Generation of hidden bistable images in a cholesteric liquid crystal device

Abstract

Generation of hidden images in a cholesteric liquid crystal device is presented. The device operation is based on the dependence of the threshold voltage for unwinding the helical molecular order in cholesteric liquid crystal (being initially ether in Grandjean or Focal conic texture) on the surface anchoring conditions of the supporting substrates. This threshold voltage, however, is different for planar and homeotropic anchoring. By patterning the substrates’ surface anchoring condition, permanently or temporarily, so-called pre-determined hidden bistable images, can be visualised and memorised by a proper electronic driving. These images are constituting of areas being either in Grandjean, Focal conic or Uniform Lying Helix (ULH) textures, that is, appearing as light reflecting, light scattering or transparent, respectively. Due to bistability of these textures (states), the visualised hidden images are bistable too. So far, the lifetime of the visualised hidden images was proven to be a decade long and being switchable to any of the other bistable states.