Understanding the Effects of Surface and Edge Functionalization on the Mechanical Properties of Graphene and Graphene Oxide.

Graphene oxide (GO) is a widely used 2D material employed in various applications due to its tunable properties. Understanding its mechanical properties is crucial to develop polymeric nanocomposites. We employ reactive molecular dynamics simulations to understand the effects of surface and edge functionalization of carbon atoms on the mechanical strength and fracture morphology of graphene and GO. We vary the extent of functionalization of hydroxyl and epoxy groups between 0.1%-70% on the GO surface and find that the tensile strength decreases with increasing functionalization. Nevertheless, there exists an optimal level of surface functionalization of 15-20% where the tensile strength of pristine graphene is retained. Additionally, we find that functionalization alters the fracture morphology from brittle to mild ductile, which is desirable in engineering applications. We also show that the edge functionalization of finite-size graphene nanosheets transfers the failure nucleation sites from the edges to the bulk, although the tensile strength decreases due to increased buckling. Interestingly, the decrement in tensile strength due to surface functionalization is larger as compared to edge functionalization. Overall, this work highlights the possibility of customizing GO's mechanical properties through targeted surface and edge functionalization, paving the way for its controlled application in nanocomposites.