Versatile Energy-Saving Smart Glass Based on Tristable Cholesteric Liquid Crystals

Abstract

Smart glass offers dynamic control over the transmission of light to address various needs in energy conservation, privacy, and information display; yet, most of the existing technologies still require continuous power for operation and are limited to single functions (usually either tint or haze control). In this work, we have developed a versatile tristable smart glass based on cholesteric liquid crystal (CLC). The smart glass is voltage-switchable among three field-free stable states of different optical transmission properties, and each corresponds to one of the following cholesteric textures: planar, focal conic, and lying helix. With a six-terminal electrode configuration, such tristable switching can be achieved in CLCs with Bragg reflections from nearultraviolet to visible and near-infrared. By incorporating a dichroic dye into the CLC, we demonstrate a smart daylighting−privacy window based on the tristable optical switch, and both the tint and haze levels of the window are electrically switchable. We also make use of the Bragg reflection of planar-state CLC and explore the applicability of the tristable optical switch to full-color see-through displays. With the demonstrated versatility in design and outstanding field-off stability, it is anticipated that the CLC smart glass can find widespread use, from intelligent control of lighting, building climate, and privacy to semistatic window displays for advertisement use and artistic design.

Smart Window Based on Angular-Selective Absorption of Solar Radiation with Guest–Host Liquid Crystals

“…Due to their dichroism, dye molecules strongly (or weakly) absorb the light that is polarized parallel (or perpendicular) to their absorption axis (Figure 2a). Moreover, a GHLC device is convenient for switching because the dye molecules can be easily aligned by the rotation of LC molecules [41][42][43][44][45][46]. In the case of normal incidence, the transmittance of a homogeneously-aligned GHLC cell can be described as follows [47,48].…”

Polymer Stabilization of Uniform Lying Helix Texture in a Bimesogen-Doped Cholesteric Liquid Crystal for Frequency-Modulated Electro-Optic Responses

“…The uniformity of ULH formed with this electric field approach has been improved by mechanically shearing the cell substrates simultaneously [10,11] or by modifying the surface alignment conditions with alternate stacking of planar and homeotropic alignment [12], or with helical-pitch-matched cholesteric alignment layer [13]. Other electric field approaches-including those based on voltage-induced electrohydrodynamic instability [14,15], flexoelectric effect [16], textural transition [17], electro-thermal effect [18], and adoption of tri-electrode configurations [19,20]-have been successively proposed for generating ULH alignment in a planar-aligned cell. Nevertheless, most ULH textures as prepared by the above-mentioned voltage pretreatments would be irreversibly destroyed or even transferred back to the most stable Grandjean planar texture after the CLC helix is partially or completely unwound by external voltages or the phase transition often occurs unwantedly by thermal variation; hence, making them incompatible for utilization of the flexoelectric or dielectric switching in extensive electro-optic applications.…”

Flexible Normally Transparent Smart Window Modulating Near‐Infrared Penetration under Ambient Conditions

“…CLCs allow smart windows to reflect solar energy regardless of environmental status, thus saving energy. [ 16–19 ]…”