Low-Cost, Robust Pressure-Responsive Smart Windows with Dynamic Switchable Transmittance

Cost-Effective Microfluidic-Based Transparency Switching Glass Visibility Control: Toward a Zero-Energy Smart Window Design

Smart window technologies are key to enhancing energy efficiency and user comfort in modern architecture. Traditional solutions like blinds and curtains face limitations in cost, maintenance, and space. This work introduces a microfluidic-based transparency-switching glass (MTSG), featuring microfluidic cavities filled with a liquid optically matched to the glass substrate. When filled, the cavities enable specular light transmission; in the absence of the liquid, internal wall roughening scatters light, rendering the cavities translucent. The MTSG achieves >85% transmittance modulation, ∼20 s switching time, with virtually no electrical power; if used, minimal power (<12 W/m2) is required, and only during switching. A unique curtain-rolling-like mechanism with the top portion maintained opaque and the bottom portion maintained transparent adds versatility and user-friendliness. This technology offers advantages over existing smart windows, including cost-effectiveness, use of readily available materials, and scalability for industrial production. Additionally, it addresses serious concerns related to power consumption, recyclability, and ease of operation. This design holds promise for smart visibility control in zero-energy buildings and sustainable architectural applications.

Smart Window with Reversible and Instantaneous Photoluminescence based on Microsphere Structure

A smart window that dynamically regulates light transmittance is crucial for modern life end-users and promising for on-demand optical devices. The advent of three-dimensional (3D) photonic crystal microspheres has enriched the functions of a smart window. However, the smart window formed by polymer microspheres encounters poor mechanical strength and microstructural defects. Herein, to solve this limitation, we report the microsphere-based smart window composed of tightly packed cross-linked polymer microspheres (as a precursor) containing organic photochromic dyes, followed by compression under a high elastic state. When excited under an ultraviolet supply, our smart window showed a rapid and reversible fluorescent photoluminescence without fatigue (50 cycles). Moreover, the bulk devices with a microsphere cross-linked network structure enable excellent mechanical strength (hardness reached 0.158 GPa) and visible-light transparency. Interestingly, a QR code can be recognized under visible light exposure but not under ultraviolet light exposure because of photoluminescence of the smart window. Our method generally provided a paradigm for various amorphous polymers, which can be regarded as a simple and effective approach to build a versatile strategy to introduce an ideal marketplace with economic and community benefits.

Toughness and Thermoresponsive Hydrogel for Sandwich Smart Window with Adaptive Solar Modulation and Energy Saving

Thermochromic hydrogels with self-regulating solar transmittance are gaining increasing attention due to their significant potential in the fields of smart windows and energy conservation. Smart windows incorporating viscosity-tough hydrogels as an interlayer exhibit enhanced advantages in resisting external forces. In this study, a tough and thermoresponsive composite hydrogel was developed by incorporating poly(N-isopropylacrylamide) nanoparticles (PNIPAM NPs) and W-doped VO2 into a polyacrylamide-agar (PAM-Agar) double network hydrogel. Upon solar irradiation, thermochromism of PNIPAM NPs could regulate the visible light transmittance of the composite hydrogel and the photothermal effect of W-VO2 contributes to the optical regulation and NIR shielding. The smart window, with the composite hydrogel as an interlayer, demonstrates excellent optical modulation capabilities, with a luminous transmittance (Tum(20 °C)) of 86.81%, high light modulation (ΔTum = 78.89%), a high solar modulation (Tsol) of 83.59%, and a lower critical solution temperature (LCST) of 32.6 °C. The composite hydrogel's superior toughness (0.215 MJ/m3) also enhances the impact resistance of the smart window glass. Additionally, the adhesion between the hydrogel and the glass, with a maximum peeling force of up to 151 N/m (attributed to interactions between the amide groups and the silicon hydroxyl groups), was confirmed through a falling ball experiment. Moreover, the hydrogel exhibits a certain degree of thermal insulation, further promoting its utility in energy-saving applications. In conclusion, this study highlights the significant potential of such composite hydrogels in the development of smart windows for energy-efficient buildings.

Guard Cell-Inspired Ion Channels: Harnessing the Photomechanical Effect via Supramolecular Assembly of Cross-Linked Azobenzene/Polymers

Stimuli-responsive ion nanochannels have attracted considerable attention in various fields because of their remote controllability of ionic transportation. For photoresponsive ion nanochannels, however, achieving precise regulation of ion conductivity is still challenging, primarily due to the difficulty of programmable structural changes in confined environments. Moreover, the relationship between noncontact photo-stimulation in nanoscale and light-induced ion conductivity has not been well understood. In this work, a versatile design for fabricating guard cell-inspired photoswitchable ion channels is presented by infiltrating azobenzene-cross-linked polymer (AAZO-PDAC) into nanoporous anodic aluminum oxide (AAO) membranes. The azobenzene-cross-linked polymer is formed by azobenzene chromophore (AAZO)-cross-linked poly(diallyldimethylammonium chloride) (PDAC) with electrostatic interactions. Under UV irradiation, the trans-AAZO isomerizes to the cis-AAZO, causing the volume compression of the polymer network, whereas, in darkness, the cis-AAZO reverts to the trans-AAZO, leading to the recovery of the structure. Consequently, the resultant nanopore sizes can be manipulated by the photomechanical effect of the AAZO-PDAC polymers. By adding ionic liquids, the ion conductivity of the light-driven ion nanochannels can be controlled with good repeatability and fast responses (within seconds) in multiple cycles. The ion channels have promising potential in the applications of biomimetic materials, sensors, and biomedical sciences.

Integration of hydrogels in microfabrication processes for bioelectronic medicine: Progress and outlook

Recent research aiming at the development of electroceuticals for the treatment of medical conditions such as degenerative diseases, cardiac arrhythmia and chronic pain, has given rise to microfabricated implanted bioelectronic devices capable of interacting with host biological tissues in synergistic modalities. Owing to their multimodal affinity to biological tissues, hydrogels have emerged as promising interface materials for bioelectronic devices. Here, we review the state-of-the-art and forefront in the techniques used by research groups for the integration of hydrogels into the microfabrication processes of bioelectronic devices, and present the manufacturability challenges to unlock their further clinical deployment.

Mechanoresponsive scatterers for high-contrast optical modulation

Smart chromatic materials with optical transmittances that can be modified by light scattering upon external stimuli are attracting extensive interest because of their appealing applications in smart windows, privacy protection, electronic displays, etc. However, the development of these scatterers, which are mostly activated by electric fields, is hindered by their intrinsic energy consumption, slow responses, and poor stability. Recently, mechanoresponsive scatterers based on a strain-driven reconfiguration of the surface or internal structure have emerged, featuring fast responses and a simple composition/fabrication. Because there is no energy consumption to maintain the transparency/opacity, this novel scheme for scatterers holds great promise to break the existing bottleneck. This article presents recent advances in the development of mechanoresponsive scatterers and compares different structural design strategies. The scatterers are categorized into 2D, 3D, and other types according to the dimensions of their functioning structures. The fabrication methods, mechanisms, and relationships between the structural parameters and optical modulating performances are discussed for each category. Next, the potential applications of these scatterers are outlined. Finally, the advantages and disadvantages of the mainstream 2D and 3D categories are summarized, followed by a perspective on future research directions.

Humidity-Driven Switch in the Transparency of a Nanofiber Film for a Smart Window

Traditional smart windows use electrical signals to transform transparency. However, this electric transmission mode greatly limits their uses. Here, we have prepared a transparent PVA-co-PE/CA composite film, which can realize the reversible transformation of transparency under the stimulation of humidity. The preparation method of the composite film included simple immersion and a thermal curing process, showing high optical transparency (96.61%) and an excellent tensile strain at break of 536.34%. Once exposed to moisture stimulation, the rapid hygroscopic swelling of the composite film led to the increase in the difference in the refractive index between the citric acid filling phase and the nanofibers, which directly led to the sharp decrease in the composite film's transparency. Moreover, the composite film can be arbitrarily attached to the surface of the transparent substrate and designed as some special visualization devices or smart windows, which have a promising future in information encryption and intelligent homes.

Tough, Transparent, and Anti-Freezing Nanocomposite Organohydrogels with Photochromic Properties

Poor mechanical properties and freezing at low temperatures of traditional photochromic hydrogels limit their applications. Here, a novel type of photochromic nanocomposite organohydrogels (NC OGHs) by adding tungsten oxide nanoparticles was prepared by a simple one-pot method. The photochromic NC OGHs demonstrated excellent integrated properties, including high transparency, high mechanical properties, low-temperature resistance, anti-dehydration, rewrite capability, and UV blocking ability. In addition, the degree of coloration of NC OGHs could be precisely controlled by UV irradiation, and the bleaching process could be controlled by the temperature and atmosphere. Besides flexible optical information storage devices and optical filters, these photochromic NC OGHs were also used for smart windows in both room temperature and cold environments. The work provides a new insight into photochromic organohydrogels.

Multifunctional glycerol/citric acid crosslinked polymer hydrophilic gel with absorptive and reducing properties

Multifunctional hydrogel based on glycerol/citric acid presents absorptive and reducing capacities, affording a hybrid gel containing AgNPs in the matrix.