How confinement-induced chiral director configurations respond to magnetic fields

Confinement can make achiral liquid crystals (LCs) twist to exhibit chiral configurations. Lyotropic chromonic liquid crystals (LCLCs) of unusual elastic properties, such as large saddle-splay and small twist modulus compared to splay and bend modulus, provide archetypal examples of this confinement-induced chiral symmetry breaking. This experimental work investigates how applied magnetic fields transform LCLC's double-twist director configuration in a cylinder. Because of LCLC's negative magnetic anisotropy, upon increasing the field strength, the twist profile along the capillary radius changes from a convex to concave curve, and the twist angle at the cylindrical wall converges to 90 deg. Elastic free-energy calculation explains well our experimental data in terms of the delicate interplay between elasticity, geometry, and external field.