Dielectric properties, refractive index and far infrared spectrum of cholesteryl oleyl carbonate

Abstract

Some dielectric, refractive index and far infrared data on cholesteryl oleyl carbonate (OCC) in the smectic, cholesteric and isotropic liquid phases are reported. The molecular dipole moment is 3.80 × 10^–30 C m (1.14 D) and the molecular polarizability ellipsoid nearly spherical. Dielectric relaxation studies show that the enthalpy of activation for molecular reorientation is (70 ± 20) kJ mol^–1 in the isotropic phase, (44 ± 20) kJ mol^–1 in the cholesteric phase and (35 ± 20) kJ mol^–1 in the smectic phase and involves the reorientation of the “lath”-like molecule probably about a lengthwise axis.

A broad absorption is observed at 78 cm^–1 in the far infrared region in the chloesteric mesophase. This is assigned to a libration of the cholesteric framework about a lengthwise axis. Quantitative aspects suggest that the mean barrier to libration in the mesophase is about 17.3 kJ mol^–1.