Structural Characteristics of the Chromonic Mesophases of C.I. Direct Blue 67

Abstract

The chromonic lyotropic liquid crystal formed from an aqueous solution of the azo dye C.I. Direct Blue 67 was investigated by means of a temperature-controlled X-ray diffraction technique, polarized optical microscopy, and UV−visible spectroscopy. The dye molecules form columnar aggregates even at low concentrations. The stacking distance of 3.4 Å was observed independent of the concentration and temperature. The addition of a small amount of anionic surfactant was found to induce a nematic phase from a more-ordered hexagonal phase and, thus, enhanced the stability of the nematic phase within a wide range of dye concentrations. The cross-sectional diameter of a column was found to be in good agreement with the molecular length of the dye, indicating that the column is comprised of unimolecular stacking.