Coalescence of dry foam under water injection
Rémy Mensire1, Keyvan Piroird, Elise Lorenceau
1Laboratoire Navier, UMR 8205 CNRS - ENPC ParisTech - IFSTTAR, Université Paris-Est, 2 allée Kepler, 77420 Champs sur Marne, France. elise.lorenceau@ifsttar.fr.
Abstract:
When a small volume of pure water - typically a drop - is injected within an aqueous foam, it locally triggers the rupture of foam films, thus opening an empty cavity in the foam's bulk. We consider the final shape of this cavity and we quantify its volume as a function of the volume of injected water, the diameter of the bubbles and the liquid fraction of the foam. We provide quantitative understanding to explain how and when this cavity appears. We epitomize the dilution of surfactants at the water-air interfaces as the main cause lying behind the coalescence process. We identify a new coalescence regime for which a critical surfactant concentration rules the stability of the foam.
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