Synthesis and properties of cryogenic phase change material microcapsules reinforcement by emulsifiers and polyethylene glycol

The binary alkane system (C₆-C₇, C₆-C₈) was comprehensively explored in this study, and the best cryogenic eutectic n-alkane (70 %C₆-30 %C₇) with freezing point of −115.8℃ and phase transition enthalpy of 123 J/g was designed. After comparing various non-ionic emulsifiers (Span 80, Tween 80, PVA 1788, Arabic gum, Xanthan gum) through volatilization test, Span 80 was selected as the best anti-volatilization emulsifier to synthesize MEPCMs. Different anionic and nonionic emulsifier ratios were studied and determined to be 9:1. Cryogenic MEPCMs were prepared by in-situ polymerization, and the energy storage, thermodynamic, anti-volatilization properties, anti-leakage, mechanical property and durability were characterized. The results show that the morphology of MEPCMs is complete, the core wall materials are well bonded, and the coating rate is 50.9 %. PEG was used as a cross-linking agent to modify the shell of MEPCMs. The characterization results show that PEG effectively improvs the flexibility of the wall material, and the enthalpy loss of the MEPCMs in the anti-leakage test is reduced from 66.4 J/g to 15.8 J/g. The preferred anti-volatilization emulsifier increases the durability of MEPCMs from 192 h to 240 h. After 60 phase transition cycles, the enthalpy value of the MEPCMs is almost unchanged. This study bridges the volatility defects of cryogenic phase change materials and strengthens the durability of MEPCMs in terms of both core-wall and wall materials, which provides an important basis for the utilization of cold energy in cryogenic systems such as LNG, liquid hydrogen, and liquid air.