Tuning interfacial structure and mechanical properties of graphene oxide sheets/polymer nanocomposites by controlling functional groups of polymer

A wide kinds of polymers have been reported to be reinforced by graphene oxide (GO) to achieve remarkable mechanical properties, which highly depends upon polymer/GO interface performances. Various functional groups of polymers pose great challenges for interface research. Herein, through molecular dynamics (MD), the effects of polymer functional groups on GO/polymer interface structure, dynamics, and mechanical properties were quantitatively studied and the relation between interface performances, H-bond density, and functional group polarity was uncovered. Results show that functional group polarity of polymer can promote the affinity between polymer and GO, but too high polarity may lead to the formation of intra-polymer H-bond and thus reduces the H-bond density across the interface and interface adhesion. The mobility of polymer chain is also restricted by H-bonding, and it increases with reducing H-bond density across the interface. Mechanically, H-bond density directly controls the relation between strength and stiffness of GO/polymer interface. An increase in H-bond density contributes to stress transfer between GO and polymer and enhances interface strength, but stiffens interface structure and reduces failure strain. Unexpectedly, the relation between interface strength and stiffness can be quantitatively estimated by the structure evolution of polymer chains in the tensile process.