Abstract
Biological organisms and artificial active particles self-organize into swarms and patterns. Open questions concern the design of emergent phenomena by choosing appropriate forms of activity and particle interactions. A particularly simple and versatile system are 3D-printed robots on a vibrating table that can perform self-propelled and self-spinning motion. Here we study a mixture of minimalistic clockwise and counter-clockwise rotating robots, called rotors. Our experiments show that rotors move collectively and exhibit super-diffusive interfacial motion and phase separate via spinodal decomposition. On long time scales, confinement favors symmetric demixing patterns. By mapping rotor motion on a Langevin equation with a constant driving torque and by comparison with computer simulations, we demonstrate that our macroscopic system is a form of active soft matter.
Highlights
Swarms of robots mimic collaboration of animals and can be programmed to arrange into shapes by information exchange among individuals[1]
We demonstrate that our setup is suitable for observing phase separation driven by active rotation[26, 27], a phenomenon reminiscent of spinodal decomposition in binary fluids with a high symmetry between both phases
We vary the density of a smaller system in the range φ = 0.3–0.7, where the system is stable against gravitational drift and still below the transition to crystallization (Fig. 2h)
Summary
Swarms of robots mimic collaboration of animals and can be programmed to arrange into shapes by information exchange among individuals[1]. Parallel legs apply translational forces (walker), while legs arranged in a circular manner apply torques (rotor, spinner or vibrot) As a result, these robots move, similar to mechanically vibrated polar disks[10, 11]. Together with biological[12] and synthetic microswimmers[13], they belong to the class of active soft matter Collectives of such particles exhibit phase separation into dense clusters and a surrounding gas phase[14,15,16,17,18,19] or self-organize into swarms and flocks[3, 10, 11]. Existing experimental realizations of rotors depend on the application of electromagnetic fields[20,21,22] This approach does not allow rotation control of individual rotors because the fields act on all particles. Our experiment is a simple yet non-trivial example for chiral symmetry breaking in a classical system, far beyond the well-known swarming and flocking behavior of active agents
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