Bistable polymer-stabilized cholesteric-liquid-crystal window based on flexoelectric and dielectric effects

Smart switchable windows for buildings and vehicles become more and more important because they can reduce energy consumption. They exhibit two optically contrasting states: a transparent state and an optically scattering (or light-absorbing) state. Most of them are, however, monostable, namely, only one of the optical states is stable in the absence of applied voltage, and the other state must be sustained under continuously applied voltage, which would consume energy. Here, we report a bistable smart window based on polymer-stabilized cholesteric liquid crystals. The window exhibits two stable states at 0 V: one of them is the transparent homeotropic state with a high transmittance and the other state is the scattering focal conic state with a low transmittance. The bistable states are achieved by using an anisotropic polymer network, known as polymer stabilization. The window is switched from the transparent state to the scattering state by a low-frequency ac voltage pulse under the flexoelectric effect and is switched from the scattering state back to the transparent state by a high-frequency ac voltage pulse under the dielectric interaction. No voltage is needed to sustain the two states of the window. Therefore, the window almost does not consume energy. The optical contrast between the two states is high, and the window is very efficient at privacy control. Due to its superior performance and very low energy consumption, this technology is expected to have a significant impact on switchable architectural and automobile windows.