Exploring motion reversal in polymer cholesteric-liquid-crystal devices

摘要

Polymer cholesteric-liquid-crystal (PCLC) flakes suspended in a fluid are used as the active medium in a novel particle-based, electro-optic technology. The motion of PCLC flakes is controlled with an electric field so that PCLC flake devices are brightly reflective in their "off" state and appear dark when an electric field is applied, causing the flakes to reorient 90°. Basic devices using a mildly conductive host fluid such as propylene carbonate are not bistable, and flakes relax to their original position within tens of seconds to minutes after the electric field is removed. We seek to control flake (mentation by designing waveforms that follow the initial drive voltage. Shaped pulses were investigated to accelerate flake relaxation. The optimal pulse for motion reversal was found to be a 1.5-s sawtooth pulse with a 3-V amplitude. We also examined the use of holding voltages, which follow the driving voltage, but have amplitudes a fraction of the driving-voltage magnitude. The holding voltage prevents flakes from relaxing, while saving on power consumption. Cells driven at several volts were found to retain their brightness with the application of a holding voltage between 0.4 to 0.5 V.