Broad band dielectric relaxation spectroscopy of a chiral smectic B-crystal phase

Abstract

By using dielectric relaxation spectroscopy it has been observed that while the molecular reorientation around the long axis in the smectic B-crystal phase is active, the rotation around the short axis is frozen. Thus we show that the molecular dynamics of the liquid crystal phase designated as smectic B-crystal is intermediate between that of crystals and that of conventional smectic phases (like smectic A, B, C etc.). The temperature dependence of the complex dielectric permittivity ε* (ε* = ε′ - jε″) has been studied in the frequency regime 10Hz to 1 GHz on a binary mixture of a chiral epoxy compound and a non-chiral compound. The measurements were carried out on the isotropic phase (110–102°C), the narrow range cholesteric phase, the chiral smectic A phase (98–59°C), a chiral smectic B phase, so far classified as smectic B-crystal (59–33°C), and a crystal phase (below 33°C). The dielectric measurements were made for planar and homeotropic orientations. From the analysis of the dielectric absorption curves in the planar and homeotropic orientations, it is found that while the molecular reorientation around the long axis is characterized by a distribution of relaxation times, the rotation times, the rotation around the short axis is described by a single relaxation mechanism.