Dynamic overlap concentration scale of active colloids

Abstract

By introducing the notion of a dynamic overlap concentration scale, we identify universal and previously unreported features of the mechanical properties of active colloids. These features are codified by recognizing that the characteristic length scale of an active particle's trajectory, the run-length, introduces a new concentration scale φ * . Large-scale simulations of repulsive active Brownian particles (ABPs) confirm that this new run-length dependent concentration, which is the trajectory-space analogue of the overlap concentration in polymer solutions, delineates distinct concentration regimes in which interparticle collisions alter particle trajectories. Using φ * and concentration scales associated with colloidal jamming, the mechanical equation-of-state for ABPs can be collapsed onto a set of principal curves that contain a number of previously 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 be of great utility in unraveling the behavior of active and driven systems.

Dynamics of active particles with translational and rotational inertia

“…Further, exploring the interplay between inertia and activity in flow-mediated transport would be an interesting area to investigate in the future [116]. To this end, it will be insightful to apply effective interactions [32,48] or hydrodynamics [94,117] and mean-field methods [118], to obtain theoretical predictions that take advantage of the intrinsic simplicity of the inertial AOUP model.…”

Swimming in potential flow

“…We discussed a single articulating body in this work, but it should be clear from the general formulation that there is no restriction on the number of self-propelled bodies. The study of many interacting self-propelled bodies has become a very vibrant area of research in the active matter community (Pooley, Alexander & Yeomans 2007; Lauga & Bartolo 2008; Cates & Tailleur 2015; Dulaney & Brady 2021; Mallory, Omar & Brady 2021). Active Stokes flow swimmers form the basis of the active Brownian particle (ABP) model for active matter, which has been shown to display very interesting collective dynamics such as motility-induced phase separation (MIPS) and coherent flocking motion.…”

Mechanical theory of nonequilibrium coexistence and motility-induced phase separation

“…This measured behavior can then be extrapolated to regions of the ϕ − ℓ 0 plane where the equations-of-state cannot be directly obtained by leveraging a number of physical considerations (e.g., p C is a monotonically increasing function of both ϕ and ℓ 0 ), as detailed in ref. 61 . In two dimensions (2d), we utilize the equations-of-state developed in ref.…”