Mechanism of switching between planar and focal conic states in a bistable cholesteric-liquid-crystal reflective display

The bistable reflective cholesteric-liquid-crystal display exhibits two stable states with contrasting optical properties at zero voltage. One is the reflecting planar state where the helical axis is perpendicular to the display substrate, and the other is the nonreflecting focal conic state where the orientation of the helical axis is random throughout the display. The display is switched directly from the planar state to the focal conic state by a low voltage. It is switched from the focal conic state back to the planar state in an indirect manner: it is switched to a third state, known as the homeotropic state, by a high voltage, and then relaxes back to the planar state when the applied high voltage is removed. Here we report a new mechanism to switch the bistable reflective display. We make use of liquid-crystal dimers, which have abnormally small bend elastic constants and exhibit a heliconical state. The bistable display is switched from the focal conic state to the heliconical state by an intermediate voltage and then relaxes back to the planar state after the applied voltage is removed. Through this mechanism the driving voltage is significantly reduced.