Theoretical study of entropy-induced friction in graphene

Abstract

The exceptional properties of graphene and other two-dimensional (2D) materials have endowed them with enormous potentials as fundamental elements in future microscale devices. With the dimension reduction in 2D materials, new friction behavior emerges: the friction is dominated by the contact edges rather than the contact areas. This edge-dominated behavior has an essentially entropic origin. Herein we develop an analytical model to describe this entropy-originated friction in graphene based on lattice dynamics theory. This edge-dominated friction is attributed to a translation effect of the surface interaction on the local vibration modes. By considering the potential stiffness on the vibration modes, the analytical model enables us to investigate the dependence of friction on sliding speed, normal load, and stiffness of the supporting surface. The analytical model is found to give accurate prediction close to those given by molecular dynamics simulations. These findings confirm that the analytical model can capture the underlying physics of graphene interlayer friction effectively. Though graphene is investigated herein, the analytical model will have general applications in characterizing the tribological behavior of other single-atom-thick 2D materials since they possess similar phononic properties as graphene.