The Dynamics of Curved Fluid Films Between Complex Interfaces

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The dynamics of thin films are critical to the coalescence of drops, foam stability, the action of lubricants of all types, as well as, “drying’’ phenomena of all kinds, including the levelling of paints and coatings. In our bodies, thin fluid films play a key role in a wide array of processes including the cleaning of the air after inhalation, the ability to see clearly under all kinds of conditions through the so-called “tear film”, and the ability of single red blood cells to transfer oxygen in capillaries. It is now known and has been demonstrated repeatedly in experiments over the last decade that very small inhomogeneities in the films (i.e. impurities), generate film thickness patterns that can be time dependent and chaotic. These dynamics can even lead to a new kind of “turbulence”. There is very little physical understanding of the formation of these complex patterns, which, once they appear, completely control the lifetime and evolution of the thin films. So, for example, they determine whether a foam is stable or unstable or whether a lubricant fails or remains useful. The research integrates theory, numerical simulations, and experiments to develop a physical understanding of these complex dynamics and the conditions in which they may occur. The knowledge learned during the research will be disseminated in two classes at Stanford, three high school teachers will be involved in the research with summer internships, and the Stanford STAR – Scientific Teaching Through Art – program will highlight the natural beauty of the dynamics of these films and visually develop appealing stories to reach a broad audience including high school and community college students.To accomplish the understanding of these thin film chaotic dynamics the research will employ direct numerical simulation (DNS) via a lubrication or “thin film” theory– thus even with the “thin film” assumption a large numerical solution is required. The research will elucidate via numerical simulation over parameter regimes associated with previously accomplished experiments, what are the conditions and mechanisms for the formation of these patterns. The simulations will be coupled with additional experiments to directly test whether a new physical understanding has been successfully modelled. The research goal is to delineate the parameter regimes where prior simplifying assumptions regarding space and time development are not valid, thus fundamentally changing the study of thin film dynamics between complex interfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.