Tribochemistry of Graphene Oxide/Graphene Confined between Iron Oxide Substrates: Implications for Graphene-Based Lubricants

Graphene has been widely tested as a lubricant material for steel sliding contact in engineering applications. The structural and chemical evolutions on friction surfaces are critical to understand the improvement of tribology performance in experiments. Here, we used the reactive molecular dynamics (ReaxFF-MD) simulations to study the friction and wear behaviors of a monolayer graphene oxide or graphene (GO/Gr) flake confined between two amorphous iron oxide substrates. The results show that when under lower loads (<4 GPa), the sliding shear between two substrates is accomplished by folding and unfolding behaviors of the confined GO/Gr flakes. When under relatively higher loads (≥4 GPa), the intensively formed interfacial C–Fe bonds promote the breakage and decomposition of the GO/Gr flakes and also the gradual damaging of the iron oxide surfaces, resulting in partial direct contacts between two substrates. We also found that the presence of functional groups on the GO flakes will affect the formation of interfacial C–Fe bonds, while the detached functional groups could passivate the iron oxide surfaces, thus having a remarkable influence on the tribological properties of steel sliding contacts. These atomistic insights into structural and chemical evolutions during friction can help to promote the usage of GO/Gr flakes as lubricant materials in engineering applications.