Molecular Origin of Superlubricity between Graphene and a Highly Hydrophobic Surface in Water.

Graphene is efficient to provide ultralow friction after the formation of an incommensurate interface but is limited to dry contact conditions and specific lattice structures. In this Letter, a new strategy is proposed to achieve the superlubricity of graphene through the creation of a sliding interface between graphene and a highly hydrophobic surface of self-assembled fluoroalkyl monolayers (SAFMs) in water. A superlow friction coefficient of μ = 0.0003 was obtained, demonstrating the extremely low shear stress between graphene and hydrophobic SAFMs in water. Molecular dynamics (MD) simulation shows that a nanometer-thick water layer is intercalated between graphene and hydrophobic SAFMs, and the weak interactions between water molecules and graphene provide a small energy barrier for water molecules sliding on graphene, which contributes to superlubricity. This finding reveals how to form a superlubricity interface by water intercalation, which has implications for minimizing the friction of layered materials and hydrophobic surfaces in water.