Temperature Dependence of the Pitch in Chiral Lyotropic Chromonic Liquid Crystals

Molecular chirality is a subtle symmetry-breaking operation, yet its presence can produce profound macroscopic effects. One example is the nematic phase of liquid crystals, in which the presence of molecular chirality causes the preferred direction of molecular orientation to rotate in helical fashion resulting in striking optical effects. The pitch of the helix is sensitive to many parameters, including the type of molecules, concentration of chiral molecules, and temperature. Most liquid crystals studied to date consist of molecules or strongly bonded molecular assemblies that are not affected by experimental conditions. One exception is a lyotropic chromonic liquid crystal (LCLC), in which the size of the assemblies depends strongly on concentration and temperature. Investigation of the pitch of the helix in such systems reveals a highly unusual temperature dependence in which the pitch diverges as the temperature increases and the assemblies decrease in size. Theoretical considerations both explain this effect and allow the basic chiral interactions to be explored.