Oscillatory Shear Response of Freely Suspended Films of Lyotropic Chromonic Liquid Crystal

Lyotropic chromonic liquid crystals (LCLCs) have received a wide interest in recent years because their fundamental viscoelastic properties are not well understood and they have potential in new bio-sensing and optics applications. They are composed of plank-like molecules that self-assemble into cylindrical aggregates when in water. Their nematic phase has a huge viscoelastic anisotropy, exhibiting fascinating behavior like spontaneous chiral symmetry breaking and colloidal sub-diffusivity. Here, we study the structural response of freely suspended, thin LCLC films to oscillatory shear using nematic DSCG at 10 to 16 wt. % concentration. Oscillating shear is generated via forcing of a suspended magnetic needle. Unlike previous shearing experiments, the fluid is weakly confined at the scale of LC defects and we image in the plane of the quasi-2D shear flow. At small strain amplitude the flow is largely reversible, while at large amplitude, defect structures store elastic energy and are advected away from the needle, reminiscent of elastic turbulence. Understanding these materials under large strain and weak confinement is a step toward bulk processing, enabling applications such as paintable polarizers and deformable optics.