Pressure of a gas of underdamped active dumbbells

TL;DR

This study investigates how the pressure exerted by underdamped active dumbbells on a wall depends on damping, revealing that inertial effects cause the force to vanish at low damping and depend complexly on damping levels.

Contribution

It introduces a model of underdamped active dumbbells to explore inertial effects on pressure, extending previous overdamped models and highlighting the role of particle trajectories near walls.

Findings

Force on the wall vanishes at low damping coefficients.

Pressure behavior depends complexly on damping at low densities.

Particle trajectories near the wall explain pressure variations.

Abstract

The pressure exerted on a wall by a gas at equilibrium does not depend on the shape of the confining potential defining the wall. In contrast, it has been shown recently [A.P. Solon et al., Nat. Phys. 11, 673 (2015)] that a gas of overdamped active particles exerts on a wall a force that depends on the confining potential, resulting in a net force on an asymmetric wall between two chambers at equal densities. Here, considering a model of underdamped self-propelled dumbbells in two dimensions, we study how the behavior of the pressure depends on the damping coefficient of the dumbbells, thus exploring inertial effects. We find in particular that the force exerted on a moving wall between two chambers at equal density continuously vanishes at low damping coefficient, and exhibits a complex dependence on the damping coefficient at low density, when collisions are scarce. We further show that this behavior of the pressure can to a significant extent be understood in terms of the trajectories of individual particles close to and in contact with the wall.