Friction of graphene oxide with water nanodroplets under high relative humidity

Tribological properties of graphene oxide (GO) in high-humidity environments are important for its application as a solid lubricant. Topography, friction, and adhesion of GO with water nanodroplet are investigated at high relative humidity using atomic force microscopy. The friction of GO inside the nanodroplet depends on the tip radius. For a sharp tip, the friction of GO inside the nanodroplet is higher than that outside because the resisting force of the nanodroplet to the tip is greater than the assisting force due to the mildly decreased adhesion. For a blunt tip, the significantly decreased adhesion inside the nanodroplet results in much lower friction inside the nanodroplet than that outside. These studies enhance the understanding of the friction behaviors of GO.