Related Experiment Video
Updated: Jun 14, 2026

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals
Published on: August 15, 2018
Models for ionic contribution to the complex dielectric constant of nematic liquid crystals
A L Alexe-Ionescu1, G Barbero, I Lelidis
1Faculty of Applied Sciences, University Politehnica of Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania.
Abstract:
We analyze the models that account the ionic contribution to the complex dielectric constant of a nematic liquid crystal. We compare the predictions of the model of [Sawada, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 318, 225 (1998)] based on the assumption that the electric field in the liquid coincides with the applied one, with the model of Macdonald where the electric field in the sample is determined in self-consistent manner by solving the equation of Poisson. We show that the model of Sawada , widely used to determine the bulk density of ions and their diffusion coefficient in liquid crystal cells, predicts a thickness dependence of the real and imaginary parts of the dielectric constant different from that predicted by the model of Macdonald. On the contrary, the predictions of the two models coincide for what concerns the frequency dependencies of the two components of the dielectric constant. By considering a typical case, we show that the numerical values of the ionic properties derived by means of the model of Sawada may differ even more than 1 order of magnitude by those predicted by the model of Macdonald. A rescaling procedure allowing to evaluate the bulk density of ions and the ionic diffusion coefficient determined by means of the model of Sawada in agreement with the one of Macdonald is proposed.
Related Concept Videos
Susceptibility, Permittivity and Dielectric Constant
Dielectric Polarization in a Capacitor
Ionic Association
The Electrical Double Layer
Electrostatic Boundary Conditions in Dielectrics
Consider a case where both the mediums across a boundary are two different dielectric materials. Recall that the electric field and electric displacement are proportional and related through the material's permittivity.
Lattice Energies of Ionic Crystals

