Cationic Surfactant Micelles Lubricate Graphitic Surface in Water

It is easy to achieve extremely low friction of graphene or graphite in dry conditions via the formation of an incommensurate interface but is difficult to achieve with water lubrication. Herein, we propose a new strategy to achieve extremely low friction on a graphitic surface in water by self-assembling cationic surfactant micelles in the contact zone. When uniform surfactant micelles are formed on silica and freshly cleaved graphene layers via self-assembly under low contact pressure, the friction coefficient between them can reduce to 0.0004. When the self-assembled micelles are ruptured in the contact zone by high pressure, the friction coefficient between them would increase to 0.005 (still in the superlubricity regime). The mechanism of the different friction behaviors was studied at the nanoscale, which was attributed to the formation of different shear planes that shifts from the interface of the micelle/micelle to surfactant molecules/graphene layers after micellar rupture. The results provide direct evidence that the cationic surfactant micelles can efficiently lubricate graphitic surface regardless of micellar rupture.