Novel liquid metal microcapsule heat conduction material

Abstract

The invention discloses a novel liquid metal microcapsule heat conduction material, and relates to the technical field of heat conduction materials, and the novel liquid metal microcapsule heat conduction material comprises the following steps: S1, microcapsule preparation; s2, dispersing and compounding; and S3, curing and applying. According to the novel liquid metal microcapsule heat conduction material, high heat conduction and insulation are synergistic, a liquid metal core provides a high heat conduction path, a polymer shell ensures insulation, the performance bottleneck of a traditional material is broken through, and according to the microcapsule structure design, liquid metal (gallium-based alloy) is packaged in a flexible polymer leather film (PDMS / PU / ACRYLIC), high heat conduction is kept, and insulation is achieved. And a composite dispersion process: uniformly dispersing the microcapsules in a liquid organic matrix by adopting an ultrasonic dispersion technology to form a three-dimensional heat-conducting network. The heat conductivity coefficient of a finished product reaches 10 W / m.K or above, the minimum thermal resistance can reach 0.02 thermal resistance DEG C * cm < 2 > / W, and meanwhile, the heat-resistant and high-viscosity flexible cable has insulativity, heat resistance, high viscosity and bendability.

Description

Technical Field

[0001] This invention relates to the field of thermal conductive materials technology, specifically to a novel liquid metal microcapsule thermal conductive material. Background Technology

[0002] Thermally conductive materials are a new type of industrial material. These materials were designed in recent years to meet the heat transfer requirements of equipment, offering excellent performance and reliability. They are suitable for various environments and requirements, provide effective solutions for potential heat conduction problems, and greatly facilitate the high integration and ultra-small, ultra-thin design of equipment. These thermally conductive products are increasingly being used in many products, improving their reliability.

[0003] With the development of 5G communication, new energy vehicles, and the integration of electronic devices, higher requirements are being placed on thermal conductive materials. Existing thermal conductive materials suffer from the following main problems:

[0004] 1. It is difficult to balance thermal conductivity and insulation performance: Metallic materials (such as copper and aluminum) have good thermal conductivity but electrical conductivity, while traditional insulating materials (such as silicone and polymers) generally have a thermal conductivity of less than 5 W / m·K.

[0005] 2. Interface thermal resistance problem: The unevenness of the microscopic surface leads to a small actual contact area, and the air gap (with a thermal conductivity of only 0.026 W / m·K) becomes the main obstacle to heat transfer.

[0006] 3. Insufficient long-term stability: Materials such as silicone gaskets are prone to aging, and phase change materials will undergo morphological changes at around 45℃, affecting their performance.

[0007] 4. Mechanical limitations: Most high thermal conductivity materials (such as ceramics) are brittle and cannot meet the requirements of bendable equipment. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a novel liquid metal microcapsule thermal conductive material, which solves the problems mentioned in the background section.

[0009] To achieve the above objectives, the present invention provides a novel liquid metal microcapsule thermal conductive material, comprising: a plurality of microcapsules dispersed in an organic matrix; the microcapsules include a liquid metal core and a polymer shell encapsulating the core; the polymer shell is made of a flexible insulating polymer.

[0010] Furthermore, the liquid metal is gallium or a gallium-based alloy, and the gallium-based alloy contains indium and / or tin.

[0011] Furthermore, the polymer shell is made of at least one of polydimethylsiloxane, silicone rubber, polyurethane, and acrylic resin.

[0012] Furthermore, the microcapsules have a particle size of 10-200 μm, and the polymer shell has a wall thickness of 1-15 μm.

[0013] Furthermore, the organic matrix is ​​selected from at least one of liquid silicone oil, mineral oil, epoxy resin precursor, and organosilicon resin.

[0014] Furthermore, the volume fraction of the microcapsules in the composite material is 50%-95%.

[0015] Furthermore, this includes the following steps:

[0016] S1. Microcapsule preparation: Microcapsules encapsulating the liquid metal are formed by reacting flexible insulating polymer monomers on the surface of liquid metal droplets through interfacial polymerization, in-situ polymerization or emulsion polymerization.

[0017] S2. Dispersion and Composite: The microcapsules obtained in step S1 are mixed with an organic matrix and ultrasonically dispersed to form a uniformly dispersed composite system.

[0018] S3. Curing and molding: The composite system obtained in step S2 is subjected to thermo-curing or photo-curing to obtain a solid or gel-state thermally conductive composite material.

[0019] Furthermore, in step S1, the interfacial polymerization method specifically includes: dissolving two monomers capable of polymerization in an aqueous phase and an oil phase respectively, dispersing liquid metal in one of the phases, forming an emulsion in the presence of an emulsifier, and the two monomers undergoing a polymerization reaction at the droplet interface to form the polymer shell.

[0020] Furthermore, in step S2, the conditions for ultrasonic dispersion are: power 300-400W, time 15-30 minutes, and temperature controlled at 40±5℃.

[0021] Furthermore, in step S3, the thermosetting conditions are 2 hours at 80°C or 10 minutes at 110°C; the photocuring conditions are UV light irradiation with a wavelength of 365nm and an intensity of 50mW / cm².

[0022] Optionally, in S1: the membrane material is PDMS (polydimethylsiloxane) or silicone rubber, and the encapsulation method is interfacial polymerization or in-situ polymerization; the temperature is 25±2℃, the stirring speed is 300-500rpm, the time is 2-4 hours, the microcapsule particle size range is 10-200µm, the wall thickness is 1-5µm, and the encapsulation rate is >95%.

[0023] Optionally, the microcapsules are made by dissolving two monomers undergoing polymerization in water and an organic solvent, respectively, with the core material dissolved in the dispersed phase solvent. An emulsifier is then added to both liquids to form an emulsion. The two reactive monomers migrate from the interior of the two phases to the droplet interface, where they react to generate a polymer that encapsulates the core material, forming the microcapsules.

[0024] Optionally, in S2, the equipment is a 500W ultrasonic disperser (frequency 20kHz), with a power of 300-400W, a time of 15-30 minutes, a temperature of 40+5°C, and a microcapsule content of 50%-95% (volume fraction); the dispersion effect is a particle size distribution D90 < 250µm with no agglomeration, and a system viscosity of 5000-15000cP.

[0025] Optionally, in S3: UV irradiation (wavelength 365nm, intensity 50mW / cm², thermal conductivity: 10-15W / m·K (ASTM D5470 standard), insulation resistance: > 10¹²Ω, heat resistance: stable from -40℃ to 200℃, hardness lower than shore0060).

[0026] This invention provides a novel liquid metal microcapsule thermally conductive material with the following advantages: 1. Interfacial polymerization method: Two monomers undergoing polymerization are dissolved in water and an organic solvent, respectively, with the core material dissolved in the dispersed phase solvent. An emulsifier is then added to both liquids to form an emulsion. The two reacting monomers migrate from the interior of the two phases to the droplet interface, where they react to generate a polymer that encapsulates the core material, forming microcapsules. This method allows reactants to enter the polymerization reaction zone more easily from the liquid phase than from the solid phase, making it particularly suitable for encapsulating liquids, and the resulting microcapsules exhibit good density.

[0027] 2. In-situ polymerization: This method is based on the premise that the polymer monomers forming the wall material are soluble while the polymer itself is insoluble. First, the polymer monomers are dissolved in an aqueous solution containing an emulsifier. Then, an insoluble core material is added. Vigorous stirring is used to disperse the monomers well in the solution, causing them to align oriented on the surface of the core material droplets. Heating is then applied to cross-link the monomers, thus forming microcapsules.

[0028] 3. Emulsion polymerization: An emulsion is formed by adding an emulsifier and stirring, and then the monomers are polymerized to form microcapsules by adding an initiator or other methods.

[0029] The synergy between high thermal conductivity and insulation: the liquid metal core provides a high thermal conductivity path, while the polymer shell ensures insulation, breaking through the performance bottlenecks of traditional materials. Microcapsule structure design: liquid metal (gallium-based alloy) is encapsulated in a polymer film (PDMS / silicone rubber), maintaining both high thermal conductivity and insulation. Composite dispersion process: ultrasonic dispersion technology is used to uniformly disperse microcapsules in a liquid organic matrix, forming a three-dimensional thermally conductive network. Multifunctional properties: the finished product has a thermal conductivity of 10-15 W / m·K, and simultaneously possesses insulation, heat resistance, high viscosity, and flexibility. Detailed Implementation

[0030] A novel liquid metal microcapsule thermal conductive material includes: a plurality of microcapsules dispersed in an organic matrix; each microcapsule includes a liquid metal core and a polymer shell encapsulating the core; the polymer shell is made of a flexible insulating polymer.

[0031] The liquid metal is gallium or a gallium-based alloy, and the gallium-based alloy contains indium and / or tin.

[0032] The polymer shell is made of at least one of polydimethylsiloxane, silicone rubber, polyurethane, and acrylic resin.

[0033] The microcapsules have a particle size of 10-200 μm, and the polymer shell has a wall thickness of 1-15 μm.

[0034] The organic matrix is ​​selected from at least one of liquid silicone oil, mineral oil, epoxy resin precursor, and organosilicon resin.

[0035] The microcapsules have a volume fraction of 50%-95% in the composite material.

[0036] This includes the following steps:

[0037] S1. Microcapsule preparation: Microcapsules encapsulating the liquid metal are formed by reacting flexible insulating polymer monomers on the surface of liquid metal droplets through interfacial polymerization, in-situ polymerization or emulsion polymerization.

[0038] S2. Dispersion and Composite: The microcapsules obtained in step S1 are mixed with an organic matrix and ultrasonically dispersed to form a uniformly dispersed composite system.

[0039] S3. Curing and molding: The composite system obtained in step S2 is subjected to thermo-curing or photo-curing to obtain a solid or gel-state thermally conductive composite material.

[0040] In step S1, the interfacial polymerization method specifically includes: dissolving two monomers capable of polymerization in an aqueous phase and an oil phase respectively, dispersing liquid metal in one of the phases, forming an emulsion in the presence of an emulsifier, and the two monomers undergoing a polymerization reaction at the droplet interface to form the polymer shell.

[0041] In step S2, the conditions for ultrasonic dispersion are: power 300-400W, time 15-30 minutes, and temperature controlled at 40±5℃.

[0042] In step S3, the thermocuring conditions are 2 hours at 80°C or 10 minutes at 110°C; the photocuring conditions are UV light irradiation with a wavelength of 365nm and an intensity of 50mW / cm².

[0043] Optionally, in S1: the membrane material is PDMS (polydimethylsiloxane) or silicone rubber, and the encapsulation method is interfacial polymerization or in-situ polymerization; the temperature is 25±2℃, the stirring speed is 300-500rpm, the time is 2-4 hours, the microcapsule particle size range is 10-200µm, the wall thickness is 1-5µm, and the encapsulation rate is >95%.

[0044] Optionally, the microcapsules are made by dissolving two monomers undergoing polymerization in water and an organic solvent, respectively, with the core material dissolved in the dispersed phase solvent. An emulsifier is then added to both liquids to form an emulsion. The two reactive monomers migrate from the interior of the two phases to the droplet interface, where they react to generate a polymer that encapsulates the core material, forming the microcapsules.

[0045] Optionally, in S2, the equipment is a 500W ultrasonic disperser (frequency 20kHz) 14, with a power of 300-400W, a time of 15-30 minutes, a temperature of 40+5°C, and a microcapsule content of 50%-95% (volume fraction); the dispersion effect is that the particle size distribution D90 < 250µm, with no agglomeration, and the system viscosity is 5000-15000cP.

[0046] Optionally, in S3: UV irradiation (wavelength 365nm, intensity 50mW / cm², thermal conductivity: 10-15W / m·K (ASTM D5470 standard), insulation resistance: >10¹²Ω, heat resistance: stable from -40℃ to 200℃, hardness lower than Shore00 60);

[0047] Example 1: A corrosion-resistant liquid metal microcapsule thermal conductive paste

[0048] S1 microcapsule preparation (interfacial polymerization method): Oil phase preparation: Weigh 10g of liquid metal alloy (composition is 68wt%Ga, 25wt%In, 7wt%Sn) and mix it evenly with 5g of toluene diisocyanate (TDI) monomer.

[0049] Aqueous phase preparation: Dissolve 1g of polyvinyl alcohol (PVA-1788, emulsifier) ​​in 100g of deionized water, and add 5g of ethylene glycol (chain extender).

[0050] Emulsification and Reaction: Under mechanical stirring at 25°C and 400 rpm, the oil phase was slowly added dropwise to the aqueous phase, and emulsification was continued for 30 minutes to form a stable emulsion. The reaction system was then heated to 60°C and stirred at this constant temperature for 4 hours. During this process, TDI in the oil phase and ethylene glycol in the aqueous phase underwent a polymerization reaction at the oil-water interface to form a polyurethane shell, which encapsulated the liquid metal droplets.

[0051] Post-processing: After the reaction was completed, the solid was collected by filtration, washed several times with deionized water and ethanol, and dried under vacuum at 40℃ for 12 hours to obtain gray powder microcapsules. Characterized by laser particle size analyzer and scanning electron microscope (SEM), the average particle size of the microcapsules was 55±15 μm, the wall thickness was about 3±1 μm, and the encapsulation efficiency was greater than 97%.

[0052] S2. Dispersion and Combination:

[0053] Weigh 60g of the above microcapsule powder (approximately 70% by volume) and mix it with 40g of dimethyl silicone oil (organic matrix) with a viscosity of 100 cSt.

[0054] The mixture was placed in an ultrasonic disperser and dispersed for 20 minutes at a power of 350W, a frequency of 20kHz, and a water bath temperature of 40℃ to obtain a uniform and fine gray paste-like composite material (uncured). The viscosity of the paste at 25℃ was approximately 9,500 cP.

[0055] S3. Performance Testing and Application:

[0056] The above paste is applied between two polished aluminum plates (6063 aluminum alloy) to form a thin layer.

[0057] Corrosion test: The assembly was placed in a 125°C forced-air drying oven for 100 hours. After cooling, the aluminum plate was separated. Optical microscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis showed that the contact surface of the aluminum plate remained bright as before, and no corrosion pits, discoloration, or signs of gallium diffusion were observed.

[0058] Basic performance: Thermal conductivity was tested according to ASTM D5470 standard and the result was 11.2 W / m·K; volume resistivity was tested according to GB / T1410 and the result was 3.5×10¹² Ω·cm.

[0059] This uncured paste can be used directly in heat dissipation applications that require subsequent maintenance or adjustment.

[0060] Example 2: A curable, pump-resistant liquid metal microcapsule thermally conductive material

[0061] S1. Microcapsule preparation:

[0062] Refer to Example 1, but change the polymer shell system to organosilicon. The oil phase uses hydrogen-containing silicone oil (0.8% hydrogen content), and the aqueous phase contains polyvinyl alcohol emulsifier and chloroplatinic acid catalyst (trace amount, pre-loaded on a carrier).

[0063] Liquid metal microcapsules encapsulated in a polysiloxane shell were formed through emulsion polymerization, with an average particle size of 45 μm.

[0064] S2. Dispersion and Combination:

[0065] Take 65g of microcapsules (approximately 68% by volume), mix them with 30g of vinyl silicone oil (matrix) and 5g of hydrogen-containing silicone oil (crosslinking agent, Si-H to Si-Vi molar ratio 1.2:1), and add platinum catalyst solution (50 ppm based on Pt).

[0066] After ultrasonic dispersion (under the same conditions as in Example 1), a gray, curable paste was obtained.

[0067] S3. Curing and Performance Testing:

[0068] The paste was applied to the test fixture and heat-cured at 110°C for 10 minutes to form an elastic solid.

[0069] Thermal conductivity and insulation: thermal conductivity 10.8 W / m·K, volume resistivity >1×10¹² Ω·cm.

[0070] Pumping resistance test: The cured sample was placed in a thermal cycling test chamber (-40℃ ~ 125℃, 30 minutes each, with a transition time of less than 1 minute) for 500 cycles. After the cycle, no material was observed to be extruded from the interface, and the change rate of thermal resistance was less than 3%.

[0071] Flexibility: The cured material has a Shore OO hardness of 50 and can be bent 180 degrees around a 3mm diameter axis without breaking.

[0072] Comparative Example 1: Corrosion Verification of Unencapsulated Liquid Metal

[0073] To highlight the necessity of the microencapsulation process in this invention, comparative experiments were conducted.

[0074] An unencapsulated liquid metal alloy (68Ga / 25In / 7Sn) with the same composition as in Example 1 was directly coated onto the same polished aluminum plate.

[0075] The sample was placed in a 125°C oven. After only 10 hours, noticeable darkening and wetting appeared on the aluminum plate surface. After 100 hours, the liquid metal had severely penetrated and corroded the aluminum plate, making the contact area brittle. SEM images showed significant intermetallic compounds and corrosion pits. This experiment demonstrates that liquid metal cannot be safely used in aluminum heat sinks without encapsulation.

Claims

1. A liquid metal microcapsule thermally conductive composite material, characterized in that, include: Multiple microcapsules dispersed in an organic matrix; each microcapsule comprises a liquid metal core and a polymer shell encapsulating the core; the polymer shell is made of a flexible insulating polymer.

2. The thermally conductive composite material according to claim 1, characterized in that, The liquid metal is gallium or a gallium-based alloy, and the gallium-based alloy contains indium and / or tin.

3. The thermally conductive composite material according to claim 1, characterized in that, The polymer shell is made of at least one of polydimethylsiloxane, silicone rubber, polyurethane, and acrylic resin.

4. The thermally conductive composite material according to claim 1, characterized in that, The microcapsules have a particle size of 10-200 μm, and the polymer shell has a wall thickness of 1-15 μm.

5. The thermally conductive composite material according to claim 1, characterized in that, The organic matrix is ​​selected from at least one of liquid silicone oil, mineral oil, epoxy resin precursor, and organosilicon resin.

6. The thermally conductive composite material according to any one of claims 1-5, characterized in that, The microcapsules have a volume fraction of 50%-95% in the composite material.

7. A method for preparing the liquid metal microcapsule thermally conductive composite material as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Microcapsule preparation: Microcapsules encapsulating the liquid metal are formed by reacting flexible insulating polymer monomers on the surface of liquid metal droplets through interfacial polymerization, in-situ polymerization or emulsion polymerization. S2. Dispersion and Composite: The microcapsules obtained in step S1 are mixed with an organic matrix and ultrasonically dispersed to form a uniformly dispersed composite system. S3. Curing and molding: The composite system obtained in step S2 is subjected to thermo-curing or photo-curing to obtain a solid or gel-state thermally conductive composite material.

8. The method according to claim 7, characterized in that, In step S1, the interfacial polymerization method specifically includes: dissolving two monomers capable of polymerization in an aqueous phase and an oil phase respectively, dispersing liquid metal in one of the phases, forming an emulsion in the presence of an emulsifier, and the two monomers undergoing a polymerization reaction at the droplet interface to form the polymer shell.

9. The method according to claim 7, characterized in that, In step S2, the conditions for ultrasonic dispersion are: power 300-400W, time 15-30 minutes, and temperature controlled at 40±5℃.

10. The method according to claim 7, characterized in that, In step S3, the thermocuring conditions are 2 hours at 80°C or 10 minutes at 110°C; the photocuring conditions are UV light irradiation with a wavelength of 365nm and an intensity of 50mW / cm².