  The force between two approaching solids in a liquid medium becomes
increasingly large with decreasing separation, a phenomenon that prevents
contact between the two solids. This growth in force occurs because of the
intervening liquid, and, studies of such physical systems constitute the
classical discipline of lubrication. Furthermore, when the solid(s) are soft,
there are quantitative as well as qualitative alterations in the force
interaction due to the solids' deformation. The underlying physics as well as
resultant system behaviour are even more complex when forces of
non-hydrodynamic origin come into play, two major classes of such forces being
the DLVO (Derjaguin-Landau-Verwey-Overbeek) forces and the non-DLVO molecular
forces. Studies assessing the coupling of these physical phenomenon are avenues
of contemporary research. With this view, we perform an analytical study of
fluid-mediated oscillatory motion of a rigid sphere over an ultra-thin soft
coating, delineating the distinctive effects of solvation force as well as
substrate compliance. Our key finding is the major augmentation in the force
and substrate-deformation characteristics of the system due to solvation force
when the confinement reduces to a few nanometers. Consideration of solvation
force leads to upto four orders of magnitude and upto three orders of magnitude
increment in force and substrate-deformation respectively. While higher
softness leads to higher deformation (as expected), its effect on force and
substrate-deformation characteristics exhibits a tendency towards amelioration
of the increment due to solvation force.
