Philip E. Watson

A Study of the Dynamics of Reflection Color, Helical Axis Orientation, and Domain Size in Cholesteric Liquid Crystal Displays

Abstract : The relaxation from the field-induced homeotropic state to the equilibrium planar state of cholesteric liquid crystals is investigated. By using an optical retro-reflection technique, we have isolated the dynamics of the orientation and pitch of cholesteric helices, and through scattering and microscopy techniques, we have determined domain size as a function of time for various surface treatments. These three factors determine the viewing angle, color, and brightness of a display. An analysis of the significance of surface selection in cholestric displays is presented.

The transition mechanism of the transient planar to planar director configuration change in cholesteric liquid crystal displays

In cholesteric liquid crystals with a positive dielectric anisotropy, the relaxation from the electric field-aligned director configuration to the stable zero field director configuration proceeds via a metastable transient planar director configuration which has a pitch distinct from the equilibrium state. The transition from the transient planar to the equilibrium zerofield state is shown here to occur via a Helfrich-type instability which continuously leads to an in-plane helical structure. The equilibrium planar state is then seen to grow continuously from the in-plane state, leaving behind walls whose length then spontaneously shrinks.

CHARACTERISTIC TIMES IN THE HOMEOTROPIC TO PLANAR TRANSITION IN CHOLESTERIC LIQUID CRYSTALS

The effect of surfaces on the relaxation from the homeotropic state to the planar state of cholesteric liquid crystals is investigated. By using an optical retro-reflection technique, the orientation and pitch of cholesteric helices as a function of time have been isolated for various surface treatments. It is found that the pitch relaxes to its minimum value in a matter of milliseconds, independent of surface treatment. Secondary pitch relaxations take place after this. The time dependence of the angular distribution of helical axes is also found to be complex, operating on several time scales.

33.2: New Back Reflector and Front Film for Improved Efficiency of Direct-lit LED Backlights for LCD TV

In this paper, we demonstrate how two new films based on 3M™ multilayer film technology can result in improved efficiency in LED backlights for LCD TV. When used together, the films decrease off axis color shift and increase axial luminance by up to 15%, allowing for reduction in number of LEDs and therefore system cost.

COMPUTER SIMULATION OF THE HOMEOTROPIC TO FOCAL CONIC TRANSITION IN CHOLESTERICS

Abstract Previous reports have proposed mechanisms for the homeotropic to focal conic transition in cholesterics. In this report, we present quantitative numerical modeling of this transition. We will show that the simulation shows the existence of the transient planar state, agreeing with previous experimental findings. We will also demonstrate that the simulations never show energy densities high enough to form isotropic regions, demonstrating that this transition is a continuous process. Instead of introducing isotropic regions, the system transforms through an undulation distortion which strongly resembles a Helfrich-Hurault distortion. This simulation is compared with two experimental samples: one with parallel boundary conditions and one with perpendicular boundary conditions. The simulations are compared with dynamical capacitive measurements and microscope photographs, and found to agree very well. We will present detailed drawings of the director configuration during this transition. The agreement of this simulation with the experimental data shows that the mechanism of this transition is now well understood