Lyotropic Cholesteric and Nematic Phases of Disodium Cromoglycate in Magnetic Fields

Abstract

Disodium cromoglycate in water (~10-15% by weight) forms a nematic liquid crystalline phase of negative diamagnetic anisotropy which readily orients in a magnetic field. The phase transition temperatures are very sensitive to the nature and concentration of the cationic species. Addition of chiral guest molecules, and in particular of amino acids, causes the phase to become cholesteric with the helix axis aligning parallel to a magnetic field. Well aligned textures of both phases are studied and a rich array of defect structures of hydrodynamic origin are observed. The pitch of the cholesteric phase can be shortened so that iridescent colors are seen at room temperature.