Electrically tunable thermoresponsive optic switch for smart window application based on dye-doped cholesteric liquid crystal

Abstract

We demonstrate a cholesteric liquid crystal (CLC) smart window that functions as a reversible thermo-optic switch between a transparent state at a low temperature and a low-transmission state at a higher temperature. This smart window is based on the addition of a thermoresponsive handedness-reversible chiral dopant in a mixture of a typical chiral dopant, a dichroic dye and nematic liquid crystal, yielding a thermosensitized CLC. In such a homeotropically anchored dye-doped CLC, the thickness-to-pitch ratio increases as the temperature rises, causing the device to switch from the homeotropic texture to the fingerprint texture. The absorption characteristic of the dichroic dye enables the homeotropic and fingerprint configurations in the dye-doped CLC to create two distinct transmission levels—the transparent and opaque optically stable states, respectively. Such a switching mechanism entails no additional electric power and, thus, is energy-saving. Moreover, the switching temperature at which the texture transition takes place can be actively increased by increasing voltage for the smart window. This allows the CLC device to be perfectly adaptable to the need of a user and, in turn, applicable to a wider variety of environments.