Calorimetric and dielectric study of a negative dielectric anisotropy alkoxy-phenyl-benzoate liquid crystal

Abstract

Modulated Differential Scanning Calorimetry (MDSC) and dielectric spectroscopy have been used to measure the complex specific heat and dielectric constant over a wide temperature range on heating and cooling for a negative dielectric anisotropy alkoxyphenylbenzoate liquid crystal, denoted 9OO4. The MDSC experimental parameters were varied in order to yield quasi-static specific heat results and the same base scan rate was used for the dielectric measurements. On cooling, 9OO4 exhibits a typical weakly first-order isotropic to nematic then a continuous nematic to smectic-A phase sequence followed by a monotropic smectic-C and smectic-B phases before crystallizing. The smectic-B conversion is very slow, even for our quasi-static scan parameters. On heating, the crystal phase super-heats and exhibits a strong first-order transition into an unknown smectic phase that itself converts to the smectic-A phase via a first-order, highly rate dependent, phase transition. The nematic-smectic-A transition has an unusual character given the molecular structure of 9OO4 that may be related to combination of molecular structure and a negative dielectric anisotropy.