Molecular Dynamics Simulations of Polyamide-6 Composite with Covalently Bonded Graphene Network for Thermal Conductivity Enhancement

Due to its ultrahigh in-plane thermal conductivity, graphene nanosheet is expected to significantly improve the thermal conductivity of polymer composites. However, it still lacks clarity that how such improvement is quantitatively influenced by the configuration of the graphene nanosheets. In this work, large-scale molecular dynamics simulations are performed to investigate the effect of size and chemical interconnectivity of the graphene nanosheets on the thermal conductivity of a graphene-reinforced polyamide-6 composite. We find that the thermal conductivity of such a composite can be appreciably improved if all of the graphene nanosheets are covalently bonded together and the average size of the graphene nanosheets is large. Fundamentally, the composite thermal conductivity benefits from more heat taking the path of the graphene architecture and less heat dissipating back into the polymer matrix through the graphene-polymer interface. Analytical modeling indicates that the configuration with large-sized graphene nanosheets systematically joined by covalent intergraphene junctions is optimal to attract heat into the graphene architecture and restrain the interfacial heat dissipation, leading to better composite thermal conductivity. Our findings are crucial to understanding the physical mechanism of thermal conductivity enhancement of graphene nanosheets within a polymer matrix, which can be applied to develop highly efficient thermal interface materials.