Tunable Transmittance Research Articles

Sulfur‐Rich Norbornadiene‐Derived Infrared Transparent Polymers by Inverse Vulcanization

Infrared (IR) transparent polymer materials prepared by inverse vulcanization, as a promising candidate to replace inorganic materials, are new materials for constructing key devices in IR optics. However, it is difficult to achieve a balance between infrared optical and thermal properties in polymers due to the intrinsic infrared absorption of organic materials. Herein, our strategy is to construct a high boiling point symmetrical molecular norbornadiene derivative cross‐linking agent (DMMD) which can be inverse vulcanized with molten sulfur, and obtain Poly(S‐r‐DMMD) with different sulfur content by controlling the feed ratio of sulfur. With the rigid core and low IR activity in DMMD, the prepared polymers exhibit tunable thermal properties (Tg: 98.3‐119.8 °C) and high IR transmittance (medium‐wave infrared region (MWIR): 42.9‐52.6 %; long‐wave infrared region (LWIR): 1.5‐5.29 %). In addition, Poly(S‐r‐DMMD) can be used to prepare large‐size free‐standing Fresnel lenses for IR imaging by simple hot‐pressing, which provides flexibility in the design and production of IR fine lenses. This study provides a novel strategy for balancing the thermal and optical properties of IR transparent polymer materials, while providing relevant references for balancing the IR optical and thermal properties of polymer materials.

Development of Advanced Solid-State Thermochromic Materials for Responsive Smart Window Applications.

This study introduces the synthesis and detailed characterization of a novel thermochromic material capable of reversible alterations in its thermotropic transmittance. Through an emulsion polymerization process, this newly developed material is composed of 75-85% octadecyl acrylate and 0-7% allyl methacrylate, demonstrating a pronounced discoloration effect across a narrow yet critical temperature range of 24.5-39 °C. The synthesized powder underwent a battery of tests, including differential scanning calorimetry and thermogravimetric analysis, as well as scanning electron microscopy. These comprehensive evaluations confirmed the material's exceptional thermal stability, uniform particle size distribution, and strong anchoring properties. Building upon these findings, we advanced the development of thermochromic polyvinyl butyral films and laminated glass products. By utilizing a coextrusion technique, we integrated these films into laminated glass, setting a new benchmark against existing glass technologies. Remarkably, the incorporation of thermochromic PVB films into laminated glass led to a significant reduction in solar irradiance of 20-30%, outperforming traditional double silver low-emissivity glass. This achievement demonstrates the exceptional shading and thermal insulation properties of the material. The research presented herein not only pioneers a valuable methodology for the engineering of smart materials with tunable thermotropic transmittance but also holds the key to unlocking enhanced energy efficiency across a spectrum of applications. The potential impact of this innovation on the realm of sustainable building materials is profound, promising significant strides toward energy conservation and environmental stewardship.

Mechanically Tunable Transmittance Convection Shield for Dynamic Radiative Cooling.

Radiative cooling is the process to dissipate heat to the outer space through an atmospheric window (8-13 μm), which has great potential for energy savings in buildings. However, the traditional "static" spectral characteristics of radiative cooling materials may result in overcooling during the cold season or at night, necessitating the development of dynamic spectral radiative cooling for enhanced energy saving potential. In this study, we showcase the realization of dynamic radiative cooling by modulating the heat transfer process using a tunable transmittance convection shield (TTCS). The transmittance of the TTCS in both solar spectrum and atmospheric window can be dynamically adjusted within ranges of 28.8-72.9 and 27.0-80.5%, with modulation capabilities of ΔTsolar = 44.1% and ΔT8-13μm = 53.5%, respectively. Field measurements demonstrate that through the modulation, the steady-state temperature of the TTCS architecture is 0.3 °C lower than that of a traditional radiative cooling architecture during the daytime and 3.3 °C higher at nighttime, indicating that the modulation strategy can effectively address the overcooling issue, offering an efficient way of energy saving through dynamic radiative cooling.

Designing an Optical Router Based on a Multimode-Interference Silicon-On-Insulator Coupler with Tunable Power Transmittance

The demand on fast and high-bandwidth data transmission is in continuous increase. These demands are highly dependent on optical signal manipulation, including switching, modulation, and routing. We demonstrate a two-port silicon optical router based on the multimode interferometer (MMI) configuration. The same MMI structure was used for both inward and backward waveguiding to reduce the total length of the device. A phase shifter consisting of two ring-like waveguides made of silicon p-n junctions was used to introduce the phase shift needed for optical routing upon voltage application. Two designs for the MMI optical router were studied: Firstly, a conventional MMI with a crosstalk ratio of 15.1 dB was investigated. Finally, an angled MMI reaching a crosstalk ratio of 18.2 dB at a wavelength of 1.55 μm was investigated.

Adaptive Thermal Management Radiative Cooling Smart Window with Perfect Near-Infrared Shielding.

The architectural window with spectrally selective features and radiative cooling is an effective way to save building energy consumption. However, architectural windows that combine both functions are currently based on micro-nano photonic structures, which undoubtedly hinder their commercial application due to the complexity of manufacture. Herein, a novel tunable visible light transmittance radiative cooling smart window (TTRC smart window) with perfect near-infrared (NIR) shielding ability is manufactured via a mass-producible scraping method. TTRC smart window presents high luminous transmittance (Tlum = 56.8%), perfect NIR shielding (TNIR = 3.4%), bidirectional transparency adjustment ability unavailable in other transparent radiative coolers based on photonic structures (ΔTlum = 54.2%), and high emittance in the atmospheric window (over 94%). Outdoor measurements confirm that smart window can reduce 8.2 and 6.6°C, respectively, compared to ordinary glass and indium tin oxide (ITO) glass. Moreover, TTRC smart window can save over 20% of annual energy in the tropics compared to ITO and ordinary glass. The simple preparation method employed in this work and the superior optical properties of the smart window have significantly broadened the scope of application of architectural windows and advanced the commercialization of architectural windows.

Bioinspired Stretchable Polymers for Dynamic Optical and Thermal Regulation

Elaborated optical and thermal modulatory systems are of great importance to the survival and evolution of organisms in nature. Inspired by these natural intelligent systems, researchers have made great efforts for developing stretchable polymers and exploring their applications in fields of communication, dynamic camouflage, thermal management, and others. Herein, an up‐to‐date account of the advancements in bioinspired stretchable polymers for dynamic optical and thermal regulation is provided. First, stretchable polymers for dynamic structural colors are presented, including cholesteric liquid crystal elastomers, photonic crystal elastomers, and emerging photonic polymers. Then stretchable polymers for dynamic infrared emissivity are introduced, which are achieved by stretch‐induced wrinkled‐flat surface or stretch‐induced cracked surface. Third, stretchable polymers for dynamic thermal management are discussed, focusing on tunable solar transmittance and dynamic radiative cooling. Moreover, the perspectives on the opportunities and challenges for future research directions of bioinspired stretchable polymers are presented at the end.

Non-polarized and ultra-narrow band filter in MIR based on multilayer metasurface

We propose an ultra narrow-band filter in the mid infrared region (MIR) using artificial metamaterials (AMM), which is suitable for the design of on-chip photonic spectrometers. 2-D rectangular holes with a cross-like layerout are adopted to enhance the filter's efficiency and precision. Considering the penetration depth of electromagnetic (EM) waves in the metal film, we opt for multi-layer films composed of metal layers and dielectric layers, instead of a single metal layer, to improve the structure's performance in the MIR. This multilayer configuration significantly enhances the efficiency and precision of the AMM structures in the MIR. The transmission peak, with a full width at half maximum (FWHM) of 30 nm, can be achieved and tuned in the wavelength range from 3.0 μm to 10.0 μm by changing the periods of the unit cell (enlarging the unit cell from 3.0 to 10.0 μm). The proposed AMM structures, with tunable narrow band transmittance in MIR, exhibit promising potential in the fabrication of narrow band photonic detectors and on-chip spectrometers.

Water-repellent and self-attachable flexible conductive patch

Achieving exceptional water-repellency and reliable reversible adhesion is crucial for the development of wearable flexible electronics. However, simultaneously achieving these properties presents a significant challenge, as water-repellency requires maximizing the presence of air while robust adhesion necessitates enhancing the solid fraction. In this study, we present a flexible and transparent conductive patch that addresses this challenge by offering simultaneous robust superhydrophobicity and strong adhesion in both dry and wet conditions. The device incorporates a unique combination of overhang micropillars, microgrids and a percolating network of carbon nanotubes. The proposed patch demonstrates outstanding water repellency with a contact angle exceeding 150°, while delivering impressive dry adhesion (>200 kPa) and wet adhesion (>150 kPa) performance. Furthermore, the device exhibits tunable electrical conductivity and optical transmittance.

Spatially confined lignin melting flow enabled a strong, tough, and light-manageable silastic-nanopaper for flexible and stretchable electronics

Flexible electronics based on cellulose paper have attracted a new surge of interest over the past decades due to their eco-sustainable, renewable, and scalable roll-to-roll manufacturing features. However, the application of traditional paper in flexible electronics is hindered by its inferior stability against heat and water, weak mechanical strength, and its large surface roughness and porosity usually result in a poor circuit continuity. Herein, the hot-pressing induced space-confined flow was adopted to drive the melted lignin spread along the cellulose nanofiber (CNF) chains, then the silastic was further integrated into the lignin uniformly coated CNF membrane to construct a silastic-nanopaper substrate for flexible and stretchable electronics. Attributed to the lignin-induced interfacial molecular bridge, the enhanced hydrogen bonding between lignin and CNF, and the adhesive interaction between lignin and silastic, the developed silastic-nanopaper demonstrates an impressive tensile strength (∼380 MPa), toughness (52.75 MJ/m3), and elongation (16.2 %), much superior to the pure CNF (200 MPa, 4.12 MJ/m3, and 3.0 %, respectively). The silastic-nanopaper also shows a low surface roughness (∼3 nm), high wet strength (>350 MPa) and thermal stability (with the maximum decomposition temperature of 480 °C), good UV-blocking capacity, and tunable transmittance haze. The electronic sensor fabricated based on such silastic-nanopaper exhibits a highly sensitive and reliable piezoresistive response to persistent stretching and twisting. The strategy of combining the advantages of lignocellulose and PDMS paves the way for the cost-effective, easy-to-operate manufacturing of electronic substrates.

Chiral Mechanical Metamaterials for Tunable Optical Transmittance (Adv. Funct. Mater. 20/2023)

Mechanical Metamaterials In article number 2214897, Katia Bertoldi, Antonio Elia Forte, and co-workers depict zoom-in on a pixel of their mechanical display that can modulate light through the programmable elastic deformation of chiral metamaterials.

Chiral Mechanical Metamaterials for Tunable Optical Transmittance

AbstractFlexible metamaterials have been increasingly harnessed to create functionality through their tunable and unconventional response. Herein, chiral unit cells based on Archimedean spirals are employed to transform a linear displacement into twisting. First, the effect of geometry on such extension‐twisting coupling is investigated. This unravels a wide range of highly nonlinear behaviors that can be programmed. Additionally, it is demonstrated that by combining the spirals with polarizing films one can create mechanical pixels capable of modulating the transmission of light through deformation. Guided by experiments and numerical analyses, pixels are arranged in 2D arrays to realize black and white and color displays, which reveal distinct images at different states of deformation. As such, the study puts forward a methodology for the design of an emerging class of flexible devices that can convert nonlinear elastic deformation to tunable optical transmittance.

All-Tunicate Cellulose Film with Good Light Management Properties for High-Efficiency Organic Solar Cells.

Tunicate nanocellulose with its unique properties, such as excellent mechanical strength, high crystallinity, and good biodegradability, has potential to be used for the preparation of light management film with tunable transmittance and haze. Herein, we prepared a whole tunicate cellulose film with tunable haze levels, by mixing tunicate microfibrillated cellulose (MFC) and tunicate cellulose nanofibrils (CNF). Then, the obtained whole tunicate cellulose film with updated light management was used to modify the organic solar cell (OSC) substrate, aiming to improve the light utilization efficiency of OSC. Results showed that the dosage of MFC based on the weight of CNF was an important factor to adjust the haze and light transmittance of the prepared cellulose film. When the dosage of MFC was 3 wt.%, the haze of the obtained film increased 74.2% compared to the pure CNF film (39.2%). Moreover, the optimized tunicate cellulose film exhibited excellent mechanical properties (e.g., tensile strength of 168 MPa, toughness of 5.7 MJ/m3) and high thermal stability, which will be beneficial to the workability and durability of OSC. More interestingly, we applied the obtained whole tunicate cellulose film with a high haze (68.3%) and high light transmittance (85.0%) as an additional layer to be adhered to the glass substrate of OSC, and a notable improvement (6.5%) of the power conversion efficiency was achieved. With the use of biodegradable tunicate cellulose, this work provides a simple strategy to enhance light management of the transparent substrate of OSC for improving power conversion efficiency.

Sustainable Thermal Energy Batteries from Fully Bio-Based Transparent Wood.

The sustainable development of functional energy-saving building materials is important for reducing thermal energy consumption and promoting natural indoor lighting. Phase-change materials embedded in wood-based materials are candidates for thermal energy storage. However, the renewable resource content is usually insufficient, the energy storage and mechanical properties are poor, and the sustainability aspect is unexplored. Here a novel fully bio-based transparent wood (TW) biocomposite for thermal energy storage, combining excellent heat storage properties, tunable optical transmittance, and mechanical performance is introduced. A bio-based matrix based on a synthesized limonene acrylate monomer and renewable 1-dodecanol is impregnated and in situ polymerized within mesoporous wood substrates. The TW demonstrates high latent heat (89Jg-1 ) exceeding commercial gypsum panels, combined with thermo-responsive optical transmittance (up to 86%) and mechanical strength up to 86MPa. The life cycle assessment shows that the bio-based TW has a 39% lower environmental impact than transparent polycarbonate panels. The bio-based TW holds great potential as scalable and sustainable transparent heat storage solution.

Oxygen-deficient tungsten oxide nanoflowers for dynamically tunable near-infrared light transmittance of smart windows

Oxygen-deficient tungsten oxide nanoflowers for dynamically tunable near-infrared light transmittance of smart windows

Innovative Approaches to Semi-Transparent Perovskite Solar Cells.

Perovskite solar cells (PSCs) are advancing rapidly and have reached a performance comparable to that of silicon solar cells. Recently, they have been expanding into a variety of applications based on the excellent photoelectric properties of perovskite. Semi-transparent PSCs (ST-PSCs) are one promising application that utilizes the tunable transmittance of perovskite photoactive layers, which can be used in tandem solar cells (TSC) and building-integrated photovoltaics (BIPV). However, the inverse relationship between light transmittance and efficiency is a challenge in the development of ST-PSCs. To overcome these challenges, numerous studies are underway, including those on band-gap tuning, high-performance charge transport layers and electrodes, and creating island-shaped microstructures. This review provides a general and concise summary of the innovative approaches in ST-PSCs, including advances in the perovskite photoactive layer, transparent electrodes, device structures and their applications in TSC and BIPV. Furthermore, the essential requirements and challenges to be addressed to realize ST-PSCs are discussed, and the prospects of ST-PSCs are presented.

Thermochromic Ni(II) Organometallics With High Optical Transparency and Low Phase-Transition Temperature for Energy-Saving Smart Windows.

Thermochromic smart windows with rational modulation in indoor temperature and brightness draw considerable interest in reducing building energy consumption, which remains a huge challenge to meet the comfortable responsive temperature and the wide transmittance modulation range from visible to near-infrared (NIR) light for their practical application. Herein, a novel thermochromic Ni(II) organometallic of [(C2 H5 )2 NH2 ]2 NiCl4 for smart windows is rationally designed and synthesized via an inexpensive mechanochemistry method, which processes a low phase-transition temperature of 46.3 °C for the reversible color evolution from transparent to blue with a tunable visible transmittance from 90.5% to 72.1%. Furthermore, cesium tungsten bronze (CWO) and antimony tin oxide (ATO) with excellent NIR absorption in 750-1500 and 1500-2600nm are introduced in the [(C2 H5 )2 NH2 ]2 NiCl4 -based smart windows, realizing a broadband sunlight modulation of a 27% visible light modulation and more than 90% of NIR shielding ability. Impressively, these smart windows demonstrate stable and reversible thermochromic cycles at room temperature. Compared with the conventional windows in the field tests, these smart windows can significantly reduce the indoor temperature by 16.1 °C, which is promising for next-generation energy-saving buildings.

Tunable broadband transmittance and Faraday effect in a magnetophotonic nanostructure with gradient thickness.

We propose a magnetic photonic crystal (MPC) nanostructure with a gradient thickness of the magnetic layer. Such a nanostructure exhibits on-the-fly adjustment of optical and magneto-optical (MO) properties. Spatial displacement of the input beam allows tuning of the spectral position of the defect mode resonance in the bandgap of both transmission and magneto-optical spectra. Meanwhile, by varying the diameter of the input beam or its focus one can control the resonance width in both optical and magneto-optical spectra.

Rhodamine-containing double-network hydrogels for smart window materials with tunable light transmittance, low-temperature warning, and deformation sensing

Smart window materials have attracted much attention because of their energy savings ability, light passage control in response to external stimuli, but most studies focus on the tunability of a single property, specifically, optical transmittance. Here, we report a rhodamine (Rh) mechanophore-functionalized PNIPAAm-based double-network (DN) hydrogel with the potential to act as multifunctional smart window materials that have the combination of a transmittance regulation ability, freezing−/compression-induced mechanochromic and mechanofluorescent properties. Benefiting from naturally reversible hydrophilic/hydrophobic phase transitions of PNIPAAm chains, DN hydrogels exhibit an excellent temperature-induced optical transmittance change between transparency and opaqueness. Because of the covalent incorporation of Rh mechanophores into the first network within DN hydrogels, the gels can display visualizable mechanochromism or mechanofluorescence upon freezing or compression. This is attributed to the generation of the colored and fluorescent ring-opened Rh spirolactams via mechanoactivation. This work is the first example of thermochromic smart window materials with a visualized low-temperature warning and damage sensing abilities and provides a new strategy to fabricate multifunctional smart window materials.

Alkane-containing polydimethylsiloxane elastomer composite films with excellent tunable light transmittance

In this study, a facile and low-cost method is proposed to construct reversible transparency switching materials with a wide optical transmittance tuning range through introducing alkanes into polydimethylsiloxane (PDMS) films. The switch from transparent to opaque state can be achieved by thermal induction, with excellent visible light adjustment ability (∼90%) and adjustable operating temperature (−30°C–50 °C). The underlying cause of the transparency switching is the transformation of the microstructure from a homogeneous and transparent state to an inhomogeneous light scattering state attributable to the phase transition of alkanes. In addition, the alkane/PDMS composite films can be reversibly adjusted between transparent and opaque many cycles without loss of overall structure and optical properties. This research can find applications in various optical devices and systems that require tunable optical transmittance.

Smart hydrogels with wide visible color tunability

Pigmentary coloration can produce viewing angle-independent uniform colors via light absorption by chromophores. However, due to the limited diversity in the changes of the molecular configuration of chromophores to undergo color change, the existing materials cannot produce a wide range of visible colors with tunable color saturation and transmittance. Herein, we propose a novel strategy to create materials with a wide visible color range and highly tunable color saturation and transmittance. We fabricated a hydrogel with poly (acrylamide-co-dopamine acrylamide) networks swollen with Fe3+-containing glycerol/water in which the covalently crosslinked polyacrylamide backbone with pendant catechols can ensure that the hydrogel maintains a very stable shape. Hydrogels containing adjustable catechol-Fe3+ coordination bonds with flexible light-interacting configuration changes can display a wide range of visible colors based on the complementary color principle. The catechol-Fe3+ complexes can dynamically switch between noncoordinated and mono-, bis- and tris-coordinated states to harvest light energy from a specific wavelength across the whole visible spectrum. Therefore, these hydrogels can be yellow, green, blue, and red, covering the three primary colors. Moreover, color saturation and transmittance can be flexibly manipulated by simply adjusting the Fe3+ content in the hydrogel networks. The versatility of these smart hydrogels has been demonstrated through diverse applications, including optical filters for color regulation and colorimetric sensors for detecting UV light and chemical vapors. This proposed smart hydrogel provides a universal color-switchable platform for the development of multifunctional optical systems such as optical filters, sensors, and detectors.