Deck the walls with tunable energy fields for colloidal particles in nematic liquid crystals

Confined nematic liquid crystals provide new opportunities to direct colloidal motion and assembly. Nematic liquid crystal director fields molded by confinement can present domains of bend, splay or twist with associated elastic energies. Colloidal particles also distort the nematic director field, and are repelled or attracted to these domains to minimize the elastic energy cost in these systems. We have been studying colloids adjacent to a wavy wall in a nematic liquid crystal with a smoothly varying, non-singular director field that features bend and splay distortions. Colloids within this field can have multi-stable states. Wall-colloid equilibrium distances and ranges of interaction can be tuned by varying wavy wall geometry. Colloids move toward and dock at attractive sites and away from repulsive loci; this repulsion can propel objects in the domain. Extensions to anisotropic colloids are discussed. Manipulation by application of external fields to complement the nematic director fields are discussed in the context of reconfigurable systems and microrobotics.