Distribution and formation of molecularly thin lubricants by thermostatic high vacuum AFM

Abstract

Distribution and formation of molecularly thin lubricants (95% Zdol and 5% X-1P) on CHx carbon surfaces has been studied by thermostatic high vacuum atomic force microscopy (THV-AFM). Results show that Zdol or/and X-1P distribute in island-shaped aggregation independent of topography of CHx surfaces at different temperatures. At 20°C, 10−7Torr, distribution of X-1P additive can be mapped distinctly without interfering features from Zdol lubes. As temperature decreases, features from Zdol gradually present both in topographic images and in phase images. Measured heights of Zdol islands increase with temperature varying from −20 to −60°C, however, the island diameters do not change significantly. At −60°C and 10−7Torr, lubricant islands have a typical height of ∼3.5nm and a typical diameter of ∼100nm. The area coverage ratio of lubricant islands to CHx surfaces is ∼0.59. To interpret these results, we present a lubricant distribution model involving an initial site-specific adsorption process in the solutions and a long time reorganization process after solvent evaporation.