Liquid flow through aqueous foams: from the plateau border-dominated regime to the node-dominated regime

The velocity of gravity-driven flow through aqueous foams (forced drainage) has been determined by using electrical conductivity measurements in foams made with solutions of different surfactants. There is always a scaling behavior (power law) between the drainage velocity V and the imposed flow rate Q: V approximately Q(alpha), but the alpha coefficient varies between the different surfactant solutions and increases with surface viscosity. An explanation of this behavior will be given in terms of a transition between a node-dominated and a Plateau border-dominated viscous dissipation, for which theory predicts respectively alpha=1/3 and alpha=1/2.