Keeping an eye on flowing liquid crystals

Flow instabilities lead to the formation of complex structures. We have established novel strategies to control the growth morphology of the viscous-fingering instability, which occurs as a less viscous fluid displaces a more viscous one in the thin gap between two parallel plates. We discuss how we can induce a morphology transition from the generic dense-branching growth characterized by repeated tip-splitting of the growing fingers to dendritic growth characterized by stable fingertips by exploiting the shear-enhanced anisotropy of lyotropic chromonic liquid crystal (LCLC) solutions in the nematic phase. We will further discuss chiral structures that emerge as the LCLC solutions are pushed out of equilibrium by a pressure-driven flow. The formation of these structures is remarkable as the LCLC itself is achiral. The chirality results from a periodic double-twist deformation of the liquid crystal and leads to striking stripe patterns vertical to the flow direction. We discuss the mechanism of this unique pathway to spontaneous mirror symmetry breaking and rationalize the selection of a well-defined period of the chiral domains.