A study on interaction of an anionic azo dye sunset yellow with cationic surfactants in micellar solutions

In the first part of the thesis, the effect of the interactions of Sunset Yellow dye (SSY) with dodecylalkylammonium bromide surfactants (DAABr) on the stabilization of different lyotropic nematic phases was investigated. SSY doped mixtures of DAABr, with different head-group sizes, were studied by polarizing optical microscopy, laser conoscopy, and small-angle x-ray scattering. It was found that the extent of the interaction of SSY with DAABr head groups on micelle surfaces affects the stabilization of different nematic phases, by causing the change in the micellar structural parameters. The results also indicated that the micelle surface curvature should be different in the three nematic phases. In the second part, the interaction of SSY with DAABr was examined as a function of SSY concentration at 25°C by electrical conductivity and UV/VIS spectroscopy. Carpena's method, combined with Aguiar's approach, was applied to the analysis of the experimental data for determining the micellization parameters such as critical micelle concentrations (cmc), degree of counterion bindings (β), and micellization Gibbs free energies (ΔmicG) from the specific conductivity-surfactant concentration curves. UV/VIS spectroscopy results provided to obtain information about the stackings of the dye molecules. According to the results, although DAABr are conventional surfactants with single alkyl chains, they may show gemini surfactant behavior at relatively high dye concentrations. Finally, the results of the two parts of the thesis were combined to make a comprehensive interpretation of the effect of the surfactant-dye interactions on the formation of different lyotropic nematic phases, especially biaxial ones.