Lubricated contact with nanoscale oil film is modeled for friction. Effect of the van der Waals pressure and the solvation pressure forces on such ultrathin lubricating oil film is considered while finding the friction and other parameters. Hydrodynamic action is represented using transient thermoelastohydrodynamics. Net pressure due to hydrodynamic, solvation, and van der Waals’ action is integrated over the contact area to find contact load. Conjunctional friction due to thermal activation of such ultrathin film is derived using the Eyring model. Effect of molecular dimension on friction is studied. 1. Introduction Ultrathin film transition is in between mixed and boundary regimes of lubrication. In mixed regime of lubrication, the contiguous surface geometry appears in film profile, while in boundary regime a total fluid film rupture occurs and the contiguous solids remain in contact. In between these two lubrication regimes, there exists a transition, where the film is in order of 0.5？nm–5？nm and is termed as ultrathin film. For such a case, the film is of about one or few molecular diameter thicknesses and subjected to solvation and van der Waals’ action. Very few attempts were made to know the mechanism of such an ultrathin film and its lubrication performance. First, Israelachvili [1] has studied the intermolecular surface forces. Henderson and Lozada-Cassou [2] developed a simplified theory to estimate the force between large spheres inside liquid, considering the effect of solvent. They simulated the alignment of the solvent dipoles in vicinity of the sphere and validated the resultant force with experimental finding. Evans and Parry [3] reviewed theoretical and computer simulated studies of atomic-order-fluid film absorbed. They focused on wet phase transition and found that the criticality in a continuously growing wetting film is due to capillary wave like fluctuation, which was best explained. Chan and Horn [4] studied the drainage of thin film between solid surfaces. They measured the transient film thickness, while it is squeezed between two mica surfaces of molecular order smoothness. In this study, film thickness of 0.5？nm is measured for OMTC (octamethyl-cyclotetrasiloxane), n-hexadecane, and n-tetradecane. For very thin film, the continuum Reynolds equation brakes as the drainage occurs in a series of abrupt steps, whose size matches the thickness of the molecular layer. Trace of water and its dramatic effect on drainage of nonpolar liquid between hydrophilic surfaces cause the film rupture, as they stated. Matsuoka and Kato [5]
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