Profile of the transition region between aqueous wetting films on quartz and the adjacent meniscus

Abstract

Between an equilibrium wetting film and the adjacent meniscus a transition region exists, its shape being determined by both capillary and surface forces. A detailed experimental study of the profile of the transition region has been performed. Using a special device, an aqueous meniscus is pressed through a tube against a quartz glass plate. The resulting circular microscopic wetting film as well as the interference pattern of the surrounding meniscus are photographed through a microscope in reflected light. The local thicknesses are evaluated from the corresponding optical densities in the photographs and used to construct the profiles of both the transition region and the meniscus. The profiles obtained for aqueous solutions of 0.1, 0.5 and 1 mmol dm −3 KCl and those theoretically calculated on the basis of a suitable disjoining pressure isotherm are found to be in good agreement.