Investigation of the Photoinduced Optical Anisotropy of Azo Dye Mesophases

The photoinduced optical anisotropy (POA) of novel aqueous azo dye systems which form chromonic mesophases upon addition of methanol or sodium chloride was investigated. The phases were characterized between crossed polarizers. For further characterization rheological and holographic transient relaxation experiments were carried out. Distinctive differences in the hologram formation and decay were found for phases which exhibit the same texture in polarization microscopy. The generated holographic gratings could be assigned to either photoinduced phase transitions or an alignment of optical axes. In the present study we concentrate on a comparison of phases with the same macroscopic birefringence; results are discussed in comparison with models in the literature.