Switchable broadband light reflection in polymer-stabilized cholesteric liquid crystals

Due to the existence of a macroscopic helical structure, oriented cholesteric liquid crystals (CLCs) can selectively reflect light. The wavelength bandwidth for these Bragg reflections is limited: typically a few tens of nanometers due to limited birefringence values available in organic mesomorphic compounds. Here, we show that larger bandwidths may be reached by associating two layers of polymer-stabilized CLCs (PSCLCs). In the case of near-IR spectrum, it is shown that the optical properties of the bilayer system are not the sum of the individual properties. Time stability is investigated because the very existence of an interdiffusion between soft matter layers. Optical characteristics of the PSCLC can be tuned by an electric field and transitions between broadband reflecting, scattering, and transparent states are possible. For applications, switchable broadband reflections in liquid concentration media are relevant for white-or-black polarizer-free flat displays and "smart" windows in buildings. (C) 2001 American Institute of Physics.