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The screening effect of dc voltage in a nematic liquid-crystal cell having polyimide alignment layers is studied experimentally and theoretically. The transmitted intensity of light passing through a liquid-crystal sample exhibits a dip arising from dc screening effects, which are never observed with ac voltage application. The dc screening effect is produced by two kinds of ionic charges in the boundary layer. One is adsorbed on the orientation film and the other compensates the adsorbed charges. The two kinds of charge model account quantitatively for the observed dip in transmission making its origin clear, and explain well the ionic conduction processes accompanying the application of dc voltage to a liquid-crystal sample.
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Akihiko Sugimura (1991) studied this question.
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