Colloids in Nematics: Attractive and Repulsive Loci Near Corrugated Boundaries

We study colloids with well-defined anchoring near a corrugated boundary with hills and dales of radii of curvature greater than the colloid radius. By tailoring wall curvature, we define sites of attraction and equilibrium loci for colloids that vary from near contact to several particle radii from contact. Colloids with hedgehogs, boojums and Saturn rings interact distinctly with these boundaries; Saturn rings transform to dipolar configurations driven by wall interactions in some cases. We also define sites of repulsion to propel colloids away from these boundaries, and find unstable loci from which colloids depart along multiple paths. Small perturbations of colloid position allow selection among these paths to propel colloids toward or away from the wall using the nematic energy landscape. These abilities to transform defect configuration, to define docking sites and to direct particles toward or away from boundaries provide new tools to steer colloid motion, defect configuration and to guide structure formation.