| Abstract: | We investigate a deceptively simple system, weakly magnetic colloids
suspended in a fluid above a floor. When forced to rotate by the
application of a rotating magnetic field, the microrollers exhibit a
cascade of instabilities; the formation of a shock front, an
instability along the shock front, and the formation of fingers that
detach and lead to moving stable autonomous clusters,
“critters”. Once formed, the critters can be readily steered by the applied
magnetic field. These persistent motile structures can form
spontaneously from hydrodynamic interactions alone with no sensing
or potential interactions conventionally associated with swarming and
flocking. Our studies include experiments and large-scale 3D
simulations. With power, speed and direction controlled remotely
these discoveries may prove useful for transport, flow, vorticity and
mixing control in fluidic systems.
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