Optical anisotropy, order parameter and its critical behavior in temperature-dependent refractive indices of nematic liquid crystals

The temperature dependence of optical birefringence, order parameter, effective geometry parameter, and normalized polarizability was determined for nematic liquid crystal mixtures by measuring the refractive indices. The effects of the adjustable parameters obtained from temperature-dependent refractive indices were analyzed appropriately for the crossover temperature and order parameter values. Besides, a four-parameter power law expression method was used for the optical birefringence measurement to address inappropriate fits in the weak first-order phase transition region. From this method, the effective second order phase transition temperature T** was determined by showing the slightly higher values than phase transition temperature. The value of the order parameter critical exponent A obtained from this method showed a good agreement with the mean field theory by demonstrating closeness to the tricritical hypothesis (beta = 025). As a consequence, the measurement of the temperature-dependent optical birefringence was successfully verified the pre-transitional phenomena accurately, and it can facilitate an insightful description of that region. (C) 2018 Elsevier B.V. All rights reserved.