A simple method is proposed for the determination of the rotational viscosity of nematic liquid crystals. Theoretical expressions for the rotational viscosity from transient displacement current in nematic liquid crystals are derived. It is demonstrated that the values of the rotational viscosity measured with this method are in excellent agreement with the Merck data.

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A simple method is presented for the determination of the rotational viscosity of nematic liquid crystals. Theoretical expressions for the rotational viscosity from transient displacement current in nematic liquid crystals are derived. The validity of the expressions is numerically examined. It is found that the rotational viscosity can be obtained with sufficient accuracy. The rotational viscosity of ZLI-2293 (Merck Ltd.) is measured at various temperatures by the present method.

A method for the determination of rotational viscosity γ1 and pretilt angle θ° in twisted nematic liquid crystal cells is proposed. The method is based on the analysis of transient current of a cell excited by a dc voltage pulse. The accuracy of γ1 and θ° values determined by the method is demonstrated by means of numerical calculation of exact basic equations. Experimental results for a ZLI2293 (Merck) cell are presented, and the γ1 values obtained are found to be in excellent agreement with values in the literature.

Low-frequency dielectric properties of nematic liquid crystal (NLC) cells with and without polyimide alignment layers have been investigated with impedance spectroscopy. It is found that the dielectric behavior in the low frequency regime of NLC cells without polyimide alignment layers can be successfully explained in terms of the diffusive motion of impurity ions. The temperature dependences of the diffusion constant and the concentration of the impurity ions a.re determined from the dielectric behavior. NLC cells with polyimide alignment layers exhibit the interfacial polarization between the polyimide layers and NLC layer in the low frequency regime. The concentration of the impurity ions dissolved from polyimide layers to NLC layer is estimated.