Emergent vortices in populations of colloidal rollers

Abstract

Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking. Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex. Combining physical experiments and numerical simulations, we elucidate this collective behavior. We demonstrate that the emergent-vortex structure lives on the verge of a phase separation, and single out the very constituents responsible for this state of polar active matter. Building on this observation, we establish a continuum theory and lay out a strong foundation for the description of vortical collective motion in a broad class of motile populations constrained by geometrical boundaries.

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• Electrohydrodynamic Quincke rotation of a prolate ellipsoid
• Modeling chemo-hydrodynamic interactions of phoretic particles: a unified framework
• Reaction processes among self-propelled particles
• Focusing of Active Particles in a Converging Flow
• Colloidal particle electrorotation in a non-uniform electric field
• Boundary induced convection in a collection of polar self-propelled particles