Dynamics and Separation of Circularly Moving Particles in Asymmetric Patterned Arrays

TL;DR

This study investigates how circularly moving particles interact with asymmetric patterned arrays, revealing rectification and separation based on swimming radius and chirality, with potential applications in particle sorting.

Contribution

It demonstrates the existence of dynamical phases and rectification effects for particles in asymmetric arrays, enabling separation of particles by radius and chirality, including robustness against thermal effects.

Findings

Particles exhibit rectified motion in specific radius windows.

Separation of particles by radius and chirality is possible.

Rectification persists and can be enhanced with thermal effects.

Abstract

There are many examples of driven and active matter systems containing particles that exhibit circular motion with different chiralities, such as swimming bacteria near surfaces or certain types of self-driven colloidal particles. Circular motion of passive particles can also be induced with an external rotating drive. Here we examine particles that move in circles and interact with a periodic array of asymmetric L-shaped obstacles. We find a series of dynamical phases as a function of swimming radius, including regimes where the particle motion is rectified, producing a net dc motion. The direction of the rectification varies with the swimming radius, permitting the separation of particles with different swimming radii. Particles with the same swimming radius but different chirality can also move in different directions over the substrate and be separated. The rectification occurs for specific windows of swimming radii corresponding to periodic orbits in which the particles interact one or more times with the barriers per rotation cycle. The rectification effects are robust against the addition of thermal or diffusive effects, and are in some cases even enhanced by these effects.