Low-Voltage Haze Tuning with Cellulose-Network Liquid Crystal Gels

Abstract

Being key components of the building envelope, glazing products with tunable optical properties are in great demand because of their potential for boosting energy efficiency and privacy features while enabling the main function of allowing natural light indoors. However, windows and skylights with electric switching of haze and transparency are rare and often require high voltages or electric currents, as well as not fully meet the stringent technical requirements for glazing applications. Here, by introducing a predesigned gel material we describe an approach dubbed “Haze-Switch” that involves low-voltage tuning of the haze coefficient in a broad range of 2–90% while maintaining high visible-range optical transmittance. The approach is based on a nanocellulose fiber gel network infiltrated by a nematic liquid crystal, which can be switched between polydomain and monodomain spatial patterns of optical axis via a dielectric coupling between the nematic domains and the applied external electric field. By utilizing a nanocellulose network of nanofibers ∼10 nm in diameter we achieve <10 V dielectric switching and <2% haze in the clear state, as needed for applications in window products. We characterize physical properties relevant to window and smart glass technologies, like the color rendering index, haze coefficient, and switching times, demonstrating that our material and envisaged products can meet the stringent requirements of the glass industry, including applications such as privacy windows, skylights, sunroofs, and daylighting.

Engineering a polyvinyl butyral hydrogel as a thermochromic interlayer for energy-saving windows

“…Thus, considerable efforts have been devoted to retrofit conventional windows, focusing on regulating the exchange of energy between the exterior and interior by means of thermal conduction, convection, conversion, and emission. 6–13…”

“…1a). Such a phase transition can be finely modulated to occur within a comfortable temperature (18–25 °C) with narrow thermal hysteresis (<5 °C), 12–15 in contrast to some pristine inorganic materials, such as VO 2 and halide perovskites, which undergo phase transition at impractically high temperatures of up to 68 °C or 105 °C, respectively, with much higher thermal hysteresis (∼20 °C). 26–28 In some cases, doping has to be utilized to lower the phase transition temperatures.…”

Transparency-changing elastomers by controlling of the refractive index of liquid inclusions

“…Many widely used products consisting of multiphasic complex materials (e.g., hand creams, paints, salad dressings) appear opaque because they contain particles or droplets dispersed throughout another fluid [1][2][3][4][5][6]. The refractive indices of the dispersed phase inclusions (particles or droplets) are usually different than the surrounding media, causing incident light to scatter as it passes through the multiphasic materials.…”