Temperature-dependent dual-mode thermal management device with net zero energy for year-round energy saving

Durable asymmetric silk fabric with rapid heat conduction, spectral selectivity and sweat transfer capabilities for effective personal thermal-moisture management

Silk fabric (SF) is a high-end textile frequently utilized in summer apparel. However, its ultraviolet absorption reduces the solar energy reflection, and the inherent hydrophilicity impedes effective sweat evaporation, thereby significantly compromising thermal-moisture comfort. Herein, we fabricated a multifunctional Janus SF with rapid heat dissipation, unidirectional moisture conduction and radiative cooling capabilities through a feasible two-step process. Briefly, hydrophilic Al2O3 nanoparticles were covalently anchored on the outer side (A-side) of Janus SF, whereas a hydrophobic boron nitride (BN) nanosheet-doped layer was fabricated on the inner side (B-side) via polycondensation reaction. The optimized Janus SF demonstrated exceptional solar reflectivity (93.62 %) and infrared emissivity (92.08 %), alongside enhanced thermal conductivities (1.45 W/K/m in-plane and 0.182 W/K/m through-plane). Additionally, the wettability gradient between the hydrophilic A-side and hydrophobic B-side provided a robust driving force for moisture transport, endowing Janus SF with a distinguished unidirectional transportation index of 809.43 % and a satisfactory water evaporation rate of 88.49 g/(m2·h), thereby ensuring prolonged thermal-moisture comfort. Notably, this Janus fabric displayed remarkable outdoor practical cooling effect (∼5.6 °C) compared to bare skin, accompanying with good biocompatibility and outstanding wearability. Overall, such durable, scalable and multifunctional Janus SF provides innovative inspiration for designing next-generation passive cooling fabrics.

A Passive Sweat-Responsive Thermoregulatory Textile with the Largest Thermal Comfort Zone

Maintaining the human body temperature within the thermally comfortable range under volatile temperatures and environments is critical from both the perspectives of human health and energy saving. Therefore, developing thermoregulatory textiles that have a large comfort zone in response to complex environmental temperature changes has been persistently pursued. Here, we demonstrate that a passive sweat-responsive thermoregulatory (PSRT) textile, composed of a unidirectional liquid-transported polycaprolactam (PA6)/metal bilayer, can tune mid-infrared (MIR) radiation and sweat evaporation simultaneously, thus achieving a substantial expansion of the thermal comfort zone in response to dynamic conditions. Specifically, for heating mode, the metalized bilayer PSRT textile intrinsically possesses low emissivity (εMIR ∼0.233) for excellent radiative heating. As the environmental temperature increases or during heavy exercise, sweat secretion by the skin increases rapidly, which triggers the autonomous switch to the cooling mode. Sweat rapidly transports to the top PA6 layer, facilitating rapid evaporation through the unidirectional liquid transport design; meanwhile, the PSRT textile automatically switches from low emissivity to high emissivity (εMIR ∼0.955) for radiative cooling. As a result, this PSRT textile expands the thermal comfort zone by 24.7 °C (8.3-33.0 °C), setting a performance record among passive thermoregulatory textiles. It is expected that the further advancement of the passive sweat-responsive thermoregulatory textile with an increasing thermal comfort zone can not only provide comfort for the human body with a minimized carbon footprint but also significantly expand the geographic and seasonal restrictions of human activity.

Integrating Radiative Cooling and Solar Heating for On-Demand Thermal Management

Passive radiative cooling has been extensively explored as a sustainable alternative to traditional cooling systems. However, relying solely on this cooling mode restricts their application in temperature-fluctuating environments and may cause overcooling on cold days. To address this challenge, researchers are increasingly developing dual-mode devices that integrate radiative cooling with solar heating, utilizing the Sun's continuous heat source for passive heating. In this perspective, we summarize the latest advancements in this field and highlight specific strategies for switchable dual-mode devices. These strategies generally fall into two categories: Janus design and all-in-one design. Finally, we discuss future challenges and opportunities in on-demand radiative cooling and solar heating, intending to advance this technology toward practical applications.

All-Biomass Derived Nanocomposite Films

Achieving simultaneous sustainability and property is a great challenge for current thermally managed composite films. The study proposes to prepare all-biomass derived nanocomposite films with excellent mechanical, thermal, and degradation properties by self-assembling carbon quantum dots (CQDs) and carbon nanosheets (CNSs) from cellulose nanofibers (CNFs). The results showed that the nanocomposite film with CQDs1@CNSs1/CF exhibited the best comprehensive properties with thermal conductivity of 0.817 W m-1 K-1, tensile strength of 39.60 MPa, elongation at break of 6.26%, tensile modulus of 5.34 GPa, degradation residual rate in water of 86.02%, degradation residual rate in PBS of 66.67%, and degradation residual rate in buried of 52%. The all-biomass derived nanocomposite films regarding the excellent thermal conductivity, biodegradability, and mechanical properties can be available with thermal management and excellent sustainability.

Anisotropic Hygroscopic Hydrogels with Synergistic Insulation-Radiation-Evaporation for High-Power and Self-Sustained Passive Daytime Cooling

Hygroscopic hydrogel is a promising evaporative-cooling material for high-power passive daytime cooling with water self-regeneration. However, undesired solar and environmental heating makes it a challenge to maintain sub-ambient daytime cooling. While different strategies have been developed to mitigate heat gains, they inevitably sacrifice the evaporation and water regeneration due to highly coupled thermal and vapor transport. Here, an anisotropic synergistically performed insulation-radiation-evaporation (ASPIRE) cooler is developed by leveraging a dual-alignment structure both internal and external to the hydrogel for coordinated thermal and water transport. The ASPIRE cooler achieves an impressive average sub-ambient cooling temperature of ~ 8.2 °C and a remarkable peak cooling power of 311 W m-2 under direct sunlight. Further examining the cooling mechanism reveals that the ASPIRE cooler reduces the solar and environmental heat gains without comprising the evaporation. Moreover, self-sustained multi-day cooling is possible with water self-regeneration at night under both clear and cloudy days. The synergistic design provides new insights toward high-power, sustainable, and all-weather passive cooling applications.

Self-adaptive and large-area sprayable thermal management coatings for energy saving

Self-adaptive thermal management over large areas is highly attractive since single-mode radiative cooling materials lead to undesired overcooling. However, it remains a challenge that dual-mode switchable materials require artificial stimuli or additional energy for switching between heating and cooling modes. Here, different from dual-mode switching materials driven by artificial stimuli or additional energy, we propose an autonomously self-adaptive dual-modal coating with assembled micro-heterostructures that can engender the multistage scattering of incident light. The resultant coating demonstrates 92% solar reflectivity and 93% emissivity in hot condition. More significantly, the coating reaches 60% visible light optical modulation, which is attributed to the formation and disruption of the conjugation region in the chromogenic molecules, to prevent overcooling in cold condition. A thermal-switchable fabric is further fabricated via large-area spraying processes, demonstrating 2.5 °C warmer in cold condition and 8.7 °C cooler in hot condition compared to white samples. The coating highlights the importance of the large-scale manufacturing of temperature-adaptive materials, providing insights into the application of dynamic radiative cooling in garment, camping, building and other fields.

Fundamental concepts, design rules and potentials in radiative cooling

Amidst the escalating environmental concerns driven by global warming and the detrimental impacts of extreme climates, energy consumption and greenhouse gas emissions associated with refrigeration have reached unprecedented levels. Radiative cooling, as an emerging renewable cooling technology, has been positioned as a pivotal strategy in the fight against global warming. This review examines the theoretical model of radiative cooling emitters and complex practical environment. We first investigate the thermodynamic interactions between environmental factors and the cooling surface, followed by an examination of innovative modulation techniques such as asymmetric/non-reciprocal radiative heat transfer mechanisms. Additionally, we summarize the latest advancements in structural design and simulation methodologies for radiative cooling materials at the device level. We then delve into potential applications of radiative cooling materials in various scenarios including energy-efficient construction, personal thermal management, photovoltaic cooling, and dynamic PDRC materials with seasonal adaptability. In conclusion, we provide a comprehensive overview of this technology's strengths and current challenges to inspire further research and application development in radiative cooling technology with a focus on contributing towards energy conservation objectives and promoting a sustainable society.

Humidity-Responsive Actuator-Based Smart Personal Thermal Management Fabrics Achieved by Solar Thermal Heating and Sweat-Evaporation Cooling

Personal thermal management (PTM) fabrics with energy efficiency and cost-effectiveness have been rapidly developed in recent years, but it still remains challenging to maintain a favorable body temperature through one cloth in complex and dynamic environments. Herein, we propose an asymmetric fabric for self-adaptive thermal management with the aim of enhancing thermal comfort in outdoor environments. This fabric consists of an electrospun polyamide (PA) fabric and a PPy@MXene coating layer integrated into a kirigami structure. The PPy@MXene coating, a highly efficient photothermal conversion material, imparts the fabric with a substantial temperature increase of 44 °C under one sun of irradiation. By leveraging the hygroscopic expansion property of the PA fabric, the PPy@MXene/PA fabric exhibits high sensitivity as an actuator in response to humidity. After incorporating a kirigami-inspired design, the patterned fabric efficiently harnesses solar energy under weak sunlight irradiation for heating purposes and automatically opens channels for heat release when evaporating perspiration. This dynamic fabric demonstrates superior self-adaptivity compared to conventional static fabrics, thus, presenting great insights in developing smart PTM systems.

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.

A highly visible-transparent thermochromic smart window with broadband infrared modulation for all-season energy savings

Thermochromic smart windows effectively reduce the energy consumption for buildings through passive light modulation including the transmission of visible (TVis) and near-infrared (TNIR) light, and the emissivity of mid-infrared (εMIR) light in response to ambient temperature change. However, thermochromic windows that maintain high TVis while modulating TNIR and εMIR simultaneously are highly desirable but still challenging. Here, we develop a thermochromic smart window based on a two-way shape memory polymer to enable reversible transformation and achieve TNIR modulation of 44.0% and εMIR modulation of 76.5% while maintaining high TVis (>50%). Compared to traditional windows based on silica glass, this device shows 4°C lower temperature in summer daytime, 2°C higher in winter daytime, and 1°C higher in spring nighttime. It is expected that our device can achieve greater annual energy savings in comparison with commercial glass anywhere in the world and promote the progress of thermochromic windows for energy-efficient buildings.

Recent Advances in Next-Generation Textiles

Textiles have played a pivotal role in human development, evolving from basic fibers into sophisticated, multifunctional materials. Advances in material science, nanotechnology, and electronics have propelled next-generation textiles beyond traditional functionalities, unlocking innovative possibilities for diverse applications. Thermal management textiles incorporate ultralight, ultrathin insulating layers and adaptive cooling technologies, optimizing temperature regulation in dynamic and extreme environments. Moisture management textiles utilize advanced structures for unidirectional transport and breathable membranes, ensuring exceptional comfort in activewear and outdoor gear. Protective textiles exhibit enhanced features, including antimicrobial, antiviral, anti-toxic gas, heat-resistant, and radiation-shielding capabilities, providing high-performance solutions for healthcare, defense, and hazardous industries. Interactive textiles integrate sensors for monitoring physical, chemical, and electrophysiological parameters, enabling real-time data collection and responses to various environmental and user-generated stimuli. Energy textiles leverage triboelectric, piezoelectric, and hygroelectric effects to improve energy harvesting and storage in wearable devices. Luminous display textiles, including electroluminescent and fiber optic systems, enable dynamic visual applications in fashion and communication. These advancements position next-generation textiles at the forefront of materials science, significantly expanding their potential across a wide range of 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.

Flexible Phase-Change Films with Exceptional Water and Temperature Resistance for Smart Personal Thermal Protection

Personal thermal protection is crucial in extreme temperature environments, and the rising global temperatures present significant challenges in managing heat stress for individuals. Phase-change materials (PCMs) can absorb or release heat during phase transition to maintain a constant temperature, thus making them ideal innovative thermal protection materials. However, it is currently a bottleneck issue for using PCMs in wearable thermal protection systems due to a balance between the mechanical properties, latent heat, temperature resistance, and rapid response on demand. Herein, a flexible composite PCM film is developed and demonstrated by incorporating superhydrophobic silica aerogel particles (SSAPs) in a cross-linked poly(ethylene glycol) (PEG) network. The cross-linked network effectively addresses the inherent solid-liquid phase-change issue of PCMs, providing self-support, high flexibility, and heat resistance. Meanwhile, the SSAP endows water resistance and synergistic thermal insulation properties to the PCM film. When the SSAP content is adjusted, a latent heat range of 113.1-146.9 J g-1 is achieved. Despite a lower latent heat of the PCM film than pure PEG films, a temperature drop of 13.8 °C is achieved at 80 °C, marking a 2.65-fold enhancement. Interestingly, the heating rate of the PCM film is decelerated by 275% compared to that of pure PEG cross-linked networks. This study not only proposes a strategy for preparing phase-change films with flexibility and temperature resistance but also demonstrates their feasibility of achieving lower latent heat while paradoxically enhancing thermal regulation capability.

Neuron-Inspired Flexible Phase Change Materials for Ambient Energy Harvesting and Respiration Monitoring

The global energy crisis and climate change pose unprecedented challenges. Wearable devices with personal thermoregulation and energy harvesting hold great promise for achieving energy savings and human thermal comfort. Here, inspired by neurons, a novel phase change material (PCM) is reported for efficient energy harvesting and respiratory monitoring via a self-assembly strategy. The use of gum arabic (GA) enabled the encapsulation of polyethylene glycol (PEG) and the targeted distribution of carboxylated multi-walled carbon nanotubes (cMWCNTs) simultaneously in poly (ethylene vinyl acetate) (EVA) matrix. The material exhibits an outstanding toughness value of 14.88 MJ m-3 and high elongation at a break of 565.67%, exhibiting remarkable flexibility. The material with sufficient melting enthalpy (71.11 J g-1) demonstrates high photothermal conversion efficiency (95.27%) under 808 nm laser irradiation (105 mW cm-2). In addition, due to the synergistic effect of GA and PEG, especially the formation of microdome structures on the surface, the material demonstrates ultrasensitive humidity responsiveness for respiratory monitoring with high precision, excellent repeatability, and fast response/recovery time (50.4/50.5 ms). Notably, it shows great potential for moisture-electric generators (MEGs) with the function of non-contact sensing. This material opens the path toward next-generation wearable devices in energy conversion and health monitoring.

Anodization-Processed Colored Radiative Thermoregulatory Film

Colored radiative thermal management materials (RTMM) not only provide superior thermoregulatory performance but also satisfy aesthetic requirements. However, the complexity of the preparation procedures and constrained color selection have hindered their widespread adoption. Here, we presented a facile one-step anodizing strategy for fabricating colored dual-mode RTMM based on titanium film (Ti) and P(VDF-HFP) with mid-infrared (MIR) emissivities of 0.07 and 0.96, respectively, which allow for on-demand temperature modulation (rise of 28.2 K and drop of 9 K) without energy consumption. Furthermore, demonstrations of a colored radiative warming membrane also validate the effectiveness of anodizing treatment. The colored Ti/nano PE membrane with 10.8 μm thickness enables a temperature rise of 2.3 K on real human skin, which is much higher than that of commercial fabric with 120 μm thickness (0.7 K). This strategy provides insights for the scalable fabrication and application of colored low emissivity materials, contributing to the goal of a sustainable society.

Dual-Mode Stretchable Emitter with Programmable Emissivity and Air Permeability

Materials with anisotropic emission characteristics have attracted considerable attention for thermal management. Although many dual-mode emitters have been developed for this purpose in the form of textiles, multilayer films, and photonic structures, multiple functionalities are essential for their versatile applications. Herein, a highly stretchable dual-mode emitter with programmable emissivity and air permeability is presented. The emitter comprises a planar Ge2Sb2Te5 (GST) cavity on one side of a perforated elastomer substrate and an infrared-reflecting metal layer on the other side. With a laser-induced phase transition from amorphous to crystalline GST, the emitter exhibits a large emissivity difference of 0.52 between both sides. The dual-mode emitter remains highly stable without mechanical failure after repeated stretching cycles to a strain of 50%. This air-permeable and stretchable emitter can be attached to any curved surface, including the human body. The GST-side emissivity can be programmed into an arbitrary emissivity pattern using a spatially modulated laser beam, ultimately enabling the printing of mutually independent visible and thermal images in a single emitter. This study provides a promising structure for multispectral optical security as well as thermal management.

Scalable Production of Functional Fibers with Nanoscale Features for Smart Textiles

Functional fibers, retaining nanoscale characteristics or nanomaterial properties, represent a significant advance in nanotechnology. Notably, the combination of scalable manufacturing with cutting-edge nanotechnology further expands their utility across numerous disciplines. Manufacturing kilometer-scale functional fibers with nanoscale properties are critical to the evolution of smart textiles, wearable electronics, and beyond. This review discusses their design principles, manufacturing technologies, and key advancements in the mass production of such fibers. In addition, it summarizes the current applications and state of progress in scalable fiber technologies and provides guidance for future advances in multifunctional smart textiles, by highlighting the upcoming impending demands for evolving nanotechnology. Challenges and directions requiring sustained effort are also discussed, including material selection, device design, large-scale manufacturing, and multifunctional integration. With advances in functional fibers and nanotechnology in large-scale production, wearable electronics, and smart textiles could potentially enhance human-machine interaction and healthcare applications.

Scalable colored Janus fabric scheme for dynamic thermal management

The art of passive thermal management lies in effectively mitigating heat stress by manipulating the optical spectra of target objects. However, a significant obstacle remains in finding a structure that can seamlessly adapt to diverse thermal environments. In response to this challenge, we posit that Janus fabrics have unique advantages for multi-scene applications when carefully engineered. A Janus fabric with an upper side exhibiting a 92% solar reflectivity and a 94% emissivity, along with a lower side possessing an infrared emissivity below 30% could enable energy savings at a large scale. It outperforms commercial products in terms of energy-saving efficiency under different climate conditions. Furthermore, the scalable manufacturing compatibility and outstanding performance make the Janus structure a promising avenue for diverse passive thermal management scenarios.

Realizing Sunlight-Induced Efficiently Dynamic Infrared Emissivity Modulation Based on Aluminum-Doped zinc Oxide Nanocrystals

Dynamic manipulation of an object's infrared radiation characteristics is a burgeoning technology with significant implications for energy and information fields. However, exploring efficient stimulus-spectral response mechanism and realizing simple device structures remains a formidable challenge. Here, a novel dynamic infrared emissivity regulation mechanism is proposed by controlling the localized surface plasmon resonance absorption of aluminum-doped zinc oxide (AZO) nanocrystals through ultraviolet photocharging/oxidative discharging. A straightforward device architecture that integrates an AZO nanocrystal film with an infrared reflective layer and a substrate, functioning as a photo-induced dynamic infrared emissivity modulator, which can be triggered by weak ultraviolet light in sunlight, is engineered. The modulator exhibits emissivity regulation amount of 0.72 and 0.61 in the 3-5 and 8-13 µm ranges, respectively. Furthermore, the modulator demonstrates efficient light triggering characteristic, broad spectral range, angular-independent emissivity, and long cyclic lifespan. The modulator allows for self-adaptive daytime radiative cooling and nighttime heating depending on the ultraviolet light in sunlight and O2 in air, thereby achieving smart thermal management for buildings with zero-energy expenditure. Moreover, the potential applications of this modulator can extend to rewritable infrared displays and deceptive infrared camouflage.

In Situ Multi-Directional Liquid Manipulation Enabled by 3D Asymmetric Fang-Structured Surface

Decorating surfaces with wetting gradients or topological structures is a prevailing strategy to control uni-directional spreading without energy input. However, current methods, limited by fixed design, cannot achieve multi-directional control of liquids, posing challenges to practical applications. Here, a structured surface composed of arrayed three-dimensional asymmetric fang-structured units is reported that enable in situ control of customized multi-directional spreading for different surface tension liquids, exhibiting five novel modes. This is attributed to bottom-up distributed multi-curvature features of surface units, which create varied Laplace pressure gradients to guide the spreading of different-wettability liquids along specific directions. The surface's capability to respond to liquid properties for multimodal control leads to innovative functions that are absent in conventional structured surfaces. Selective multi-path circuits can be constructed by taking advantage of rich liquid behaviors with the surface; surface tensions of wetting liquids can be portably indicated with a resolution scope of 0.3-3.4 mN m-1 using the surface; temperature-mediated change of liquid properties is utilized to smartly manipulate liquid behavior and achieve the spatiotemporal-controllable targeted cooling of the surface at its heated state. These novel applications open new avenues for developing advanced surfaces for liquid manipulation.

Reversible Solar Heating and Radiative Cooling Devices via Mechanically Guided Assembly of 3D Macro/Microstructures

Solar heating and radiative cooling are promising solutions for decreasing global energy consumption because these strategies use the Sun (≈5800 K) as a heating source and outer space (≈3 K) as a cooling source. Although high-performance thermal management can be achieved using these eco-friendly methods, they are limited by daily temperature fluctuations and seasonal changes because of single-mode actuation. Herein, reversible solar heating and radiative cooling devices formed via the mechanically guided assembly of 3D architectures are demonstrated. The fabricated devices exhibit the following properties: i) The devices reversibly change between solar heating and radiative cooling under uniaxial strain, called dual-mode actuation. ii) The 3D platforms in the devices can use rigid/soft materials for functional layers owing to the optimized designs. iii) The devices can be used for dual-mode thermal management on a macro/microscale. The devices use black paint-coated polyimide (PI) films as solar absorbers with multilayered films comprising thin layers of polydimethylsiloxane/silver/PI, achieving heating and cooling temperatures of 59.5 and -11.9 °C, respectively. Moreover, mode changes according to the angle of the 3D structures are demonstrated and the heating/cooling performance with skin, glass, steel, aluminum, copper, and PI substrates is investigated.

Strain-Temperature Dual Sensor Based on Deep Learning Strategy for Human-Computer Interaction Systems

Thermoelectric (TE) hydrogels, mimicking human skin, possessing temperature and strain sensing capabilities, are well-suited for human-machine interaction interfaces and wearable devices. In this study, a TE hydrogel with high toughness and temperature responsiveness was created using the Hofmeister effect and TE current effect, achieved through the cross-linking of PVA/PAA/carboxymethyl cellulose triple networks. The Hofmeister effect, facilitated by Na+ and SO42- ions coordination, notably increased the hydrogel's tensile strength (800 kPa). Introduction of Fe2+/Fe3+ as redox pairs conferred a high Seebeck coefficient (2.3 mV K-1), thereby enhancing temperature responsiveness. Using this dual-responsive sensor, successful demonstration of a feedback mechanism combining deep learning with a robotic hand was accomplished (with a recognition accuracy of 95.30%), alongside temperature warnings at various levels. It is expected to replace manual work through the control of the manipulator in some high-temperature and high-risk scenarios, thereby improving the safety factor, underscoring the vast potential of TE hydrogel sensors in motion monitoring and human-machine interaction applications.

Bioinspired Superhydrophobic All-In-One Coating for Adaptive Thermoregulation

The development of scalable and passive coatings that can adapt to seasonal temperature changes while maintaining superhydrophobic self-cleaning functions is crucial for their practical applications. However, the incorporation of passive cooling and heating functions with conflicting optical properties in a superhydrophobic coating is still challenging. Herein, an all-in-one coating inspired by the hierarchical structure of a lotus leaf that combines surface wettability, optical structure, and temperature self-adaptation is obtained through a simple one-step phase separation process. This coating exhibits an asymmetrical gradient structure with surface-embedded hydrophobic SiO2 particles and subsurface thermochromic microcapsules within vertically distributed hierarchical porous structures. Moreover, the coating imparts superhydrophobicity, high infrared emission, and thermo-switchable sunlight reflectivity, enabling autonomous transitions between radiative cooling and solar warming. The all-in-one coating prevents contamination and over-cooling caused by traditional radiative cooling materials, opening up new prospects for the large-scale manufacturing of intelligent thermoregulatory coatings.

Switchable and Tunable Radiative Cooling: Mechanisms, Applications, and Perspectives

The cost of annual energy consumption in buildings in the United States exceeds 430 billion dollars ( Science 2019, 364 (6442), 760-763), of which about 48% is used for space thermal management (https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019), revealing the urgent need for efficient thermal management of buildings and dwellings. Radiative cooling technologies, combined with the booming photonic and microfabrication technologies ( Nature 2014, 515 (7528), 540-544), enable energy-free cooling by radiative heat transfer to outer space through the atmospheric transparent window ( Nat. Commun. 2024, 15 (1), 815). To pursue all-season energy savings in climates with large temperature variations, switchable and tunable radiative coolers (STRC) have emerged in recent years and quickly gained broad attention. This Perspective introduces the existing STRC technologies and analyzes their benefits and challenges in future large-scale applications, suggesting ways for the development of future STRCs.

Annual Energy-Saving Smart Windows with Actively Controllable Passive Radiative Cooling and Multimode Heating Regulation

Smart windows with radiative heat management capability using the sun and outer space as zero-energy thermodynamic resources have gained prominence, demonstrating a minimum carbon footprint. However, realizing on-demand thermal management throughout all seasons while reducing fossil energy consumption remains a formidable challenge. Herein, an energy-efficient smart window that enables actively tunable passive radiative cooling (PRC) and multimode heating regulation is demonstrated by integrating the emission-enhanced polymer-dispersed liquid crystal (SiO2@PRC PDLC) film and a low-emission layer deposited with carbon nanotubes. Specifically, this device can achieve a temperature close to the chamber interior ambient under solar irradiance of 700 W m-2, as well as a temperature drop of 2.3 °C at sunlight of 500 W m-2, whose multistage PRC efficiency can be rapidly adjusted by a moderate voltage. Meanwhile, synchronous cooperation of passive radiative heating (PRH), solar heating (SH), and electric heating (EH) endows this smart window with the capability to handle complicated heating situations during cold weather. Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer SiO2@PRC PDLC, normal glass, and commercial low-E glass when applied in different climate zones. This work provides a feasible pathway for year-round thermal management, presenting a huge potential in energy-saving applications.

Transparent grating-based metamaterials for dynamic infrared radiative regulation smart windows

Dynamic infrared radiation regulation has been widely explored for smart windows because of its vital importance for comfortable and energy-efficient buildings. However, it remains a great challenge to synchronously achieve high visible transmittance and pronounced infrared tunability. Here, we propose a dynamic infrared tunable metamaterial composed of indium tin oxide (ITO) gratings, an air insulator, and an ITO reflector. The ITO grating-based infrared radiation regulator exhibits a high emissivity tunability of 0.73 at 8-13 μm while maintaining a high visible transmittance of 0.65 and 0.72 before and after actuation, respectively. By adjusting the geometric parameters, the tunable bandwidth can be further extended to 3-30 μm and the ultra-broadband tunability reaches 0.62. The excellent infrared tunable performance arises from the insulator thickness-dependent effect of Fabry-Pérot and propagating surface plasmon resonance coupling and decoupling, which lead to perfect and low absorption, respectively. This work provides potential for the advancement of smart window technology and makes a significant contribution to sustainable buildings.

Personal Thermal Management by Radiative Cooling and Heating

Maintaining thermal comfort within the human body is crucial for optimal health and overall well-being. By merely broadening the set-point of indoor temperatures, we could significantly slash energy usage in building heating, ventilation, and air-conditioning systems. In recent years, there has been a surge in advancements in personal thermal management (PTM), aiming to regulate heat and moisture transfer within our immediate surroundings, clothing, and skin. The advent of PTM is driven by the rapid development in nano/micro-materials and energy science and engineering. An emerging research area in PTM is personal radiative thermal management (PRTM), which demonstrates immense potential with its high radiative heat transfer efficiency and ease of regulation. However, it is less taken into account in traditional textiles, and there currently lies a gap in our knowledge and understanding of PRTM. In this review, we aim to present a thorough analysis of advanced textile materials and technologies for PRTM. Specifically, we will introduce and discuss the underlying radiation heat transfer mechanisms, fabrication methods of textiles, and various indoor/outdoor applications in light of their different regulation functionalities, including radiative cooling, radiative heating, and dual-mode thermoregulation. Furthermore, we will shine a light on the current hurdles, propose potential strategies, and delve into future technology trends for PRTM with an emphasis on functionalities and applications.

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.

Switchable radiative cooling and solar heating for sustainable thermal management

Radiative thermal management technologies that utilize thermal radiation from nano/microstructure for cooling and heating have gained significant attention in sustainable energy research. Passive radiative cooling and solar heating operate continuously, which may lead to additional heating or cooling energy consumption due to undesired cooling or heating during cold nighttime/winters or hot daytime/summers. To overcome the limitation, recent studies have focused on developing radiative thermal management technologies that can toggle radiative cooling on and off or possess switchable dual cooling and heating modes to realize sustainable and efficient thermal management. This review will explore the fundamental concepts of radiative thermal management and its switching mechanisms, utilizing novel systems composed of various materials and nano/microstructures. Additionally, we will delve into the potential future research directions in radiative thermal management technologies.

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.

Patterned liquid metal embedded in brush-shaped polymers for dynamic thermal management

Interface thermal resistance has become a crucial barrier to effective thermal management in high-performance electronics and sensors. The growing complexity of operational conditions, such as irregular and dynamic surfaces, demands thermal interface materials (TIMs) to possess high thermal conductivity and soft elasticity. However, developing materials that simultaneously combine soft elasticity and high thermal conductivity remains a challenging task. Herein, we utilize a vertically oriented graphene aerogel (VGA) and rationally design liquid metal (LM) networks to achieve directional and adjustable pathways within the composite. Subsequently, we leverage the advantages of the low elastic modulus and high deformation capabilities of brush-shaped polydimethylsiloxane (BPDMS), together with the bicontinuous thermal conduction path constructed by VGA and LM networks. Ultimately, the designed composite of patterned liquid metal/vertically oriented graphene aerogel/brush-shaped PDMS (LM-VGA/BPDMS) shows a high thermal conductivity (7.11 W m-1 K-1), an ultra-low elastic modulus (10.13 kPa), excellent resilience, and a low interface thermal resistance (14.1 K mm2 W-1). This LM-VGA/BPDMS soft composite showcases a stable heat dissipation capability at dynamically changing interfaces, as well as excellent adaptability to different irregular surfaces. This strategy holds important application prospects in the fields of interface thermal management and thermal sensing in extremely complex environments.

Recent advances in dynamic dual mode systems for daytime radiative cooling and solar heating

Thermal management, including heating and cooling, plays an important role in human productive activities and daily life. Nevertheless, in the actual environment, almost all the ambient scenarios come with the challenge that the objects are located in a quite dynamic and variable environment, which includes fluctuations in aspects such as space, time, sunlight, season, and temperature. It is imperative to develop low-energy or even zero-energy thermal-management technologies with renewable and clean energy. In this review, we summarised the latest technological advances and the prospects in this burgeoning field. First, we present the fundamental principles of the daytime passive radiative cooling (PDRC) thermal management device. Next, In the domain of dual-mode systems, they are classified into various types based on the diverse mechanisms of transitioning between cooling and heating states, including electrical responsive, mechanical responsive, temperature responsive, and solution responsive. Furthermore, we conducted an in-depth analysis of the principles and design methodologies associated with these categories, followed by a comparative assessment of their performance in radiative cooling and solar heating applications. Finally, this review presents the challenges and opportunities of dynamic dual mode thermal management, while also identifying future directions.

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.

A smart thermal-gated bilayer membrane for temperature-adaptive radiative cooling and solar heating

Due to the huge energy consumption of traditional cooling- and heating-based electricity, passive radiative cooling and solar heating with a minimum carbon footprint using the outer space and Sun as natural thermodynamic resources have attracted much attention. However, most passive devices are static and monofunctional, and cannot meet the practical requirements of dynamic cooling and heating under various conditions. Here, we demonstrate a smart thermal-gated (STG) bilayer membrane that enables fully automatic and temperature-adaptive radiative cooling and solar heating. Specifically, this device can switch from reflective to absorptive (white to black) in the solar wavelength with the reduction in optical scattering upon ambient temperature, corresponding to a sunlight reflectivity change from 0.962 to 0.059 when the temperature drops below ∼30 °C, whereas its mid-infrared emissivity remains at ∼0.95. Consequently, this STG membrane achieves a temperature of ∼5 °C below ambient (a key signature of radiative cooling) under direct sunlight (peak solar irradiance >900 W m-2) in summer and a solar heating power of ∼550 W m-2 in winter. Theoretical analysis reveals the substantial advantage of this switchable cooling/heating device in potential energy saving compared with cooling-only and heating-only strategies when widely used in different climates. It is expected that this work will pave a new pathway for designing temperature-adaptive devices with zero energy consumption and provide an innovative way to achieve sustainable energy.

A Hierarchically Nanofibrous Self-Cleaning Textile for Efficient Personal Thermal Management in Severe Hot and Cold Environments

Climate change has recently caused more and more severe temperatures, inducing a growing demand for personal thermal management at outdoors. However, designing textiles that can achieve personal thermoregulation without energy consumption in severely hot and cold environments remains a huge challenge. Herein, a hierarchically nanofibrous (HNF) textile with improved thermal insulation and radiative thermal management functions is fabricated for efficient personal thermal management in severe temperatures. The textile consists of a radiative cooling layer, an intermediate thermal insulation layer, and a radiative heating layer, wherein the porous lignocellulose aerogel membrane (LCAM) as intermediate layer has low thermal conductivity (0.0366 W·m-1·K-1), ensuring less heat loss in cold weather and blocking external heat in hot weather. The introduction of polydimethylsiloxane (PDMS) increases the thermal emissivity (90.4%) of the radiative cooling layer in the atmospheric window and also endows it with a perfect self-cleaning performance. Solar absorptivity (80.1%) of the radiative heating layer is dramatically increased by adding only 0.05 wt% of carbon nanotubes (CNTs) into polyacrylonitrile. An outdoor test demonstrates that the HNF textile can achieve a temperature drop of 7.2 °C compared with white cotton in a hot environment and can be as high as 12.2 °C warmer than black cotton in a cold environment. In addition, the HNF textile possesses excellent moisture permeability, breathability, and directional perspiration performances, making it promising for personal thermal management in severely hot and cold environments.

Scalable Bacterial Cellulose-Based Radiative Cooling Materials with Switchable Transparency for Thermal Management and Enhanced Solar Energy Harvesting

Radiative cooling materials that can dynamically control solar transmittance and emit thermal radiation into cold outer space are critical for smart thermal management and sustainable energy-efficient buildings. This work reports the judicious design and scalable fabrication of biosynthetic bacterial cellulose (BC)-based radiative cooling (Bio-RC) materials with switchable solar transmittance, which are developed by entangling silica microspheres with continuously secreted cellulose nanofibers during in situ cultivation. Theresulting film shows a high solar reflection (95.3%) that can be facilely switched between an opaque state and a transparent state upon wetting. Interestingly, the Bio-RC film exhibits a high mid-infrared emissivity (93.4%) and an average sub-ambient temperature drop of ≈3.7 °C at noon. When integrating with a commercially available semi-transparent solar cell, the switchable solar transmittance of Bio-RC film enables an enhancement of solar power conversion efficiency (opaque state: 0.92%, transparent state: 0.57%, bare solar cell: 0.33%). As a proof-of-concept illustration, an energy-efficient model house with its roof built with Bio-RC-integrated semi-transparent solar cell is demonstrated. This research can shine new light on the design and emerging applications of advanced radiative cooling materials.

Temperature-adaptive rooftop covering with synergetic modulation of solar and thermal radiation for maximal energy saving

The energy consumption for maintaining desired indoor temperature accounts for 20% of primary energy use worldwide. Passive rooftop modulation of solar/thermal radiation without external energy input has a great potential in building energy saving. However, existing passive rooftop modulation techniques failed to simultaneously modulate solar/thermal radiation in response to rooftop surface temperature which is closely related to the building thermal loads, leading to limited or even counter-productive overall energy saving. Here, we report the development of a surface temperature-adaptive rooftop covering with synergetic solar and thermal modulations. The covering, made of a scalable metalized polyethylene film, demonstrated excellent solar absorptance modulation (72.5%) and thermal emissivity modulation (79%) in response to its temperature change from 22°C (indoor heating setpoint) to 25°C (indoor cooling setpoint), and vice versa. Building energy simulations demonstrate that the proposed rooftop covering can achieve all-season energy savings across all climate regions.

Nanopolyhybrids: Materials, Engineering Designs, and Advances in Thermal Management

The fundamental requirements for thermal comfort along with the unbalanced growth in the energy demand and consumption worldwide have triggered the development and innovation of advanced materials for high thermal-management capabilities. However, continuous development remains a significant challenge in designing thermally robust materials for the efficient thermal management of industrial devices and manufacturing technologies. The notable achievements thus far in nanopolyhybrid design technologies include multiresponsive energy harvesting/conversion (e.g., light, magnetic, and electric), thermoregulation (including microclimate), energy saving in construction, as well as the miniaturization, integration, and intelligentization of electronic systems. These are achieved by integrating nanomaterials and polymers with desired engineering strategies. Herein, fundamental design approaches that consider diverse nanomaterials and the properties of nanopolyhybrids are introduced, and the emerging applications of hybrid composites such as personal and electronic thermal management and advanced medical applications are highlighted. Finally, current challenges and outlook for future trends and prospects are summarized to develop nanopolyhybrid materials.

Solar-Radiation-Dependent Anisotropic Thermal Management Device with Net Zero Energy from 4D Printing Shape Memory Polymer-Based Composites

Reports have pointed out that nearly 50% of the global total energy demand for buildings is used for daily heating and cooling. Therefore, it is very important to develop various high-performance thermal management techniques with low energy consumption. In this work, we present an intelligent shape memory polymers (SMPs)-based device with programmable anisotropic thermal conductivity fabricated by a 4D printing technique to assist in thermal management with net zero energy. Highly thermal conductive BN nanosheets were textured in a poly (lactic acid) (PLA) matrix by 3D printing, and the printed composites lamina exhibited significant anisotropic thermal conductivity. The direction of heat flow in devices could be switched programmably, accompanying the light-activated deformation controlled by grayscale of composite, which was demonstrated by the "windows" arrays composed of in-plate thermal conductivity facets and SMPs-based hinge joints, achieving the programmable movement of opening and closing under different light conditions. Based on solar radiation-dependent SMPs coupled with the adjustment of heat flow along anisotropic thermal conductivity, the 4D printed device has been proved in concept for potential applications in thermal management in a building envelop for dynamic climate adaptation, taking place automatically based on the environment.

Scalable Fabrication of Dual-Function Fabric for Zero-Energy Thermal Environmental Management through Multiband, Synergistic, and Asymmetric Optical Modulations

Solar heating and radiative cooling techniques have been proposed for passive space thermal management to reduce the global energy burden. However, the currently used single-function envelope/coating materials can only achieve static temperature regulation, presenting limited energy savings and poor adaption to dynamic environments. In this study, a sandwich-structured fabric, composed of vertical graphene, graphene glass fiber fabric, and polyacrylonitrile nanofibers is developed, with heating and cooling functions integrated through multiband, synergistic, (solar spectrum and mid-infrared ranges) and asymmetric optical modulations on two sides of the fabric. The dual-function fabric demonstrates high adaption to the dynamic environment and superior performance in a zero-energy-input temperature regulation. Furthermore, it demonstrates ≈15.5 and ≈31.1 MJ m^-2 y^-1 higher annual energy savings compared to those of their cooling-only and heating-only counterparts, corresponding to ≈173.7 MT reduction in the global CO₂ emission. The fabric exhibits high scalability for batch manufacturing with commercially abundant raw materials and facile technologies, providing a favorable guarantee of its mass production and use.

Engineering Structural Janus MXene-nanofibrils Aerogels for Season-Adaptive Radiative Thermal Regulation

Aerogels have provided a significant platform for passive radiation-enabled thermal regulation, arousing extensive interest due to their capabilities of radiative cooling or heating. However, there still remains challenge of developing functionally integrated aerogels for sustainable thermal regulation in both hot and cold environment. Here, Janus structured MXene-nanofibrils aerogel (JMNA) is rationally designed via a facile and efficient way. The achieved aerogel presents the characteristic of high porosity (≈98.2%), good mechanical strength (tensile stress of ≈2 MPa, compressive stress of ≈115 kPa), and macroscopic shaping property. Based on the asymmetric structure, the JMNA with switchable functional layers can alternatively enable passive radiative heating and cooling in winter and summer, respectively. As a proof of concept, JMNA can function as a switchable thermal-regulated roof to effectively enable the inner house model to maintain >25 °C in winter and <30 °C in hot summer. This design of Janus structured aerogels with compatible and expandable capabilities is promising to widely benefit the low-energy thermal regulation in changeable climate.

Engineering PEDOT:PSS/PEG Fibers with a Textured Surface toward Comprehensive Personal Thermal Management

The wild environment is unpredictable where soaring or plummeting temperatures in extreme weather events can pose serious threats to human lives. Incorporating passive evaporative cooling and controllable electric heating into clothing could effectively protect human beings from such harsh environments. In this work, poly(3,4-ethylene dioxy thiophene):poly(styrene sulfonate)/poly(ethylene glycol) (PPP) fibers with the core-shell structure and attractively textured surface have been successfully prepared via a single-nozzle wet-spinning technique. Results show that the fibers possess fascinating specific surface area (184.8 m2·g-1), electrical conductivity (50 S·cm-1), and stretchability (>100%) because of the novel preparation method and hierarchical morphological design. Through simple textile manufacturing routes, PPP fibers can be woven into fabrics easily, which exhibit desirable breathability, washability, and mechanical strength for smart textiles while maintaining favorable hygroscopicity. Benefiting from the textured structure with large specific surface area, PPP fabric exhibits attractile evaporative cooling rate. Practical application tests have demonstrated that under direct sunlight, the surface temperature of the PPP fabric is ∼5.2 and ∼10.8 °C lower than commercial cotton and polyester fabrics, respectively. Meanwhile, as conductive fibers, the resultant PPP fabric can heat under low-power electricity, therefore achieving the effect of "warmth in winter and coolness in summer". The facile fabrication process and elevated performance of PPP fibers present significant advantages for applications in intelligent garments and textiles, as well as comprehensive personal thermal management, which opens a new avenue for future design in these fields.

In Situ Mineralizing Spinning of Strong and Tough Silk Fibers for Optical Waveguides

Biopolymer-based optical waveguides with low-loss light guiding performance and good biocompatibility are highly desired for applications in biomedical photonic devices. Herein, we report the preparation of silk optical fiber waveguides through bioinspired in situ mineralizing spinning, which possess excellent mechanical properties and low light loss. Natural silk fibroin was used as the main precursor for the wet spinning of the regenerated silk fibroin (RSF) fibers. Calcium carbonate nanocrystals (CaCO₃ NCs) were in situ grown in the RSF network and served as nucleation templates for mineralization during the spinning, leading to the formation of strong and tough fibers. CaCO₃ NCs can guide the structure transformation of silk fibroin from random coils to β-sheets, contributing to enhanced mechanical properties. The tensile strength and toughness of the obtained fibers are up to 0.83 ± 0.15 GPa and 181.98 ± 52.42 MJ·m^-3, obviously higher than those of natural silkworm silks and even comparable to spider silks. We further investigated the performance of the fibers as optical waveguides and observed a low light loss of 0.46 dB·cm^-1, which is much lower than natural silk fibers. We believed that these silk-based fibers with excellent mechanical and light propagation properties are promising for applications in biomedical light imaging and therapy.

Combining ab initio and ab initio molecular dynamics simulations to predict the complex refractive indices of organic polymers

Organic polymers have attracted widespread interest in various fields ranging from optic and optoelectronic devices to optical system design owing to their light weight, high machinability, excellent thermal performance and reasonable costs. The complex refractive index is an inherent property of organic polymers and directly affects the accuracy of optical system simulation. This study introduces a theoretical protocol to accurately predict the complex refractive indices of organic polymers in the 0-5000 cm^-1 region for guiding the discovery and design of high-refractive index materials. In the proposed protocol, we computed the refractive indices of polymers with different monomer units using ab initio calculated static polarizability and mass density obtained by classical isothermal-isobaric ensemble simulations based on the Lorentz-Lorenz equation; we proposed a "Polymer Polarizability Fragment Segmentation" method to extrapolate the polarizabilities of polymers with longer chain lengths; meanwhile, the imaginary part of the dielectric functions of the polymers was calculated using the ab initio molecular dynamics (AIMD) method, and the real part of the dielectric functions was obtained using the Kramers-Kronig relation. We calculated the complex refractive indices of four commonly used organic polymers, i.e. polyethylene, polyvinyl chloride, polyvinyl alcohol and polylactic acid, to demonstrate the performance of the theoretical protocol. The approach combining ab initio and AIMD simulations is effective and economical to predict the complex refractive indices of organic polymers and other organic materials.

Passive Daytime Radiative Cooling of Silica Aerogels

Silica aerogels are one of the most widely used aerogels, exhibiting excellent thermal insulation performance and ultralow density. However, owing to their plenitude of Si-O-Si bonds, they possess high infrared emissivity in the range of 8-13 µm and are potentially robust passive radiative cooling (PRC) materials. In this study, the PRC behavior of traditional silica aerogels prepared from methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) in outdoor environments was investigated. The silica aerogels possessed low thermal conductivity of 0.035 W/m·K and showed excellent thermal insulation performance in room environments. However, sub-ambient cooling of 12 °C was observed on a clear night and sub-ambient cooling of up to 7.5 °C was achieved in the daytime, which indicated that in these cases the silica aerogel became a robust cooling material rather than a thermal insulator owing to its high IR emissivity of 0.932 and high solar reflectance of 0.924. In summary, this study shows the PRC performance of silica aerogels, and the findings guide the utilization of silica aerogels by considering their application environments for achieving optimal thermal management behavior.

Polarization-driven thermal emission regulator based on self-aligned GST nanocolumns

The increasing advances in thermal radiation regulators have attracted growing interest, particularly in infrared sources, thermal management, and camouflage. Despite many advances in dynamic thermal emitters with great controllability, sustained external energy is required to maintain the desired emission. In this study, we present a polarization-driven thermal emission regulator based on a two-way control: i) phase change and ii) polarization tuning. Based on a conventional, non-volatile phase change material, i.e., Ge₂Sb₂Te₅ (GST), we newly introduce an anisotropic medium for facile emissivity regulation without heat energy consumption. A rigorous coupled-wave analysis method provides design guidelines for finding optimal structural parameters. We utilized a simple glancing angle deposition process which induces tilted self-aligned nanocolumns with anisotropic properties. The fabricated sample shows polarization-sensitive thermal regulation through thermal imaging spectroscopic measurement. Additionally, we manufactured a multispectral visibly/thermally camouflaged patch that identifies encrypted information at a specific polarization state for a proof-of-concept demonstration.