Co-authors: Isabelle Cantat
Location: Institut de Physique de Rennes, Université Rennes 1, Rennes, France
At the edge of a soap film, at the connection between the flat film and the curved meniscus, the gradient of interface curvature generates a drainage flow from the film to the meniscus. As shown by Aradian, Raphael and de Gennes, for incompressible interfaces, this results in a marginal pinch.
We first showed theoretically that the pinch is unstable and that it is hence reorganized by capillary forces to group together regions of similar heights, which minimizes the total area of the film. This reorganization occurs only for large wavelengths. The critical wavelength is computed based on the initial profile of the pinch and can also be well described by scaling laws.
We also performed experiments to observe this initial pinch and its destabilization. Combining a fast camera and a hyperspectral camera, we obtained a precise description of the evolution of the pinch. We observed that the pinch destabilizes indeed, and that the wavelength is in very good agreement with the computation and scaling-law predictions.
This shed new light to the phenomenon of marginal regeneration, which is involved in film drainage and ruptures, two major phenomenon responsible for foam aging.