Collective dynamics in a binary mixture of hydrodynamically coupled micro-rotors

TL;DR

This study uses numerical simulations to explore how hydrodynamic interactions influence the collective behavior of self-rotating particles in a monolayer, revealing pattern formations like clustering, phase separation, and crystal structures.

Contribution

It demonstrates the significant impact of many-body hydrodynamic interactions on the phase behavior of active rotors, a factor often neglected in dry system models.

Findings

Hydrodynamic interactions induce clustering of opposite-spin rotors.

Same-spin rotors undergo phase separation at higher densities.

Hexagonal crystal structures emerge above a critical density.

Abstract

We study, numerically, the collective dynamics of self-rotating nonaligning particles by considering a monolayer of spheres driven by constant clockwise or counterclockwise torques. We show that hydrodynamic interactions alter the emergence of large-scale dynamical patterns compared to those observed in dry systems. In dilute suspensions, the flow stirred by the rotors induces clustering of opposite-spin rotors, while at higher densities same-spin rotors phase separate. Above a critical rotor density, dynamic hexagonal crystals form. Our findings underscore the importance of inclusion of the many-body, long-range hydrodynamic interactions in predicting the phase behavior of active particles.