Microswimmer separation in complex confining geometries

Microswimmers of either biological or synthetic nature exhibit a variety of nonequilibrium collective behavior, including aggregation and phase separation. In particular, situations that tend to be overlooked concern the separation under confinement of mixtures of microswimmers that differ in their propulsion mechanism. In this case, understanding the system parameters that control the degree of the separation requires understanding the hydrodynamic forces at play. Given the complex confining geometries, these forces can only be resolved numerically. We leverage recent advances in massively parallel colloidal hydrodynamic simulations to model a mixture of two styles of swimmers, "pushers" and "pullers," which separate due to hydrodynamic interactions with nearby surfaces. Through systematic variation of confining geometries we construct a series of filters for species separation. Our findings provide insight for the design of activity-based separation methods of active colloids.