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 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 scaling arguments for the characteristic length scale of the vertical bands that account for the independence of the selected length scale on flow velocity and for the dependence on the microfluidic cell geometry. We further discuss the director field that underlies the structure of the vertical bands.