Physical properties of three bicyclohexane compounds possessing smectic B phase .2. Refractive index and density measurements

We have measured the refractive indices and densities of three bicyclohexane alkenyl/alkenyloxy compounds in smectic B and nematic phases. These values of refractive indices and densities have been used to calculate orientational order parameters in both smectic B and nematic phases. The order parameter values are compared with those previously obtained by us for these mesogens from X-ray diffraction studies. Reasons for discrepancy between the two sets of order parameter data are discussed. For two of these compounds, the density change at the smectic B-nematic transition is significantly greater than that at the nematic-isotropic transition. This implies greater entropy change at the smectic B-nematic transition than nematic-isotropic transition.