Frictional anisotropy of metal nanoparticles adsorbed on graphene

Friction force acting on silver and nickel nanoparticles sheared on a graphene sheet in different lateral directions is investigated using classical molecular dynamics simulations. The results reveal the existence of frictional anisotropy for both metals. In most cases, the maximum value of the friction force is about two times larger than the minimum one. The form of dependencies of instantaneous values of the friction force components on the corresponding lateral components of the position of the centre of mass of the nanoislands strongly depends on sliding direction, varying between the sawtooth and the irregular one. A qualitative explanation of the results based on the "patch" model is proposed.