Inertial effects on entropic transport of active Brownian particles in an asymmetric channel

Micro- and nano-swimmers diffusing in a liquid solvent confined by structures where entropic barriers arise naturally 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 (termed micro- and nano-flyers) 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 mass of particles increases. Furthermore, the average particle velocity has a maximum as a function of the mass, indicating that particles with an optimal mass $m_{op}$ can be sorted from a mixture with particles of other masses. In particular, we show 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 $m_{op}$ on the rotational diffusion rate, self-propulsion force, aspect ratio of the channel, and effective 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.