Friction induced structural transformations of water monolayers at graphene/Cu interfaces

Tribological and structural properties of water monolayers confined at interfaces between graphene and Cu substrates at cryogenic and room temperatures are extensively studied using molecular dynamics simulations and first-principles calculations. The frictions caused by the sliding of graphene sheets and increasing temperature will reduce the interfacial density of water molecules and lead to structural transformations of water monolayers and direct contacts of graphene with the underlying Cu substrates. Such changes in water structures give rise to higher friction forces and shear strengths at the graphene/Cu interfaces. Depending on the water coverage density and temperature, the motions of graphene on monolayer water covered Cu exhibit stick-slip and continuous slipping behaviors. The strong association of friction characteristics with structural transformations of water molecules could be used to unveil interfacial information of graphene on water adsorbed metal surfaces.