Molecular dynamics investigation of the lubrication mechanism of carbon nano-onions

Carbon nano-onions have been shown to provide exceptional friction and wear reduction through a rolling and sliding mechanism of the nano-onions at the interface, but the influence of this behavior on the their tribological properties is not well documented. Understanding the lubrication mechanisms of such nanostructured materials aids in determining their frictional properties and promotes the use of these materials in tribological applications. Here, we characterize the mechanisms of rolling and sliding through which carbon nano-onions provide low coefficients of friction by performing atomistic molecular dynamics simulations of carbon nano-onions sliding between diamond-like carbon substrates. The results indicate that the ability of the nano-onions to roll is inhibited both by increased contact pressure and the presence of a diamond core within the nanoparticles that enhances the formation of interfacial bonds during friction. The transition from rolling to sliding behavior is accompanied by a significant increase in the coefficient of friction.