Continuum Theory of Phase Separation Kinetics for Active Brownian Particles

J Stenhammar and A Tiribocchi and RJ Allen and D Marenduzzo and ME Cates, PHYSICAL REVIEW LETTERS, 111, 145702 (2013).

DOI: 10.1103/PhysRevLett.111.145702

Active Brownian particles (ABPs), when subject to purely repulsive interactions, are known to undergo activity-induced phase separation broadly resembling an equilibrium (attraction-induced) gas-liquid coexistence. Here we present an accurate continuum theory for the dynamics of phase-separating ABPs, derived by direct coarse graining, capturing leading-order density gradient terms alongside an effective bulk free energy. Such gradient terms do not obey detailed balance; yet we find coarsening dynamics closely resembling that of equilibrium phase separation. Our continuum theory is numerically compared to large-scale direct simulations of ABPs and accurately accounts for domain growth kinetics, domain topologies, and coexistence densities.

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