A Triple-Mode Midinfrared Modulator for Radiative Heat Management of Objects with Various Emissivity

Tuning infrared emissivity of multilayer graphene using ionic liquid gel electrolytes

Actively controlling the infrared (IR) emissivity of materials is critical for numerous applications, such as radiative cooling and thermal camouflage. Multilayer graphene (MLG) has shown significant potential as a functional material with tunable IR emissivity. However, the poor long-term stability of currently reported MLG-based IR modulators greatly limits their practical applications. Herein, ionic liquid gel electrolytes (ILGPEs) are prepared and used as doping sources to assemble MLG-based IR modulators with a sandwich-like structure. The modulator lifetime is dramatically improved, while the modulation depth and dynamic response are retained at levels comparable to those using pure ionic liquids. Microscopic structural analyses, including Raman spectroscopy and X-ray diffraction, are correlated with the ionic conductivity of the ILGPE and the IR radiation of the MLG. The results indicate that the improvement in device performance is likely due to an improved interface between the ILGPE and MLG, as well as limited ion diffusion within the ILGPE, which preserves the structural integrity of the MLG. These findings shed light on the optimization of IR modulators based on ion intercalation.

Decorating Natural Silk Nanofiber Aerogel with a Hierarchical Structure via TiO2 for Improved UV Protection and Radiation Cooling

Daytime radiant cooling achieves a sustainable cooling effect by reflecting sunlight and radiant heat. However, absorption of sunlight by emitters and parasitic heat gain can significantly reduce radiative cooling temperatures. To improve the light reflectivity and emissivity in the mid-infrared band, SNF@TiO2 aerogel with high stability and efficient radiative cooling effect was constructed using nanosilk and titanium dioxide. The hierarchical structure of the aerogel stores more air, which reduces the thermal conductivity (0.0333 W·m-1·K-1) and parasitic heat gain. TiO2 provides excellent UV resistance while increasing solar reflectance and atmospheric window emissivity. The average solar reflectance and average IR emissivity of SNF@TiO2 were 89.4 and 92.3%, respectively. Compared with the subambient (I: 800 W·m-2, PE-covered air) temperature, the average cooling temperature of SNF@TiO2 under direct sunlight reached 11.5 °C. Meanwhile, the outdoor subambient (I: 900 W·m-2, PE-covered air) average temperature drop of SNF@TiO2 reached 12.1 °C after UV (40 mW·cm-2) continuous radiation for 10 days (6 h per day), displaying highly stable radiative cooling properties. In addition, the SNF@TiO2 aerogel has good mechanical elasticity and thermal insulation properties. This study offers great potential for silk fiber materials for outdoor radiant heat management.

Fast-Developing Dynamic Radiative Thermal Management: Full-Scale Fundamentals, Switching Methods, Applications, and Challenges

Rapid population growth in recent decades has intensified both the global energy crisis and the challenges posed by climate change, including global warming. Currently, the increased frequency of extreme weather events and large fluctuations in ambient temperature disrupt thermal comfort and negatively impact health, driving a growing dependence on cooling and heating energy sources. Consequently, efficient thermal management has become a central focus of energy research. Traditional thermal management systems consume substantial energy, further contributing to greenhouse gas emissions. In contrast, emergent radiant thermal management technologies that rely on renewable energy have been proposed as sustainable alternatives. However, achieving year-round thermal management without additional energy input remains a formidable challenge. Recently, dynamic radiative thermal management technologies have emerged as the most promising solution, offering the potential for energy-efficient adaptation across seasonal variations. This review systematically presents recent advancements in dynamic radiative thermal management, covering fundamental principles, switching mechanisms, primary materials, and application areas. Additionally, the key challenges hindering the broader adoption of dynamic radiative thermal management technologies are discussed. By highlighting their transformative potential, this review provides insights into the design and industrial scalability of these innovations, with the ultimate aim of promoting renewable energy integration in thermal management applications.

Materials in Radiative Cooling Technologies

Radiative cooling (RC) is a carbon-neutral cooling technology that utilizes thermal radiation to dissipate heat from the Earth's surface to the cold outer space. Research in the field of RC has garnered increasing interest from both academia and industry due to its potential to drive sustainable economic and environmental benefits to human society by reducing energy consumption and greenhouse gas emissions from conventional cooling systems. Materials innovation is the key to fully exploit the potential of RC. This review aims to elucidate the materials development with a focus on the design strategy including their intrinsic properties, structural formations, and performance improvement. The main types of RC materials, i.e., static-homogeneous, static-composite, dynamic, and multifunctional materials, are systematically overviewed. Future trends, possible challenges, and potential solutions are presented with perspectives in the concluding part, aiming to provide a roadmap for the future development of advanced RC materials.

Pushing Radiative Cooling Technology to Real Applications

Radiative cooling is achieved by controlling surface optical behavior toward solar and thermal radiation, offering promising solutions for mitigating global warming, promoting energy saving, and enhancing environmental protection. Despite significant efforts to develop optical surfaces in various forms, five primary challenges remain for practical applications: enhancing optical efficiency, maintaining appearance, managing overcooling, improving durability, and enabling scalable manufacturing. However, a comprehensive review bridging these gaps is currently lacking. This work begins by introducing the optical fundamentals of radiative cooling and its potential applications. It then explores the challenges and discusses advanced solutions through structural design, material selection, and fabrication processes. It aims to provide guidance for future research and industrial development of radiative cooling technology.

Chameleon-inspired tunable multi-layered infrared-modulating system via stretchable liquid metal microdroplets in elastomer film

This report presents liquid metal-based infrared-modulating materials and systems with multiple modes to regulate the infrared reflection. Inspired by the brightness adjustment in chameleon skin, shape-morphing liquid metal droplets in silicone elastomer (Ecoflex) matrix are used to resemble the dispersed "melanophores". In the system, Ecoflex acts as hormone to drive the deformation of liquid metal droplets. Both total and specular reflectance-based infrared camouflage are achieved. Typically, the total and specular reflectances show change of ~44.8% and 61.2%, respectively, which are among the highest values reported for infrared camouflage. Programmable infrared encoding/decoding is explored by adjusting the concentration of liquid metal and applying areal strains. By introducing alloys with different melting points, temperature-dependent infrared painting/writing can be achieved. Furthermore, the multi-layered structure of infrared-modulating system is designed, where the liquid metal-based infrared modulating materials are integrated with an evaporated metallic film for enhanced performance of such system.

Solution-Processed Metallic Nanowire Network for Wearable Transparent Thermal Radiation Shield

Heating requirements for residential and commercial dwellings result in significant energy consumption and deleterious environmental effects. Personal radiative thermal management textiles regulate the wearer's body temperature by controlling the material's intrinsic optical properties. Passive heating textiles suppress radiative heat losses and therefore significantly reduce the energy consumption required for building heating systems. Guided by an optical theoretical approach, a transparent radiation shield (TRS) is designed based on silver nanowires (AgNWs) that can suppress human body heat with simultaneous visible light transmittance anticipated for practical fabrics. We experimentally demonstrated a TRS with large infrared light reflectance (low emissivity of 35%) and a visible (VIS) transparency value of 75% (400-800 nm). The results are well corroborated by the Mie scattering theory and the wire-mesh equivalent sheet impedance model, which provide fundamental mechanism understanding and guidance toward higher performance. The TRS is fabricated by a simple, solution-processing method with thermoplastic elastomer protective layers, granting notable stretching capabilities, mechanical robustness, and conformability to any body shape or object. The rigorous theoretical strategy enables the scalable synthesis of low-emissivity and visibly transparent textiles for personal thermal comfort.

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 ΔT8-13 μm = 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.

Personal Thermoregulation by Moisture-Engineered Materials

Personal thermal management can effectively manage the skin microenvironment, improve human comfort, and reduce energy consumption. In personal thermal-management technology, owing to the high latent heat of water evaporation in wet-response textiles, heat- and moisture-transfer coexist and interact with each other. In the last few years, with rapid advances in materials science and innovative polymers, humidity-sensitive textiles have been developed for personal thermal management. However, a large gap exists between the conceptual laboratory-scale design and actual textile. Here, moisture-responsive textiles based on flap opening and closing, those based on yarn/fiber deformation, and sweat-evaporation regulation based on textile design for personal thermoregulation are reviewed, and the corresponding mechanisms and research progress are discussed. Finally, the existing engineering and scientific limitations and future developments are considered to resolve the existing issues and accelerate the practical application of moisture-responsive textiles and related technologies.

Radiative cooling: arising from practice and in turn serving practice

Radiative cooling, as a renewable cooling technology, is expected to mitigate growing global warming. However, the barrier when promoting radiative cooling from the laboratory to practice is still a blind spot and needs to be discussed right now. Here, on the basis of review for brief history, we propose a developing thread that the studies on radiative cooling arise from practice and in turn serves practice at the end. This perspective orderly elaborates fundamental limit in theory, realization of spectral-selective materials, practice on criteria for cooling performance, challenges and corresponding possible solutions in practice, and focusing on serving practice. We hope that the criticism for our own opinion could trigger researchers to deeply consider how to make achievement of radiative cooling better serving practice in the future.

Reverse-switching radiative cooling for synchronizing indoor air conditioning

Switchable radiative cooling based on the phase-change material vanadium dioxide (VO2) automatically modulates thermal emission in response to varying ambient temperature. However, it is still challenging to achieve constant indoor temperature control solely using a VO2-based radiative cooling system, especially at low ambient temperatures. Here, we propose a reverse-switching VO2-based radiative cooling system, assisting indoor air conditioning to obtain precise indoor temperature control. Unlike previous VO2-based radiative cooling systems, the reverse VO2-based radiative cooler turns on radiative cooling at low ambient temperatures and turns off radiative cooling at high ambient temperatures, thereby synchronizing its cooling modes with the heating and cooling cycles of the indoor air conditioning during the actual process of precise temperature control. Calculations demonstrate that our proposed VO2-based radiative cooling system significantly reduces the energy consumption by nearly 30 % for heating and cooling by indoor air conditioning while maintaining a constant indoor temperature, even surpassing the performance of an ideal radiative cooler. This work advances the intelligent thermal regulation of radiative cooling in conjunction with the traditional air conditioning technology.

A Facile and Effective Design for Dynamic Thermal Management Based on Synchronous Solar and Thermal Radiation Regulation

Passive solar heating and radiative cooling have attracted great interest in global energy consumption reduction due to their unique electricity-free advantage. However, static single radiation cooling or solar heating would lead to overcooling or overheating in cold and hot weather, respectively. To achieve a facile, effective approach for dynamic thermal management, a novel structured polyethylene (PE) film was engineered with a switchable cooling and heating mode obtained through a moisture transfer technique. The 100 μm PE film showed excellent solar modulation from 0.92 (dried state) to 0.32 (wetted state) and thermal modulation from 0.86 (dried state) to 0.05 (wetted state). Outdoor experiments demonstrated effective thermal regulation during both daytime and nighttime. Furthermore, our designed PE film can save 1.3-41.0% of annual energy consumption across the whole country of China. This dual solar and thermal regulation mechanism is very promising for guiding scalable approaches to energy-saving temperature regulation.

Cephalopod-inspired polymer composites with mechanically tunable infrared properties

Cephalopods have evolved an all-soft skin that can rapidly display colors for protection, predation, or communication. Development of synthetic analogs to mimic such color-changing abilities in the infrared (IR) region is pivotal to a variety of technologies ranging from soft robotics, flexible displays, dynamic thermoregulatory systems, to adaptive IR disguise platforms. However, the integration of tissue-like mechanical properties and rapid IR modulation ability into smart materials remains challenging. Here, by drawing inspiration from cephalopod skin, we develop an all-soft adaptive IR composite that can dynamically change its IR appearance upon equiaxial stretching. The biomimetic composite is built entirely from soft materials of liquid metal droplets and elastic elastomer, which are analogs of chromatophores and dermal layer of cephalopod skin, respectively. Driven by externally applied strains, the liquid metal inclusions transition between a contracted droplet state with corrugated surface and an expanded platelet state with relatively smooth surface, enabling dynamic variations in the IR reflectance/emissivity of the composite and ultimately resulting in reversible IR adaption. Strain-actuated flexible IR displays and pneumatically-driven soft devices that can dynamically manipulate their IR appearance are demonstrated as examples of the applicability of this material in emerging adaptive soft electronics.

Thermochromic Conductive Fibers with Modifiable Solar Absorption for Personal Thermal Management and Temperature Visualization

Thermal management textiles provide an energy-efficient strategy for personal thermal comfort by regulating heat flow between the human body and the environment. However, textiles with a single heating or cooling mode cannot realize temperature regulation under dynamic weather. Furthermore, monocolor textiles do not satisfy aesthetic requirements in a garment. Here, we develop a thermochromic (TC) conductive fiber with a coaxial structure composed of a conductive core and thermochromic shell. The TC conductive fiber-woven fabric has the ability of low-energy dynamic thermal management by combining Joule heating and modulation of solar absorption. Compared with commercial white fabrics, TC conductive fabrics exhibit a maximum temperature drop of 2.5 K, while the temperature of colored commercial fabrics is 7.5-16 K higher than that of commercial white fabrics in the hot. In the cold, the combination of Joule heating and the photothermal effect can provide desired thermal comfort for humans. Meanwhile, heat obtained from solar absorption brings the temperature of a fabric to a predetermined level, which saves energy of 625 W/m2 compared to a conductive-fiber-based textile. In addition, TC conductive fabrics with trichromatic evolution provide a sensitive and instant temperature visualization capable of identification of invisible and intense infrared radiation. These results provide another path to expand potential applications of wearable, flexible electronics.

Preparation of Flexible Wavelength-Selective Metasurface for Infrared Radiation Regulation

Perpetual advancements in modern detection techniques have augmented the requirement of infrared camouflage; however, its development is impeded by multiband compatible regulation and curved application targets. Here, a flexible wavelength-selective metasurface based on two metal-dielectric-metal resonators is experimentally demonstrated for infrared radiation regulation with thermal management utilizing magnetic polariton. Low emissivity in atmosphere windows (infrared stealth) and high emissivity in the wavelength of 5-8 μm nonatmospheric window (radiative cooling) are simultaneously achieved. In comparison with conventional hard substrates, it is for the first time the composite wavelength-length metasurface is successfully prepared directly on a flexible polyimide film via applying polyimide double-sided tapes and S1805/LOR5A bilayer stack lift-off technology. Not only does this method successfully overcome the debonding problem of photoresist on the flexible substrate, but it also solves the bulging problem of the substrate as well as the limitation of high temperature. Besides, the temperature and infrared radiation distributions of flexible wavelength-selective metasurfaces with different curvatures are first investigated. The compared results reveal that the metasurface with larger curvature has a better infrared camouflage performance. Furthermore, the cycle stability of the flexible metasurface is tested, and the results show that the infrared radiation regulation is stable after 30 cycles with essentially no change. This study provides a guideline for preparing flexible composite metasurfaces and avoids the trouble of replacing the metal/dielectric material of the initial structure with a flexible material to improve the structure for application to curved surfaces, thus broadening implications in enhancing the effective bonding of metasurfaces to target surfaces.

Design and Print Terahertz Metamaterials Based on Electrohydrodynamic Jet

Terahertz metamaterials are some of the core components of the new generation of high-frequency optoelectronic devices, which have excellent properties that natural materials do not have. The unit structures are generally much smaller than the wavelength, so preparation is mainly based on semiconductor processes, such as coating, photolithography and etching. Although the processing resolution is high, it is also limited by complex processing, long cycles, and high cost. In this paper, a design method for dual-band terahertz metamaterials and a simple, rapid, low-cost metamaterial preparation scheme based on step-motor-driven electrohydrodynamic jet technology are proposed. By transforming an open-source 3D printer, the metamaterial structures can be directly printed without complex semiconductor processes. To verify effectiveness, the sample was directly printed using nano conductive silver paste as consumable material. Then, a fiber-based multi-mode terahertz time-domain spectroscopy system was built for testing. The experimental results were in good agreement with the theoretical simulation.

High-strength, low infrared-emission nonmetallic films for highly efficient Joule/solar heating, electromagnetic interference shielding and thermal camouflage

High-strength nonmetallic materials with low infrared (IR) emission are rare in nature, yet highly anticipated especially in military and aerospace fields for thermal camouflage, IR stealth, energy-saving heating. Here, we reported a high-strength (422 MPa) nonmetallic film with very low IR emissivity (12%), realized by constructing alternating multilayered structures consisting of successive MXene functionalized outer layers and continuous GO reinforced inner layers. This nonmetallic film is capable of competing with typical stainless steel (415 MPa, 15.5%), and exhibits remarkable thermal camouflage performance (ΔT = 335 °C), ultrahigh Joule heating capability (350 °C at 2 V), excellent solar-to-thermal conversion efficiency (70.2%), and ultrahigh specific electromagnetic interference shielding effectiveness (83 429 dB cm^-1). Impressively, these functionalities can be maintained well after prolonged outdoor aging, and even after undergoing harsh application conditions including strong acid/alkali and boiling water immersion, and cryogenic (-196 °C) temperature.

Bioinspired zero-energy thermal-management device based on visible and infrared thermochromism for all-season energy saving

Radiative thermal management provides a zero-energy strategy to reduce the demands of fossil energy for active thermal management. However, whether solar heating or radiative cooling, one-way temperature control will exacerbate all-season energy consumption during hot summers or cold winters. Inspired by the Himalayan rabbit's hair and Mimosa pudica's leaves, we proposed a dual-mode thermal-management device with two differently selective electromagnetic spectrums. The combination of visible and infrared "thermochromism" enables this device to freely switch between solar heating and radiative cooling modes by spontaneously perceiving the temperature without any external energy consumption. Numerical prediction shows that a dual-mode device exhibits an outstanding potential for all-season energy saving in terms of thermal management beyond most static or single-wavelength, range-regulable, temperature-responsive designs. Such a scalable and cost-efficient device represents a more efficient radiative thermal-management strategy toward applying in a practical scenario with dynamic daily and seasonal variations.

A Superhydrophobic Dual-Mode Film for Energy-Free Radiative Cooling and Solar Heating

Traditional electric cooling in summer and coal heating in winter consume a huge amount of energy and lead to a greenhouse effect. Herein, we developed an energy-free dual-mode superhydrophobic film, which consists of a white side with porous coating of styrene-ethylene-butylene-styrene/SiO₂ for radiative cooling and a black side with nanocomposite coating of carbon nanotubes/polydimethylsiloxane for solar heating. In the cooling mode with the white side, the film achieved a high sunlight reflection of 94% and a strong long-wave infrared emission of 92% in the range of 8-13 μm to contribute to a temperature drop of ∼11 °C. In the heating mode with the black side, the film achieved a high solar absorption of 98% to induce heating to raise the air temperature beneath by ΔT of ∼35.6 °C. Importantly, both sides of the film are superhydrophobic with a contact angle over 165° and a sliding angle near 0°, showing typical self-cleaning effects, which defend the surfaces from outdoor contamination, thus conducive to long-term cooling and heating. This dual-mode film shows great potential in outdoor applications as coverings for both cooling in hot summer and heating in winter without an energy input.

Dual-Emitter Graphene Glass Fiber Fabric for Radiant Heating

Radiant heating, as a significant thermal management technique, is best known for its high thermal effect, media-free operation, good penetration, and compatibility for different heated shapes. To promote sustainable development in this area, developing advanced infrared radiation material is in high demand. In this work, a lightweight, flexible dual-emitter infrared electrothermal material, graphene glass fiber (GGF), is developed by chemical vapor deposition (CVD) method, with both graphene and glass fiber as the radiation elements. Large-area GGF fabric (GGFF) exhibits wavelength-independent high infrared emissivity (0.92) and thermal radiation efficiency (79.4%), as well as ultrafast electrothermal response (190.7 °C s^-1 at 9.30 W cm^-2) and uniform heating temperature. The superior radiant heating capability of GGFF to traditional alloy heating wires can achieve 33.3% energy saving. GGF can promote the development of efficient and energy-saving heat management technology.