A new approach to the textural interpretation of magnetically aligned nematic and cholesteric lyotropic mesophases by using plate-? Accessory

Lyotropic liquid crystals are substances formed by anisotropic micelles. Their unit structure change with the concentration and temperature and, as a consequence, the optical anisotropy changes. A measurable optical parameter, which reflects these anisotropies, is the refractive indices. Using these indices, it is possible to represent the anisotropic medium by indicatrix figures. In this sense, the indicatrix orientations will be interpreted in this work along the discotic nematic $\lpar {{\rm N}_{\rm D}} \rpar$(ND) - biaxial nematic $\lpar {{\rm N}_{\rm B}} \rpar$(NB) - calamitic nematic $\lpar {{\rm N}_{\rm C}} \rpar$(NC) phases using a plate-$\lambda$lambda accessory, from the polarized light microscopy, to modify the interference colors along the Michel-Levy chart of the textures exhibited by the sample. Furthermore, the discotic cholesteric $\lpar {{\rm C}{\rm h}_{\rm D}} \rpar$(ChD) - biaxial cholesteric $\lpar {{\rm C}{\rm h}_{\rm B}} \rpar$(ChB) - ${\rm N}_{\rm C}<^>{\rm \ast } {\rm \; }\lsqb$NC*[unwounded calamitic cholesteric $\lpar {{\rm C}{\rm h}_{\rm C}} \rpar$(ChC)$\rsqb \;$] phases are also investigated by the same methodology. The optic sign is also discussed here. In addition, we will also present a procedure that may help us to recognize the ${\rm N}_{\rm B}-{\rm N}_{\rm C}$NB-NC phase transition from the microscopic textures.