Inertial effects of self-propelled particles: from active Brownian to active Langevin motion

TL;DR

This paper reviews recent advances in understanding the dynamics of inertial active particles, highlighting how inertia influences their motion, collective behavior, and phase separation, extending models from overdamped to underdamped regimes.

Contribution

It summarizes recent developments in modeling active particles with inertia, including inertial delay, diffusion tuning, fictitious forces, and phase separation effects.

Findings

Inertial delay affects particle velocity and propulsion alignment.

Inertia can tune long-time self-diffusion coefficients.

Inertia influences motility-induced phase separation.

Abstract

Active particles which are self-propelled by converting energy into mechanical motion represent an expanding research realm in physics and chemistry. For micron-sized particles moving in a liquid ("microswimmers"), most of the basic features have been described by using the model of overdamped active Brownian motion. However, for macroscopic particles or microparticles moving in a gas, inertial effects become relevant such that the dynamics is underdamped. Therefore, recently, active particles with inertia have been described by extending the active Brownian motion model to active Langevin dynamics which include inertia. In this perspective article recent developments of active particles with inertia ("microflyers") are summarized both for single particle properties and for collective effects of many particles. There include: inertial delay effects between particle velocity and self-propulsion direction, tuning of the long-time self-diffusion by the moment of inertia, effects of fictitious forces in non-inertial frames, and the influence of inertia on motility-induced phase separation. Possible future developments and perspectives are also proposed and discussed.