Cholesteric liquid crystals with an electrically controllable reflection bandwidth based on ionic polymer networks and chiral ions

Abstract

The reflection bandwidth of cholesteric liquid crystals is typically on the order of 50–100 nm in the visible region. Static bandwidths greater than 100 nm can be observed in polymer stabilized cholesteric liquid crystals (PSCLCs) that possess a pitch gradient throughout the thickness of the cell. This work presents PSCLCs based on ionic polymer networks and chiral ions, which exhibit large reflection bandwidth tunability under a small applied direct current (DC) electric field. The reflection colors dynamically switch between white, orange, red and transparent. The underlying mechanism of the electrically controllable bandwidth in PSCLCs is the redistribution of the chiral ions under DC electric fields resulting in a pitch gradient variation along the optical axis. Removal of the electric field returns the PSCLC to its original optical properties due to the strong electronic attraction between the ionic polymer network and chiral ions. Moreover, the reflection bandwidth is also sensitive to the temperature.