Relaxation of Slow Ions in Nematic Liquid Crystal Device

Ionic motion can crucially affect the performance of liquid crystal devices under an electric field. In this study, the adsorption and the relaxation of slow ions induced by a sufficiently strong DC voltage were observed in a liquid crystal cell using an electro-optical method. After a DC voltage had been applied for a given time, the transient transmission was measured using a fixed AC voltage. Even though the external DC voltage was zero, an effective voltage due to the adsorbed ions existed. We obtained the density and the mobility of ions and compared the results with those obtained using a simple model calculation. The density was in the range of 10(15) similar to 10(16) /m(3) in the bulk and the mobility was in the range of 10(-15) similar to 10-13 m(2)/Vs. Both varied sensitively with the DC voltage rather than the applied time.