A simulation study of films of n-hexane and n-perfluorohexane on a solid surface

The behaviour of silica-supported films of liquid n-hexane and n-perfluorohexane has been investigated by means of molecular dynamics simulations of model compounds. Thin films of both neat liquids and equimolar mixtures were studied with different surface interaction strengths at room temperature (300 K). The molecules tend to form layers parallel to the surface of the substrate. In agreement with recent experimental results for hexane, a low density region was found near the surface, provided that the interaction strength was low. There is no corresponding low density region for perfluorohexane. The study of the mixture indicates that perfluorohexane is preferentially adsorbed at both solid-liquid and liquid-vapour interfaces while the molecules of hexane are concentrated inside the film.