Effects of functionalization on energy storage properties and thermal conductivity of graphene/n-octadecane composite phase change materials

Paraffin-based nanocomposites are widely used in the energy, microelectronics and aerospace industry as thermal energy storage materials due to their outstanding thermophysical properties. This paper investigates the effects of functionalization on thermal properties of graphene/n-octadecane nanocomposite during phase transition by using non-equilibrium molecular dynamics simulation. Different composite systems containing pristine graphene and graphene functionalized by hydroxyl, carboxyl and ethyl are constructed and studied. The results indicate that the thermal properties like diffusion coefficient, phase change temperature, heat capacity and thermal conductivity can be changed by both the functional types and functional coverage. Comparing with the unfunctionalized system, the system functionalized by ethyl obtained a 10 K increase in phase change temperature, a 12% increase in isobaric heat capacity at 300 K and a 59.8% increase in thermal conductivity at 320 K, and these values are larger than that of the systems functionalized by carboxyl and ethyl. The present findings provide a better understanding of the thermal mechanism of graphene/paraffin nanocomposites and effective guidance for improving their thermophysical properties.