Formation of ultra-thin bi-molecular boundary adsorbed films

Abstract

An analytical method based on statistical mechanics is proposed to predict ultra-thin adsorbed films of physical fluids with molecular diversity formed on smooth surfaces. The model is representative of molecular interactions at the smooth summits of surface asperities in the nano-scale. At this physical scale the constraining effect of the solid barriers promotes discretization of the fluid volume into molecular layers. These layers are usually ejected from the contact in a stepwise manner. The integrated effect of intermolecular forces as well as their interactions with the contiguous surfaces is responsible for the discontinuous drainage of the fluid. However, at the same time, the adsorption energy of the molecular species strives to form a molecular monolayer upon the boundary solids. The net result of these complex interactions is an ultra-thin adsorbed film, whose shear characteristics depends on a competition between the repulsive solvation pressure and the energy of molecular adsorption. It is shown that very thin low shear strength films are formed in this manner. This would depend on the molecular concentration and the wall adsorption energy. An important implication is that boundary adherent films should be viewed as a result of surface-fluid combination for which the choice of concentration and fraction content of particular species are crucial.