Study on the applicability of photoswitch molecules to optically-controlled thermal energy in different organic phase change materials

Abstract

As a photoresponsive molecule, azobenzene molecule can realize optically-controlled phase change through the regulation of molecular structure, and store photothermal solar energy and phase change heat simultaneously, expected to achieve long-term heat storage and optically-controlled heat release of phase change materials (PCMs). In this paper, the photo-triggered controllable phase change behavior of two different grafting groups (AZO-A-14, AZO-O-14) photoswitch molecules mixed with straight-chain alkane, fatty alcohol and fatty acid PCMs at different ratios was investigated. The results show that the photoswitch molecules are more suitable for the phase change temperature control of fatty alcohol or fatty acid PCMs, and this is true for different concentrations. Using a photoswitch with similar polarity to the substrate, the trans-photoswitch that are not fully isomerized as well as cis-photoswitch can be well dispersed in PCMs, thus hindering their nucleation. In addition, the total enthalpies of the two photoswitch molecules are 233.45 J/g and 229.21 J/g, and the enthalpies of the optically-controlled PCMs ranged from 176.15 J/g to 229.06 J/g. For fatty acid, the doped photoswitch molecules can significantly improve the total energy storage density, and considering the energy storage density and temperature difference of the optically-controlled phase change, the combination of alcohol and ether-grafted optically-controlled PCMs is the best choice. This study provides ideas for the improvement, development and application of optically-controlled PCMs in the future.