Phase behaviour and birefringence studies of a liquid crystal binary mixture

The phase diagram of binary system of 4-n-pentyl 4'-cyanobiphenyl (5CB) and 4-pentyl phenyl trans-4 pentyl cyclohexane carboxylate (D55) is presented, which shows the presence of an injected smectic-A phase and a higher order smectic phase (SmG). Refractive indices (n(o),n(e)) and densities for different compositions of this mixture and for one pure compound (D55) are measured. The orientational order parameters <P-2> are determined from the polarizability values (alpha(o),alpha(e)) which are calculated using both Vuks' as well as Neugebauer's internal held models. The experimental order parameter values for the samples having smectic A phase have been compared with McMillan's theory and with Maier-Saupe theory for the nematic cases.