DETERMINATION OF VISCOELASTIC COEFFICIENTS FROM THE OPTICAL-TRANSMISSION OF A PLANAR LIQUID-CRYSTAL CELL WITH LOW-FREQUENCY MODULATED VOLTAGE

The viscoelastic response of the nematic director field to low-frequen cy modulations of the driving voltage was studied by means of optical transmission measurements. An external ac voltage above the critical f ield U(c) was weakly amplitude modulated with frequencies in the range of 1 to 100 Hz. The viscosity coefficients alpha1, gamma1, gamma2, an d eta(b) influence the time dependence of the director field. They wer e determined by fitting the phase and amplitude of theoretically calcu lated optical transmission curves to measured data.