Confinement Effects on the Collective Behavior of Active Matter

Active colloidal matter can exhibit different collective phases in response to changes in the active particles' propulsion characteristics. Moreover, hydrodynamic interactions between colloidal particles and obstacles can also modulate their dynamics. The coupling between these two effects is not well understood, in part because resolving the hydrodynamic boundary conditions between many active colloids and many stationary obstacles is computationally very demanding. Only recently, the development of colloidal hydrodynamic simulation methods, such as the Smoothed Profile Method, have made this class of problems tractable. Using this method, we simulate dense active colloidal dispersions in strongly confined geometries and observe transitions in their collective behavior dependent on the interplay between the propulsion characteristics and the confinement.