Abstract

Assemblies of soap bubbles in close contact display geometrical patterns dictated by the principle of energy minimization. Thus Joseph Plateau formulated in the 19th century that soap films and Plateau borders, which are the liquid channels found at the intersection between three films, exhibit regular angles. What is not formulated in Plateau’s laws is why such assemblies are (meta)stable. For instance, it is at first surprising that Plateau borders are not subject to the Rayleigh Plateau instability unlike liquid filaments. During this foam-lunch I will present experiments that probe the stability of the Plateau borders using several types of perturbations. We will make the link between the stability and a negative effective surface tension that drives the relaxation dynamics. For some regimes, this relaxation is strong enough to trigger fast and inertial flows characterized by strongly nonlinear features such as hydraulic jumps and solitons.