Controlling Active Nematic Topological Chaos Through Defect Pinning on Sharp Boundary Features*

In active nematic liquid crystals, topological defects drive chaotic flows in the bulk. Confined geometries with uniform curvature have been shown to produce ordered defect motion and flows. However, little is known about ordered defect motion enabled by boundaries with varying curvature. To explore how varying curvature can control the active steady state, we simulate an active nematic system using active Beris-Edwards nematodynamics with curved boundary walls. In particular, we investigate the effects of varying bulk topological charge via pinning defects on boundary features. We show that locally convex and concave boundary features have defect pinning effects on positive and negative topological charge respectively, and demonstrate a scheme to tune the strength of defect pinning, expanding the possibilities of ordered states. We also examine how fluid-boundary slipping can stimulate defect nucleation, and can in turn destabilize otherwise periodically stable states. Our findings suggest routes to controllable bulk active flows utilizing boundary features.