Recent Progress in Liquid Crystal‐Based Smart Windows: Materials, Structures, and Design

Abstract

As the vital elements for building environments, windows are utilized to bring light as well as thermal irradiation into the interior places and afford the medium for the communication between the interior and exterior of buildings. Liquid crystal (LC)‐based smart windows, which are mainly made of LC materials or polymer/LC composites, can dynamically modulate light transmittance and regulate the heat radiation entering buildings from the sun via the orientation variation of the LC molecules. Such smart windows play an important role in intelligent buildings and building energy conservation, which contributes to providing a more comfortable and low‐energy‐consumption living environment for mankind. In this review, recent progress in LC‐based smart windows of each category is overviewed. New materials, new ideas, and new methods to improve the performance of conventional LC‐based smart windows and create novel smart window technologies are outlined. Different advanced LC‐based smart window technologies, including electrochromism, thermochromism, photochromism, humidity‐triggered chromism, mechanical self‐powered technique, and dynamic infrared regulating mechanisms, are discussed systematically. The applications of LC‐based smart windows in indoor illumination/privacy protection switching, human‐machine interaction, and thermal regulation for intelligent buildings are highlighted. Last, the challenges and perspectives of LC‐based smart windows are also provided.

Recent advances in solar infrared light regulating smart windows based on organic materials

“…Again, this review focuses on systems with the active materials being organics, generally avoiding papers in which the active elements are primarily inorganic, differentiating this work from other reviews on NIR control elements. [13][14][15][16][17][18][19][20] Organics provide several potential advantages over using inorganic materials, including organics do not interfere with, among others, radio signals, GPS, or cell phones, [21] nor do they corrode. In addition, processing of organic materials often requires lower temperatures and simpler processes than inorganic materials.…”

Preparation of polymer‐stabilized cholesteric liquid crystal films capable of broadband reflection using a three‐layer system of self‐diffusion

“…The results show that this phenomenon obeys the Bragg formula of crystal diffraction. The central wavelength of the reflection band is λ = n * P *cos𝜃, reflection bandwidth is Δ λ = Δ nP , where P , n , 𝜃, and Δ n denote the pitch, average refractive index of CLCs, incident angle of light with respect to the normal, and the birefringence of CLCs, respectively 7,8 . However, the usual Δ n is generally less than 0.3, and the corresponding Δλ is only less than 100 nm.…”

“…The central wavelength of the reflection band is λ = n*P*cosθ, reflection bandwidth is Δλ = ΔnP, where P, n, θ, and Δn denote the pitch, average refractive index of CLCs, incident angle of light with respect to the normal, and the birefringence of CLCs, respectively. 7,8 However, the usual Δn is generally less than 0.3, and the corresponding Δλ is only less than 100 nm. Therefore, in order to obtain extremely high birefringence cholesteric liquid crystal materials, we can only rely on synthesis, but this material is very difficult to synthesize, and in the ideal state, Δn is only 0.5.…”

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

“…Despite several emerging materials and technologies, possibilities to actively manipulate the ensuing optical properties in gel-like systems are still limited, rarely scalable, and often require high electrical energy input, which are widely recognized technological challenges. , Although high transmission and high haze properties have been achieved simultaneously in conventional gel-like materials developed from isotropic constituents, however, so far only in a static manner, − a suitable composition with optically anisotropic materials promises to enable orientation-dependent properties that can be regulated externally with weak stimuli like fields. In this direction, gel materials with combinations of an isotropic host network and anisotropic guest liquid or vice versa have been investigated, where one of the components is optically anisotropic.…”

“…The robust and reliable modulation of optical transparency in P-LC composite materials has shown potential impacts in diverse optical technologies ranging from smart windows ,, and information displays − to vision therapy, , optical security devices, and many more. , Yet, electrical switching in P-LC composites, including the commercially available PDLCs, suffers from the requirement of a high driving voltage, which is a key limiting factor for smart glass applications, especially in terms of power efficiency and both costs and safety considerations associated with high-voltage wiring of window units. These fundamental problems, along with the challenges of scalable, cost-effective manufacturing, have hindered the widespread adoption of P-LC materials for building-envelope technological applications. , Similar drawbacks also exist in alternate modes for controlling optical transmission with electrochromic materials and suspended particle devices . These methods provide a broad-band optical response covering UV to vis-NIR wavelengths but rely primarily on absorption mechanisms for optical tunability.…”