Ruben Zakine : The elusive surface tension of active fluids скачать в хорошем качестве

Ruben Zakine : The elusive surface tension of active fluids

Bacteria colonies, schools of fish, flocks of birds,... in these systems, agents inject energy and momentum at their microscopic level, and the resulting macroscopic fluid of agents cannot be described with the classical tools of equilibrium statistical physics. Instead, these assemblies of agents can be described from a macroscopic viewpoint with hydrodynamics equations that interestingly predict condensations and phase transitions. Yet, the stability of the interfaces is usually difficult to characterize because relying on an energetic approach of surface tension is impossible in these systems. In this seminar, I will propose a purely mechanical definition of surface tension in assemblies of self-propelled particles. Notably, the probes we use in our simulations, inspired by the mechanical probes commonly used in the lab, enable one to measure the fluid-solid and the liquid-gas surface tensions, which paves the way of recovering an analogue of the Young-Dupré law for active liquid spreading at a boundary. To finish, I will discuss other quantities that show some relevance to define a surface tension out of equilibrium.