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Conf’luence A-L Biance

23 novembre 2018

Electroosmosis in liquid foams

Conf’luence Anne Laure Biance - (Chargée de recherche Institut Lumière et Matière, Campus LyonTech-la Doua)

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Mercredi 5 décembre à 10 h 30 - Amphithéâtre Nougaro

Though involved in daily life situations and many industrial processes, liquid foams are short-lived materials that irreversibly evolve and, as usually observed in a foam bath, eventually collapse. An important mechanism at play in this process is the drainage induced by gravity, which is unavoidable. We investigated here a way to reverse it : electro-osmosis. In short, if the surfactant (soap) molecules that stabilize the foam are ions, the water in the foam is charged in the vicinity of the interfaces, and can be set into motion by an external electric field. By controlling the magnitude of the field, we will show how a foam could be maintained in a stable state or be destroyed on demand.

Much is known about electro-osmosis in solid materials, but the case of foams is fundamentally different for various reasons. First, a liquid foam is a deformable porous medium, adapting constantly its shape when flows are involved. Second, the interfacial ionic charges (at the origin of electro-osmosis) are carried by the surfactants molecules, who have their own dynamics (adsorption, mobility). Third, the hydrodynamic boundary condition at this liquid-gas interface is more complex.

We will discuss these three particularities of liquid foams by performing experiments, simulations and analysis at each scale of the foam to get a full picture of the phenomena involved.