Dispersive power and crossover temperature, TCO, of two polar nematic liquid crystals in the visible spectral region

Abstract

Refractive index studies are carried out on two highly polar liquid crystals: 1. N-(p-n-methoxy benzylidene)-pamino benzonitrile, PmBAB, 2. N-(p-n-ethoxy benzylidene)-p-amino benzonitrile, PeBAB. The experimental investigations are carried out in the visible region at four different wavelengths, namely, 633, 589, 546 and 436 nm. The two compounds exhibit only the nematic liquid crystalline phase in between the isotropic and crystalline solid. The dispersive power ω is estimated for two consecutive wavelengths for the case of <n>, ne and no for different wavelengths and found to be constant with temperature. Further the temperature gradients of ne and no are estimated, and the crossover temperature is obtained using dno/dT for all the wavelengths.