dr. Gašper Kokot (MF UL): Nonequillibrium shape fluctuations and spontaneous propulsion of a droplet enclosing active particles
We will introduce the topic of active matter as a system that is driven out of thermodynamic equilibrium by energy infusion. We will see a few specific examples in magnetic systems, before dwelling on details of a recent development on active particles enclosed by soft, deformable boundaries, that is responsive to the particles’ activity. We will reveal that a fluid droplet enclosing motile colloids powered by the Quincke effect (Quincke rollers) exhibits strong shape fluctuations, and while the rollers do self-organize into a single vortex, it fills the droplet interior. We demonstrate that the shape fluctuations have a power spectrum consistent with active fluctuations driven by particle-interface collisions, and a broken detailed balance confirms the nonequilibrium nature of the shape dynamics. We further find that the rollers activity coupled to soft boundary fluctuations can result in a spontaneous symmetry breaking and vortex splitting. The droplet acquires motility while the vortex doublet exists. Our findings provide insights into the complex collective behavior of active colloidal suspensions in soft confinement.
