Particle anisotropy tunes emergent behavior in active colloidal systems*

Since early studies of active systems, investigators have sought to understand the role of particle interactions on a system’s emergent collective behavior. Particle anisotropy has been shown to impact the collective behavior of active systems, but studies to date have been qualified demonstrations of concept rather than systematic treatments. In this computational work, we investigate the role of particle anisotropy in shape and driving force director on the phase behavior of an active colloidal system. We find that these anisotropic interactions can combine to enable critical densities lower than those found in systems of isotropic particles, while in some cases actually elevating the critical density. Specifically, we find that tailoring particle anisotropy can enable more “effective'' inter-particle collisions to tune the critical system density for phase separation. Additionally, we observe nucleation of multiple clusters in the phase separation regime, similar to those observed in biological systems. In designing programmable active colloidal systems, steric interactions such as those described here may offer a simple route for tailoring emergent behaviors in active materials.