PHYSICAL-PROPERTIES OF 3 BICYCLOHEXANE COMPOUNDS POSSESSING SMECTIC B-PHASE .2. REFRACTIVE-INDEX AND DENSITY-MEASUREMENTS

We have measured the refractive indices and densities of three bicyclo hexane alkenyl/alkenyloxy compounds in smectic B and nematic phases. T hese values of refractive indices and densities have been used to calc ulate orientational order parameters in both smectic B and nematic pha ses. The order parameter values are compared with those previously obt ained by us for these mesogens from X-ray diffraction studies. Reasons for discrepancy between the two sets of order parameter data are disc ussed. 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 smect ic B-nematic transition than nematic-isotropic transition.