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Optical birefringence and order parameter of pure cholesteric liquid crystals and their mixture

Rajiv Manohar, A.K.Srivastava, K.K.Pandey, Avneesh Kumar Singh, J.P.Shukla

The refractive indices and densities of liquid crystals Cholesteryl Pelargonate and Cholesteryl Butyrate and their mixtures of different ratio of 25:75, 50:50 and 75:25 (by weight) have been reported as a function of temperature. The effective polarizabilities áeand áo in the cholesteric phase has been calculated by using the anisotropic internal field model of Neugebauer, Saupe and Maier and isotropic field model of Vuks, from ne and no values. The order parameters as evaluated by using different local field models for both the pure samples and their mixture of different concentration have been compared. The values of principal polarizabilities are found to be slightly different although the order parameters S evaluated from above models are in good agreement. These order parameters have also been compared with that calculated by two other direct methods.All these results seem to be in good agreement. The variation of different parameters with the percentage concentration of sample has been reported and discussed giving probable reason.