Origin of static friction and its relationship to adhesion at the atomic scale

Using atomic scale interfaces consisting of slabs of the same materials, we study the relationship between adhesion and static friction. The work of separation, which is a measure of adhesion, and the spatial variation of the interface potential energy along the sliding direction are computed for both commensurate and incommensurate Al2O3/Al2O3 interfaces, and incommensurate smooth and rough Al/Al interfaces. These values are compared with the predicted static friction stress resulting from constant force and constant velocity molecular dynamics simulations. Simulation results show that static friction is not determined by the absolute value of adhesion. Rather, it is determined by the change of potential energy along the sliding direction.