Field-controlling patterns of sheared ferrofluid droplets

TL;DR

This study explores how external magnetic fields influence the self-organization of ferrofluid droplets in shear flow, revealing controllable pattern transitions from chains to crystals through simulations and analysis.

Contribution

It introduces a comprehensive phase diagram and critical conditions for pattern transitions, highlighting magnetic field direction as a control parameter.

Findings

Ferrofluid droplets form chain-like structures under weak magnetic fields.

Strong magnetic fields induce crystal-like droplet arrangements.

Pattern transitions can be controlled by magnetic field orientation.

Abstract

We investigate how ferrofluid droplets suspended in a wall-bounded shear flow can organise when subjected to an external magnetic field. By tuning the magnitude of the external magnetic field, we find that the ferrofluid droplets form chain-like structures in the flow direction when the magnetic field is weak, while forming a crystal-like pattern in a strong magnetic field. We provide the phase diagram and the critical conditions for this chain-to-crystal transition, by applying both numerical simulations and analytic calculations. We also examine how the organised patterns of the ferrofluid droplets can be controlled by simply changing the direction of the magnetic field. This work demonstrates new aspects of field-controllable ferrofluid droplets as a configurable and reprocessable metamaterial.