Electrically active and thermally passive liquid-crystal device toward smart glass

Abstract

Cholesteric liquid crystals (CLCs) are an important soft material for display and sensing technologies due to their unique optical and thermal properties, which are susceptible to external perturbations such as the electric field and temperature variation. The typically periodic structure of a CLC with a twist between molecular layers permits its chiral photonic crystallinity and the resulting selective reflection of a bandwidth in the otherwise generally high transmission spectrum of incident light. Here we report on a novel dual-mode CLC device as smart glass that enables the transparency to be self-adaptive to temperature and is simultaneously characterized by a fully on-demand, electrically controlled function, allowing users to regulate the suitable or desired extent of transparency in accordance with their living climate zones or personal needs. The working principle is based on the controllable strength of voltage-induced electrohydrodynamic flow, generating temperature-dependent dynamic scattering for passive control. Moreover, the transmission can be reversibly modulated and switched by applied AC voltage for active control between the transparent and opaque states. As a proof of concept, the characteristic Bragg reflection can be designed to sit in the near-infrared region to partially block unwanted thermal radiation in the optically transparent state.