Multiscale Phase Separation in Chemophoretic Active Matter

Nonreciprocal interactions in active matter provide interesting structure and dynamics. Here we investigate chemophoretic systems in which nonreciprocity arises from the asymmetric coupling between agents: first species produces certain chemicals and the other phoretically responds to it. This leads to phase separation at varying scales. Our study uncovers a re-entrant steady-state phase diagram as the nature of the coupling changes from chemoattractive to chemorepulsive character. Chemoattraction provides sustained domain growth, leading to macrophase separation via cluster coalescence. Aggregation in the chemorepulsive case, on the other hand, leads to a steady-state situation that displays phase separation only at a microscale, owing to strong caging effect and frequent fragmentation. The overall far-from-steady-state dynamics is quantified via calculations of growth exponents, cluster transition matrices, and mean-squared displacements.