SURFACE FORCES IN ADSORBED MULTILAYERS OF WATER ON QUARTZ

The adsorption of water vapor on smooth crystalline quartz at pressures close to saturation has been determined by ellipsometry, particular attention being paid to excluding gel layers and contamination. Contrary to some literature reports, such surfaces proved to be perfectly hydrophilic, showing thick adsorption multilayers and zero (or very low) contact angle. Quartz dehydroxylated by heating, or slightly contaminated, or deliberately methylated, showed thinner films and finite contact angles ranging from 20 to 80°. Films on clean quartz at saturation are consistent with calculated electrical double layer repulsion. But below saturation they are much thicker than expected on current theory of DLVO-type forces. Contact angles apparently arise from changes in short-range forces of a structural" type. © 1979."