Broadband reflective liquid crystalline films prepared from liquid crystals with negative dielectric anisotropy

Abstract

When a certain range of frequencies of AC electric fields are applied to a chiral nematic (N*) liquid crystal (LC) with negative dielectric anisotropy ((N*-LCN), usually prepared from a nematic LC with negative dielectric anisotropy (N-LCN) doped with a chiral dopant (CD), the long axes of the LC molecules will be oriented perpendicular to the electric field, which will be helpful to improve the orientation degree compared with the orientation induced by rubbing on the inner surfaces of the substrates sandwiching the LC. After a photopolymerisable N*-LC monomer/N-LCN/CD/an ultraviolet (UV) absorber/a photoinitiator mixture with an appropriate composition is irradiated with UV light, while an electric field with an appropriate frequency and intensity is being applied to it during the UV curing, not only the planar orientation of a high degree but also a pitch gradient of the helical structure of the LC molecules are formed in the resulted polymer network/N*-LCN composite.