Velocity measurements in draining foam films (INVITED)

Abstract eng:
Foam fihn drainage under gravity is a key ingredient controlling foams and bubbles stability. It has been shown by Mysels et al. in a pioneering work [1] that the drainage time is proportional to the fihn width, which was qualitatively explained at that time by the dominant role of the menisci at the fihn boundaries. This implies a complex flow within the draining fihn that we measure here for the first time using a tracer-free innovative velocimetry technique. Fluorescein is added in the fihn and a dark spot is photo-bleached. This spot then acts as a perfect passive tracer during fractions of second, before disappearing by diffusion or mixing. We evidence the lateral part of the film moving upward and the central part moving downward and we propose scaling laws for the associated velocities [ 2 ] .

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