Coarsening Kinetics in Active Model B+: Macroscale and Microscale Phase Separation

We perform a comprehensive numerical investigation of the coarsening kinetics of active Brownian particles modeled by the {\it Active Model B+} (AMB+). This model was introduced by Tjhung et al. [Phys. Rev. X {\bf 8}, 031080 (2018)] and is a generalization of Model B for a conserved order parameter, with two additional activity terms. These terms correspond to rotation-free current (of strength $\lambda$) and rotational current (of strength $\xi$). We find that the presence of rotational current $(\xi \neq 0)$ significantly affects growth kinetics. Depending on the parameter values, AMB+ exhibits either {\it macroscale phase separation} (MPS) or {\it microscale phase separation} ($\mu$PS). We present detailed results for the kinetics of MPS and $\mu$PS in AMB+ with critical composition.

Pradeep Kumar Yadav, Shradha Mishra, Sanjay Puri · 2025