Double-layer transfer film enabled by graphene oxide-assembled hydrophobic ionic liquids for low friction under high humidity

Achieving outstanding friction reduction and wear resistance on engineering steel by using graphene oxide (GO)-based films has attracted growing interest because of the easy shear, modification, and availability of these materials. However, maintaining excellent friction performance under high relative humidity (RH) over a long duration is a major challenge for GO films. Therefore, we report that a double-layer transfer film enabled by a unique lubrication mechanism, which is based on a GO interface assembly composed of hydrophobic ionic liquids (ILs), triggers excellent tribological properties under high humidity. Moreover, the stainless steel GO–IL film (SS–GO–IL) showed excellent tribological properties in air (average friction coefficient of 0.24, wear volume of 2.54×10⁻⁷ mm³) and at 85% RH (average friction coefficient of 0.28, wear volume of 2.33×10⁻⁷ mm³), and the wear volume was reduced to one-thousandth that of the SS–GO film. At 85% RH, the molecular dynamics (MD) simulation results demonstrated that the interaction between GO and ILs was weakened under the action of water molecules. The unique lubrication mechanism was enabled by the double-layer transfer film formed on the steel balls, along with tribochemical reactions and hydrolysis, which created an adaptable, easy-shear interface.