Flow-Induced Structures in Lyotropic Chromonic Liquid Crystals

Lyotropic chromonic liquid crystals (LCLCs) are materials of interest for their biocompatibility and unique structural properties compared to traditional thermotropic liquid crystals. Their response to shear, however, remains largely unknown. We show that nematic LCLC solutions arrange into intriguing large-scale structures at high flow rates when pushed out of equilibrium by a pressure-driven flow in a microfluidic cell. We align a LCLC solution perpendicular to the flow direction. At low flow rates, the liquid crystal solution remains stable in this alignment adopting a 'log-rolling' state. At a range of higher flow rates, transient horizontal stripes appear along the flow direction; these stripes subsequently break up into subunits that self-assemble into steady-state vertical band structures. We present the instabilities that emerge in the transition from a uniform director field to the textures formed under flow, and the underlying structures of the subsequent director fields. We further discuss the experimental parameters that tune the characteristics of these structures, particularly the significance of the system geometry and flow velocity to the characteristic length scales of both the horizontal stripes and vertical bands.