Switching the Roles of Wettability-based Patterns Through Solutal Marangoni Effect

Abstract

Controlling the dynamics of thin liquid films on solid surfaces is illustrated by a combination of substrate patterning and solutal Marangoni effect. A solid surface, patterned based on wettability differences, can trigger film instability due to wettability gradient-driven flows. Additionally, if insoluble surfactants are introduced at the liquid film surface, the surfactant transport can cause surface-tension gradients across the film, and a solutal Marangoni flow results. By using suitable non-uniform initial surfactant concentration distributions, the rate and direction of Marangoni flow can be manipulated to compete with the wettability gradient-driven flows. It is found that film dewetting can be reversed in selected problem parameter space. Dewetting can be engendered on more wettable patches of the bounding solid, with a consequent accumulation of the liquid on less wettable regions. The importance of length scales of the less and more wettable patches on switching the roles of wetting behaviour is also investigated.