Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor Belt

TL;DR

This paper investigates how microscopic colloidal rotors self-assemble into worms that propel themselves in a viscous fluid through cooperative hydrodynamic flows generated by an elliptically polarized rotating magnetic field.

Contribution

It introduces a novel mechanism of propulsion via a cooperative hydrodynamic conveyor belt formed by colloidal rotors, combining experimental and theoretical analysis.

Findings

Chains of rotors move faster than individual particles.

Propulsion speed saturates at certain distances due to flow additivity limits.

The propulsion mechanism is fully characterized by field parameters.

Abstract

We study propulsion arising from microscopic colloidal rotors dynamically assembled and driven in a viscous fluid upon application of an elliptically polarized rotating magnetic field. Close to a confining plate, the motion of this self-assembled microscopic worm results from the cooperative flow generated by the spinning particles which act as a hydrodynamic "conveyor belt." Chains of rotors propel faster than individual ones, until reaching a saturation speed at distances where induced-flow additivity vanishes. By combining experiments and theoretical arguments, we elucidate the mechanism of motion and fully characterize the propulsion speed in terms of the field parameters.