Environmental effects on nanoscale friction at graphite basal plane and step edge

Abstract

Graphite is typically regarded as a good solid lubricant, but its effectiveness as a lubricant can vary depending on environmental conditions. Since macroscopic contact with graphite involves both basal planes and step edges of micro- or nano-crystalline particulates, it is critical to understand their individual contributions to the environment-dependent friction. To that end, this study used atomic force microscopy with a Si probe to investigate the effect of adsorption of water and n-pentanol from the gas phase on the nanoscale friction of the basal plane and step edge of graphite. The results showed that as the ambient humidity increases, friction on the basal plane increases monotonically, while friction at the step edge first increases and then decreases. Additionally, when n-pentanol is adsorbed, the friction of both basal plane and step edge decreases. These findings could be correlated with the isotherm and structure of the adsorbed molecules in the sliding interface, which alters the degree of commensurate interactions between the probe and the basal plane, as well as the transient chemical interactions between the probe and the step edge.