Effects of electric double layer and space charge polarization by plural kinds of ions on complex dielectric constant of liquid crystal materials

The complex dielectric constant of a liquid crystal material, 4-cyano-4'-alkyl-biphenyl (5CB), was measured in low-frequency regions below 1000 Hz. The anomalous increasing behavior was analyzed using an equivalent circuit which takes two kinds of contributions into account: one is from the electric double layer and the other is from the space charge polarization. It was found by numerical calculations that these two effects exhibit different dependences of dielectric dispersion on the thickness of a specimen, and both effects were successfully distinguished in the experimental results. In the analysis of the space charge polarization, the experimental results were best fitted by the calculated results with five kinds of ions in terms of the diffusion coefficient. These measurements can be applied to a precise determination of the attributes of plural kinds of ions, such as the diffusion coefficient and the number density.