Continuum theory of phase separation kinetics for active Brownian particles

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Active Brownian particles (ABPs) with repulsive interactions spontaneously phase separate.
• This phenomenon mimics equilibrium gas-liquid coexistence driven by attractive forces.
• Understanding the dynamics of such non-equilibrium systems is crucial.

Purpose of the Study:

• To develop an accurate continuum theory for phase-separating ABPs.
• To capture the essential dynamics, including density gradients and coarsening.
• To validate the theory against large-scale direct simulations.

Main Methods:

• Derivation of a continuum theory via direct coarse-graining.
• Inclusion of leading-order density gradient terms and effective bulk free energy.
• Numerical comparison of the theory with direct particle simulations.

Main Results:

• The derived gradient terms do not obey detailed balance.
• Coarsening dynamics closely resemble those of equilibrium phase separation.
• The theory accurately predicts domain growth kinetics, topologies, and coexistence densities.

Conclusions:

• The continuum theory provides a robust framework for understanding ABP phase separation.
• Activity-induced phase separation shares dynamic similarities with equilibrium systems.
• The model accurately bridges microscopic particle behavior to macroscopic continuum dynamics.