Preparation and performance study of azobenzene-based optically-controlled phase change material

Phase change materials (PCMs) can store thermal energy in the form of latent heat. However, traditional PCMs suffer from spontaneous solidification and uncontrolled heat release in the absence of effective insulation or continuous energy input, severely limiting their practical application. To address this, optically-controlled PCMs have emerged as a novel solution, developed by integrating molecular photoswitches into traditional PCM matrices. Solar energy can be converted and stored in the form of photochemical enthalpy and phase change enthalpy, and the thermophysical properties of the materials can be changed through photoisomerization. In this paper, 4-octanoyloxyazobenzene (4-OcOAzo), an azophenyl photo controlled PCM, was prepared experimentally. The phase transition temperatures for the cis and trans isomers were determined to be 294.37 K and 335.76 K, respectively. The material exhibits an energy storage density of 139.356 kJ/kg, and the thermal conductivity was 0.292 W/(m·K) at room temperature. Subsequently, a microscopic model of 4-OcOAzo was established, and its thermophysical properties were analyzed based on molecular dynamics. The calculated results show that the phase transition temperature of the trans sample is 333 K, the phase transition temperature of the cis sample is 296.41 K, and the thermal conductivity at room temperature is 0.282 ± 0.017 W/(m·K), which is highly consistent with the experimental results. In addition, through the analysis of microstructure parameters, the mechanism of optically controlled phase transition can also be clarified.