Surface force apparatus and thin film rheology for additive-treated lubricant

A surface force apparatus was used to experimentally study the thin-film rheology of an additive-treated lubricant. Results show that the lubricant, expected to be a Newtonian fluid in its bulk state, exhibits nonlinear shear response when the film thickness is reduces to the nano-meter scale. The effective viscosity of the lubricant increases as the film thickness decreases, approaching infinity when the film thickness reaches a critical point. When mixed with only additives, the lubricant has a lower effective viscosity and a smaller value of the critical film thickness, indicating that the thin films rheology is related to tribological properties of the interfaces. A sandwich model for thin film rheology provides a better understanding of the experimental phenomena.