phase change microcapsules with good monodispersity, controllable particle size and shell thickness, and encapsulation efficiency of no less than 65%, providing a good material basis for optimizing the performance of composite systems.

[0006] Although existing technologies have been extensively researched around phase change microcapsule / thermal conductive filler / PDMS composite systems, and have achieved preliminary applications in laboratories and some low-end scenarios, they have not yet broken through the core technological bottlenecks and cannot meet the stringent performance requirements of high-end electronics, spacecraft thermal management, and other scenarios. The core shortcomings are as follows: First, the surface modification process for thermally conductive fillers is imperfect, resulting in poor compatibility with the matrix and microcapsules. Existing technologies for surface modification of thermally conductive fillers mostly employ simple physical adsorption or conventional chemical grafting methods. The selection of modifiers lacks specificity, and key parameters such as modification temperature, modification time, and modifier dosage are not precisely controlled. This leads to the modified thermally conductive fillers still possessing high surface energy, making it difficult to form a good interfacial bond with the PDMS matrix and phase change microcapsule shell material. This easily causes filler agglomeration and increases interfacial thermal resistance, hindering the effective construction of the thermally conductive network. Furthermore, some modification processes are complex and costly, and may even damage the filler's crystal structure during modification, introducing new phonon scattering centers, which in turn restricts the improvement of the composite system's thermal conductivity. Simultaneously, existing modification schemes do not fully consider the compatibility of modifiers with the PDMS matrix and microcapsule shell material, further exacerbating the interfacial compatibility problem.

[0007] Secondly, the dispersion method is poorly designed, resulting in poor dispersion uniformity between the filler and microcapsules. In existing technologies, the dispersion of phase change microcapsules and thermally conductive fillers in PDMS matrices often employs either single mechanical stirring or single ultrasonic dispersion, lacking synergistic coordination and parameter optimization between the two methods. Excessive stirring speed can easily lead to rupture of the phase change microcapsule shell, causing core material leakage; excessive ultrasonic power can easily cause secondary agglomeration of the thermally conductive filler; mismatched stirring and ultrasonic parameters can lead to uneven dispersion of microcapsules and fillers, resulting in localized agglomeration and stratification, failing to form a continuous and efficient thermally conductive network. This not only affects the thermal conductivity of the composite system but also reduces its mechanical properties and processing stability, making it prone to porosity and defects during subsequent hot-pressing film formation, thus failing to meet practical application requirements. Furthermore, existing dispersion processes have not been adapted and optimized for the uniform particle size and unique surface characteristics of microcapsules prepared under microfluidic conditions, further limiting the dispersion effect.

[0008] Third, the composite system suffers from weak interfacial bonding, resulting in insufficient overall performance and long-term stability. Due to imperfect modification of the thermally conductive filler, poor compatibility between the microcapsules and the PDMS matrix, and insufficient dispersion uniformity, the interfacial bonding between the phase change microcapsules, thermally conductive filler, and PDMS matrix is ​​weak. Defects such as interfacial separation and porosity easily occur within the composite system, which further increases the interfacial thermal resistance, causing the actual thermal conductivity of the composite system to only reach 30%-50% of the theoretical prediction value, failing to meet the heat dissipation requirements of high-power devices. It also causes a decline in the mechanical properties of the composite system, manifested as a decrease in elongation at break and tensile strength, making it prone to cracking and detachment during long-term use, seriously affecting the service life and reliability of the material.

[0009] In summary, developing a phase change microcapsule thermally conductive composite material preparation scheme that can simultaneously solve core problems such as agglomeration of thermally conductive fillers, poor compatibility between microcapsules and the matrix, discontinuous thermal conductive network, and weak interfacial bonding, and achieving synergistic improvement in the material's thermal storage performance, thermal conductivity, mechanical properties, and stability, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing a phase change microcapsule thermally conductive composite material. This method precisely controls the surface modification process of the thermally conductive filler, the composite ratio and dispersion mode of the phase change microcapsules and the thermally conductive filler, so as to achieve uniform dispersion of the two in the PDMS matrix and construct an efficient and continuous thermally conductive network, while significantly improving the interfacial compatibility and bonding force between the composite system and the PDMS matrix.

[0011] The objective of this invention is achieved through the following technical solution: This invention provides a microphase change capsule thermally conductive composite material, comprising polydimethylsiloxane, and aminated phase change microcapsules and modified thermally conductive fillers dispersed in the polydimethylsiloxane; the filling amount of the aminated phase change microcapsules is 10-50 wt% of the mass of the polydimethylsiloxane, and the addition amount of the modified thermally conductive filler is 5-10 wt% of the mass of the polydimethylsiloxane.

[0012] Furthermore, the aminated phase change microcapsules use an organic phase change material as the core material and trimethylolpropane tris(3-mercaptopropionic acid), mercaptoethylamine hydrochloride, and polyethylene glycol diacrylate as polymeric shell materials; the organic phase change material is hexadecane.

[0013] Furthermore, the amination phase change microcapsules have a particle size of 200±15μm, a shell thickness of 10-15μm, and an encapsulation efficiency of not less than 65%; the modified thermally conductive filler is a thermally conductive filler modified with silane coupling agent KH-560, and the thermally conductive filler is selected from one or more of silver powder, copper powder, silicon nitride, boron nitride, alumina, diamond, flake graphite, graphene, and short carbon fibers.

[0014] Furthermore, the thermally conductive filler is short carbon fiber, and the amount of silane coupling agent KH-560 added is 2-5% of the mass of the short carbon fiber; the polydimethylsiloxane is obtained by mixing the base adhesive and the curing agent at a mass ratio of 10:1.

[0015] The present invention also provides a method for preparing the phase change microcapsule thermally conductive composite material, comprising the following steps: S1 uses microfluidic technology to prepare surface-aminated phase change microcapsules; S2 mixes aminated phase change microcapsules, modified thermally conductive fillers and polydimethylsiloxane, and then degasses to obtain a composite system; S3 uses a dynamic force field hot pressing process to form the composite system into a membrane material, and then performs post-processing to obtain a phase change microcapsule thermally conductive composite material.

[0016] Furthermore, step S1 specifically includes: S1.1 Prepare the core material solution, shell material solution, and continuous phase solution; the core material solution is hexadecane, the shell material solution contains trimethylolpropane tris(3-mercaptopropionic acid), mercaptoethylamine hydrochloride, polyethylene glycol diacrylate, and photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the continuous phase solution is a deionized aqueous solution containing Span-80; S1.2 uses a glass capillary microfluidic device to regulate the flow rates of the core material, shell material, and continuous phase, forming oil-in-oil-in-water double emulsion droplets within the microchannel; S1.3 uses ultraviolet light to polymerize and solidify the shell material, and after centrifugation, washing, and vacuum drying, aminated phase change microcapsules are obtained.

[0017] Furthermore, step S2 specifically includes: S2.1 Disperse the thermally conductive filler in anhydrous ethanol, add silane coupling agent KH-560, stir at 60-70℃ for 2-3 hours, and centrifuge and dry to obtain the modified thermally conductive filler; S2.2 The base adhesive of polydimethylsiloxane and the curing agent are mixed at a mass ratio of 10:1, and aminated phase change microcapsules and modified thermally conductive fillers are added. The mixture is then mixed evenly by high-speed stirring combined with ultrasonic dispersion. S2.3 The mixed materials are degassed under a vacuum of -0.08 to -0.1 MPa for 10-15 minutes to obtain a composite system.

[0018] Furthermore, step S3 specifically includes: S3.1 The composite system is spread in a stainless steel mold coated with a release agent to a thickness of 0.1-0.5 mm; S3.2 Place the mold in a dynamic force field hot press and hold it under pressure for 15-30 minutes at 80-120℃, 0.5-2.0MPa, and 10-20Hz. S3.3 After cooling to room temperature, demold the film and keep it at 60℃ for 2-4 hours to obtain the finished phase change microcapsule thermally conductive composite material.

[0019] Furthermore, in step S1, the core material flow rate is 0.1-0.5 mL / h, the shell material flow rate is 0.3-1.0 mL / h, and the continuous phase flow rate is 1.0-3.0 mL / h; the ultraviolet light wavelength is 365 nm, and the power is 10-20 W; the centrifugation speed is 3000-5000 r / min, and the time is 5-10 min; the vacuum drying temperature is 60-80℃, and the time is 2-4 h. In step S2.2, the high-speed stirring speed is 1500-2000 r / min and the time is 10-15 min; the ultrasonic dispersion power is 200-300 W and the time is 5-8 min.

[0020] The present invention also provides an application of the phase change microcapsule thermally conductive composite material in the fields of flexible electronics, smart wearables, and spacecraft thermal management.

[0021] The beneficial effects of this invention are as follows: This invention addresses the core technical shortcomings of existing phase change microcapsule thermally conductive composite materials, such as easy agglomeration of thermally conductive fillers, poor compatibility with the matrix and microcapsules, discontinuous thermal conductive network, easy leakage of phase change materials, and difficulty in synergistic improvement of heat storage, thermal conductivity, and mechanical properties. Through multi-stage process optimization and material structure design, this invention achieves a comprehensive improvement in the overall performance of composite materials. All performance effects are derived from the technical solution of this invention and measured data.

[0022] This invention, in the microfluidic preparation of phase change microcapsules, introduces mercaptoethylamine hydrochloride into the shell material system, giving the surface of the resulting microcapsule shell material active amino groups. Simultaneously, the surface of the thermally conductive filler is modified using the silane coupling agent KH-560, grafting epoxy groups that react with amino groups onto the surface of the thermally conductive filler. Through the chemical reaction between amino and epoxy groups, a uniform distribution of the thermally conductive filler on the microcapsule surface can be achieved, significantly reducing the surface energy of the thermally conductive filler and decreasing the van der Waals forces between filler particles, thus fundamentally inhibiting filler agglomeration. Furthermore, the active groups on the surfaces of the microcapsules and the thermally conductive filler significantly enhance the interfacial bonding force between both and the PDMS matrix, effectively reducing the interfacial thermal resistance of the composite system. This lays the foundation for constructing a continuous and efficient thermally conductive network, ultimately achieving a composite material with a thermal conductivity of up to 2.5 W / (m²). K), under the same filling conditions, the thermal conductivity is better than that of the control sample that has not undergone amination modification.

[0023] This invention employs a synergistic dispersion process combining high-speed stirring and ultrasonic dispersion, with precise matching and optimization of dispersion parameters. Medium-high speed stirring at 1500-2000 r / min achieves initial uniform mixing of the filler, microcapsules, and matrix, avoiding microcapsule shell rupture and phase change core material leakage caused by excessive stirring speed. Simultaneously, low-power ultrasonic dispersion at 200-300W breaks up any potential micro-agglomerates within the system, preventing secondary agglomeration of the thermally conductive filler caused by excessive ultrasonic power. Ultimately, this achieves uniform dispersion of the phase change microcapsules and thermally conductive filler in the PDMS matrix, ensuring the continuity and integrity of the thermally conductive network. Furthermore, the amination-modified phase change microcapsules prepared using microfluidic technology have an encapsulation efficiency of no less than 65% and can withstand more than 100 melt-crystallization cycles without leakage. Combined with the gentle synergistic dispersion process, this effectively avoids phase change core material leakage problems during composite material processing and long-term use, ensuring the long-term stability of material performance.

[0024] This invention utilizes microfluidic technology to precisely control the particle size and shell thickness of phase change microcapsules. Furthermore, by adjusting the filling amount of amination-modified phase change microcapsules in a PDMS matrix, the thermal storage performance of the composite material can be precisely controlled. When the microcapsule filling amount is adjusted within the range of 10-50 wt%, the phase change enthalpy of the composite material can linearly change from 43 J / g to 156 J / g, adapting to the thermal storage and temperature control requirements of different application scenarios. Under the same condition of 40 wt% microcapsule filling, the phase change enthalpy of the composite material prepared by this invention reaches 127 J / g, significantly higher than the 109 J / g of the control sample without amination modification and the 101 J / g of the control sample using unmodified thermally conductive filler. This demonstrates that the interface modification and synergistic dispersion system of this invention effectively reduces processing losses and leakage of the phase change core material, significantly improving the effective thermal storage efficiency of the composite material.

[0025] This invention enhances the interfacial bonding between phase change microcapsules, thermally conductive fillers, and the PDMS matrix through interface modification. It avoids local agglomeration and structural defects within the system through a synergistic dispersion process. Combined with a dynamic force field hot pressing molding process, it achieves uniform stress distribution during molding, effectively mitigating the mechanical property degradation caused by increasing the filling amount of high-functionality fillers. The resulting composite material maintains high thermal conductivity and high heat storage performance, while achieving an elongation at break of up to 37%. Under the same filling conditions, its flexibility is superior to that of the unmodified control sample. In addition, all samples passed the 60℃ heat deformation test without significant heat deformation, demonstrating excellent temperature resistance and dimensional stability. It can be fully adapted to application scenarios such as flexible electronics and smart wearables, which have stringent requirements for material flexibility and temperature resistance.

[0026] The entire process of this invention features precise and controllable preparation parameters, eliminating the need for complex equipment upgrades. The modification process is simple and cost-effective, and it does not damage the intrinsic crystal structure of the thermally conductive filler. This allows for the improvement of composite material performance while ensuring the economy and repeatability of the process. Furthermore, the process scheme of this invention can be customized for different types of phase change microcapsules, thermally conductive fillers, and PDMS matrices to meet the performance requirements of different application scenarios. This provides a novel and efficient solution for the large-scale preparation and high-end application of polymer-based thermally conductive phase change composite materials. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the 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.

[0028] Figure 1 This is an electron microscope image of the amination phase change microcapsules in Example 1 of the present invention; Figure 2 The DSC curve of the aminated phase change microcapsules in Example 1 of this invention; Figure 3 This is an electron microscope image of the aminated phase change microcapsule / modified short carbon fiber / PDMS composite membrane material in Example 1 of the present invention; Figure 4 This is a digital photograph of the aminated phase change microcapsule / modified short carbon fiber / PDMS composite membrane material in Example 3 of the present invention; Figure 5 This is an electron microscope image of the phase change microcapsules in Comparative Example 1 of the present invention. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] The phase change microcapsule thermally conductive composite material provided by this invention uses polydimethylsiloxane (PDMS) as a matrix, filled with aminated phase change microcapsules and modified thermally conductive fillers; wherein, the aminated phase change microcapsules are filled with 10-50 wt% of the PDMS mass, and the modified thermally conductive fillers are added with 5-10 wt% of the PDMS mass. The aminated phase change microcapsules are prepared using microfluidic technology with an organic phase change material as the core material and trimethylolpropane tris(3-mercaptopropionic acid), mercaptoethylamine hydrochloride, and polyethylene glycol diacrylate as the shell material; the modified thermally conductive filler is a thermally conductive filler modified with silane coupling agent KH-560, and the thermally conductive filler can be selected from one or more of silver powder, copper powder, silicon nitride, boron nitride, alumina, diamond, flake graphite, graphene, and short carbon fibers.

[0035] The preparation method of the phase change microcapsule thermally conductive composite material in this invention includes three core steps: microfluidic preparation of surface-aminated phase change microcapsules, preparation of the phase change microcapsule / thermally conductive filler / PDMS composite system, and dynamic force field forming hot pressing film deposition. The specific preparation method is as follows: Step 1: Preparation of surface-aminated phase change microcapsules using microfluidic technology 1.1 Raw material preparation: Organic phase change materials (such as hexadecane) were selected as the core material, and trimethylolpropane tris(3-mercaptopropionic acid), mercaptoethylamine hydrochloride, and polyethylene glycol diacrylate were selected as the shell material. 2-hydroxy-2-methyl-1-phenyl-1-propanone (based on the thiol-ene photoclick chemistry system) was added as a photoinitiator, and Span-80 dispersant was added at the same time to prepare core material solutions, shell material solutions, and continuous phase solutions (deionized water + emulsifier) ​​respectively. 1.2 Microfluidic device debugging: A Lego-style glass capillary microfluidic device (multi-channel collaborative structure) was adopted. The inner diameter of the microchannel and the spacing of the coaxial capillaries were adjusted, and the fluid flow rates of the core material, shell material and continuous phase were set: core material flow rate 0.1-0.5 mL / h, shell material flow rate 0.3-1.0 mL / h, and continuous phase flow rate 1.0-3.0 mL / h. By adjusting the flow rate ratio, the precise control of the microcapsule particle size of 200±15 μm and the shell thickness of 10-15 μm was achieved. 1.3 Microcapsule Forming and Curing: The core material solution, shell material solution, and continuous phase solution are injected into the corresponding channels of the microfluidic device, forming oil-in-oil-in-water (O / O / W) double emulsion droplets within the microchannels. After the emulsion droplets flow out of the microchannels, they are irradiated with ultraviolet light at a wavelength of 365nm and a power of 10-20W. The shell material is rapidly polymerized and cured using thiol-olefin click chemistry to form monodisperse phase change microcapsules. 1.4 Microcapsule post-processing: The solidified microcapsule suspension is centrifuged at 3000-5000 r / min for 5-10 min. The supernatant is removed, and the microcapsule is washed 2-3 times with anhydrous ethanol to remove residual emulsifier and unreacted shell material. Then, it is vacuum dried at 60-80℃ for 2-4 h to obtain dried amination phase change microcapsules with an encapsulation efficiency of not less than 65% and can withstand more than 100 melt-crystallization cycles without leakage.

[0036] Step 2: Preparation of the phase change microcapsule / thermal conductive filler / PDMS composite system 2.1 Modification of thermally conductive filler: The thermally conductive filler is dispersed in anhydrous ethanol, and silane coupling agent KH-560 is added (the amount added is 2-5% of the mass of the thermally conductive filler). The mixture is stirred at 60-70℃ for 2-3 hours, and after centrifugation and drying, the modified thermally conductive filler containing epoxy groups is obtained. 2.2 Preparation of the composite system: Weigh the PDMS matrix (base adhesive to curing agent ratio 10:1), aminated phase change microcapsules and epoxidized modified thermally conductive filler according to the mass ratio. Mix the PDMS base adhesive and curing agent thoroughly, add the phase change microcapsules and modified thermally conductive filler, and mix by high-speed stirring + ultrasonic dispersion. The high-speed stirring parameters are 1500-2000 r / min and 10-15 min, and the ultrasonic dispersion parameters are 200-300 W and 5-8 min, so that the microcapsules and thermally conductive filler are uniformly dispersed in the PDMS matrix without obvious agglomeration. 2.3 Degassing treatment: Place the prepared composite system into a vacuum degassing machine and degas for 10-15 minutes under a vacuum of -0.08~-0.1MPa to remove air bubbles from the system.

[0037] Step 3: Dynamic force field forming hot pressing film deposition 3.1 Hot pressing mold preparation: Select a stainless steel mold, apply a release agent to the mold surface, and spread the degassed composite system evenly in the mold, controlling the spreading thickness to be 0.1-0.5mm; 3.2 Setting of dynamic force field hot pressing parameters: Place the mold in the dynamic force field hot press, set the hot pressing temperature to 80-120℃, the dynamic pressure to 0.5-2.0MPa, the dynamic pressing frequency to 10-20Hz, and the holding time to 15-30min; 3.3 Molding and Demolding: After hot pressing, turn off the heating device and let the mold cool naturally to room temperature (25±2℃). Release the dynamic pressure, open the mold, take out the composite film, remove the excess part at the edge, and obtain the phase change microcapsule-thermal conductive filler-PDMS composite film. 3.4 Post-treatment of membrane material: Place the composite membrane material in a constant temperature drying oven and keep it at 60℃ for 2-4 hours to further cure it, improve the mechanical properties and interfacial bonding of the membrane material, and obtain the finished phase change microcapsule thermal conductive composite material.

[0038] The raw material information used in the following embodiments and comparative examples of this invention is as follows: Hexadecane: Aladdin reagent, analytical grade; Trimethylolpropane tris(3-mercaptopropionic acid): Inokai reagent, analytical grade; Mercaptoethylamine hydrochloride: Aladdin reagent, analytical grade; Polyethylene glycol diacrylate: Beijing Innocare Technology Co., Ltd., analytical grade; 2-Hydroxy-2-methyl-1-phenyl-1-propanone: Commercially available analytical grade; Span-80: Commercially available analytical grade; PDMS: Dow Corning, model SYLGARD 184; Short carbon fiber: Shanghai Qijie Co., Ltd., model TCGP DL06M.500HE, diameter 10μm, length 6mm; Silane coupling agent KH-560: Shanghai Aladdin Biochemical Technology Co., Ltd., analytical grade; Anhydrous ethanol: commercially available analytical grade.

[0039] Example 1 1.1 Raw materials and proportions (1) Raw materials for preparing amination phase change microcapsules: the core material is hexadecane, the shell material is trimethylolpropane tris(3-mercaptopropionic acid), mercaptoethylamine hydrochloride and polyethylene glycol diacrylate, the amount of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone added is 3% of the shell material weight, and the continuous phase is deionized water + 0.5wt% Span-80 emulsifier; (2) Composite system ratio: PDMS total mass 100g, of which the ratio of base adhesive to curing agent is 10:1 (base adhesive 90.9g, curing agent 9.1g); the amount of aminated phase change microcapsules is 10wt% of the mass of PDMS, i.e. 10g; the modified thermally conductive filler is short carbon fiber, the amount added is 5wt% of the mass of PDMS, i.e. 5g; the amount of silane coupling agent KH-560 added is 2% of the mass of short carbon fiber.

[0040] 1.2 Preparation steps (1) Microfluidic preparation of amination phase change microcapsules: A coaxial flow glass capillary microfluidic device was used, with the core material flow rate set to 0.2 mL / h, the shell material flow rate to 0.5 mL / h, and the continuous phase flow rate to 1.5 mL / h. After the emulsion droplets flowed out, they were cured by ultraviolet light with a wavelength of 365 nm and a power of 15 W. The cured suspension was centrifuged at 4000 r / min for 8 min, washed 2-3 times with anhydrous ethanol, and then vacuum dried at 70 °C for 3 h to obtain amination phase change microcapsules with a particle size of 200 ± 15 μm and a shell thickness of 2 μm. The encapsulation efficiency was tested to be 65.4%, and the phase change enthalpy value was measured to be 190.86 J / g by differential scanning calorimetry (DSC). Electron microscope images of the amination phase change microcapsules are shown below. Figure 1 As shown, the DSC curve of the amination phase change microcapsules is as follows: Figure 2 As shown; (2) Modification of thermally conductive filler: 5g of short carbon fibers were dispersed in anhydrous ethanol, 0.1g of KH-560 was added, and the mixture was stirred at 65℃ for 2.5h. After centrifugation and drying, modified short carbon fibers were obtained. (3) Preparation of composite system: 100g of PDMS base adhesive and curing agent are thoroughly mixed, 10g of aminated phase change microcapsules and 5g of modified short carbon fibers are added, and the mixture is uniformly mixed by high-speed stirring (1800r / min, time 12min) + ultrasonic dispersion (250W, time 6min), and then degassed under a vacuum of -0.09MPa for 12min; (4) Dynamic force field hot pressing film formation: The degassed composite system is evenly spread in a stainless steel mold coated with a release agent, with a spreading thickness of 0.2 mm; the mold is placed in a dynamic force field hot press, and the hot pressing temperature is set to 100℃, the dynamic pressure to 1.0 MPa, the dynamic pressing frequency to 15 Hz, and the holding time to 20 min; after hot pressing, the film is naturally cooled to room temperature and demolded, and the resulting film is dried at 60℃ for 3 h to obtain the finished composite film. The electron microscope image of the aminated phase change microcapsule / modified short carbon fiber / PDMS composite film is shown below. Figure 3 As shown.

[0041] Example 2 2.1 Raw materials and proportions Composite system formulation: 100g total mass of PDMS, with a base adhesive to curing agent ratio of 10:1; aminated phase change microcapsules filled with 20wt% of the mass of PDMS, i.e., 20g; modified thermally conductive filler is short carbon fiber, added at 5wt% of the mass of PDMS, i.e., 5g; silane coupling agent KH-560 added at 2% of the mass of short carbon fiber.

[0042] 2.2 Preparation steps (1) Preparation of aminated phase change microcapsules: Same as the preparation method of aminated phase change microcapsules in Example 1; (2) Modification of thermally conductive filler: same as the modification method of short carbon fibers in Example 1; (3) Preparation of composite system: 100g of PDMS base adhesive and curing agent are thoroughly mixed, 20g of aminated phase change microcapsules and 5g of modified short carbon fibers are added, and the mixture is uniformly mixed by high-speed stirring (1800r / min, time 12min) + ultrasonic dispersion (250W, time 6min), and then degassed under a vacuum of -0.09MPa for 12min; (4) Dynamic force field hot pressing film formation: the hot pressing film formation and post-processing steps in Example 1 are the same to obtain the finished composite film material.

[0043] Example 3 3.1 Raw materials and proportions Composite system formulation: 100g total mass of PDMS, with a base adhesive to curing agent ratio of 10:1; the amount of aminated phase change microcapsules is 30wt% of the mass of PDMS, i.e., 30g; the modified thermally conductive filler is short carbon fiber, with an addition amount of 5wt% of the mass of PDMS, i.e., 5g; the amount of silane coupling agent KH-560 added is 2% of the mass of short carbon fiber.

[0044] 3.2 Preparation steps (1) Preparation of aminated phase change microcapsules: Same as the preparation method of aminated phase change microcapsules in Example 1; (2) Modification of thermally conductive filler: same as the modification method of short carbon fibers in Example 1; (3) Preparation of composite system: 100g of PDMS base adhesive and curing agent are thoroughly mixed, 30g of aminated phase change microcapsules and 5g of modified short carbon fibers are added, and the mixture is uniformly mixed by high-speed stirring (1800r / min, time 12min) + ultrasonic dispersion (250W, time 6min), and then degassed under a vacuum of -0.09MPa for 12min; (4) Dynamic force field hot pressing film formation: The hot pressing film formation and post-processing steps are the same as in Example 1 to obtain the finished composite film material. Digital photos of the aminated phase change microcapsule / modified short carbon fiber / PDMS composite film material are shown below. Figure 4 As shown.

[0045] Example 4 4.1 Raw materials and proportions Composite system formulation: 100g total mass of PDMS, with a base adhesive to curing agent ratio of 10:1; the amount of aminated phase change microcapsules is 40wt% of the mass of PDMS, i.e., 40g; the modified thermally conductive filler is short carbon fiber, with an addition amount of 5wt% of the mass of PDMS, i.e., 5g; the amount of silane coupling agent KH-560 added is 2% of the mass of short carbon fiber.

[0046] 4.2 Preparation steps (1) Preparation of aminated phase change microcapsules: Same as the preparation method of aminated phase change microcapsules in Example 1; (2) Modification of thermally conductive filler: same as the modification method of short carbon fibers in Example 1; (3) Preparation of composite system: 100g of PDMS base adhesive and curing agent are thoroughly mixed, 40g of aminated phase change microcapsules and 5g of modified short carbon fibers are added, and the mixture is mixed evenly by high-speed stirring (1800r / min, time 12min) + ultrasonic dispersion (250W, time 6min), and then degassed under a vacuum of -0.09MPa for 12min; (4) Dynamic force field hot pressing film formation: the hot pressing film formation and post-processing steps in Example 1 are the same to obtain the finished composite film material.

[0047] Example 5 5.1 Raw materials and proportions Composite system formulation: 100g total mass of PDMS, with a base adhesive to curing agent ratio of 10:1; the amount of aminated phase change microcapsules is 50wt% of the mass of PDMS, i.e., 50g; the modified thermally conductive filler is short carbon fiber, with an addition amount of 5wt% of the mass of PDMS, i.e., 5g; the amount of silane coupling agent KH-560 added is 2% of the mass of short carbon fiber.

[0048] 5.2 Preparation steps (1) Preparation of aminated phase change microcapsules: Same as the preparation method of aminated phase change microcapsules in Example 1; (2) Modification of thermally conductive filler: same as the modification method of short carbon fibers in Example 1; (3) Preparation of composite system: 100g of PDMS base adhesive and curing agent are thoroughly mixed, 50g of aminated phase change microcapsules and 5g of modified short carbon fibers are added, and the mixture is uniformly mixed by high-speed stirring (1800r / min, time 12min) + ultrasonic dispersion (250W, time 6min), and then degassed under a vacuum of -0.09MPa for 12min; (4) Dynamic force field hot pressing film formation: the hot pressing film formation and post-processing steps in Example 1 are the same to obtain the finished composite film material.

[0049] Comparative Example 1 1.1 Raw materials and proportions (1) Raw materials for the preparation of phase change microcapsules: the core material is hexadecane, the shell material is trimethylolpropane tris(3-mercaptopropionic acid) ester and polyethylene glycol diacrylate, the amount of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone added is 3% of the shell material weight, and the continuous phase is deionized water + 0.5wt% Span-80 emulsifier; (2) Composite system ratio: PDMS total mass 100g, of which the ratio of base adhesive to curing agent is 10:1; the phase change microcapsule filling amount is 40wt% of PDMS mass, i.e. 40g; the modified thermally conductive filler is short carbon fiber, the addition amount is 5wt% of PDMS mass, i.e. 5g; the silane coupling agent KH-560 addition amount is 2% of the short carbon fiber mass.

[0050] 1.2 Preparation steps (1) Microfluidic preparation of phase change microcapsules: A coaxial flow glass capillary microfluidic device was used, with the core material flow rate set to 0.2 mL / h, the shell material flow rate to 0.5 mL / h, and the continuous phase flow rate to 1.5 mL / h. After the emulsion droplets flowed out, they were cured by ultraviolet light with a wavelength of 365 nm and a power of 15 W. The cured suspension was centrifuged at 4000 r / min for 8 min, washed 2-3 times with anhydrous ethanol, and then vacuum dried at 70 °C for 3 h to obtain phase change microcapsules with a particle size of 200 ± 15 μm and a shell thickness of 2 μm. The encapsulation efficiency was tested to be 68.2%. Electron microscope images of the phase change microcapsules are shown below. Figure 5 As shown; (2) Modification of thermally conductive filler: same as the modification method of short carbon fibers in Example 1; (3) Preparation of composite system: 100g of PDMS base adhesive and curing agent are thoroughly mixed, 40g of the above phase change microcapsules and 5g of modified short carbon fibers are added, and the mixture is mixed evenly by high-speed stirring (1800r / min, time 12min) + ultrasonic dispersion (250W, time 6min), and then degassed under a vacuum of -0.09MPa for 12min; (4) Dynamic force field hot pressing film formation: the hot pressing film formation and post-processing steps in Example 1 are the same to obtain the finished composite film material.

[0051] Comparative Example 2 2.1 Raw materials and proportions Composite system formulation: 100g of PDMS total mass, with a base adhesive to curing agent ratio of 10:1; phase change microcapsule filling amount of 40wt% of PDMS mass, i.e., 40g; thermally conductive filler is unmodified short carbon fiber, with an addition amount of 5wt% of PDMS mass, i.e., 5g.

[0052] 2.2 Preparation steps (1) Preparation of phase change microcapsules: Same as the preparation method of phase change microcapsules in Comparative Example 1; (2) Preparation of composite system: 100g of PDMS base adhesive and curing agent are thoroughly mixed, 40g of the above phase change microcapsules and 5g of unmodified short carbon fibers are added, and the mixture is mixed evenly by high-speed stirring (1800r / min, time 12min) + ultrasonic dispersion (250W, time 6min), and then degassed under a vacuum of -0.09MPa for 12min; (3) Dynamic force field hot pressing film formation: the hot pressing film formation and post-processing steps in Example 1 are the same to obtain the finished composite film material.

[0053] Experimental Example 1 The component composition of each embodiment and the comparative example is compared in Table 1 below.

[0054] Table 1. Component composition of Examples 1-5 and Comparative Examples 1-2 (unit: g)

[0055] The performance test results of the composite membrane materials of each embodiment and comparative example are shown in Table 2 below.

[0056] Table 2 Performance test results of composite membranes prepared in Examples 1-5 and Comparative Examples 1-2

[0057] Based on the above, in Examples 1-5 of this application, as the filling amount of the aminated phase change microcapsules increases from 10g to 50g, the phase change enthalpy of the composite membrane material linearly increases from 43J / g to 156J / g. This indicates that the heat storage capacity of the composite membrane material of this invention can be precisely controlled by the filling amount of the aminated phase change microcapsules to adapt to the heat storage requirements of different scenarios. With a microcapsule filling amount of 40g, the enthalpy of the composite membrane material in Example 4 is 127J / g, significantly higher than 109J / g in Comparative Example 1 and 101J / g in Comparative Example 2. Combined with the characteristic of the aminated phase change microcapsules disclosed in this invention that they can withstand more than 100 melt-crystallization cycles without leakage, this indicates that the synergistic system of the aminated microcapsules and modified fillers of this invention can effectively reduce leakage of the phase change core material during processing and use, and improve the effective heat storage capacity of the composite system.

[0058] The thermal conductivity of the composite membrane materials in Examples 1-5 remained between 2.2 and 2.5 W / (m²). The thermal conductivity of K) is at a relatively high level, with Example 4 achieving a maximum value of 2.5 W / (m²). K), which is superior to 2.3 W / (m³) in Comparative Example 1 with the same filler content. K) and Comparative Example 2's 2.2W / (m K). This invention demonstrates that through the interfacial reaction between aminated phase change microcapsules and epoxy-modified thermally conductive fillers, and the high-speed stirring + ultrasonic synergistic dispersion process, the fillers and microcapsules can be uniformly dispersed in a PDMS matrix, constructing a continuous and efficient thermally conductive network, effectively reducing interfacial thermal resistance, achieving a stable improvement in the thermal conductivity of the composite system, and avoiding the decrease in thermal conductivity under high microcapsule loading.

[0059] The elongation at break of the composite membranes in Examples 1-5 decreased from 37% to 20% with increasing microcapsule loading, while the elastic modulus increased from 1.4 MPa to 2.1 MPa. This indicates that the mechanical properties of the composite membranes of the present invention can be controlled by the microcapsule loading to adapt to different flexible application scenarios. With a microcapsule loading of 40 g, the elongation at break of Example 4 was 24%, which is superior to 21% in Comparative Example 1 and 21% in Comparative Example 2. This demonstrates that the surface modification and synergistic dispersion process of the present invention can effectively improve the interfacial bonding force between the phase change microcapsules, thermally conductive fillers, and the PDMS matrix, improve the mechanical flexibility of the composite system, and alleviate the problem of mechanical property degradation under high loading levels.

[0060] All composite films in the embodiments and comparative examples passed the 60°C heat deformation test and showed no significant heat deformation, indicating that the composite film prepared by the present invention has good temperature resistance and can meet the operating temperature requirements of conventional electronic device thermal management scenarios.

[0061] It is evident that the phase change microcapsule thermally conductive composite material prepared by this invention possesses tunable heat storage performance, excellent thermal conductivity, and mechanical flexibility, and can be applied to thermal management-related fields such as flexible electronics, smart wearables, and spacecraft thermal management.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A phase change microcapsule thermally conductive composite material, characterized by, It includes polydimethylsiloxane, and amination phase change microcapsules and modified thermally conductive fillers dispersed in the polydimethylsiloxane; the filling amount of the amination phase change microcapsules is 10-50 wt% of the mass of the polydimethylsiloxane, and the addition amount of the modified thermally conductive filler is 5-10 wt% of the mass of the polydimethylsiloxane.

2. The phase change microcapsule thermally conductive composite material according to claim 1, characterized in that, The aminated phase change microcapsules use an organic phase change material as the core material and trimethylolpropane tris(3-mercaptopropionic acid), mercaptoethylamine hydrochloride, and polyethylene glycol diacrylate as polymeric shell materials; the organic phase change material is hexadecane.

3. The phase change microcapsule thermally conductive composite material according to claim 2, characterized in that, The aminated phase change microcapsules have a particle size of 200±15μm, a shell thickness of 10-15μm, and an encapsulation efficiency of not less than 65%; the modified thermally conductive filler is a thermally conductive filler modified with silane coupling agent KH-560, and the thermally conductive filler is selected from one or more of silver powder, copper powder, silicon nitride, boron nitride, alumina, diamond, flake graphite, graphene, and short carbon fibers.

4. The phase change microcapsule thermally conductive composite material according to claim 3, characterized in that, The thermally conductive filler is short carbon fiber, and the amount of silane coupling agent KH-560 added is 2-5% of the mass of the short carbon fiber; the polydimethylsiloxane is obtained by mixing the base adhesive and the curing agent at a mass ratio of 10:

1.

5. A method for preparing the phase change microcapsule thermally conductive composite material according to any one of claims 1-4, characterized in that, Includes the following steps: S1 uses microfluidic technology to prepare surface-aminated phase change microcapsules; S2 mixes aminated phase change microcapsules, modified thermally conductive fillers and polydimethylsiloxane, and then degasses to obtain a composite system; S3 uses a dynamic force field hot pressing process to form the composite system into a membrane material, and then performs post-processing to obtain a phase change microcapsule thermally conductive composite material.

6. The method according to claim 5, characterized in that, Step S1 specifically involves: S1.1 Prepare the core material solution, shell material solution, and continuous phase solution; the core material solution is hexadecane, the shell material solution contains trimethylolpropane tris(3-mercaptopropionic acid), mercaptoethylamine hydrochloride, polyethylene glycol diacrylate, and photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the continuous phase solution is a deionized aqueous solution containing Span-80; S1.2 uses a glass capillary microfluidic device to regulate the flow rates of the core material, shell material, and continuous phase, forming oil-in-oil-in-water double emulsion droplets within the microchannel; S1.3 uses ultraviolet light to polymerize and solidify the shell material, and after centrifugation, washing, and vacuum drying, aminated phase change microcapsules are obtained.

7. The method according to claim 5, characterized in that, Step S2 specifically involves: S2.1 Disperse the thermally conductive filler in anhydrous ethanol, add silane coupling agent KH-560, stir at 60-70℃ for 2-3 hours, and centrifuge and dry to obtain the modified thermally conductive filler; S2.2 The base adhesive of polydimethylsiloxane and the curing agent are mixed at a mass ratio of 10:1, and aminated phase change microcapsules and modified thermally conductive fillers are added. The mixture is then mixed evenly by high-speed stirring combined with ultrasonic dispersion. S2.3 The mixed materials are degassed under a vacuum of -0.08 to -0.1 MPa for 10-15 minutes to obtain a composite system.

8. The method according to claim 5, characterized in that, Step S3 specifically involves: S3.1 The composite system is spread in a stainless steel mold coated with a release agent to a thickness of 0.1-0.5 mm; S3.2 Place the mold in a dynamic force field hot press and hold it under pressure for 15-30 minutes at 80-120℃, 0.5-2.0MPa, and 10-20Hz. S3.3 After cooling to room temperature, demold the film and keep it at 60℃ for 2-4 hours to obtain the finished phase change microcapsule thermally conductive composite material.

9. The method according to any one of claims 6-8, characterized in that, In step S1, the core material flow rate is 0.1-0.5 mL / h, the shell material flow rate is 0.3-1.0 mL / h, and the continuous phase flow rate is 1.0-3.0 mL / h; the ultraviolet light wavelength is 365 nm, and the power is 10-20 W; the centrifugation speed is 3000-5000 r / min, and the time is 5-10 min; the vacuum drying temperature is 60-80℃, and the time is 2-4 h. In step S2.2, the high-speed stirring speed is 1500-2000 r / min and the time is 10-15 min; the ultrasonic dispersion power is 200-300 W and the time is 5-8 min.

10. The application of the phase change microcapsule thermally conductive composite material according to any one of claims 1-4 in the fields of flexible electronics, smart wearables, and spacecraft thermal management.

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