Using Thermal Ratchet Mechanism to Achieve Net Motility in Magnetic Microswimmers

TL;DR

This paper demonstrates how thermal ratchet principles can induce net movement in magnetic microswimmers by breaking reciprocal symmetry with asymmetric actuation, leading to enhanced diffusivity and potential for active matter studies.

Contribution

The study introduces a novel method to achieve directed motion in magnetic colloids using thermal ratchet mechanisms with asymmetric magnetic actuation.

Findings

Magnetic microswimmers exhibit net motility under asymmetric actuation.

Enhanced diffusivity observed in the experimental system.

Numerical calculations agree with experimental results.

Abstract

Thermal ratchets can extract useful work from random fluctuations. This is common in the molecular scale, such as motor proteins, and has also been used to achieve directional transport in microfluidic devices. In this work, we use the ratchet principle to induce net motility in an externally powered magnetic colloid, which otherwise shows reciprocal (back and forth) motion. The experimental system is based on ferromagnetic micro helices driven by oscillating magnetic fields, where the reciprocal symmetry is broken through asymmetric actuation timescales. The swimmers show net motility with an enhanced diffusivity, in agreement with the numerical calculations. This new class of microscale, magnetically powered, active colloids can provide a promising experimental platform to simulate diverse active matter phenomena in the natural world.