Experimental evidence for Ohmic behavior of a 5CB planar cell limited by ITO-electrodes in the DC limit

The influence of the electrode properties on the electric response of nematic liquid crystal cell limited by ITO surfaces is investigated. From electrochemical impedance spectroscopy measurements (EIS) of the real and imaginary parts of the electric impedance of the cell it is evident that in the DC limit the cell behaves as a pure resistance, since its reactance tends to zero linearly with the frequency of the applied voltage. The spectrum of the real part of the impedance shows the presence of two plateaux, one related to the bulk properties of the cell, and the other to the electrode properties. The experimental data can be interpreted in terms of Poisson– Nernst–Planckmodel, assuming that the presence of the non-blocking electrodes is described by a boundary condition according to which the conduction current across the electrode due to the charge exchange between ions and electrons is due to the surface electric field, as in Ohmic electrodes, and to the variation of the bulk density of ions just in front to the electrodes, as in the Chang–Jaffe model