Liyotropik sıvı kristal karışımlarda sürfaktant moleküllerin alkil zinciri uzunluğunun nematik tek eksenli-çift eksenli faz geçişleri üzerine etkisi

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulfates (NaCxS) surfactants, where x is the number of the carbon atom in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the formation of lyotropic nematic phases. For this purpose, we synthesized some KCX and NaCXS molecules where X varied from 8 to 16, i.e. from KC8, potassium octanoate, (NaC8S, sodium octylsulfate) to KC16, potassium hexadecanoate, (NaC16S, sodium hexadecylsulfate). The lyotropic mixtures were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb2SO4/DeOH/water (Na2SO4/DeOH/water), separately. The uniaxial-to-biaxial nematic phase transitions were evaluated from the temperature dependence of the birefringences of the nematic phases via laser conoscopy. The results indicated that even if one methylene group, −CH2, is added into the surfactant alkyl chain length, the phase topology completely changed and the birefringences of the nematic phases were approximately doubled. Since some parameters obtained from the isotropic micellar solutions include some supporting information to lyotropic phases, the surfactant packing parameter, which was evaluated from the surface tension measurements, seem to be an adequate parameter to explain the effect of the packing of the surfactant molecules in the micelles on the nematic phase sequence on the lyotropic partial phase diagrams.