Liquid Superlubricity Enabled by the Synergy Effect of Graphene Oxide and Lithium Salts

In this study, graphene oxide (GO) nanoflakes and lithium salt (LiPF₆) were utilized as lubrication additives in ether bond-containing dihydric alcohol aqueous solutions (DA(aq)) to improve lubrication performances. The apparent friction reduction and superlubricity were realized at the Si₃N₄/sapphire interface. The conditions and laws for superlubricity realization have been concluded. The underlying mechanism was the synergy effect of GO and LiPF₆. It was proven that a GO adsorption layer was formed at the interface, which caused the shearing interface to transfer from solid asperities to GO interlayers (weak interlayer interactions), resulting in friction reduction and superlubricity realization. In addition to the GO adsorption layer, a boundary layer containing phosphates and fluorides was formed by tribochemical reactions of LiPF₆ and was conducive to low friction. Additionally, a fluid layer contributed to friction reduction as well. This work proved that GO-family materials are promising for friction reduction, and provided new insights into realizing liquid superlubricity at macroscale by combining GO with other materials.