Surfactant Liquid Crystals: Phase Diagrams and Phase Behavior

Abstract

The heat capacity associated with the nematic (N) to neat soap (NS) and nematic (N) to isotropic (I) phase transitions has been measured in binary mixtures of cesium perfluoro-octanoate (CsPFO) and water. Previous NMR measurements¹ have established the existence of a tricritical point on the N-NS transition line at 4.9 mole % of CsPFO. Magnetic birefringence studies² have suggested another tricritical point at the N-I transition line below 2.6 mole % of CsPFO. Heat capacity has been measured in mixtures with 4.3, 3.2 and 2.7 mole % CsPFO. The I- N transition is found to be first order for all mixtures, while the N -NS transition is first order for the 4.3 mole % and second order for the 3.2 and 2.7 mole % mixtures. Analysis of our data, with a single correction-to-scaling term, yields α = 0.01 and 0.02 for the 2.7 and 3.2 mole % concentrations of CsPFO, respectively. The effect of the addition of small amounts of polyethylene oxide (PEO) on these transitions is also being studied.