The phase diagram is an interesting field of research, particulary in lyotropic liquid crystals (LLC). In this way, one of the most important phase diagrams of this LLC system was reported by Yu and Saupe. Two uniaxial (calamitic --NC and discotic --ND) and one biaxial nematic (NB) phases were determined by these authors. Furthermore, in this phase diagram the classical isotropic phase (I was observed at high temperature as well as a reentrant isotropic phase (IRE) which takes place at lower temperature. Later, this phase diagram was also studied by several authors and in all cases the IRE-NC-I phase transitions were not observed. In this work, we present a study of this phase diagram through digital image processing and refractometry optical techniques. The occurrence of these phase transitions is investigated and characterized. In addition, the order parameter is obtained based on the Vuks hypothesis from a particular point, in the range of the NC phase, where the absolute value of the optical birefringence (Δn is maximum.
61.30.-v Liquid crystals 61.30.St Lyotropic phases 64.70.M- Transitions in liquid crystals 64.70.mj Experimental studies of liquid crystal transitions
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