Understanding the Mechanical and Viscoelastic Properties of Graphene Reinforced Polycarbonate Nanocomposites Using Coarse-Grained Molecular Dynamics Simulations.

Incorporating graphene nanosheets into a polymer matrix is a promising way to utilize the remarkable electronic, thermal, and mechanical properties of graphene. However, the underlying mechanisms near the graphene-polymer interface remain poorly understood. In this study, we employ coarse-grained molecular dynamics (MD) simulations to investigate the nanoscale mechanisms present in graphene-reinforced polycarbonate (GRPC) and the effect of those mechanisms on GRPC's mechanical properties. With a mean-squared displacement analysis, we find that the polymer chains near the GRPC interface exhibit lower mobility than the chains further from the graphene sheet. We also show that the embedding of graphene increases Young's modulus and yield strength of bulk PC. Through non-equilibrium MD simulations and a close look into the deformation mechanisms, we find that early strain localization arises in GRPC, with voids being concentrated further away from the graphene sheet. These results indicate that graphene nanosheets promote the heterogeneous deformation of GRPC. Additionally, to gain deeper insight into the mechanical, interfacial, and viscoelastic properties of GRPC, we study the effects of varying PC chain lengths and interfacial interactions as well as the comparative performance of GRPC and PC under small amplitude oscillatory shear tests. We find that increasing the interfacial interaction leads to an increase in both storage and loss moduli, whereas varying chain length has minimal influence on the dynamic modulus of GRPC. This study contributes to the fundamental understanding of the nanoscale failure mechanisms and structure-property relationships of graphene reinforced polymer nanocomposites.