On the nematic-isotropic phase transition in liquid amyl-ethoxy-cyanstilbene

Measurements of the index of refraction were used to evaluate the temperature dependence of the order parameterS in amyl-ethoxy-cyanstilbene (AECS). The results obtained may be described successfully in the frame of the Landau theory of phase transitions.Dedicated to Academician Vladimír Hajko on the occasion of his 65th birthday.One of us (O. V.) would like to express her sincere gratitude to Dr. L. Bata and his co-workers at the Laboratory of Liquid Crystals, Central Research Institute for Physics of the Hungarian Academy of Sciences, Budapest, for having enabled her to perform some of the measurements in their Laboratory and for their friendly help and hospitality.