DEWETTING MODES OF SURFACTANT SOLUTION AS A FUNCTION OF THE SPREADINGCOEFFICIENT

The surface coverage of an adsorbed monolayer of octadecylphosphonic a cid on mica was varied via solution concentration and immersion time, thereby controlling the surface free energy. For low surface coverage, a stable wetting layer of deposition solution was formed. For slightl y greater coverage, the substrate was initially wetted by a thin liqui d layer which quickly ruptured, leaving the sample dry. For large cove rage, the liquid layer receded from the sample edge. Atomic force micr oscopy and video microscopy showed that the intermediate regime corres ponds to dewetting via nucleation and growth of holes (0.25-5 mu m in diameter) in the liquid layer while the dewetting at large coverage pr oceeds from the sample edge. The dependence of the wetting mode upon s urface coverage and solution concentration was explained in terms of a competition between two rates: the nucleation rate of holes in the li quid layer and the speed at which the three-phase line advances.