Spontaneous self-propulsion and nonequilibrium shape fluctuations of a droplet enclosing active particles

Abstract Active particles, such as swimming bacteria or self-propelled colloids, spontaneously assemble into large-scale dynamic structures. Geometric boundaries often enforce different spatio-temporal patterns compared to unconfined environment and thus provide a platform control the behavior of active matter. Here, we report collective dynamics particles enclosed by soft, deformable boundary, that is responsive particles’ activity. We reveal quasi two-dimensional fluid droplet enclosing motile colloids powered Quincke effect (Quincke rollers) exhibits strong shape fluctuations with power spectrum consistent driven particle-interface collisions. A broken detailed balance confirms nonequilibrium nature dynamics. further find rollers self-organize single drop-spanning vortex, which can undergo spontaneous symmetry breaking vortex splitting. The acquires motility while doublet exists. Our findings insights complex colloidal suspensions in soft confinement.