No abstract

Hydrodynamic effects are known to significantly affect the collective behavior of wet active matter systems. However, the non‐linear many‐body nature of these interactions makes them very challenging to analyze, particularly in dense suspensions. Quincke rollers are one of the canonical examples of artificial microswimmers. These are active particles that move freely above a plate due to the torque generated by a uniform DC electric field. A system involving many such particles exhibits a variety of collective dynamics, such as the disordered gas, polar liquid, and active crystal states. This work accomplishes numerical simulations of a 3D system containing many rollers in order to explicitly resolve the hydrodynamic interactions and understand the role these play in the resulting active dynamics. It reveals that the far‐field hydrodynamic effects tend to drive ordered collective motion, while the near‐field effects tend to drive disordered collective behavior, and reproduce diverse collective behavior while capturing the role of hydrodynamic effects between rollers without resorting to the approximations previously employed.

A Quincke roller is a unique active particle that can run and tumble freely on a flat plate due to the torque generated by a uniform DC electric field applied perpendicular to the plate[1]. A system involving many such particles exhibits a variety of collective dynamics, such as the disordered gas, polar liquid, and active crystal states[1-8]. We performed direct numerical simulations of a threedimensional system containing many self-rotating particles to explicitly resolve the hydrodynamic interactions among rotating particles. The collective motion depends on the magnitude of the dipole moments induced on the dielectric particles, the area fraction of particles, and the strength of interparticle attraction. We find that the highly ordered polar liquid state is destabilized by the hydrodynamic interaction between rotating particles at high densities: the near-field lubrication interaction becomes dominant over far-field effects as the interparticle separation becomes shorter.