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 dist ribution called weak disorder. Advancing and receding contact angles w ere determined as a function of surface coverage and compared with com putations based on the Cassie equation. The surface coverage is increa sed from 0% (uncovered glass surface) to 100% (resin surface). In the case of random distribution of heterogeneities, both advancing and rec eding 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 cove rage of about 60%. This behavior may be explain by taking into account the local morphology of the three-phase contact line. (C) 1998 Publis hed by Elsevier Science B.V. All rights reserved.