Refractive index measurements in a reentrant isotropic-calamitic nematic phase transition

In this work the temperature dependence of the extraordinary/ordinary refractive indices and optical birefringence are determined near the reentrant isotropic (I(RE))-calamitic nematic (N(C)) and N(C)-isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol, and water. This reentrant isotropic phase is verified by our experimental data and discussed in terms of thermal variation of the micellar shape anisotropy. The results showed also, with basis in the Vuks's equation, that near the maximum optical birefringence in the range of N(C) phase the extraordinary coefficient of electronic polarizability (phi(parallel)) is equal to the ordinary coefficient (phi( perpendicular)).