OPTICAL BIREFRINGENCE, DENSITY AND ORDER-PARAMETER OF AN ESTER-BIPHENYL MIXTURE EXHIBITING AN INJECTED SMECTIC PHASE

The phase diagram of binary system of 4-n-pentyl 4'cyanobiphenyl (comp onent 1) and 4-n pentylphenyl 4-n'hexyloxy benzoate (component 2) is p resented, which shows the presence of an injected smetic phase. Refrac tive indices and densities for ten different compositions of this mixt ure and for one pure component are measured. The molecular polarizabil ities are calculated from refractive indices using Vuks' method. The o rientational order parameters are determined from the polarizability v alues. Experimental order parameters are compared with McMillan's theo ry for mixtures having injected smectic phase, and with Maier-Saupe th eory for others having a nematic phase only. Mixtures having almost eq ual molar concentrations are less orientationaly ordered compared to o thers. The change in physical parameters is continuous for mixtures wi th x > 0.5, whereas there is an abrupt change of the values of the par ameters in going from smectic to nematic phase for mixtures having x < 0.5, x being the mole fraction of component 1. For most of the mixtur es two-phase coexistence region for both N/S and N/I transitions are o bserved.