Novel characterization method of ions in liquid crystal materials by complex dielectric constant measurements

The frequency dependence of the complex dielectric constant of liquid crystal materials doped with tetra-n-butylammonium iodide (TBAI) is investigated in the low-frequency region, and the experimental results are analyzed in terms of space charge polarization. The contribution from an electric double layer is also taken into consideration in the analysis. By means of curve fitting utilizing theoretical expressions of the space charge polarization, five sets of diffusion coefficient and density values are obtained for mobile ions. It is confirmed by experiments on the temperature dependence that five kinds of ions follow Walden's rule, and verified from the viewpoint of ion radii that two of the five kinds of ions are TBA(+) and I-. The frequency-dependent dielectric properties, which are characteristic of the behaviors of ions, can be well explained by this study and the analytical method introduced here is considered to be powerful for the evaluation of the attributes of mobile ions.