Temperature dependence of the refractive index near the reentrant-isotropic–calamitic-nematic phase transition

The laser-induced nonlinear optical response of a lyotropic liquid crystal system in the reentrant-isotropic and calamitic-nematic phases is investigated by the use of the thermal lens technique. The occurrence of an inversion in the temperature coefficient of the ordinary refractive index, dn(radially)/dT, near the reentrant-isotropic-calamitic-nematic phase transition, is discussed. This effect is attributed to the behavior of the electronic polarizability due to the change in micelle shape near the isotropic-nematic transition, and correlated with the results obtained near the nematic-isotropic transition, previously reported.