Abstract
Active particles that are self-propelled by converting energy into mechanical motion represent an expanding research realm in physics and chemistry. For micrometer-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 that include inertia. In this perspective article, recent developments of active particles with inertia ("microflyers," "hoppers," or "runners") are summarized both for single particle properties and for collective effects of many particles. These 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 noninertial frames, and the influence of inertia on motility-induced phase separation. Possible future developments and perspectives are also proposed and discussed.
Highlights
The dynamics of self-propelled particles that are perpetually moving by converting energy (“fuel”) into mechanical motion represent a nonequilibrium phenomenon
We extend the model toward active Langevin motion including inertia and summarize recent developments
The new phenomenon for active Langevin motion in this setup is that additional fictitious forces have to be added to the equations of motion if the equations are expressed in the noninertial frame
Summary
The dynamics of self-propelled particles that are perpetually moving by converting energy (“fuel”) into mechanical motion represent a nonequilibrium phenomenon. Further examples for self-propelled particles with inertia range from minirobots and macroscopic swimmers (see Ref. 29 for a recent review) to beetles flying or swimming at water interfaces and whirling fruits self-propelling in air.32 In this perspective article, we first briefly review basic features and predictions of active Brownian motion discussing both swimmers moving on average on a straight line (“linear” or equivalently “achiral,” “left-right symmetric” swimmers) and particles swimming on a circle (“circle” or “chiral” swimmers). We first briefly review basic features and predictions of active Brownian motion discussing both swimmers moving on average on a straight line (“linear” or equivalently “achiral,” “left-right symmetric” swimmers) and particles swimming on a circle (“circle” or “chiral” swimmers) Both single particle properties and collective effects such as motility-induced phase separation (MIPS) are briefly discussed. We distinguish between linear swimmers and circle swimmers, which experience a systematic torque
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