Pretransitional behavior of conductivity and dielectric properties above a smectic C–nematic transition in 4-4′-di(n-alkyloxy)azoxybenzenes

Abstract

Electrical conductivity and dielectric relaxation measurements have been made in the nematic phases of the 4-4′-di(n-alkoxy)azoxybenzenes. The higher members of this series have a smectic C phase at lower temperatures. In that case, we have observed that (1) the ratio of the conductivities parallel and perpendicular to the local optical axis is abnormally low (<1) above the smectic–nematic phase transition and increases with temperature, and (2) the activation energy corresponding to the molecular rotational diffusion in the frequency range 0.1–10 MHz is significantly larger than for the lower homologs. We tentatively suggest that our results are due to fluctuations of the smectic order in the nematic phase as first pointed out by Chystiakov and Chaikowsky [Mol. Cryst. Liq. Cryst. 7, 269 (1969)] through observation of x-ray diagrams.