Viscosity measurement in nematic/lamellar phase transition of lyotropic liquid crystal

Viscosity of the binary perfluorosurfactant/water systems: i) Ammonium perfluoro-octanoate (NH₄PFO)+water and ii) Cesium perfluoro-octanoate (CsPFO)+water, has been measured using a simple capillary method. Both systems clearly show discontinuity in viscosity for high concentrations of surfactant (≥45wt%) as the temperature decreases from the isotropic to the nematic phase transition temperature, and a collapse in the viscosity at the nematic to lamellar phase transition temperature for all concentrations, thus allowing us to determine the phase transition temperature which is consistent with that obtained by optical microscopic study. The reversal in activation energy, i.e., a higher activation energy in the nematic phase than in the isotropic phase is observed as the concentration of the surfactants decreases. The polymer effect on the viscosity of lyotropic liquid crystals is also discussed.