IONIC CONDUCTION IN NEMATIC AND SMECTIC A LIQUID CRYSTALS

Permittivity dispersion measurements in a very low frequency range were made on n-pentyl (5CB) and n-octyl 8CB cyano biphenyls, providing characterization of mobile ions by the diffusion coefficient, or the mobility, and their temperature dependence in the nematic phase and/or the smectic A phase. Ionic conduction was confirmed in the nematic and the smectic A phases from the continuity of these temperature-dependent properties in the isotropic, the nematic, and the smectic A phases with reasonable changes at the transition temperatures. The Walden rule was found to be applicable to the ionic conduction in the nematic phase of 5CB without a pre-transitional phenomemon near the nematic-smectic phase transition, when appropriate mean values are taken for both the anisotropic mobility of ions and the anisotropic viscosity of the liquid crystal substance. It was also pointed out that care should be taken for the applicability of the Walden rule to liquid crystals in the case when the anisotropy of ionic conduction is argued, especially for liquid crystal materials containing mobile ions with a far less anisotropic shape than the liquid crystal molecules.