Measurements of electric conductivity and reorientation times for the cesium perfluorooctanoate–D2O micellar system

Abstract

Measurements of the electric conductivity and the relaxation times for reorientation in magnetic fields are presented for the cesium perfluorooctanoate (CsPFO)–${\mathrm{D}}_2$O micellar system, as a function of temperature and concentration. Five sample concentrations are presented, namely 41%, 48%, 50%, 55%, and 60% of CsPFO in ${\mathrm{D}}_2$O by weight. At these concentrations, the system shows a nematic liquid crystal, between a lower-temperature lamellar smectic and a higher-temperature isotropic micellar phase. At the transition from the nematic to lamellar phase, the principal conductivities change rather continuously, and do not show any marked features. The measurements show that at the same reduced temperature, the structure of the nematic phase becomes more anisotropic and the relaxation times become longer with decreasing CsPFO concentration in the system, suggesting that at the same reduced temperature, the size of the nematic micelles increases with decreasing CsPFO concentration. Comparison of the conductivity anisotropy data with values calculated from structural models allows estimates of the aspect ratio of the micelles and the fraction of the area of the smectic planes that is covered by water. The behavior of the relaxation times at the nematic-to-lamellar transition shows dependence on the concentration. The relaxation times at the nematic-to-lamellar transition for the four lower concentrations diverge; the critical exponents in order of increasing CsPFO concentration are 0.71, 0.76, 0.77, and 0.85. The 60% sample does not show any pretransitional behavior at this transition.