On the dynamics of non-planar thin liquid films

Thin liquid films are fluid structures with perpendicular length scale, typically of the O(< 10 μm), being much smaller than the lateral length scale, typically of the O(> 1 mm). From foams and emulsions to tear films on eyes, they widely occur in industrial processes and natural phenomena. Depending on the wetting energies between its different interfaces, it is susceptible to developing an instability which can lead to its subsequent rupture. It is a great example of how dynamics at microscopic scale influence large scale physical behaviour, with instabilities at micron scale influencing a foam collapse or the blinking action of an eye. The subject of this thesis focuses on non-planar thin liquid films that are found, for instance, in between two foam bubbles or in partial wetting systems in microfluidic channels. The dynamics of such non-planar films is governed by two thinning mechanisms. The first mechanism involves drainage due to curvature differences, and results in a localized depression, commonly referred to as a dimple, at the connection between the planar and curved regions. The second thinning mechanism involves growth of a fluctuation originated instability arising from the competition between a stabilizing surface tension and destabilizing van der Waals forces. For this second thinning mechanism to manifest, the film’s lateral length (radius) needs to be large enough to accommodate unstable waves to fit within the film. We study thin film dynamics, by performing numerical simulations that incorporate all these crucial physical processes in the thin film equation...