Normal-strain induced change in lattice-type for confined cyclohexane films

One to three layer cyclohexane films confined between mica-like surfaces are studied to elucidate changes in the film's lattice-type. The laterally confined film in equilibrium with the bulk fluid that is well into the liquid regime of its phase diagram. Monte Carlo simulations are conducted at constant chemical potential, temperature, and V = Ah, where A is the lateral area and h is the separation between the walls. One and two layers of fluid freeze as h increases. The one layer fluid has a triangular lattice, while the two layer fluid exhibits first a square lattice and then a triangular lattice with increasing surface separation. In contrast to previous studies, solidlike order is induced primarily by the strong fluid-solid interaction and is largely a function of pore width. A shift in the relative alignment of the surfaces perturbs the solidlike fluid structure but does not cause the sudden shear melting transition associated with epitaxial alignment of the fluid atoms with the surface. There is a correlation between the shear stress calculated in the computer experiments and that measured in Surface Forces Apparatus experiments.