Chemotactic motility-induced phase separation

In the past decade, extensive research has elucidated the mechanism and generalized thermodynamics of motility-induced phase separation (MIPS), where randomly oriented and self-propelled agents known as active Brownian particles separate into dilute and dense phases. However, it is unclear how chemotaxis, directed motion along a chemical gradient, can affect MIPS—despite its ubiquity in many biological systems such as microbes, eukaryotic cells, and even enzymes, as well as synthetic forms of active matter such as chemically-responsive colloids and robots. Here, we combine continuum models for MIPS and chemotaxis and use linear stability analysis and numerical simulations to study chemotactic MIPS. We find that chemotaxis can dramatically suppress MIPS, arrest Ostwald ripening, and lead to the formation of a fascinating array of oscillatory patterns. These results therefore expand our understanding of the rich phenomenology of MIPS.