# Response of active Brownian particles to boundary driving

## TL;DR

This study investigates how underdamped active Brownian particles respond to boundary shear, revealing complex behaviors like flow reversal and polarization effects due to the interplay of activity, interactions, and boundary conditions.

## Contribution

It introduces a detailed computational analysis of underdamped active particles under shear, highlighting novel phenomena such as flow reversal and boundary-induced polarization.

## Key findings

- Flow reversal near the wall observed under certain conditions
- Particle momentum transfer depends on friction and self-propulsion
- Boundary interactions induce polarization of particle directions

## Abstract

We computationally study the behavior of underdamped active Brownian particles in a sheared channel geometry. Due to their underdamped dynamics, the particles carry momentum a characteristic distance away from the boundary before it is dissipated into the substrate. We correlate this distance with the persistence of particle trajectories, determined jointly by their friction and self-propulsion. Within this characteristic length, we observe new and counterintuitive phenomena stemming from the interplay of activity, interparticle interactions, and the boundary driving. Depending on values of friction and self-propulsion, interparticle interactions can either aid or hinder momentum transport. More dramatically, in certain cases we observe a flow reversal near the wall, which we correlate with an induced polarization of the particle self-propulsion directions. We rationalize these results in terms of a simple kinetic picture of particle trajectories.