Effect of the acidity ppof aqueous solutions on the wettability of diamond, graphite and pyrocarbon surfaces

The contact angle theta between the solid/liquid/gas interface was measured in dependence on the pH of the liquid on different carbon surfaces (CVD-diamond films, graphite and pyrocarbon films). As function of the pH, the theta values show significant changes with maxima and minima. This behavior is interpreted as being due to the presence of surface acidic groups with different acidic strength. The appearance of maxima and minima in the theta(pH) curves are caused by the reduction of the solid surface interaction with a minimum dissociation of the individual functional groups. (C) 2000 Published by Elsevier Science S.A. All rights reserved.