Spontaneous emergence of twist and the formation of a monodomain in lyotropic chromonic liquid crystals confined to capillaries

Having a well-aligned monodomain is critical to performing fundamental studies on liquid crystals as well as exploiting them for technological applications. Unlike conventional nematics, lyotropic chromonic liquid crystals are notoriously hard to align. Here, we report on the homogeneous planar alignment of Sunset Yellow in a flat rectangular capillary. Remarkably, the in-plane director aligns perpendicular to the long axis of the rectangular capillary resulting in a counterintuitive configuration. We rationalize the evolution of this configuration from a metastable twisted configuration by considering the coupling of the curvature of the edges of the rectangle to the Frank free energy via the saddle-splay contribution. In contrast, for a square capillary, the doubly-twisted configuration is the final ground state. Using a simple scaling argument, we show that the aspect ratio of the confining geometry determines the ground state.