Dynamic overlap concentration scale of active colloids

By introducing the notion of a dynamic overlap concentration scale, we identify additional universal features of the mechanical properties of active colloids. We codify these features by recognizing that the characteristic length scale of an active particle's trajectory, the run length, introduces a concentration scale phi*. Large-scale simulations of repulsive active Brownian particles (ABPs) confirm that this run-length dependent concentration, the trajectory-space analog of the overlap concentration in polymer solutions, delineates distinct concentration regimes in which interparticle collisions alter particle trajectories. Using phi* and concentration scales associated with colloidal jamming, the mechanical equation of state for ABPs collapses onto a set of principal curves that contain several overlooked features. The inclusion of these features qualitatively alters previous predictions of the behavior for active colloids, as we demonstrate by computing the spinodal for a suspension of purely repulsive ABPs. Our findings suggest that dynamic overlap concentration scales should help unravel the behavior of active and driven systems.

Automated summary

By introducing the concept of dynamic overlap concentration scales, additional universal features of the mechanical properties of active colloids have been identified. Through large-scale simulations of repulsive active Brownian particles, it has been confirmed that the run-length dependent concentration delineates distinct concentration regimes where interparticle collisions alter particle trajectories. The inclusion of these features qualitatively alters previous predictions of the behavior for active colloids.