Low-frequency dielectric relaxations of a nonchiral liquid crystal, 8CB

Low-frequency dielectric measurements are performed on a nonchiral liquid crystal (8CB) for two different cell thicknesses 4.5 µm and 1.6 µm, as functions of temperature at various amplitudes of the probe field. Relaxation peak frequencies are observed at ~10 Hz for the 4.5 µm thick sample and ~100 Hz for the 1.6 µm cell. When the external-field amplitude was increased, the relaxation peak frequency was shifted to lower frequency for the 4.5 µm cell but hardly changed for the 1.6 µm cell. To explain this odd result from experimental observations, we performed a numerical simulation, where the ionic impurities were assumed to encounter ionization-recombination processes in addition to a translational diffusion. We were able to confirm that there are two separate contributions from ionic impurities to the low-frequency dielectric relaxations in this system - that is, from fast ions in the single-particle diffusion and slow ions in the ionization-recombination-assisted diffusion.