Superlubric polycrystalline graphene interfaces

The effects of corrugated grain boundaries on the frictional properties of extended planar graphitic contacts incorporating a polycrystalline surface are investigated via molecular dynamics simulations. The kinetic friction is found to be dominated by shear induced buckling and unbuckling of corrugated grain boundary dislocations, leading to a nonmonotonic behavior of the friction with normal load and temperature. The underlying mechanism involves two effects, where an increase of dislocation buckling probability competes with a decrease of the dissipated energy per buckling event. These effects are well captured by a phenomenological two-state model, that allows for characterizing the tribological properties of any large-scale polycrystalline layered interface, while circumventing the need for demanding atomistic simulations. The resulting negative differential friction coefficients obtained in the high-load regime can reduce the expected linear scaling of grain-boundary friction with surface area and restore structural superlubricity at increasing length-scales. Achieving ultra-low friction at macroscopic scales is highly desirable. In this work molecular dynamics simulations of graphitic contacts incorporating corrugated grain boundaries reveal an unusual non-monotonic variation of friction with normal load and temperature due to dynamic buckling effects.

Automated summary

The investigation of corrugated grain boundaries on the frictional properties of extended planar graphitic contacts reveals a nonmonotonic behavior in friction due to dynamic buckling effects. The resulting negative differential friction coefficients can reduce linear scaling of grain-boundary friction with surface area and restore structural superlubricity at increasing length scales. Achieving ultra-low friction at macroscopic scales is highly desirable.