Ionic contribution to the dielectric properties of a nematic liquid crystal in thin cells

We report measurements on dielectric properties of a nematic liquid crystal in planar aligned cells with two different thicknesses (1.2 and 6.7 mum). The nematic has a wide thermal range and the temperature variation of the effective dielectric constant (epsilon (perpendicular to)) of the thick cell reflects that of the orientational order parameter. On the other hand, the thin cell exhibits a higher value of epsilon (perpendicular to) which is essentially temperature independent. We have conducted detailed dielectric measurements in the frequency range of 10 Hz-1.1 kHz on both the cells and analyzed the data using a simplified model which takes into account the ionic contribution. It leads to an estimation of the temperature dependencies of the number density and diffusion coefficient of the impurity ions. (C) 2001 American Institute of Physics.