Transient pattern formation in an active matter contact poisoning model

One of the most notable features in repulsive particle based active matter systems is motility-induced-phase separation (MIPS) where a dense, often crystalline phase and low density fluid coexist. Most active matter studies involve time-dependent activity; however, there are many active systems where individual particles transition from living or moving to dead or nonmotile due to lack of fuel, infection, or poisoning. Here we consider an active matter particle system at densities where MIPS does not occur. When we add a small number of infected particles that can poison other particles, rendering them nonmotile, we find a rich variety of time dependent pattern formation, including MIPS, a wetting phase, and a fragmented state formed when mobile particles plow through a nonmotile packing. We map the patterns as a function of time scaled by epidemic duration, and show that the pattern formation is robust for a wide range of poisoning rates and activity levels. We also show that pattern formation does not occur in a random death model, but requires the promotion of nucleation by contact poisoning. Our results should be relevant to biological and active matter systems where there is some form of poisoning, death, or transition to nonmotility. Self-motile active matter particles form a motility-induced phase separation (MIPS) state for high density and activity. By introducing an infection that causes particles to become nonmotile, MIPS clustering can arise outside the MIPS regime and exhibits time-dependent patterning from MIPS to a wetting phase and a fragmented state.

Automated summary

This article investigates time-dependent pattern formation in active matter particle systems, including motility-induced phase separation (MIPS), wetting phase, and fragmented state. The study shows that pattern formation is influenced by poisoning rates and activity levels, and contact poisoning can promote nucleation in certain cases.