Synergistic friction-reducing effects between the transverse direction of anisotropic surface roughness and the high-density adsorbed films under a boundary lubrication regime

The friction-reducing effect of an adsorbed film at transverse roughness was investigated by focusing on the adsorption ability of polar compounds. Gradual reduction in friction under the low speed condition in case of the adsorbed film is formed from stearic acid or polymethacrylate. This is probably because the friction-reducing effect varied according to the adsorption ability and the number of the functional group. The results implied that the friction-reducing effect could be explained not only by the micro-EHL effect derived from transverse roughness but also by some other load-bearing effect, which depends on the formation state of the adsorbed film.

► Friction-reducing effect depended on the adsorption ability of functional groups.
► Stearic acid showed a gradual reduction in friction at the transverse roughness.
► The polymer showed relatively low friction coefficients at the transverse roughness.
► The high-density adsorbed film induced higher osmotic pressure at the contact.
► The osmotic pressure helped to support the load-bearing function of the film.