Structural transition and solid-like behavior of alkane films confined in nano-spacing

By carrying out accurate molecular simulation of dodecane fluid confined between mica surfaces using molecular models appropriately describing wall–fluid interaction, we show that the state condition of the confined fluid is strongly influenced by the wall–fluid interaction. At ambient condition, for strongly attractive surfaces, the effective density is significantly higher than the bulk density and increases with the narrowing of the confinement spacing. This increase results in the density crossing over into a density region higher than bulk freezing density when the confined film becomes narrower than about six molecular layers, driving the transition to solid-like structure. At six molecular layers, the confined film forms distinct layers as well as in-plane orientational order and inter-plane packing correlation. The results suggest that the strong interfacial interaction is the driving force for the dramatic effects observed in experiment.