Macroscale superlubricity under extreme pressure enabled by the combination of graphene-oxide nanosheets with ionic liquid

The liquid-superlubricity state has rarely been studied under an average contact pressure exceeding 300 MPa at the macroscale. In this work, a robust macroscale liquid-superlubricity state (mu approximate to 0.005) under an extreme pressure of 600 MPa was reported, which was enabled by the combination of graphene-oxide (GO) nanosheets with an ionic liquid (IL) between the frictional pairs of Si3N4 /sapphire. The analysis indicated that a composite boundary layer (formed by IL) at the interface contributed to the excellent antiwear performance, thereby providing a lubricating condition under extreme pressure. Notably, GO nanosheets were directly observed to adsorb on worn surfaces, thereby proving the transformation of the shear interface from Si3N4/sapphire into GO/GO nanosheets. The extreme pressure property and extremely low shear stress between the interlayers of GO nanosheets contributed to the achievement of superlubricity. Therefore, the synergistic effect between GO nanosheets and IL played a dominant role in achieving liquid-superlubricity under extreme pressure at the macroscale. This study provided a novel method to achieve liquid-superlubricity under extreme conditions-by the synergistic effect of 2D materials and liquid molecules-accelerating the achievement of liquid-superlubricity in industrial applications. (C) 2019 Elsevier Ltd. All rights reserved.