Color tuning in thermo-sensitive chiral photonic liquid crystals based on the pseudo-dielectric heating effect

Abstract

The ability of electro-thermal tuning in center wavelength (λc) of the Bragg reflection band is promoted in cholesteric liquid crystal (CLC) containing a positive-dielectric-anisotropy liquid crystal host (E7) and a binary chiral dopant (R-811 and R-5011). In the CLC mixtures with a fixed R-811 content of 30 wt%, the transition temperature of the smectic-A phase to CLC phase decreases when the R-5011 loading increases. The CLC systems are temperature-sensitive, each exhibiting a temperature range of about 9–12 °C in the CLC phase. Optimization of the content of R-5011 at 1.5 wt% allows for the remarkably effective thermal tuning in λc from 780 nm to 380 nm in response to a temperature increase of merely 3 °C from the room temperature. Under the mechanism of pseudo-dielectric heating, the tunable λc can shift in the entire visible spectrum by an applied voltage as low as 7 Vrms at a frequency of 2 MHz across the cell gap of a 4.8-μm-thick cell. Furthermore, a multifunctional and operation-reversible device is demonstrated by the control of the applied AC voltage, yielding an optical device in which the reflection band can be tuned and the mode can be switched among the reflection, scattering, and transparent states.