BROAD-BAND DIELECTRIC-RELAXATION SPECTROSCOPY OF A CHIRAL SMECTIC-B-CRYSTAL PHASE

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 froze n. Thus we show that the molecular dynamics of the liquid crystal phas e designated as smectic B-crystal is intermediate between that of crys tals and that of conventional smectic phases (like smectic A, B, C etc .). The temperature dependence of the complex dielectric permittivity epsilon (epsilon* = epsilon' - jepsilon'') has been studied in the fr equency regime 10 Hz to 1 GHz on a binary mixture of a chiral epoxy co mpound and a non-chiral compound. The measurements were carried out on the isotropic phase (110-102-degrees-C), the narrow range cholesteric phase, the chiral smectic A phase (98-59-degrees-C), a chiral smectic B phase, so far classified as smectic B-crystal (59-33-degrees-C), an d a crystal phase (below 33-degrees-C). The dielectric measurements we re made for planar and homeotropic orientations. From the analysis of the dielectric absorption curves in the planar and homeotropic orienta tions, it is found that while the molecular reorientation around the l ong axis is characterized by a distribution of relaxation times, the r otation times, the rotation around the short axis is described by a si ngle relaxation mechanism.