Interfacial slip of liquids along graphene: effects of layering and substrate-induced doping

Understanding modulation of liquid molecule slippage along graphene surfaces is crucial for many promising applications of two-dimensional materials, such as in sensors, nanofluidic devices and biological systems. In this investigation we use atomic force microscopy (AFM) to directly measure hydrodynamic, solvation, and frictional forces along substrate supported graphene in seven liquids. The results show that the greater slip lengths correlate with the interfacial ordering of the liquid molecules, suggesting that increased ordering in the liquid phase promotes slip while less structured liquids significantly hinder it. This phenomenon is relevant in addition to the commonly referenced wetting behavior and solid-liquid interaction energy. Furthermore, the slip boundary condition of the liquids along the graphene plane is sensitive to the substrate-induced doping of graphene. Because interfacial slip can have prominent consequences on the pressure drop, electrical and diffusive transport through nanochannels and on lubrication, this work can inspire innovation in many applications through the selective doping of graphene surfaces and interfacial order of the contacting liquid.