Molecular dynamics simulations on the heat and mass transfer of hypercrosslinked shell structure of phase change nanocapsules as thermal energy storage materials

Four different trihydroxy crosslinkers were respectively used to construct molecular models of hypercrosslinked polyurethanes as shell materials of phase change nanocapsules for thermal energy storage so as to investigate the heat and mass transfer properties. The impacts of microscopic characteristics of crosslinkers on glass transition temperature, thermal expansion and diffusion, interaction energy, thermal conductivity, mechanical properties under tensile and shear stress as well as some of thermal properties after packing water molecules into the hypercrosslinked polyurethanes were simulated and analyzed based on equilibrium or non-equilibrium molecular dynamics methods. The results showed that the detailed molecular structure of crosslinkers, namely the positions of hydroxyl groups, the geometric features of skeleton and even involved element type, will determine the structural characteristics of the hypercrosslinked polyurethanes, such as the formed micro cavities, the dangling functional groups as well as stiffness of short chain, and then affect the heat and mass transfer as well as mechanical properties. Furthermore, the hypercrosslinked polyurethanes possess relatively high glass transition temperature, better heat transfer performance and excellent mechanical properties compared to the polyurethanes with low crosslink density. (C) 2018 Elsevier Ltd. All rights reserved.