A flexible composite phase change material based on in-situ encapsulation using a water-in-oil Pickering emulsion method and its preparation method.

Abstract

This invention discloses a flexible composite phase change material based on in-situ encapsulation using a water-in-oil Pickering emulsion method and its preparation method. The method is characterized by using a flexible rubber matrix dissolved in cyclohexane as the oil phase solution, and the phase change material, graphene oxide (GO), and cellulose nanocrystals (CNC) as the aqueous phase solution. Under high-speed shearing, the synergistic amphiphilicity of GO and CNC spontaneously enriches at the oil-water interface to form a dense particle film, resulting in a uniformly sized and long-term stable water-in-oil (W / O) type Pickering emulsion. The emulsion is further poured into a mold for pre-freezing and shaping, and then vacuum freeze-drying is performed to simultaneously remove the aqueous and oil phase solvents. No subsequent compounding or vulcanization steps are required, directly obtaining an integrally formed flexible composite phase change material.

Description

Technical Field

[0001] This invention relates to the field of polymer phase change energy storage materials, and in particular to a flexible composite phase change material based on in-situ encapsulation using a water-in-oil Pickering emulsion method and its preparation method. Background Technology

[0002] Phase change materials (PCMs) can absorb or release a large amount of latent heat during phase transitions while maintaining a relatively stable temperature, thus showing broad application prospects in thermal energy storage and temperature control. Organic PCMs such as paraffin wax and polyethylene glycol have been extensively studied due to their high phase transition enthalpy and stable performance. However, these materials generally suffer from low thermal conductivity and are prone to leakage during solid-liquid phase transitions, severely limiting their practical applications.

[0003] To address leakage issues, microencapsulation technology has become the most widely used strategy. This technology effectively restricts the flow of liquids during phase change by encapsulating phase change materials within a polymer or inorganic shell to form a core-shell structure. However, existing microencapsulation technologies still have significant drawbacks: dense shells further reduce the thermal conductivity of the material, leading to a slow thermal response; the preparation process requires the addition of large amounts of small-molecule surfactants, whose residues reduce the material's flexibility and thermal stability, and also raise environmental concerns.

[0004] To overcome the shortcomings of traditional microcapsules, the Pickering emulsion template method has become a research hotspot. This method uses solid particles instead of surfactants, avoiding surfactant residue problems and simultaneously improving material properties by utilizing the thermal conductivity of solid particles. However, phase change microcapsules prepared by existing methods are mostly in powder form, with low mechanical strength, making them unsuitable for direct molding and use. They require composite processing with matrices such as coatings, plastics, and rubber, which significantly increases process complexity and production costs, and is also prone to deterioration of overall material performance due to poor interfacial compatibility.

[0005] Chinese patent CN114808192A discloses an emulsion-based thermal storage fiber and its preparation method. It uses sodium alginate and water-soluble polymers such as polyvinyl alcohol as the aqueous phase and a phase change material as the oil phase. After preparing an oil-in-water emulsion, it undergoes wet spinning and freeze-drying to obtain the thermal storage fiber. Chinese patent CN109576823A discloses a phase change energy storage material with a core-sheath fiber structure and its preparation method. It dissolves polyacrylonitrile in an organic solvent as the oil phase and dissolves a water-soluble phase change material in water as the aqueous phase. After preparing a water-in-oil emulsion, it undergoes electrospinning and freeze-drying to obtain a hollow fiber material. While these materials successfully encapsulate phase change materials, their preparation processes are too complex for large-scale application. Chinese patent CN119286477A discloses a method for preparing phase change energy storage microcapsules and multifunctional composite phase change materials. The method involves preparing a Pickering emulsion using cellulose nanocrystals as a stabilizer, then double-coating the phase change core material with melamine resin and polypyrrole to obtain microcapsules. Finally, these microcapsules are composited with polypyrrole-modified bacterial cellulose and thermoplastic polyurethane to obtain the target material. However, these microcapsules are in powder form and must be compounded with an additional matrix to be molded and used. Furthermore, the preparation process is cumbersome and costly. Therefore, researching and preparing directly applicable flexible shape-stabilized phase change materials using easily scalable, low-cost, and efficient methods remains challenging. Summary of the Invention

[0006] The purpose of this invention is to provide a flexible composite phase change material based on in-situ encapsulation using a water-in-oil Pickering emulsion method and its preparation method, addressing the shortcomings of existing technologies. Its key feature is the use of the synergistic amphiphilic properties of graphene oxide (GO) and cellulose nanocrystals (CNC) to construct a stable water-in-oil (W / O) type Pickering emulsion system. A flexible rubber matrix dissolved in cyclohexane serves as the continuous oil phase, while a GO / CNC aqueous dispersion containing the phase change material serves as the dispersed aqueous phase. GO and CNC spontaneously accumulate at the oil-water interface to form a dense particulate film, which, after freeze-drying, forms a continuous thermally conductive network in situ, simultaneously improving the material's thermal conductivity and photothermal conversion efficiency. Vacuum freeze-drying simultaneously achieves in-situ encapsulation of the phase change material and integrated molding of the material. The three-dimensional elastic support framework formed by the self-assembly of flexible rubber molecular chains tightly encapsulates the phase change material microspheres. The resulting flexible composite phase change material can be used directly without additional composite with a flexible matrix. This fundamentally avoids the problems of complex processes, poor interfacial compatibility, and performance degradation caused by powdered microcapsule composite processing. At the same time, it significantly improves the material's mechanical strength, shape stability, photothermal conversion ability, and thermal conductivity. The preparation process is simple, low-cost, and easy to scale up.

[0007] The objective of this invention is achieved by the following technical solution, wherein the raw material fractions, unless otherwise specified, are all parts by mass.

[0008] A flexible composite phase change material based on in-situ encapsulation using a water-in-oil Pickering emulsion and its preparation method, characterized in that it is obtained by freeze-drying a water-in-oil Pickering emulsion in a single process, with the raw materials comprising the following parts by mass: 100-200 parts of phase change material 100 parts of rubber matrix Graphene oxide (GO) 10-20 parts Cellulose nanocrystals (CNC) 10-20 parts The phase change material is any one of polyethylene glycol, erythritol, xylitol, and sorbitol. The flexible rubber matrix is ​​any one of EPDM rubber, butadiene rubber, and styrene-butadiene rubber. The flexible composite phase change material and its preparation method include the following steps: S1: Preparation of rubber oil phase solution 100 parts of rubber matrix were added to 200 parts of cyclohexane and stirred at 40°C for 12 hours until completely dissolved to obtain a rubber oil phase solution.

[0009] S2: Preparation of aqueous solutions of phase change materials Add 100-200 parts of phase change material to deionized water and stir until completely dissolved. Then add 10-20 parts of GO to the solution and sonicate by CNC for 30 minutes to disperse it evenly. Stir until completely dissolved to obtain an aqueous solution.

[0010] S3: Preparation of Flexible Phase Change Composite Materials The aqueous phase solution is slowly added dropwise to the oil phase solution, and the mixture is sheared at high speed at 8000-15000 rpm for 5-15 min to obtain a uniform water-in-oil (W / O) emulsion. The water-in-oil emulsion is then poured into a mold and pre-frozen at -40℃ to -60℃ for 2-4 h, followed by vacuum freeze-drying for 24-48 h to obtain the flexible phase change composite material.

[0011] The present invention has the following advantages: Traditional phase change microcapsules require the addition of small molecule surfactants to stabilize the system, and their residues can reduce the thermal stability and environmental friendliness of the material. While existing phase change microcapsules prepared by the Pickering emulsion method avoid the surfactant problem, the resulting products are all in powder form with low mechanical strength. They must be compounded with an additional matrix to be molded and used, which not only increases the complexity of the process and production costs, but also easily leads to a decline in the overall performance of the material due to poor interfacial compatibility. This invention utilizes the synergistic amphiphilic properties of graphene oxide and cellulose nanocrystals to construct a stable water-in-oil Pickering emulsion system, thus avoiding the negative impact of surfactant residue at the source. Through vacuum freeze-drying, in-situ encapsulation and integrated molding of the phase change material are simultaneously achieved. Flexible rubber molecular chains self-assemble to form a continuous three-dimensional elastic support framework, tightly encapsulating the phase change material microspheres in situ, fundamentally solving the liquid leakage problem during the solid-liquid phase change process, while significantly improving the material's mechanical strength and shape stability. Graphene oxide and cellulose nanocrystals enriched at the oil-water interface form a continuous thermally enhanced network in situ after freeze-drying, enhancing the material's photothermal conversion capability and thermal conductivity. The entire preparation process requires no additional microcapsule preparation, matrix composite, or vulcanization steps, making it simple, low-cost, environmentally friendly, and easy to scale up, offering significant application advantages. Attached Figure Description

[0012] Figure 1 A polarized light microscope image of a water-in-oil Pickering emulsion. Figure 2 Scanning electron microscope (SEM) images of the structural morphology of flexible composite phase change materials. Detailed Implementation

[0013] The present invention will be further described below through specific embodiments. It should be noted that the embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make non-essential improvements and adjustments to the present invention based on the above content. Example 1

[0014] 100 parts of ethylene propylene diene monomer (EPDM) rubber were added to 200 parts of cyclohexane and stirred at 40°C for 12 hours until completely dissolved, yielding a transparent and homogeneous EPDM oil phase solution. 150 parts of polyethylene glycol (PEG) were added to 150 parts of deionized water and stirred until completely dissolved. Then, 15 parts of graphene oxide (GO) and 15 parts of cellulose nanocrystals (CNC) were added to the solution and sonicated for 30 minutes to disperse them evenly, yielding an aqueous phase solution.

[0015] The aqueous solution was slowly added dropwise to the oil solution, and the mixture was sheared at 12,000 rpm for 10 minutes to obtain a uniform and stable water-in-oil (W / O) emulsion. The emulsion was then poured into a square polytetrafluoroethylene mold, pre-frozen at -50°C for 3 hours, and then freeze-dried under vacuum at 1 Pa and a cold trap temperature of -60°C for 36 hours to obtain the flexible composite phase change material.

[0016] Tests showed that the composite phase change material had a phase change temperature of 58.3℃, a phase change melting enthalpy of 143.2 J / g, a thermal conductivity of 0.82 W / (m·K), an elongation at break of 205%, and no leakage when heated at 80℃ for 2 hours. Example 2

[0017] 100 parts of styrene-butadiene rubber (SBR) were added to 200 parts of cyclohexane and stirred at 40°C for 12 hours until completely dissolved, yielding a transparent and homogeneous SBR oil phase solution. 120 parts of polyethylene glycol (PEG) were added to 120 parts of deionized water and stirred until completely dissolved. Then, 12 parts of graphene oxide (GO) and 12 parts of cellulose nanocrystals (CNC) were added to the solution and sonicated for 30 minutes to disperse them evenly, yielding an aqueous phase solution.

[0018] The aqueous solution was slowly added dropwise to the oil solution, and the mixture was sheared at 10,000 rpm for 12 minutes to obtain a uniform and stable water-in-oil (W / O) emulsion. The emulsion was then poured into a square polytetrafluoroethylene mold, pre-frozen at -45°C for 3.5 hours, and then freeze-dried under vacuum at 1 Pa and a cold trap temperature of -55°C for 42 hours to obtain the flexible composite phase change material.

[0019] Tests showed that the composite phase change material had a phase change temperature of 52.6℃, a melting enthalpy of 152.4 J / g, a thermal conductivity of 0.75 W / (m·K), an elongation at break of 186%, and no leakage when heated at 80℃ for 2 hours. Example 3

[0020] 100 parts of butadiene rubber (BR) were added to 200 parts of cyclohexane and stirred at 40°C for 12 hours until completely dissolved, yielding a transparent and homogeneous BR oil phase solution. 180 parts of polyethylene glycol (PEG) were added to 180 parts of deionized water and stirred until completely dissolved. Then, 18 parts of graphene oxide (GO) and 18 parts of cellulose nanocrystals (CNC) were added to the solution and sonicated for 30 minutes to disperse them evenly, yielding an aqueous phase solution.

[0021] The aqueous solution was slowly added dropwise to the oil solution, and the mixture was sheared at 14,000 rpm for 8 minutes to obtain a uniform and stable water-in-oil (W / O) emulsion. The emulsion was then poured into a square polytetrafluoroethylene mold, pre-frozen at -55°C for 2.5 hours, and then freeze-dried under vacuum at 1 Pa and a cold trap temperature of -65°C for 30 hours to obtain the flexible composite phase change material.

[0022] Tests showed that the composite phase change material had a phase change temperature of 63.5℃, a melting enthalpy of 131.7 J / g, a thermal conductivity of 0.91 W / (m·K), an elongation at break of 228%, and no leakage when heated at 80℃ for 2 hours. Example 4

[0023] 100 parts of ethylene propylene diene monomer (EPDM) rubber were added to 200 parts of cyclohexane and stirred at 40°C for 12 hours until completely dissolved, yielding a transparent and homogeneous EPDM oil phase solution. 50 parts of erythritol (ERY) were added to 100 parts of deionized water and stirred until completely dissolved. Then, 10 parts of graphene oxide (GO) and 10 parts of cellulose nanocrystals (CNC) were added to the solution, and the mixture was sonicated for 30 minutes to disperse it uniformly, yielding an aqueous phase solution.

[0024] The aqueous solution was slowly added dropwise to the oil solution, and the mixture was sheared at 11,000 rpm for 10 minutes to obtain a uniform and stable water-in-oil (W / O) emulsion. The emulsion was then poured into a square polytetrafluoroethylene mold, pre-frozen at -50°C for 3 hours, and then freeze-dried under vacuum at 1 Pa and a cold trap temperature of -60°C for 36 hours to obtain the flexible composite phase change material.

[0025] Tests showed that the composite phase change material had a phase change temperature of 122.9℃, a melting enthalpy of 211.5 J / g, a thermal conductivity of 0.72 W / (m·K), an elongation at break of 213%, and no leakage when heated at 130℃ for 2 hours. Example 5

[0026] 100 parts of ethylene propylene diene monomer (EPDM) rubber were added to 200 parts of cyclohexane and stirred at 40°C for 12 hours until completely dissolved, yielding a transparent and homogeneous EPDM oil phase solution. 50 parts of sorbitol (SOR) were added to 100 parts of deionized water and stirred until completely dissolved. Then, 10 parts of graphene oxide (GO) and 10 parts of cellulose nanocrystals (CNC) were added to the solution, and the mixture was sonicated for 30 minutes to disperse it uniformly, yielding an aqueous phase solution.

[0027] The aqueous solution was slowly added dropwise to the oil solution, and the mixture was sheared at 11,000 rpm for 10 minutes to obtain a uniform and stable water-in-oil (W / O) emulsion. The emulsion was then poured into a square polytetrafluoroethylene mold, pre-frozen at -50°C for 3 hours, and then freeze-dried under vacuum at 1 Pa and a cold trap temperature of -60°C for 36 hours to obtain the flexible composite phase change material.

[0028] The composite phase change material was tested and found to have a phase change temperature of 96.2℃, a melting enthalpy of 211.5 J / g, a thermal conductivity of 0.72 W / (m·K), an elongation at break of 213%, and no leakage after heating at 100℃ for 2 hours. Example 6

[0029] 100 parts of ethylene propylene diene monomer (EPDM) rubber were added to 200 parts of cyclohexane and stirred at 40°C for 12 hours until completely dissolved, yielding a transparent and homogeneous EPDM oil phase solution. 200 parts of polyethylene glycol (PEG6000) were added to 200 parts of deionized water and stirred until completely dissolved. Then, 20 parts of graphene oxide (GO) and 20 parts of cellulose nanocrystals (CNC) were added to the solution, and the mixture was sonicated for 30 minutes to disperse it uniformly, yielding an aqueous phase solution.

[0030] The aqueous solution was slowly added dropwise to the oil solution, and the mixture was sheared at 13,000 rpm for 9 minutes to obtain a uniform and stable water-in-oil (W / O) emulsion. The emulsion was then poured into a square polytetrafluoroethylene mold, pre-frozen at -50°C for 3 hours, and then freeze-dried under vacuum at 1 Pa and a cold trap temperature of -60°C for 36 hours to obtain the flexible composite phase change material.

[0031] Tests showed that the composite phase change material had a phase change temperature of 58.7℃, a melting enthalpy of 159.3 J / g, a thermal conductivity of 0.96 W / (m·K), an elongation at break of 194%, and no leakage when heated at 80℃ for 2 hours.

[0032] In summary, the embodiments of the present invention employ graphene oxide and cellulose nanocrystals to synergistically stabilize Pickering emulsion, which significantly improves the encapsulation effect, mechanical properties, and thermal properties of composite phase change materials, while taking into account excellent flexibility, shape stability, and efficient photothermal and thermal conductivity.

[0033] Using a flexible rubber matrix dissolved in cyclohexane as the oil phase solution, and phase change material, graphene oxide (GO), and cellulose nanocrystals (CNC) as the aqueous phase solution, under high-speed shearing, the synergistic amphiphilicity of GO and CNC spontaneously enriches at the oil-water interface to form a dense particle film, resulting in a water-in-oil (W / O) type Pickering emulsion with uniform particle size and long-term stability. The emulsion is then poured into a mold for pre-freezing and shaping, and vacuum freeze-drying is performed to simultaneously remove the aqueous and oil phase solvents. No subsequent compounding or vulcanization steps are required to directly obtain an integrated flexible composite phase change material. During freeze-drying, rubber molecular chains entangle with each other as the solvent evaporates, forming a continuous three-dimensional elastic support framework that tightly encapsulates the phase change material microspheres in situ. GO and CNC, originally concentrated at the oil-water interface, then construct a continuous thermally enhanced network on the microsphere surface, forming a double interpenetrating structure of elastic support, phase change energy storage, and thermally enhanced properties. This fundamentally solves the liquid leakage problem during the solid-liquid phase change process, simultaneously endowing the material with excellent mechanical strength, shape stability, photothermal conversion capability, and thermal conductivity. It avoids the problems of complex processes, poor interfacial compatibility, and performance degradation associated with powdered microcapsule composite processing. This invention's method is simple, low-cost, environmentally friendly, and easy to scale up for production, making it widely applicable in fields such as thermal management of electronic devices, building energy conservation, and photothermal energy storage.

[0034] The above embodiments have described the specific content of the present invention in detail, but the present invention is not limited to the embodiments described. Those skilled in the art can make equivalent substitutions, all of which should be covered within the protection scope of the present invention.

Claims

1. A flexible composite phase change material based on in-situ encapsulation using a water-in-oil Pickering emulsion method, characterized in that... It is obtained by freeze-drying and integral molding of water-in-oil Pickering emulsion. The raw materials are as follows by mass: 100-200 parts of phase change material 100 parts of rubber matrix Graphene oxide (GO) 10-20 parts Cellulose nanocrystals (CNC) 10-20 parts The phase change material is any one of polyethylene glycol, erythritol, xylitol, and sorbitol. The flexible rubber matrix is ​​any one of EPDM rubber, butadiene rubber, and styrene-butadiene rubber.

2. A method for preparing the flexible composite phase change material based on the water-in-oil Pickering emulsion method for in-situ encapsulation as described in claim 1, characterized in that: The preparation method includes the following steps: S1: Preparation of rubber oil phase solution 100 parts of rubber matrix were added to 200 parts of cyclohexane, sealed, and stirred at 40°C for 12 hours until completely dissolved to obtain a rubber oil phase solution. S2: Preparation of aqueous solutions of phase change materials Add 100-200 parts of phase change material to deionized water and stir until completely dissolved. Then add 10-20 parts of GO to the solution and sonicate by CNC for 30 minutes to disperse it evenly. Stir until completely dissolved to obtain an aqueous solution. S3: Preparation of Flexible Phase Change Composite Materials The aqueous phase solution is slowly added dropwise to the oil phase solution, and the mixture is sheared at high speed at 8000-15000 rpm for 5-15 min to obtain a uniform water-in-oil (W / O) emulsion. The water-in-oil emulsion is then poured into a mold and pre-frozen at -40℃ to -60℃ for 2-4 h, followed by vacuum freeze-drying for 24-48 h to obtain the flexible phase change composite material.

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