Transport Coefficients in Dense Active Brownian Particle Systems: Mode-Coupling Theory and Simulation Results

TL;DR

This paper develops a mode-coupling theory for dense active Brownian particles, validating it with simulations and experiments, and explores how activity influences glass transition dynamics and transport properties.

Contribution

It introduces a novel mode-coupling theory for active particles and demonstrates its accuracy through simulations and experimental comparisons.

Findings

Good agreement between theory, simulation, and experiment for mean squared displacement.

Self-propulsion affects the Stokes-Einstein relation in dense active systems.

Effective swim velocity predictions align qualitatively with simulation data near the glass transition.

Abstract

We discuss recent advances in developing a mode-coupling theory of the glass transition (MCT) of two-dimensional systems of active Brownian particles (ABP). We specifically discuss the case of a single ABP tracer in a glass-forming passive host suspension; a case that has recently been studied in experiments on colloidal Janus particles. We employ event-driven Brownian dynamics (ED-BD) computer simulations to test the ABP-MCT, and find good agreement between the two for the MSD. The ED-BD simulation results also compare well to experimental data, although a peculiar non-monotonic mapping of self-propulsion velocities is required. The ABP-MCT predicts a specific self-propulsion dependence of the Stokes-Einstein relation between the long-time diffusion coefficient and the host-system viscosity that matches well the results from simulation. An application of ABP-MCT within the integration-through transients (ITT) framework to calculate the density-renormalized effective swim velocity of the interacting ABP agrees qualitatively with the ED-BD simulation data at densities close to the glass transition, and quantitatively for the full density range only after the mapping of packing fractions employed for the passive system.