Birefringence and temperature-gradient refractive index study of a laterally Fluorinated Terphenyl LC compound.

Abstract

The temperature behaviour of the refractive indices in the nematic range of a laterally fluorinated terphenyl LC compound, viz, 2,3-difluoro-I,4 bis(4',4"-dipropyl phenyl) benzene was determined using the thin prism experiment. Birefringence of this LC compound was calculated from the measured refractive indices. Using the four parameter model, the temperature variation of the refractive indices and birefringence were theoretically fitted. The compound is found to have high value of birefringence. The temperature gradients of refractive indices i.e, and dne/dT and dne/dT were determined, as a result, a cross over temperature was also found. The values of order parameter were obtained in two ways one by direct calculation using the effective geometry parameter αeg . and the other by using the modified Vuks' method. Both show the same trend. It has been observed also αeg changes almost linearly with the birefringence.