Liquid crystal polymers and networks for display applications

Photopolymerization of liquid-crystalline [LC] monomers produces polymer films with a spatial control over the molecular organization. A powerful tool for creating even more complex molecular architectures than by LC order alone is photo-induced diffusion during polymerization of these monomers. Photo-induced diffusion during polymerization of chiral-nematic monomers yields a cholesteric network in which the helical pitch gradually changes over the cross-section of the film. The polarization selective reflection band can thus be made much wider than those of single pitch materials and may expand the whole visible spectrum. Performing photo-induced diffusion on a length-scale of half the cholesteric pitch by using a liquid-crystalline photoinitiator yields a cholesteric network with a deformed helix. Helix deformation gives higher order reflections and a built-in optical retardation. When the deformed helix is combined with a pitch gradient over the film thickness, the built-in retardation can be used for wide-band cholesteric polarizers that directly generate linearly polarized light without an additional quarter-wave foil.