We report a light waveguide liquid crystal display (LCD) based on the flexoelectric effect. The display consists of two parallel flat substrates with a layer of flexoelectric liquid crystal sandwiched between them. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display by total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state due to flexoelectric interaction and becomes scattering. The incident light is deflected from the waveguide mode and comes out of the viewing side of the display. We achieved thin-film-transistor active matrix compatible driving voltage by doping liquid crystal dimers with large flexoelectric coefficients. The light waveguide LCD does not use polarizers as in conventional LCDs. It has an ultrahigh transmittance near 90% in the voltage-off state. It is very suitable for transparent display, which can be used for head-up display and augmented reality display.
Global warming, due to the consumption of fossil energy, is one of the biggest challenges in recent days. Air conditioning (cooling and heating) of office and residential buildings is one of the largest energy consumptions. One way to reduce the energy consumption is to use switchable architectural windows, which can control radiant energy flow. Herein, a smart thermally switchable window with transmittance sensitive to ambient temperature is reported. This smart window is based on a liquid crystal (LC) whose orientation varies with temperature. At temperatures lower than a low threshold temperature, such as in winter, the LC orients perpendicular to the window substrate, and the window is transparent and lets sunlight pass it to warm interiors of buildings. At temperatures higher than a high threshold temperature, such as in summer, the LC orients parallel to the substrate. The window becomes absorbing and blocks sunlight, resulting in a reduction of the solar heating. When temperature varies between these two thresholds, the window has gray‐level transmittances. It does not use electricity and is very energy‐saving, and has an immense potential in applications of smart architectural and vehicle windows.
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