Morphological Stability and Nonlinear Evolution of Capillary Ridges
Roy RV, Schwartz LW
Proceedings of the Third European Coating Symposium, (Ed. F. Durst), 1999.

The study of the physics of dewetting and breakup of thin liquid films is of paramount importance for many applications. Many complex issues remain unanswered or incompletely understood, especially with regards to problems involving the motion of contact lines. Dewetting can of course drastically modify the original intended configuration of a thin liquid film. Two mechanisms are known for the process of dewetting: a film can dewet (1) via nucleation and growth of a circular hole, or (2) via capillary instabilities. We concentrate on the latter mechanism.

We present analytical, numerical and experimental studies of capillary ridges, that is, of long, narrow strips of liquid partially wetting a flat or curved substrate. Such thin film geometries possess both free boundaries and moving contact lines, and are known to display a large variety of instability phenomena. They provide an excellent example of the mechanism of dewetting due to capillary instability. Here, the possibility of dewetting and subsequent breaking of the continuous liquid strip into a sequence of droplets is essentially the result of flow induced by an excess of interfacial energies of the liquid/vapor, liquid/solid, and solid/vapor interfaces. We address two fundamental questions: (i) under what geometric and material conditions such solid/liquid configurations remain absolutely stable, and (ii) how the degree of contact line slip affects the liquid ridge morphological changes, dewetting growth rate, most unstable wavelength of instability, and long-term breakup times.