Polymer-Stabilized Uniform Lying Helix Cholesteric Liquid Crystals for Reversible Oblique-Incidence Reflective-to-Transparent Switching

Abstract Uniform lying helix (ULH) cholesteric liquid crystals (CLCs) are promising electro-optic (EO) materials for fast light modulation because the helix axis lies parallel to the substrate, enabling unique angular optical responses and field-driven switching. However, the ULH state is typically metastable and relaxes to the thermodynamically favored planar texture after removal of the applied field, limiting practical device integration. Here, we report polymer-stabilized ULH (PS-ULH) CLCs prepared by in situ photopolymerization of an LC monomer within an electrically induced ULH texture and systematically investigate the effect of polymer concentration on structural stability and EO switching behavior. At normal incidence, PS-ULH CLCs exhibit diffraction-associated spectral oscillations, whereas at an oblique incidence angle of 30°, they show a pronounced low-transmission band consistent with strong selective reflection. Application of an AC electric field unwinds the helicoidal structure and switches the material from a reflective ULH state to a transparent homeotropic state. Polymer concentration critically governs the stability, reversibility, and voltage requirements of this switching behavior. At low polymer loading (1 wt %), the ULH texture is not retained after curing, while 3 wt % polymer provides initial stabilization but fails to preserve the ULH state under repeated electrical cycling. In contrast, a polymer concentration window of 4–8 wt % enables reversible switching, stable recovery of the reflective state, and fast electro-optic response with rise and fall times of approximately 5 ms and 30–40 ms, respectively. At still higher polymer loading (10 wt %), the ULH state is maintained, but the switching voltage increases substantially. Among the tested compositions, 4–6 wt % is the more practically attractive range because it provides ULH stabilization and recovery at a substantially lower switching voltage than 8 wt %. These results clarify the trade-off between polymer-mediated ULH stabilization and electrical addressability in PS-ULH CLCs.