Microscopic study of thin film lubrication and its contributions to macroscopic tribology

This review article summarizes recent progress in investigation of nano-rheology and thin film lubrication, as well as their contributions to conventional tribology. As the thickness of a lubricating film becomes comparable to molecular dimensions, a lubricant confined between solid walls undergoes a dramatic transition in its rheological properties and physical state, including the formation of ordered structure, enhanced viscosity and slow relaxation, glass transition or solidification, and consequent stick-slip motion. As a result, it is recognized that there is special regime between EHL and boundary lubrication, identified as thin film lubrication, where lubricant flow and hydrodynamics are still in action but behave differently from expectations of the classical theory. Generalized theories of thin film lubrication are under development. Microscopic studies of thin film lubrication provide a solid theoretical basis to the development of high-tech and micro devices, the understanding of lubrication failure, the generalization of classical lubrication theory, and friction control and interface design.