Effect of density and spatial distribution of wettability heterogeneities on contact angle

Dynamic contact angles have been measured using the Wilhelmy technique on solid surfaces with two different distributions of heterogeneities: a random distribution called strong disorder and a more uniform distribution called weak disorder. Advancing and receding contact angles were determined as a function of surface coverage and compared with computations based on the Cassie equation. The surface coverage is increased from 0% (uncovered glass surface) to 100% (resin surface). In the case of random distribution of heterogeneities, both advancing and receding contact angles are in good agreement with calculations based on the Cassie equation. For the weak disorder distribution, the measured angles are more important than the predicted angles up to surface coverage of about 60%. This behavior may be explain by taking into account the local morphology of the three-phase contact line. (C) 1998 Published by Elsevier Science B.V. All rights reserved.