Effects of adsorbate coverage and capillary on nano-asperity friction in atmosphere containing organic vapor

The influence of alcohol adsorption on the nano-asperity friction of silicon oxide surfaces under equilibrium conditions was studied with atomic force microscopy (AFM). In the intermediate regime of the relative partial pressure (P/P_sat) of alcohol, the friction versus applied load (F-L) curve deviates from the expected DMT behavior, while the F-L curve in dry and near saturation vapor conditions follows the DMT contact mechanics. The full analysis of the observed P/P_sat dependence of the F-L data with theoretical models reveals clearly that the shear stress of the contact is governed by the coverage of the adsorbed alcohol on the surface while the friction near the critical snap-off is governed by the capillary meniscus formed at the nano-asperity contact.