Active phase separation triggered by chemotactic defects.

When initial conditions are uniformly random, numerical simulations of Motility-Induced Phase Separation (MIPS) in active suspensions with average packing fractions above a specific (spinodal) threshold require relatively short run times. The question remains of how phase separation can be achieved within a feasible run time at lower packing fractions (binodal region). We demonstrate that defects functioning as attractive chemotactic centers can rapidly initiate the formation of local particle aggregates, which, under certain conditions, can detach and grow until phase separation is fully realized. Here, we provide a detailed investigation of defect-triggered MIPS in the binodal region. We suggest that this mechanism may facilitate the aggregation of bacteria into biofilms, with nutrient particles acting as chemotactic attractors.