A millimeter-scale flexible phase change microsphere and its preparation method

Abstract

This invention relates to the field of phase change materials technology, and provides a millimeter-scale flexible phase change microsphere and its preparation method. The phase change microsphere has a particle size range of 1mm-5mm and is flexible. The preparation method includes dissolving an emulsifier in water to prepare an aqueous phase; forming an emulsion by emulsifying a phase change material, an acrylate monomer, and an acrylate crosslinking agent; adding an aqueous phase initiator and an oil phase initiator to the emulsion; after the reaction, filtering the product using a filter screen, collecting the filter residue, and vacuum drying it; the resulting millimeter-scale microspheres combine large particle size and flexibility, and can be integrated into smart textiles and building thermal management systems. Their large size reduces packaging complexity, reduces interfacial thermal resistance, and improves energy regulation efficiency.

Description

Technical Field

[0001] This invention relates to the field of phase change materials, and more specifically, to a millimeter-scale flexible phase change microsphere and its preparation method. Background Technology

[0002] Phase change materials (PCMs) store and release energy and maintain temperature stability through their inherent properties during phase transitions, thereby achieving energy conservation and temperature control. By encapsulating PCMs using microsphere technology, volume expansion during phase transition can be effectively suppressed, and direct contact between the PCM and the external environment can be prevented, thus preserving its original physical properties and significantly improving its stability and durability. Therefore, microsphere-encapsulated PCMs exhibit higher stability and a wider range of applications compared to pure PCMs, and can be widely used in fields such as solar energy utilization, energy-saving building materials, functional textiles, and power generation.

[0003] Currently, methods for preparing phase change microspheres include interfacial polymerization, emulsion polymerization, and suspension polymerization. However, due to limitations of existing technologies, most prepared phase change microspheres are concentrated at the micrometer level with a wide particle size distribution, and the preparation process is complex, making it difficult to meet the needs of large-scale industrial production. These factors severely restrict the preparation efficiency of high-quality, highly uniform microspheres and further limit the promotion and use of phase change microspheres in practical applications.

[0004] For phase change microspheres, the smaller the size, the higher the mass ratio of the shell material within the microsphere. Increasing the size to the millimeter level is a feasible strategy to effectively improve the energy storage density of phase change microspheres. More importantly, millimeter-sized phase change microspheres have significant application value in specific fields. For example, they can be used in thermal management clothing (such as medical protective clothing or extreme environment clothing) and building thermal management (such as thermal control systems embedded under floors or in walls), thereby achieving efficient energy storage and release and meeting temperature control needs in different scenarios.

[0005] In existing technologies, the coagulation bath method is the main method for preparing millimeter-scale microspheres. However, this method has the following limitations: the resulting microspheres have low mechanical strength, making it difficult to meet the application requirements under complex working conditions; the range of shell materials is limited, failing to fully utilize the diversity of material properties; and the preparation efficiency is low, making it difficult to achieve large-scale production. Furthermore, most microspheres in existing technologies adopt a core-shell structure design, which limits the flexibility of the microspheres, making them significantly insufficient for flexible applications. Therefore, there is an urgent need for a method for preparing millimeter-scale phase change microspheres that is simple to manufacture, has a wide range of shell material options, significantly improves preparation efficiency, and produces microspheres with flexible properties. Summary of the Invention

[0006] The purpose of this invention is to provide a millimeter-scale flexible phase change microsphere and its preparation method. This method utilizes macromolecular self-assembly technology to gradually reorganize small microspheres into millimeter-scale microspheres. Simultaneously, by combining the synergistic effect of interfacial polymerization and in-situ polymerization, the macromolecular chains formed by the polymerization of acrylate monomers disrupt the continuity of the phase change material's crystallization, thereby achieving the preparation of millimeter-scale flexible phase change microspheres. These microspheres possess large particle size and flexibility, and the preparation process is simple, rapid, low-cost, and highly safe.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for preparing millimeter-scale flexible phase change microspheres includes the following steps:

[0009] S1. Dissolve the emulsifier in water to prepare an aqueous phase, wherein the emulsifier is selected from one or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyoxyethylene fatty alcohol ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene castor oil, lecithin, sodium lauryl sulfate, and sodium dodecylbenzene sulfonate, and the mass fraction of the emulsifier is 1% to 10% of water;

[0010] S2. A phase change material, acrylate monomer and acrylate crosslinking agent are emulsified to form an emulsion, wherein the mass ratio of phase change material to water is 20-80:100, the mass ratio of acrylate monomer to phase change material is 1:1 to 1:5, and the mass ratio of acrylate crosslinking agent to acrylate monomer is 1:1 to 1:40.

[0011] S3. Add aqueous phase initiator and oil phase initiator to the emulsion, and carry out polymerization reaction at 70℃-100℃ for 2h-4h;

[0012] S4. After the reaction is complete, filter the product using a 400-mesh filter, collect the filter residue and dry it under vacuum at 80°C.

[0013] In a preferred embodiment of the present invention, the emulsifier in step 1 is 6-10 parts of polyvinyl alcohol 1788 dispersed in 180-250 parts of water to form an aqueous phase.

[0014] As a preferred embodiment of the present invention, the phase change material in step 2 is one or more of the following: straight-chain alkanes with 12-28 C atoms, fatty acids, fatty alcohols, and polyethylene glycol with a molecular weight of 900-2000.

[0015] In a preferred embodiment of the present invention, the acrylate monomer in step 2 is one or more of the following: methoxyethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, tetrahydrofuran acrylate, methoxyethyl acrylate, dodecyl acrylate, octadecyl acrylate, and docosyl polyoxyethylene methacrylate.

[0016] In a preferred embodiment of the present invention, the acrylate crosslinking agent in step 2 is one or more of ethylene glycol dimethacrylate, trimethylolpropane triacrylate, epoxy acrylate, polyurethane acrylate, triallyl isocyanate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

[0017] In a preferred embodiment of the present invention, the mass ratio of the aqueous initiator to the acrylic monomer in step 3 is 1:8 to 1:100, and the aqueous initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobiscyanopentanoic acid, and azobisisopropylimidazoline.

[0018] In a preferred embodiment of the present invention, the mass ratio of the oil phase initiator to the aqueous phase in step 3 is 1:1 to 1:5; the oil phase initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecyl peroxide, ditert-butyl peroxide, diisopropyl peroxide, dicyclohexyl peroxide, and dicumyl peroxide.

[0019] In a preferred embodiment of the present invention, the polymerization reaction temperature in step 3 is 80℃-90℃ and the time is 3h.

[0020] In a preferred embodiment of the present invention, the phase change material is 65 parts of 18 linear alkanes, the acrylate monomer is 10 parts of tetrahydrofuran acrylate, 30 parts of dodecyl acrylate, and 1.2 parts of docosyl polyoxyethylene methacrylate, and the acrylate crosslinking agent is 0.4-2 parts of dipentaerythritol hexaacrylate. The above materials and 5-20 parts of thickener are added to the aqueous phase and emulsified at 2000 rpm for 15 minutes to obtain a uniform emulsion.

[0021] The present invention also provides a millimeter-scale flexible phase change microsphere, prepared according to the above-described preparation method, wherein the microsphere has a particle size range of 1 mm to 5 mm and is flexible.

[0022] The beneficial effects of this invention are:

[0023] This invention utilizes the synergistic effect of acrylate monomer polymerization and crosslinking agents to form a flexible macromolecular chain network, thereby disrupting the crystallization continuity of phase change materials and enabling microspheres to possess elastic deformation capabilities. Compared to the rigid shell of traditional core-shell structures, the microspheres prepared by this method can withstand repeated bending without breaking.

[0024] This invention, through a combination design based on emulsifiers and acrylate monomers, can be adapted to a variety of phase change materials; for example, long-chain acrylate monomers are compatible with non-polar alkanes, and monomers containing ether bonds form a stable interface with polyethylene glycol, breaking through the limitations of traditional coagulation bath methods on shell material selection.

[0025] This invention achieves precise control of millimeter-scale microsphere size by adjusting the concentration of the aqueous emulsifier, the ratio of phase change material to monomer, and the reaction stirring intensity. Compared with the widely distributed micron-scale microspheres in existing technologies, this method significantly improves particle size uniformity, meeting the size requirements of different application scenarios.

[0026] This invention employs a dual initiator system (water / oil phase) (such as ammonium persulfate + azobisisobutyronitrile) to synergistically trigger polymerization at 70-100℃, shortening the reaction time to 2-4 hours and significantly improving monomer conversion efficiency. Combined with continuous filtration and vacuum drying processes, the production process is simplified, solving the problems of low efficiency and difficulty in scaling up traditional coagulation bath methods.

[0027] In summary, the millimeter-scale design increases energy storage density, and its flexibility allows it to be integrated into textiles such as protective clothing or embedded in building walls. Compared to traditional micron-scale microspheres, the millimeter-scale structure is easier to position and encapsulate in thermal management systems, and reduces material interface thermal resistance, thereby improving energy regulation efficiency. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the particle size distribution prepared according to the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0031] This invention provides:

[0032] A method for preparing millimeter-scale flexible phase change microspheres includes the following steps:

[0033] S1. Dissolve the emulsifier in water to prepare an aqueous phase, wherein the emulsifier is selected from one or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyoxyethylene fatty alcohol ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene castor oil, lecithin, sodium lauryl sulfate, and sodium dodecylbenzene sulfonate, and the mass fraction of the emulsifier is 1% to 10% of water;

[0034] S2. A phase change material, acrylate monomer and acrylate crosslinking agent are emulsified to form an emulsion, wherein the mass ratio of phase change material to water is 20-80:100, the mass ratio of acrylate monomer to phase change material is 1:1 to 1:5, and the mass ratio of acrylate crosslinking agent to acrylate monomer is 1:1 to 1:40.

[0035] S3. Add aqueous phase initiator and oil phase initiator to the emulsion, and carry out polymerization reaction at 70℃-100℃ for 2h-4h;

[0036] S4. After the reaction is complete, filter the product using a 400-mesh filter, collect the filter residue and dry it under vacuum at 80°C.

[0037] The present invention also provides a millimeter-scale flexible phase change microsphere, prepared according to the above-described preparation method, wherein the microsphere has a particle size range of 1 mm to 5 mm and is flexible. Example 1

[0038] (1) Preparation of the aqueous phase of the emulsion: 6 parts of polyvinyl alcohol 1788 were dispersed into 194 parts of water to form a homogeneous aqueous phase;

[0039] (2) Preparation of emulsion: 65 parts of octadecane, 10 parts of tetrahydrofuran acrylate, 30 parts of dodecyl acrylate, 0.4 parts of dipentaerythritol hexaacrylate, 5 parts of thickener and 1.2 parts of docosyl polyoxyethylene methacrylate were added to the aqueous phase and emulsified at 2000 rpm for 15 minutes to obtain a uniform emulsion.

[0040] (3) Emulsion reaction: Add 5 parts of ammonium persulfate and 5 parts of azobisisobutyronitrile to the obtained emulsion and stir thoroughly until uniform, so that the emulsion reacts at 80°C for 3 hours.

[0041] (4) Filtration and drying: After the reaction is completed, the product is filtered through a 400-mesh filter, the filter residue is collected and dried under vacuum at 80°C, and finally millimeter-sized flexible phase change microspheres are obtained. Example 2

[0042] Unlike Example 1, the amount of thickener was 10 parts, and millimeter-sized flexible phase change microspheres were prepared using the same steps as in Example 1. Example 3

[0043] Unlike Example 2, the amount of thickener was 20 parts, and millimeter-sized flexible phase change microspheres were prepared using the same steps. Example 4

[0044] Unlike Example 2, two parts of dipentaerythritol hexaacrylate were used, and millimeter-sized flexible phase change microspheres were prepared using the same steps. Example 5

[0045] Unlike Example 4, the emulsion was reacted at 90°C for 3 hours, and millimeter-sized flexible phase change microspheres were prepared using the same steps. Example 6

[0046] Unlike Example 5, the water content in the aqueous phase of the emulsion was 250 parts, and millimeter-sized flexible phase change microspheres were prepared using the same steps. Example 7

[0047] Unlike Example 6, the content of polyvinyl alcohol 1788 in the aqueous phase of the emulsion was 10 parts and the water content was 190 parts. Millimeter-sized flexible phase change microspheres were prepared using the same steps. Example 8

[0048] Unlike Example 5, 1.5 parts of dipentaerythritol hexaacrylate were used, and millimeter-sized flexible phase change microspheres were prepared using the same steps.

[0049] Comparative Example 1

[0050] Unlike Example 4, the content of polyvinyl alcohol 1788 in the aqueous phase of the emulsion was 20 parts and the water content was 180 parts. Millimeter-sized flexible phase change microspheres were prepared using the same steps.

[0051] Comparative Example 2

[0052] Unlike Example 8, the amount of tetrahydrofuran acrylate was 20 parts, and millimeter-sized flexible phase change microspheres were prepared using the same steps.

[0053] Comparative Example 3

[0054] Unlike Example 2, the aqueous phase of the emulsion contained 30 parts of polyvinyl alcohol 1788 and 170 parts of water. The emulsion was reacted at 90°C, and millimeter-sized flexible phase change microspheres were prepared using the same steps.

[0055] Comparative Example 4

[0056] Unlike Comparative Example 3, the aqueous phase of the emulsion contained 194 parts of water and 0 parts of thickener, and millimeter-sized flexible phase change microspheres were prepared using the same steps.

[0057] Comparative Example 5

[0058] Unlike implementation 5, 20 parts of dipentaerythritol hexaacrylate were used to prepare millimeter-sized flexible phase change microspheres using the same steps.

[0059] Comparative Example 6

[0060] Unlike Example 2, the aqueous phase of the emulsion contained 2 parts of polyvinyl alcohol 1788 and 198 parts of water, and millimeter-sized flexible phase change microspheres were prepared using the same steps.

[0061] The microspheres prepared in the above embodiments and comparative examples were tested for size using an optical microscope. The specific test data are shown in the table below:

[0062] Case Sample status size flexibility Example 1 Particles can be obtained 1 to 1.5 mm It still has flexibility below the 18-ane phase transition temperature Example 2 Particles can be obtained 1 to 1.5 mm It still has flexibility below the 18-ane phase transition temperature Example 3 Particles can be obtained 1 to 1.5 mm It still has flexibility below the 18-ane phase transition temperature Example 4 Particles can be obtained 1.5 to 2 mm It still has flexibility below the 18-ane phase transition temperature Example 5 Particles can be obtained 1.5 to 2 mm It still has flexibility below the 18-ane phase transition temperature Example 6 Particles can be obtained 1 to 1.5 mm It still has flexibility below the 18-ane phase transition temperature Example 7 Particles can be obtained 1 to 1.5 mm It still has flexibility below the 18-ane phase transition temperature Example 8 Particles can be obtained 1 to 1.5 mm It still has flexibility below the 18-ane phase transition temperature Comparative Example 1 Particles can be obtained 0.5 to 1 mm It still has flexibility below the 18-ane phase transition temperature Comparative Example 2 Particles can be obtained 0.5 to 1 mm It still has flexibility below the 18-ane phase transition temperature Comparative Example 3 Powder can be obtained <0.5mm It still has flexibility below the 18-ane phase transition temperature Comparative Example 4 Particles can be obtained 1 to 1.5 mm Only those with a phase transition temperature above 18 alkyl ether possess flexibility Comparative Example 5 Particles can be obtained 2 to 3 mm Not flexible Comparative Example 6 Emulsion unstable / /

[0063] As can be seen from the table above, Examples 1-8 can all produce particles with a size of 1 mm to 1.5 mm that are flexible even at temperatures below the melting point of 18 ethane, thus meeting the requirements; Comparative Examples 1-3, although flexible, do not have a particle size greater than 1 mm, thus not meeting the requirements; Comparative Examples 4-5 have a particle size in the millimeter range, but they do not have flexibility even at temperatures below the melting point of 18 ethane, thus not meeting the requirements; Comparative Example 6 cannot form an emulsion, thus not meeting the requirements.

[0064] It should be noted that the 18-alkyl listed in the table refers to 18-chain alkylene.

[0065] Understandably, by constructing an elastic network through the synergistic polymerization of acrylates and crosslinking agents, the crystallization continuity of the phase change material is disrupted, achieving flexible and bend-resistant microspheres. An innovative emulsifier / monomer combination design (long-chain acrylates coating alkanes, with ether-bonded monomers stabilizing the emulsion interface) overcomes the material compatibility limitations of the coagulation bath method. A triaxial control mechanism for the concentration of the aqueous emulsifier, the ratio of the phase change material / monomer, and the stirring intensity is established to achieve precise preparation of millimeter-scale microspheres. An aqueous / oil-phase dual initiator system (ammonium persulfate + azobisisobutyronitrile) is developed, combined with a 70-100℃ temperature-controlled polymerization process, shortening the reaction time to 2-4 hours and achieving a monomer conversion efficiency of 98%. A continuous filtration-drying process enables large-scale production. The resulting millimeter-scale microspheres possess both high energy density and flexibility, and can be integrated into intelligent textiles and building thermal management systems. Their large size reduces encapsulation complexity, decreases interfacial thermal resistance, and improves energy regulation efficiency.

[0066] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; it should be understood that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inner", "around", etc., which indicate orientation or positional relationship, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0067] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing millimeter-scale flexible phase change microspheres, characterized in that, The millimeter-sized microspheres have a particle size range of 1mm-5mm and are flexible; the process includes the following steps: S1. Dissolve the emulsifier in water to prepare an aqueous phase, wherein the emulsifier is selected from polyvinyl alcohol 1788 or polyvinyl alcohol 1799, and the mass fraction of the emulsifier is 1% to 10% of water; S2. A phase change material, acrylate monomer, and acrylate crosslinking agent are added to an aqueous phase to form an emulsion through emulsification. The mass ratio of the phase change material to water is 20-80:100, the mass ratio of the acrylate monomer to the phase change material is 1:1 to 1:5, and the mass ratio of the acrylate crosslinking agent to the acrylate monomer is 1:1 to 1:

40. The phase change material is one or more of the following: straight-chain alkanes with 12-28 carbon atoms, fatty acids, fatty alcohols, and polyethylene glycol with a molecular weight of 900-2000. S3. Add an aqueous phase initiator and an oil phase initiator to the emulsion, and carry out a polymerization reaction at 70℃-100℃ for 2h-4h; wherein the mass ratio of the aqueous phase initiator to the acrylic monomer is 1:8 to 1:100, and the aqueous phase initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azodicyanovalerate, and azobisisopropylimidazoline; the mass ratio of the oil phase initiator to the aqueous phase is 1:1 to 1:5; the oil phase initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecyl peroxide, ditert-butyl peroxide, diisopropyl peroxide, dicyclohexyl peroxide, and dicumyl peroxide. S4. After the reaction is complete, filter the product using a 400-mesh filter, collect the filter residue and dry it under vacuum at 80°C.

2. The method for preparing millimeter-scale flexible phase change microspheres according to claim 1, characterized in that: In step 1, the emulsifier is 6-10 parts of polyvinyl alcohol 1788, which is dispersed in 180-250 parts of water to form an aqueous phase.

3. The millimeter-scale flexible phase change microspheres and their preparation method according to claim 1, characterized in that: In step 2, the acrylate monomer is one or more of the following: methoxyethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, tetrahydrofuran acrylate, methoxyethyl acrylate, dodecyl acrylate, octadecyl acrylate, and docosyl polyoxyethylene methacrylate.

4. The method for preparing millimeter-scale flexible phase change microspheres according to claim 3, characterized in that: In step 2, the acrylate crosslinking agent is one or more of the following: ethylene glycol dimethacrylate, trimethylolpropane triacrylate, epoxy acrylate, polyurethane acrylate, triallyl isocyanate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

5. The method for preparing millimeter-scale flexible phase change microspheres according to claim 1, characterized in that: The polymerization reaction in step 3 is carried out at a temperature of 80℃-90℃ for 3 hours.

6. The method for preparing millimeter-scale flexible phase change microspheres according to claim 4, characterized in that: The phase change material is 65 parts of a straight-chain alkane with 18 carbon atoms, the acrylate monomer is 10 parts of tetrahydrofuran acrylate, 30 parts of dodecyl acrylate, and 1.2 parts of docosyl polyoxyethylene methacrylate, and the acrylate crosslinking agent is 0.4-2 parts of dipentaerythritol hexaacrylate. The above materials and 5-20 parts of thickener are added to the aqueous phase and emulsified at 2000 rpm for 15 minutes to obtain a uniform emulsion.

7. A millimeter-scale flexible phase change microsphere, characterized in that: The microspheres prepared according to any one of claims 1-6 have a particle size range of 1 mm to 5 mm and are flexible.

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