Deformed chiral-nematic networks obtained by polarized excitation of a dichroic photoinitiator

Photo-initiated polymerization of chiral-nematic monomers leads to helicoidal networks with well-defined and stable reflection bands. Exposure of the monomer mixtures to polarized UV light in the presence of a dichroic photoinitiator causes photo-induced diffusion simultaneously with the polymerization process. The diffusion is on a length scale equal to half of the cholesteric pitch and deforms the chiral-nematic helix. The films that are produced exhibit extraordinary optical properties such as in-plane birefringence, polarization conversion and polarization dependent higher order reflections. When combined with photo-induced diffusion on the length scale of the film thickness, wideband polarizing reflectors are obtained that transmit linearly polarized light rather than circularly polarized light as is the case for conventional chiral-nematic networks.