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Physics of foamsFoams are polyhedral cells filled with air and separated by liquid films. Gravity leads to the drainage of the liquid along the bubble edges and the so-called "Plateau borders" which are the meeting lines of bubbles edges. Please note that Joseph Plateau, pioneer in the study of foams, got his PhD at the University of Liege ! The fluid motion along Plateau borders is complex because it involves many parameters like the bubble sizes, the fluid characteristics (viscosity, density) and the packing of surfactant molecules along the air/liquid interfaces. Foam drainage The GRASP investigates the motion of fluid in thin films and in Plateau borders. The drainage of liquid along Plateau borders is indeed related with the global stability (collapse) of the foam. This work is done in collaboration with Colgate-Palmolive. By looking at the motion of interference fringes appearing on thin films, we have developped a method for tracking the micro-flows.  Foams in microgravity In microgravity, the foam drainage disappears. In space, the only forces acting on the liquid are capillary forces. We have performed experiments in microgravity (parabolic flights). Bubbles of the foam are seen to become rounded and the foam looses its rigidity because large amounts of liquid accumulates in the Plateau borders. See our paper on this effect. Avalanches of popping bubbles We have also investigated the collapse of foams by recording the sound emitted by the successive bubble pops. In our records, we have observed the occurence of "avalanches" of popping bubbles. Such cascades are quite similar to power law cascades usually studied in Statistical Physics. [1] N.Vandewalle, J.F.Lentz, S.Dorbolo and F.Brisbois, Avalanches of popping bubbles in collapsing foams, Phys. Rev. Lett. 86, 179 (2001) [2] N.Vandewalle and J.F.Lentz, Cascades of popping bubbles along air/foam interfaces, Phys. Rev. E 64, 021507 (2001) [3] N.Vandewalle, H.Caps and S.Dorbolo, Cascades of popping bubbles, Physica A 314, 320 (2002) Links |
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