Active Brownian particles near straight or curved walls: Pressure and boundary layers

TL;DR

This paper investigates how active Brownian particles behave near walls of different curvatures, analyzing density, pressure, and boundary layers through analytic and simulation methods, revealing new relationships and predictive models.

Contribution

It provides new analytic and simulation insights into density and pressure profiles near walls, including effects of curvature, in active matter systems.

Findings

Density and pressure are enhanced near walls.

A simple relationship links density and pressure enhancements.

Pressure depends on wall curvature, affecting particle motion and rectification.

Abstract

Unlike equilibrium systems, active matter is not governed by the conventional laws of thermodynamics. Through a series of analytic calculations and Langevin dynamics simulations, we explore how systems cross over from equilibrium to active behavior as the activity is increased. In particular, we calculate the profiles of density and orientational order near straight or circular walls, and show the characteristic width of the boundary layers. We find a simple relationship between the enhancements of density and pressure near a wall. Based on these results, we determine how the pressure depends on wall curvature, and hence make approximate analytic predictions for the motion of curved tracers, as well as the rectification of active particles around small openings in confined geometries.