Time response of a nematic liquid-crystal cell in a switched dc electric field

When a nematic liquid-crystal cell is driven by a dc electric field, the capacitance of the cell increases in the first several tens of milliseconds, but after that the capacitance tends to decrease with a rather long relaxation time of the order of 1 s. This phenomenon can be explained by impurity ions which form the electrical double layer at the surface. The results calculated using this simple model qualitatively agreed with the exprimental results. The amount of charge in the double layer and the ion mobility are derived as 2×1011 ions/cm2 and 2.7×10−7 cm2/V s, respectively.