Enhanced thermal properties and light-to-thermal conversion of polyethylene glycol-based composite phase change materials enabled by photoisomerization of azo-C16 compound

In this study, a hexadecylated Azo compound (Azo-C16) was synthesized by grafting hexadecyl chains onto an azobenzene molecule, and the polyethylene glycol (PEG)-based composite phase change materials (PEG@AzoC16) were prepared by blending various contents of Azo-C16 compound from 1 to 20 wt%. The interactions of alkyl chains and interfacial compatibility between PEG and Azo-C16 ensure enhanced shape stability, good thermal properties, and higher light-to-thermal conversion capability for the PEG@Azo-C16 composites owing to the improved chain entanglements and physical adsorption role of Azo-C16 compound. And, the PEG@Azo-C16 composites give a faster temperature-increase tendency and 3 degrees C higher thermal delay, further demonstrating the contribution of Azo-C16 photoisomerization. Meanwhile, the excited PEG@Azo-C16 composites by UV light present the maximum temperature difference (6 degrees C) and PEG@Azo-C16-20 displays 90.9 % light-to-thermal conversion efficiency and 5-time light-to-thermal conversion cycle. A 4.3 degrees C temperature difference confirms its utilization of PEG@Azo-C16-20 as a solar water heater. Therefore, the PEG@Azo-C16 composites open a facile method by physically blending light-absorption compounds to explore high-performance PCMs with highly efficient thermal energy storage and light-to-thermal conversion capability.