Inertial effects on rectification and diffusion of active Brownian particles in an asymmetric channel

TL;DR

This study investigates how inertia influences the movement and diffusion of active Brownian particles in asymmetric channels, revealing optimal particle masses for sorting and enhanced diffusion effects.

Contribution

It introduces the role of inertia in active particle dynamics within asymmetric channels, highlighting effects on accumulation, velocity, and diffusion not captured by overdamped models.

Findings

Particles accumulate at channel walls with increasing mass

Optimal particle mass maximizes average velocity and diffusion

Enhanced diffusion peak occurs at specific particle masses

Abstract

Micro- and nano-swimmers moving in a fluid solvent confined by structures that produce entropic barriers are often described by overdamped active Brownian particle dynamics, where viscous effects are large and inertia plays no role. However, inertial effects should be considered for confined swimmers moving in media where viscous effects are no longer dominant. Here, we study how inertia affects the rectification and diffusion of self-propelled particles in a two-dimensional asymmetric channel. We show that most of the particles accumulate at the channel walls as the masses of the particles increase. Furthermore, the average particle velocity has a maximum as a function of the mass, indicating that particles with an optimal mass $M^{*}_{\rm op}$ can be sorted from a mixture with particles of other masses. In particular, we find that the effective diffusion coefficient exhibits an enhanced diffusion peak as a function of the mass, which is a signature of the accumulation of most of the particles at the channel walls. The dependence of $M^{*}_{\rm op}$ on the rotational diffusion rate, self-propulsion force, aspect ratio of the channel, and active torque is also determined. The results of this study could stimulate the development of strategies for controlling the diffusion of self-propelled particles in entropic ratchet systems.