Experimental study of phase separation in films of molecular dimensions

Abstract

Phase separation induced by the close proximity of two surfaces occurs in thin films of incompletely miscible liquids. This phenomenon is thermodynamically analogous to capillary condensation of liquid from vapor and leads to a discontinuity in the force between two surfaces across the liquid. We present measurements of the distance at which phase separation takes place in nonpolar liquids containing water at activities from 0.7 to 1 between two kinds of chemically different mica surfaces. The generality of the effect is established by similar results obtained with other sparingly soluble solutes. The importance of surface adsorption and kinetic effects is discussed and comparisons are made with a modified Kelvin equation. The results are relevant to recent theoretical and simulation studies of the phase behavior of liquids in narrow pores and thin films.