8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Fri 911:10-14:00P6.35What is the mechanism of soap film entrainment?Laurie Saulnier, 1 Frédéric Restagno, 2 Jérôme Delacotte, 3 Dominique Langevin, 2and Emmanuelle Rio 21 Laboratoire de Physique des Solides, B 510 Campus Universitaire, Université Paris-Sud11 91400, Orsay, France2 Laboratoire de Physique des Solides, Orsay, France3 Laboratoire de Physique Statistique, Paris, FranceThe classical Frankel law describes the formation of soap films and their evolution upon stretching,a model situation of film dynamics in foams (formation, rheology and destabilization). With thepurpose of relating film stretching to foam dynamics, we have built an improved experiment, inwhich we determine simultaneously the velocity of the frame pulled out of a soapy solution andthe shape of the liquid film. We found that only the lower part of the films is of uniform thicknessand follows the Frankel’s law, provided the entrainment velocity is small. We show that this is dueto confinement effects : there is not enough surfactant in the bulk to fully cover the newly createdsurfaces which give rise to huge Marangoni stresses. At large velocities, the surfaces becomemobile and the Frankel’s law breaks down. These findings explain the large dispersion of previousexperimental data reported during the last 40 years [1] and clarify the stretching phenomenon ofthin liquid films.[1] E. A. Van Nierop, B. Scheid, and H. A. Stone, Journal of Fluid Mechanics 630, 443(2009)35