The Electrooptic Characteristics of a Nematic Liquid Crystals Cell with Asymmetrically Treated Electrodes

Abstract

We present electrooptic measurements on sandwich nematic liquid crystal cells with asymmetri-cally coated electrodes. The cells have one electrode coated with silicon monoxide at an oblique angle and the other is either rubbed or coated with aluminium oxide. Most of the observations have been made on materials with positive dielectric anisotropy, and a few observations on materials with negative dielectric anisotropy. With salt dopants, there is vigorous electrohydrodynamic motion under an applied field beyond a threshold value if the SiO-coated electrode is positive. The motion is subdued when the voltage is reversed. If the medium is viewed between crossed polarizers, there is a considerable change in the transmission coefficient when the polarity of the exciting voltage is reversed. The phenomenon is attributed to the fact that it is mainly the positively charged ions that carry the current in such cells. If the medium is doped with an electron acceptor, the situation is reversed since in this case negatively charged ions carry the current. Both DC and AC responses are reported.