HIGHLY ORDERED AGGREGATES IN DILUTE DYE WATER-SYSTEMS

Polarizing optical microscopy and X-ray diffraction measurements have been made on liquid crystals formed by two dyes in water. The dyes, one a cyanine dye and the second an azo dye, both form mesophases above ca. 0.2 wt %. Low angle X-ray diffraction data show that the cyanine dye forms a layer (''smectic'') phase (spacings up to 750 Angstrom), while the azo dye forms columnar nematic and hexagonal mesophases. For both dyes the aggregates appear to be rigid and well ordered, giving rise to multiple low angle diffraction peaks (up to 6 orders). The thickness of the layers is equal to the width of one molecule, but the cross section of the columns is equal to about 6 times the dye molecular area. We propose a columnar pipe structure for these phases. The observation of multiple high-angle X-ray diffraction peaks suggests that the molecules are well ordered at short range within the layers and columns. Hence the mesophases have high order at both the molecular and mesoscopic distance scale.