Séminaire Ruben Zakine

The elusive surface tension of active fluids

Phase transitions and phase separations in active matter systems are now ubiquitous. Nonetheless, since relying on a free energy-based definition of surface tension is impossible in these systems, the stability of the interfaces is usually difficult to characterize. In this seminar, I will discuss various quantities that show some relevance to define a surface tension out of equilibrium. In particular, I will propose a purely mechanical definition of surface tension in assemblies of self-propelled particles. Notably, the mechanical probes we use in our simulations 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.

Image: Active particles condensing at a wall (by Yongfeng Zhao)