Ab initio insights into graphene lubricity

We illustrate how ab initio calculations can be applied to derive a comprehensive understanding of the tribological properties of graphene. First we provide a quantitative estimate of the interlayer shear strength of graphene films and compare it with other layered materials as MoS2, revealing the superior intrinsic lubricity of graphene. Then we analyze the nature of the interlayer interactions and charge distribution to uncover the fundamental origin of frictional forces and their dependence on load. In the second part of the chapter, we provide an explanation for the observed capability of graphene to make iron surfaces slippery, which is very relevant for macroscale applications. Finally we discuss the detrimental effects of defects, such as edges and puckers, on graphene lubricity. By quantum mechanics-molecular mechanics simulations, we show how the reactivity of these defects can be quenched down by passivating molecules. The comparison between O2 and H2O highlights the superior effects of humidity due to cooperative mechanisms and hydrogen bonding.