Chiral Active Particles are Sensitive Reporter to Environmental Geometry

TL;DR

This study investigates how chiral active particles' movement and diffusivity are affected by environmental obstacle structures, revealing their potential for sorting and sensing applications based on chirality.

Contribution

We demonstrate that chiral active particles exhibit unique sensitivity to obstacle lattice geometry, enabling their use in sorting and environmental sensing.

Findings

Effective diffusivity depends on obstacle lattice structure.

Reentrant directional locking enables sorting of particles with different activities.

Parallelogram lattices can separate clockwise and counter-clockwise particles.

Abstract

Chiral active particles (CAPs) are self-propelling particles that break time-reversal symmetry by orbiting or spinning, leading to intriguing behaviors. Here, we examined the dynamics of CAPs moving in 2D lattices of disk obstacles through active Brownian dynamics simulations and granular experiments with grass seeds. We find that the effective diffusivity of the CAPs is sensitive to the structure of the obstacle lattice, a feature absent in achiral active particles. We further studied the transport of CAPs in obstacle arrays under an external field and found a reentrant directional locking effect, which can be used to sort CAPs with different activities. Finally, we demonstrated that the parallelogram lattice of obstacles without mirror symmetry can separate clockwise and counter-clockwise CAPs. The mechanisms of the above three novel phenomena are qualitatively explained. As such, our work provides a basis for designing chirality-based tools for single-cell diagnosis and separation, and active particle-based environmental sensors.