Directed autonomous motion of active Janus particles induced by wall-particle alignment interactions

TL;DR

This paper introduces a highly efficient method to direct active particle motion using wall-particle alignment interactions, enabling control and sorting of microswimmers based on chirality and propulsion characteristics.

Contribution

It demonstrates a novel rectification mechanism for active particles via wall interactions, effective even with slight asymmetries, and explores conditions for achiral swimmer rectification.

Findings

Over 60% efficiency in rectifying chiral active particles.

Rectification is robust against variations in propulsion and chirality.

Achiral swimmers can be directed using fluid flow-induced orbiting.

Abstract

We propose a highly efficient mechanism to rectify the motion of active particles by exploiting particle-wall alignment interactions. Through numerical simulations of active particles' dynamics in a narrow channel, we demonstrate that a slight difference in alignment strength between the top and bottom walls or a small gravitational drag suffices to break upside-down symmetry, leading to rectifying the motion of chiral active particles with over 60% efficiency. In contrast, for achiral swimmers to achieve rectified motion using this protocol, an unbiased fluid flow is necessary that can induce orbiting motion in the particle's dynamics. Thus, an achiral particle subject to Couette flow exhibits spontaneous directed motion due to an upside-down asymmetry in particle-wall alignment interaction. The rectification effects caused by alignment we report are robust against variations in self-propulsion properties, particle's chirality, and the most stable orientation of self-propulsion velocities relative to the walls. Our findings offer insights into controlled active matter transport and could be useful to sort artificial as well as natural microswimmers (such as bacteria and sperm cells) based on their chirality and self-propulsion velocities.