The Dynamics of Curved Thin Films Under Soluto-Capillary Forces

Interfacial film dynamics is ubiquitous and is interesting in the presence of bulk and/or interfacial heterogeneity. To control the stability of thin films over different substrates, we need a fundamental understanding of the physical forces that affect the film, particularly when the film is heterogeneous. In the present study, we examine the thin film dynamics of a binary mixture subject to evaporation and drainage atop both a glass dome and an air bubble. Experimentally, we observe the film thickness profiles via a custom-made dynamic fluid-film interferometer. In the parallel computer simulations, we develop a lubrication theory to compute the film thickness evolution under the effects of capillarity, gravity, Marangoni forces, and van der Waals interactions with the substrate. We find the dynamics are quite complex and subject to long-lived time dependent states -- thus soluto-capillary forces stabilize the film. Moreover, we find that stabilizing van der Waals forces are crucial to create the conditions forMarangoni regeneration for drainage over a solid substrate. For a draining, heterogeneous thin film over a bubble surface, we find sustained, nonlinear thickness oscillations are rather easily accessible.