Clogging Dynamics of Active and Passive Disks in Complex Environments

Directional locking occurs when a particle moving over a periodic substrate can travel only along certain substrate symmetry directions. We study the directional locking and clogging of passive disks and active run-and-tumble particles interacting with a periodic array of obstacles. In the absence of an external biasing force, the active particle motion locks to various symmetry directions of the substrate when the run time between tumbles is large. The number of possible locking directions depends on the array density and the relative size of the obstacles. For large obstacles under biased driving, a trapping behavior occurs that is non-monotonic as a function of increasing run length or increasing self-propulsion force, and the trapping diminishes when the run length is sufficiently large. Passive disks exhibit a drive-direction-dependent clogging behavior when the disk density is sufficiently large. The clogged states are fragile and can be unclogged by changing the driving angle. For large obstacle sizes, we find a uniform clogged state that is distinct from the collective clogging regime. Within the clogged phases, depinning transitions can occur as a function of increasing driving force, with strongly intermittent motion appearing just above the depinning threshold.