Dynamical process of switch-off in a supertwisted nematic cell

Abstract

The switch-off dynamics of a 180° supertwisted nematic (STN) are explored in detail by using a convergent beam system and the fully leaky guided-mode technique. From the dynamical guided-mode data and using the Ericksen–Leslie theory, the director structure in the cell at different times during switch-off is obtained. We have studied the dynamic switch-off from different applied voltages and have found that the relaxation time is independent of the voltage. From fitting the optical data, the effective viscosities are obtained. It appears that two viscosity coefficients, γ and η1, largely control the dynamics of switch-off. From the analysis of the director tilt profile in the cell, it is found that there is no backflow-induced increased tilt at the cell center in the STN cell during the switch-off. From liquid crystal hydrodynamics, this no-backflow dynamic process in the STN cell is well explained.