Advances in nanofriction of ionic liquids confined at graphene-based materials

Graphene and graphene-based materials are increasingly integrated into micro- and nanoelectromechanical systems, flexible electronics, and energy devices, wherein interfacial friction poses critical challenges. Ionic liquids (ILs), owing to their negligible volatility, high stability, and structural tunability, are promising lubricants for these systems. When confined on a graphene surface, ILs form layered films that are markedly distinct from their bulk structures and exhibit unique nanofrictional behaviors. This review establishes a mechanism-oriented substrate–IL–stimuli framework to connect interfacial descriptors (the surface properties of graphene, the molecular architecture of ILs, and external stimuli, i.e., humidity, temperature, and electric field) to interfacial ion structuring and nanofrictional outputs. Insights from atomic force microscopy (AFM), surface force apparatus (SFA), and molecular dynamics (MD) simulation studies are integrated to explain how the interfacial ion structure governs nanoscale friction. Transferable structure–property relationships are extracted from recent advances from AFM, SFA, and MD simulations to identify key challenges and propose a roadmap toward programmable graphene–IL lubrication for advanced nanodevices.