Refractive indices, order parameter and principal polarizability of cholesteric liquid crystals and their mixtures

Measurements of refractive indices (n e , n o ) and birefringence (Delta n) have been made in solid, cholesteric and isotropic phases of cholesteryl carbonate, cholesteryl stearate and their three homogeneous mixtures of concentration 0.25, 0.50 and 0.77 at varying temperature in the range of 18 degrees C to 35 degrees C. the results clearly indicates that various transitions are of the first order. For accurate measurement of Delta n, a modified wedge method was used. Using n e and n o , principal polarizability (alpha e , alpha o ), internal field factor (gamma e , gamma o ) and order parameter (S) have been evaluated, and their temperature dependence is discussed. The order parameter has been determined using the isotropic internal field model (Vuks approach) and the anisotropic internal field model (Neugebauer's approach), and both values agree up to average deviation of 0.7%.