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

By carrying out accurate molecular simulation of dodecane fluid confined be tween mica surfaces using molecular models appropriately describing wall-fl uid interaction, we show that the state condition of the confined fluid is strongly influenced by the wall-fluid interaction. At ambient condition, fo r strongly attractive surfaces, the effective density is significantly high er than the bulk density and increases with the narrowing of the confinemen t spacing. This increase results in the density crossing over into a densit y region higher than bulk freezing density when the confined film becomes n arrower than about six molecular layers, driving the transition to solid-li ke structure. At six molecular layers, the confined film forms distinct lay ers as well as in-plane orientational order and inter-plane packing, correl ation. The results suggest that the strong interfacial interaction is the d riving force for the dramatic effects observed in experiment. (C) 2001 Else vier Science B.V. All rights reserved.