Effect of Surface Chemistry on the Squeeze-Thin Film and Friction of Boundary Films

An approach combining adsorption characterization and lubricity effectiveness of amine-based friction modifier molecules has been performed using chemically controlled surfaces, coated either with cobalt or carbon, while keeping the surface roughness constant and sub-nanometric. Through squeeze measurements and numerical modeling, we have identified the mechanical properties of both adsorbed amine films, as a function of the surface on which they were formed. On the one hand, we were able to evidence that the fluid structuring at the vicinity of the adsorbed boundary film differed as a function of the latter mechanical properties, directly resulting from its molecular organization. On the other hand, we showed that the coverage ratio of the monolayer associated with the shear elastic modulus of the boundary film governed the friction level. Changing the surface chemistry while keeping the roughness constant controls the final organization in the boundary layer, the correlated mechanical properties, and the level of friction dissipation.