Interfacial structure within thin films of decane isomers adsorbed on a metal substrate

Abstract

Canonical-ensemble Monte Carlo simulations were used to examine the solid–liquid interfacial structure within neat and multicomponent solutions of decane isomers at 350 K. As seen both experimentally and computationally for many fluids, layering within the liquid film near the solid substrate was exhibited in all fluids examined here. The amount of branching within a molecule, though, limited the range of density oscillations, particularly for multicomponent fluids. Analysis of molecular orientation within the first layer showed a strong preference in most cases for molecules to adopt orientations that enhance the energy of adsorption. To this end, preferential absorption was observed in all fluid mixtures with n-decane present. For both n-decane and 2,2-dimethyloctane, whether neat or in solution, the preference for orientations that maximise interactions between the alkane backbone of the molecule and the substrate led to additional in-plane alignment between adjacent adsorbed molecules. In contrast, for 4-propylheptane little in-plane alignment or orientation preference was observed at the interface.