Interface and volume exchanges between deformed soap films of an elementary foam.*

In many industrial processes, liquid foams are notably used for their viscoelastic behaviour. Given that their liquid matrices are Newtonian fluids with viscosities lower by several orders of magnitude, their strong dissipative properties are surprising, and recent advances have shown that they may originate from a very localised zone near the junctions between the foam films. To further investigate the different mechanisms involved there, we designed a special frame allowing us to create and observe three soap films connected together with a meniscus. We can control the lengths of the films using three synchronized motors to explore different geometries of deformation. As we did in our previous work, we monitor the outgoing thick films from the meniscus with a fluorescent dye and we track the thickness profile of our films with a spectral camera. We also developed a new technique allowing us to directly track the size of the meniscus using the fluorescence of our soap solution and a ray tracing-based criterium. Thus, the whole setup allows us to quantify both the exchanges of interface and volume between the films. Looking at various geometries of deformation, we witness that the viscoelastic response of a single soap film strongly depends on the stress state of its neighbours.