Collective hydrodynamic transport of magnetic microrollers

TL;DR

This study explores how microscopic magnetic rollers collectively move near surfaces under rotating magnetic fields, revealing that hydrodynamic interactions significantly influence their velocity and clustering behavior.

Contribution

It demonstrates the dominant role of hydrodynamics in collective transport and clustering of magnetic microrollers, providing new insights into their dynamic behavior.

Findings

Mean velocity increases linearly with particle density when hydrodynamics dominate.

Hydrodynamic interactions induce anisotropic clustering perpendicular to the driving direction.

Dynamic clusters form and break during propulsion, influenced by particle interactions.

Abstract

We investigate the collective transport properties of microscopic magnetic rollers that propel close to a surface due to a circularly polarized, rotating magnetic field. The applied field exerts a torque to the particles, which induces a net rolling motion close to a surface. The collective dynamics of the particles result from the balance between magnetic dipolar interactions and hydrodynamic ones. We show that, when hydrodynamics dominate, i.e. for high particle spinning, the collective mean velocity linearly increases with the particle density. In this regime we analyse the clustering kinetics, and find that hydrodynamic interactions between the anisotropic, elongated particles, induce preferential cluster growth along a direction perpendicular to the driving one, leading to dynamic clusters that easily break and reform during propulsion.