Evaporation Driven Oscillatory Marangoni-Capillary Flow in Thin Films of a Binary Mixture

Thin film systems are ubiquitous: from soap bubbles to industrial lubricants. It is well known that inhomogeneities in thin film composition can generate a surface tension gradient leading to soluto-Marangoni flows. One simple system that exhibits such behavior is a binary liquid thin film over a bubble surface. If the liquid film contains miscible components with different surface tension and evaporation rate, then when the evaporative species leaves the film, the surface tension of the mixture changes and liquid is drawn toward the high surface tension region, thereby increasing the film curvature. We demonstrate that under certain conditions the capillary pressure may ultimately overwhelm the Marangoni effects such that the film thickness and composition are again homogenized. Evaporation then recreates a composition gradient and the above interplay between Marangoni and capillary stresses repeats, resulting in an oscillatory flow. Such an oscillatory flow was observed both in numerical simulations and in dynamic fluid-film interferometer experiments with binary mixtures of low molecular weight silicone oil. This talk will focus on elucidating the interplay among evaporation, soluto-Marangoni flow, and capillary flow and their effects on oscillation amplitude and frequency.