Foam film tension and steady dynamical thickness in extensional oscillatory regime *

Foam films are bounded by menisci at a lower pressure and are therefore draining until they break or are stabilized by the disjoining pressure. Above 100 nm, the film thickness is therefore unsteady and a pinch grows at the boundary between the film and the meniscus [1]. Using the lubrication approximation, we numerically determine the evolution of a film of initial thickness h_0, when it is periodically pushed into or pulled out of the meniscus. The film profile is periodically deformed close to the meniscus, but a finite steady thickness, different from h_0, propagates through the film, asymptotically invading the entire film [2]. This asymptotic thickness depends on the forcing amplitude and frequency. A steady one micron thick film can finally be obtained in the entire film without disjoining pressure: this surprising result may help stabilize foam, using oscillatory shear-induced film rejuvenation, similarly to the observation of Tregouet and Saint-Jalmes under steady shear in a 3D sample [3]. Moreover, an oscillatory film tension variation of steady amplitude is observed, which may contribute to liquid foam visco-elasticity.

[1] Aradian et al. EPL, 2001

[2] Tregouet, Lebreton, Saint-Jalmes, Cantat, preprint

[3] Tregouet, Saint-Jalmes, preprint