Enhanced diffusion and ordering of self-propelled rods

TL;DR

This paper develops a theoretical framework for self-propelled rods, revealing how self-propulsion influences diffusion, phase transition density, and boundary effects in two-dimensional systems.

Contribution

It introduces a modified Smoluchowski equation for self-propelled rods, capturing enhanced diffusion and altered phase behavior compared to passive systems.

Findings

Self-propulsion increases longitudinal diffusion.

Self-propulsion lowers the isotropic-nematic transition density.

Boundary effects are significantly enhanced in confined systems.

Abstract

Starting from a minimal physical model of self propelled hard rods on a substrate in two dimensions, we derive a modified Smoluchowski equation for the system. Self -propulsion enhances longitudinal diffusion and modifies the mean field excluded volume interaction. From the Smoluchowski equation we obtain hydrodynamic equations for rod concentration, polarization and nematic order parameter. New results at large scales are a lowering of the density of the isotropic-nematic transition and a strong enhancement of boundary effects in confined self-propelled systems.