Molecular layering in thin-film elastohydrodynamics

Liquid molecules take on a layered structure in the immediate vicinity of the solid surface and the effect of this structure on the tribological characteristics cannot be neglected when the lubricant film thickness between solid surfaces is less than several times the molecular diameter. The layered structure of liquid molecules is due to the non-uniform potential energy distribution of solid molecules. The molecular layering increases the strength of the film owing to the solid-like, ordered structure of liquid molecules and increases the liquid film thickness. In addition, the layering exerts a force (structural force or solvation force) on the solid surfaces. Although this force is small, namely comparable with the van der Waals force, the surface deforms elastically and the amount of deformation is of the order of the film thickness. This work examines the layering effect in a contact lubricated with a very thin film and shows the elastohydrodynamic (EHD) calculation in which the solvation force is involved.