Competing Active and Passive Interactions Drive Amoeba-like Living Crystallites and Ordered Bands

Abstract

Swimmers and self-propelled particles are physical models for the collective behaviour and motility of a wide variety of living systems, such as bacteria colonies, bird flocks and fish schools. Such artificial active materials are amenable to physical models which reveal the microscopic mechanisms underlying the collective behaviour. Here we study colloids in a DC electric field. Our quasi-two-dimensional system of electrically-driven particles exhibits a rich and exotic phase behaviour. At low field strengths, electrohydrodynamic flows lead to self-organisation into crystallites with hexagonal order. Upon self-propulsion of the particles due to Quincke rotation, we find an ordered phase of active matter in which the motile crystallites constantly change shape and collide with one another. At higher field strengths, this "dissolves" to an active gas. We parameterise a particulate simulation model which reproduces the experimentally observed phases and, at higher field strengths predicts an activity-driven demixing to band-like structures.

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Cited by in corpus (5)

• Two-dimensional localized states in an active phase-field-crystal model
• Active Brownian Particles in Random and Porous Environments
• Collective Motion of Quincke Rollers with Fully Resolved Hydrodynamics
• Active crystallization from power functional theory
• Effective interactions in active Brownian particles