Electrode and Interface Polarizations in Nematic Liquid Crystal Cells

Low-frequency dielectric properties were measured for study of the transport properties of impurity ions in nematic liquid crystal (NLC: 4-cyano-4'-pentyl biphenyl) cells with and without polyimide alignment layers. It was found that the dielectric behavior of the NLC cells without polyimide alignment layers is due to the electrode polarization. The diffusion constant and the concentration of the impurity ions are determined from the dielectric behavior. The NLC cells with polyimide alignment layers exhibit interface polarization between the polyimide alignment layers and the NLC slab. The ion concentration is estimated from the frequency at the dielectric loss peak of the interface polarization. The ion concentration is much higher in the NLC cells with polyimide alignment layers than in the cells without polyimide alignment layers, indicating that a considerable amount of impurity ions are dissolved from the polyimide layers. The temporal variations of the dielectric properties of the NLC cells with and without polyimide alignment layers after the cell preparation were also measured.