The effect of defects on the interfacial mechanical properties of graphene/epoxy composites

In this study, the effect of defects on the interfacial mechanical properties of graphene/epoxy composites has been investigated by using molecular dynamics simulations. Three common types of defects with different concentrations, i.e., single-vacancy, double-vacancy, and Stone-Wales, were considered. Two typical separations, i.e., normal separation and shear separation, were conducted to evaluate the graphene/epoxy interfacial cohesive strength and interfacial shear strength, respectively. The pull-out energy and corresponding forces during the whole process were determined. It was found that the vacancy defects, including single-vacancy and double-vacancy, would degrade the interfacial mechanical properties. In contrast, the Stone-Wales defect could enhance the interfacial strength, especially the interfacial shear strength. Besides, the effect of graphene agglomeration on the graphene/epoxy interfacial shear stress was also investigated. The results showed that the interaction between graphene sheets was much stronger than that between graphene and polymer. Additionally, the graphene agglomerated structure was found to weaken the graphene sheet and epoxy interfacial load transfer, which agreed with the observations in previous experimental results in the literature.