Effect of covalent functionalization and phase change matrix on heat transfer across graphene/phase change material interfaces

Owing to the superior thermal conductivity (TC) of graphene, graphene/phase change material (G/PCM) have the potential as the thermal interface materials (TIMs) dissipating heat for electronic packages. In this paper, the effect of three functional groups, i.e., hydroxyl (OH), carboxyl (COOH), butyl (C4H9) relative to pristine graphene (PG) and three PCM matrices, i.e., octadecane (OD), octadecanol (OA), stearic acid (SA), on the interfacial heat transfer between the PCM matrix and graphene was investigated by using molecular dynamic simulations. The simulation results show that the longer the chain of the covalent group, the stronger the van der Waals force will be, which will further enhance the interfacial coupling, and finally decrease the interface thermal resistance (ITR). For different PCM matrices, G/SA has the best heat transfer performance, followed by G/OA, and finally G/OD. The ITR of PG-OH/SA and PG-COOH/OA is remarkably reduced because the hydrogen bond formed by electrostatic attraction enhances the interfacial coupling. Additionally, based on the obtained ITR results and the effective medium theory, TC of G/PCM was studied. It was found that TC of PG/PCM increased as the volume fraction of the filler increased, and TC of PG/SA was always the largest, followed by PG/OA, and the smallest was PG/OD. At a filler volume fraction of 9%, PG-C4H9/PCM has the highest TC, followed by PG-COOH/PCM and PG-OH/PCM, and the smallest is PG/PCM. For different phase change matrices, TC of G/SA is generally the highest, followed by G/OA, and the lowest is G/OD. The high TC of PG-OH/SA and PG-COOH/OA is also due to enhanced interfacial coupling by hydrogen bonding.