Dynamics of the Freedericksz Transition in the Electric Field in Non Ideally Oriented Nematic Layers at Subthreshold and Above Threshold Voltages

Abstract

The DAP-effect is studied in homeotropic nematic layers of ZLI–207 (Merck) with initial inclination. In such case the effect loses its threshold character and deformations at subthreshold voltages are observed. The dynamics of deformations at switching on and switching off of the voltage is studied theoretically in small angle approximation and experimentally as well. While in the steady state the threshold disappears, threshold character of the effect is preserved in the transient regime. There exist different regimes of deformations with entirely different relaxation turnon behaviour. At subthreshold voltage the relaxation time increases with increasing the voltage. Just the opposite is the behaviour above the threshold. So divergence of the relaxation times is observed at the two sides of the limiting voltage. The observed decrease of the limiting voltage with decreasing of the layer thickness shows that boundary conditions are “soft” and permits us to determine the anchoring energy. The bend elastic constant and the rotational viscosity coefficient for this material are also determined.