Dependence of the formation of lyotropic uniaxial and biaxial nematic phases on the existence of Hofmeister ions in the intermicellar region

In the frame of this thesis, the physicochemical properties of some lyotropic mixtures, composed of surfactant, electrolyte, decanol, and water, were studied using different electrolytes including Hofmeister series anions and cations. The effect of the ions present in the intermicellar region was analyzed by comparing it with the effect of the ions located at the micelle surfaces. Three experimental techniques were performed to investigate the lyotropic nematic phase properties of the samples. The textures of the lyotropic phases were characterized using a polarizing optical microscope. The transitions from the uniaxial to the biaxial nematic phases were determined from the temperature dependences of the birefringences of the nematic phases via laser conoscopy technique. Some structural parameters such as micelle' core average dimensions, micelle shape anisotropy, and average area per surfactant head group at the micelle surface were obtained from the analysis of Small-angle X-ray Scattering data. The results show for the first time that the interactions between ionic species in the Gouy-Chapman layer and/or in the intermicellar region play a crucial role in the formation of the lyotropic nematic phases.