Evaporation-driven solutocapillary flow of thin films over curved substrates*

Evaporation-driven solutocapillary flows arise when the evaporation of a volatile species induces concentration nonuniformities that give rise to spatial gradients in surface tension and subsequent Marangoni flows. These flows are prevalent in foams and emulsions, biological systems, and coating processes. We study evaporation-driven solutocapillarity in the context of ultrathin liquid films resting atop solid, spherical substrates in contact with a fluid reservoir. Experiments are conducted with low molecular weight silicone oil mixtures composed of a volatile solvent and trace amounts of a nonvolatile solute. A theoretical model based on the thin-film approximation is developed and numerically solved to give the film thickness, solute concentration, and pressure profiles. Our results reveal that both Marangoni stresses and stabilizing van der Waals interactions between the substrate and free surface can induce flow reversals and film regeneration. Furthermore, increasing the solvent’s rate of evaporation enhances the rate of film regeneration. This talk focuses on these effects and their resulting film profiles.