Interaction between surfaces in ethanol: Adsorption, capillary condensation, and solvation forces

Abstract

When two surfaces in a condensable vapor are brought together, the vapor will capillary condense in the narrow gap between the surfaces. The surface forces apparatus, (SFA) has been used to study this condensation process with mica surfaces in ethanol vapor close to saturation. In particular, the critical surface separation at which the condensed bridge forms has been quantified. For thin adsorbed films (≤2 nm), the results are not consistent with a model of a liquid bridge formed by adsorbed films thickening under the influence of van der Waals forces. Instead, nucleation from vapor in the gap between the surfaces is possibly contributing to the formation of the bridge. The short-range interaction of mica surfaces in near-saturated ethanol vapor is also presented. The contact adhesion is much smaller than in nonpolar liquids due to the shielding of the ionic components of the adhesion. The solvation force is found to be similar to that in nonpolar liquids, except that the innermost minima are deeper. This is attributed to the amphiphilic nature of the ethanol molecule.