Marina Ruths, Chemistry
The adhesion and lubrication properties of confined, molecularly thin films are highly important in systems containing miniaturized moving parts. The goals of this study are to obtain an understanding at the molecular and nanoscopic level of the protective action of confined surface active molecules in a sliding contact, and to eventually extend the work to rough (multi-asperity) surfaces. The presentation will focus on the effects of adhesion, contact area, and pressure on the friction of SAM-covered surfaces in single-asperity contacts where the strength of the adhesion was altered by working in different environments. In systems with low adhesion, a linear increase in friction force with load is typically obtained, whereas higher adhesion results in an apparently area-dependent friction force. The use of a modern contact mechanics model for layered, adhesive systems will be discussed as well as the limitations of simple models for the dependence of friction on load.