Time Dependence of Impedance Characteristic of Nematic Liquid Crystal Cell

The frequency dependence of the impedance of a liquid crystal cell was measured for 4-n-pentyl-4'-cyanobiphenyl. The resistivity of a liquid crystal layer decreases due to two relaxation processes. The relaxation time for the slow process is about 4000 h, and that for the fast process is of the order of 100 h. This implies that the carrier ion concentration increases over a long period of time. A surface double layer was detected at the polyimide in the low frequency region, the thickness of which tends to decrease with time.