Analytical and numerical calculations of threshold behavior and electro-optical characteristics in twisted chiral nematic layers are presented, when weak anchoring in the tilt and twist angle of the director is assumed. An analytical expression for the effective twist angle and the Freedericksz threshold voltage is derived. In cells with bistabilities, we investigate the influence of the anchoring parameters and device parameters on the width of the hysteresis. Using the 4X4-matrix formalism ofBerreman [J. Opt. Soc. Am. 62, 502 (1972)], we demonstrate the influence of the weak anchoring on the transmission-versus-voltage characteristic.

The viscoelastic response of the nematic director field to low-frequency modulations of the driving voltage was studied by means of optical transmission measurements. An external ac voltage above the critical field Uc was weakly amplitude modulated with frequencies in the range of 1 to 100Hz. The viscosity coefficients a 1 , r 11 r 2 , and 'Tfb influence the time dependence of the director field. They were determined by fitting the phase and amplitude of theoretically calculated optical transmission curves to measured data.

Numerical calculations are presented on the dynamics of twisted chiral nematic cells. We are emphasizing the influence of surface effects on the optical switching behavior. Apart from the anchoring strength we have taken into account viscous effects at the surface by constructing a surface dissipation function. The dynamical light transmission curve has been determined for different strengths of the surface anchoring and various viscosity parameters by computer simulation.

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