Grape-like phase change microcapsules based on vinyl monomer polymers and a method for preparing the same

Abstract

The application discloses a kind of based on olefin monomer polymer pomegranate-like phase change microcapsule and preparation method thereof.The core of the pomegranate-like phase change microcapsule of the application is composed of solid-liquid phase change material and a large number of microspheres of olefin monomer polymer, and the shell is composed of olefin monomer polymer and inorganic non-metallic nanoparticles attached to the olefin monomer polymer.By adjusting the ratio of olefin monomer and crosslinking agent, the structure of the phase change microcapsule based on olefin monomer polymer can be controlled, and the pomegranate-like phase change microcapsule is prepared.The pomegranate-like phase change microcapsule has excellent shape stability, fundamentally solves the problem of poor thermal stability caused by a large number of depressions on the surface of the phase change microcapsule based on olefin monomer polymer, and eliminates the concerns of the application of the phase change microcapsule based on olefin monomer polymer in the field of thermal management.Meanwhile, the application is simple to operate, and the preparation of phase change microcapsule with excellent shape stability can be realized in one step, which is easy to realize large-scale.

Description

Technical Field

[0001] This invention belongs to the field of phase change energy storage materials technology, and particularly relates to a garnet-shaped phase change microcapsule based on olefin monomer polymer and its preparation method. Background Technology

[0002] Phase change materials (PCMs) are materials that can store or release a large amount of latent heat during a phase change process. Solid-liquid PCMs, in particular, possess advantages such as high energy density, small volume change, and relatively constant phase change temperature, making them promising candidates for thermal management. However, solid-liquid PCMs are prone to leakage during phase change, limiting their application in the thermal management of electronic devices. Microencapsulation technology, by encapsulating PCMs in organic or inorganic shells to prepare nano- to micron-sized microcapsule PCMs (MEPCMs), can effectively solve the leakage problem during phase change. Organic polymers are used as shell materials for PCMs due to their low cost, excellent mechanical properties, ease of processing, and good compatibility with various PCMs. Among them, polystyrene is a good shell material for preparing MEPCMs due to its low cost, ease of processing, excellent mechanical properties, and environmental protection. Zhao et al. (Enhanced photothermal conversion and thermal conductivity of phase change n-octadecane microcapsules shelled with nano-SiCdoped crosslinked polystyrene. Energy Storage and Saving 2022, 1 (4), 284-292) prepared MEPCM with n-octadecane (ODE) as the core material and nano-silicon carbide-modified polystyrene (CLPS) as the shell material via suspension emulsion polymerization. The prepared MEPCM had certain surface depressions. Tian Xingyou's research group (Phasechange microcapsules with a polystyrene / boron nitride nanosheet hybrid shell for enhanced thermal management of electronics. Langmuir 2022, 38 (51), 16055-16066) synthesized MEPCM with paraffin as the core material and boron nitride nanosheet-modified polystyrene as the shell material via Pickering emulsion polymerization. The surface of the synthesized MEPCM also had a large number of depressions. The MEPCMs prepared using polystyrene as the shell material mentioned in the above reports all exhibit numerous surface depressions. This is a common phenomenon caused by the mismatch between the shrinkage and expansion of the core and shell materials during the phase change process. When such MEPCMs are actually applied in the field of thermal management, their stability decreases rapidly during repeated heating and cooling processes. In more serious cases, a large number of MEPCMs may even rupture. Therefore, the leakage problem of phase change materials has not been fundamentally solved. Summary of the Invention

[0003] This invention addresses the problem of numerous surface depressions in current MEPCMs based on olefin monomer polymers. Through in-depth investigation of the influence mechanism on the structure of MEPCMs based on olefin monomer polymers, it was learned that the ratio of olefin monomer to crosslinking agent determines its final structure. A garnet-shaped phase change microcapsule based on an olefin monomer polymer and its preparation method are proposed, fundamentally solving the problem of numerous surface depressions in phase change microcapsules based on olefin monomer polymers. The prepared phase change microcapsules have a diameter of 10-80 μm and exhibit excellent shape stability. Specifically, this invention is achieved using the following technical solution: The present invention discloses a garnet-shaped phase change microcapsule based on an olefin monomer polymer, comprising a core and a shell. The core is mainly composed of a solid-liquid phase change material and a large number of microspheres of the olefin monomer polymer, the microspheres having a size of 100 nm-1 μm. The shell is mainly composed of the olefin monomer polymer and inorganic non-metallic nanoparticles attached to the olefin monomer polymer, the inorganic non-metallic nanoparticles acting as Pickering emulsifiers and stabilizing agents. The phase change microcapsule has a diameter of 10-80 μm.

[0004] The pomegranate-shaped phase change microcapsules described above, wherein the solid-liquid phase change material is one or more of paraffin, fatty alcohol, aliphatic hydrocarbons and their derivatives; and the olefin monomer is one or more of ethylene, propylene, butadiene, styrene, methyl acrylate, methyl methacrylate, and acrylonitrile.

[0005] The method for preparing garnet-shaped phase change microcapsules based on olefin monomer polymers according to the present invention includes aqueous phase preparation, oil phase preparation, mixing and emulsifying the aqueous and oil phases to obtain a Pickering emulsion, and emulsion heating polymerization.

[0006] In the above-described preparation method, preferably, the aqueous phase preparation involves dispersing nanoparticles in water to prepare an aqueous phase; the nanoparticles are inorganic non-metallic nanoparticles, including one or more of boron nitride particles, alumina particles, and silicon dioxide particles, and the mass ratio of nanoparticles to water in the aqueous phase is 0.1-3.0%.

[0007] In the above-described preparation method, preferably, the oil phase is prepared by heating and melting the solid-liquid phase change material and then mixing it uniformly with olefin monomers, crosslinking agents, and initiators to obtain the oil phase.

[0008] In the preparation method described above, preferably, the crosslinking agent is one or more of divinylbenzene, diisocyanate, and N,N-methylenebisacrylamide, and the mass ratio of the crosslinking agent to the olefin monomer is 0.05-20:1, preferably 1-20:1, more preferably 9-20:1, and especially 9-15:1.

[0009] In the preparation method described above, preferably, the initiator is an oil-soluble free radical initiator, including at least one of azobisisobutyronitrile and azobisisoheptanenitrile, and the amount used is 0.5-6% of the total mass of the olefin monomer and the crosslinking agent.

[0010] A preferred preparation method may include the following steps: Step (1): Disperse nanoparticles in water to prepare an aqueous phase; Step (2): After heating and melting the solid-liquid phase change material, mix it evenly with olefin monomers, crosslinking agents and initiators to obtain an oil phase; Step (3): After mixing the above aqueous phase and oil phase, emulsify them using an emulsifier to obtain Pickering emulsion; Step (4): The Pickering emulsion obtained in step (3) is heated to 60-100℃ for polymerization, and then purified and dried to obtain phase change microcapsules.

[0011] In step (3), the emulsifier speed is 6000-12000 rpm, preferably 6000-9000 rpm, and most preferably 8000 rpm, and the emulsification time is 2-15 minutes. In step (4), it is best to heat to 70-80℃ for polymerization.

[0012] This invention allows for the control of the structure of phase change microcapsules based on olefin monomer polymers by adjusting the ratio of olefin monomers and crosslinking agents, resulting in the preparation of pomegranate-shaped and coconut-shaped phase change microcapsules. The pomegranate-shaped phase change microcapsules exhibit excellent shape stability, fundamentally solving the problem of poor thermal stability caused by numerous surface depressions in olefin monomer polymer-based phase change microcapsules, thus eliminating concerns about their application in thermal management. Furthermore, this invention is simple to operate, enabling the preparation of phase change microcapsules with excellent shape stability in a one-step process, and is easily scalable. Attached Figure Description

[0013] Figure 1 This is a scanning electron microscope image of the polystyrene-based coconut-shaped phase change microcapsule from Example 1.

[0014] Figure 2 This is a scanning electron microscope image of the polystyrene-based garnet-shaped phase change microcapsules from Example 2.

[0015] Figure 3 This is a scanning electron microscope image of the polystyrene-based garnet-shaped phase change microcapsules of Example 3.

[0016] Figure 4 This is a scanning electron microscope image of the polystyrene-based garnet-shaped phase change microcapsules from Example 4.

[0017] Figure 5This is a scanning electron microscope image of the polystyrene-based garnet-shaped phase change microcapsules from Example 5.

[0018] Figure 6 This is a scanning electron microscope image of the polystyrene-based garnet-shaped phase change microcapsule from Example 6. Detailed Implementation

[0019] The following embodiments are further illustrations of the present invention and serve as explanations of the technical content of the present invention. However, the essence of the present invention is not limited to the embodiments described below. Those skilled in the art can and should know that any simple changes or substitutions based on the spirit of the present invention should fall within the scope of protection claimed by the present invention.

[0020] Example 1 Step (1) Disperse 0.35 g of boron nitride nanosheets in 100 ml of deionized water to obtain an aqueous phase; Step (2): Mix 5.21 g of molten paraffin, 0 g of divinylbenzene (DVB), 1.79 g of styrene (St) and 0.09 g of azobisisobutyronitrile (AIBN) at 80 °C to obtain an oil phase, wherein the ratio of DVB / St is 0. Step (3): After mixing the aqueous phase from step (1) and the oil phase from step (2), the mixture is homogenized by stirring at a speed of 8000 rpm to obtain the Pickering emulsion. Step (4): The Pickering emulsion obtained in step (3) is heated to 75°C for polymerization, and then purified and dried to obtain coconut-shaped phase change microcapsules. Example 2

[0021] Step (1) Disperse 0.35 g of boron nitride nanosheets in 100 ml of deionized water to obtain an aqueous phase; Step (2): Mix 5.21 g of molten paraffin, 0.16 g of divinylbenzene (DVB), 1.63 g of styrene (St) and 0.09 g of azobisisobutyronitrile (AIBN) at 80 degrees Celsius to obtain an oil phase, wherein the ratio of DVB / St is approximately 1 / 10; Step (3): After mixing the aqueous phase from step (1) and the oil phase from step (2), the mixture is homogenized by stirring at a speed of 8000 rpm to obtain the Pickering emulsion. Step (4): The Pickering emulsion obtained in step (3) is heated to 75°C for polymerization, and after purification and drying, pomegranate-shaped phase change microcapsules are obtained. Example 3

[0022] Unlike Example 2, in step (2), 0.30 g of divinylbenzene (DVB) and 1.49 g of styrene (St) were added, with the DVB / St ratio being approximately 1 / 5. The rest was the same as in Example 2. Example 4

[0023] Unlike Example 2, in step (2), 0.90 g of divinylbenzene (DVB) and 0.90 g of styrene (St) are added, with the DVB / St ratio being 1 / 1. The rest is the same as in Example 2. Example 5

[0024] Unlike Example 2, in step (2), 1.49 g of divinylbenzene (DVB) and 0.30 g of styrene (St) were added, with the DVB / St ratio being approximately 5 / 1. The rest was the same as in Example 2. Example 6

[0025] Unlike Example 2, in step (2), 1.63 g of divinylbenzene (DVB) and 0.16 g of styrene (St) were added, with the DVB / St ratio being approximately 10 / 1. The rest of the steps were the same as in Example 2.

[0026] Example 1 did not introduce the crosslinking agent divinylbenzene (DVB), while Examples 2-6 introduced DVB. The introduction of DVB determined the final structure. Without DVB, non-crosslinked polystyrene was obtained, while with DVB, crosslinked polystyrene was obtained. The non-crosslinked polystyrene microspheres fused into larger polystyrene microspheres and completely deposited at the interface to act as the shell material, thus forming coconut-shaped phase change microcapsules. Because the coconut-shaped phase change microcapsules lack internal polystyrene microsphere support, repeated phase changes lead to numerous depressions, even if the initially prepared microcapsules did not have depressions. In contrast, the crosslinked polystyrene microspheres have a significantly lower fusion probability and smaller size, resulting in a much lower probability of deposition at the interface. Part of the crosslinked polystyrene exists as polystyrene microspheres in the core material, while the rest is deposited at the interface to act as the shell material, thus forming garnet-shaped phase change microcapsules.

[0027] Experiments have found that, for example Figure 1 When no cross-linking agent DVB was added (DVB / St=0), coconut-shaped phase change microcapsules were obtained; such as Figure 2-6 When a crosslinking agent (20 > DVB / St > 0) was added, garnet-shaped phase change microcapsules were obtained. As the DVB content increased, surface depressions decreased and sphericity increased until DVB / St was approximately 10, at which point surface depressions were virtually nonexistent. The presence of numerous polystyrene microspheres within the garnet-shaped phase change microcapsules provides support. By adjusting the styrene (St) / divinylbenzene (DVB) ratio, regularly spherical phase change microcapsules can be prepared, exhibiting excellent shape stability without depressions even after repeated phase changes.

[0028] This invention allows for the control of the structure of phase change microcapsules based on olefin monomer polymers by adjusting the ratio of olefin monomers and crosslinking agents, resulting in pomegranate-shaped and coconut-shaped phase change microcapsules. The pomegranate-shaped phase change microcapsules exhibit excellent shape stability due to the presence of numerous olefin monomer polymer microspheres supporting the microcapsule. The discovery of pomegranate-shaped phase change microcapsules based on olefin monomer polymers fundamentally solves the problem of poor thermal stability caused by numerous surface depressions, eliminating concerns about their application in thermal management. This has significant potential value for improving the thermal stability of phase change microcapsules.

[0029] It should be noted that the above-described technical content of this invention is merely an explanation and clarification to enable those skilled in the art to understand the technical essence of this invention, and therefore is not intended to limit the scope of protection of this invention. The scope of protection of this invention should be determined by the claims. Those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made based on the essential spirit of this invention should be within the scope of protection of this invention.

Claims

1. A method for preparing garnet-shaped phase change microcapsules based on olefin monomer polymers, comprising aqueous phase preparation, oil phase preparation, mixing and emulsifying the aqueous and oil phases to obtain a Pickering emulsion, and emulsion heating polymerization; The pomegranate-shaped phase change microcapsule includes a core and a shell. The core is mainly composed of a solid-liquid phase change material and a large number of olefin monomer polymer microspheres with a size of 100 nm-1 μm. The shell is mainly composed of olefin monomer polymers and inorganic non-metallic nanoparticles attached to the olefin monomer polymers. The phase change microcapsule has a diameter of 10-80 μm. The solid-liquid phase change material is one or more of paraffin, fatty alcohol, aliphatic hydrocarbon and their derivatives; the olefin monomer is one or more of ethylene, propylene, butadiene, styrene, methyl acrylate, methyl methacrylate and acrylonitrile. The aqueous phase preparation involves dispersing nanoparticles in water to prepare an aqueous phase; the nanoparticles are inorganic non-metallic nanoparticles, including one or more of boron nitride particles, alumina particles, and silica particles, and the mass ratio of nanoparticles to water in the aqueous phase is 0.1-3.0%; The oil phase is prepared by heating and melting the solid-liquid phase change material and then mixing it uniformly with an olefin monomer, a crosslinking agent, and an initiator to obtain the oil phase; the crosslinking agent is one or more of divinylbenzene, diisocyanate, and N,N-methylenebisacrylamide, and the mass ratio of the crosslinking agent to the olefin monomer is 9-20:

1.

2. The preparation method according to claim 1, characterized in that, The initiator is an oil-soluble free radical initiator, including at least one of azobisisobutyronitrile and azobisisoheptanenitrile, and is used in an amount of 0.5-6% of the total mass of the olefin monomer and the crosslinking agent.

3. The preparation method according to claim 1, characterized in that, Includes the following steps: Step (1): Disperse nanoparticles in water to prepare an aqueous phase; Step (2): After heating and melting the solid-liquid phase change material, mix it evenly with olefin monomers, crosslinking agents and initiators to obtain an oil phase; Step (3): After mixing the above aqueous phase and oil phase, emulsify them using an emulsifier to obtain Pickering emulsion; Step (4): The Pickering emulsion obtained in step (3) is heated and polymerized, and then purified and dried to obtain phase change microcapsules.

4. The preparation method according to claim 3, characterized in that, Step (3) The emulsifier speed is 6000-12000 rpm, and the emulsification time is 2-15 minutes.

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