Broadband reflection mechanism of polymer stabilised cholesteric liquid crystal (PSChLC) with pitch gradient

In order to reveal the nature of the formation of a broadband reflection property for polymer stabilised cholesteric liquid crystal, the spatially periodic helix structure of epoxy cholesteric liquid crystal is 'frozen' by cationic polymerisation following the formation of a polymer network induced by ultraviolet radical polymerisation of acrylate monomer. The fracture of the helix structure is observed by scanning electron microscopy, which reveals the presence of pitch gradient. Since the liquid crystal monomers have a UV absorption characteristic, a polymer network concentration gradient is formed after ultraviolet radical polymerisation. Using an attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum, the concentration gradient of the polymer network and that of the chiral dopant, with the opposite trends, are confirmed. The existence of both gradients, resulting in the formation of the pitch gradient, are considered as the natural mechanism for the formation of the broadband reflection.