Phase Change Material Enhanced Radiative Cooler for Temperature-Adaptive Thermal Regulation

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.

Temperature-adaptive dual-modal photonic textiles for thermal management

Maintaining a thermally comfortable living and working environment with renewable energy sources is crucial for human health. However, achieving temperature self-regulation in individual textiles without external interventions remains a challenge. Here, we present a dual-modal photonic textile capable of autonomously achieving both low-temperature solar heating and high-temperature radiative cooling under sunlight. This innovative textile is primarily composed of textile fibers that are functionalized with thermochromic microcapsules encapsulated in graphene and barium sulfate coatings, which exhibit approximately 80% visible light optical modulation when integrated into the fabric. We demonstrate that garment and tent (3.5 m × 2.9 m × 1.3 m) fabricated from these textiles can achieve temperature-adaptive, all-weather thermal management, expanding the thermal comfort range by 8.5°C. This research showcases notable potential for applications in fabric-related heat management and highlights the importance of exploring temperature-adaptive solutions for a sustainable and healthy lifestyle.

Particle-Solid Transition Architecture for Efficient Passive Building Cooling

Electricity consumption for building cooling accounts for a significant portion of global energy usage and carbon emissions. To address this challenge, passive daytime radiative cooling (PDRC) has emerged as a promising technique for cooling buildings without electricity input. However, existing radiative coolers face material mismatch issues, particularly on cementitious composites like concrete, limiting their practical application. Here, we propose a cementitious radiative cooling armor based on a particle-solid transition architecture (PSTA) to overcome these challenges. The PSTA design features an asymmetric yet monolithic morphology and an all-inorganic nature, decoupling radiative cooling from building compatibility while ensuring UV resistance. In the PSTA design, nanoparticles on the surface serve as sunlight scatterers and thermal emitters, while those embedded within a cementitious substrate provide build compatibility and cohesiveness. This configuration results in enhanced interfacial bonding strength, high solar reflectance, and strong mid-infrared emittance. Specifically, the PSTA delivers an enhanced interfacial shear strength (0.93 MPa), several-fold higher than that in control groups (metal, glass, plastic) along with a cooling performance (a subambient temperature drop of ∼6.6 °C and a cooling power of ∼92.8 W under a direct solar irradiance of ∼680 W/m2) that rivals or outperforms previous reports. Importantly, the design concept of the PSTA is applicable to various particles and solids, facilitating the practical application of PDRC technology in building scenarios.

Anti-UV Passive Radiative Cooling Chiral Nematic Liquid Crystal Films for Thermal Management

Passive radiative cooling (PRC) can spontaneously dissipate heat to outer space through atmospheric transparent windows, providing a promising path to meet sustainable development goals. However, achieving simultaneously high transparency, color-customizable, and thermal management of PRC anti ultraviolet (anti-UV) films remains a challenge. Herein, a simple strategy is proposed to utilize liquid crystalline polymer, with high mid-infrared emissive, forming customizable structural color film by molecular self-assembly and polymerization-induced pitch gradient, which guarantees the balance of transparency in visible spectrum and sunlight reflection, rendering anti-UV colored window for thermal management. By performing tests, temperature fall of 5.4 and 7.9 °C are demonstrated at noon with solar intensity of 717 W m-2 and night, respectively. Vivid red-, green-, blue-structured colors, and colorless films are designed and implemented to suppress the solar input and control the effective visible light transmissivity considering the efficiency function of human vision. In addition, temperature rise of 11.1 °C is achieved by applying an alternating current field on the PRC film. This study provides a new perspective on the thermal management and aesthetic functionalities of smart windows and wearables.

Stretchable Metamaterials with Tunable Infrared Emissivity for Dynamic Thermal Management

Manipulation of infrared emissivity, which is closely related to surface structure and optical parameters of materials, is a crucial approach for realizing dynamic thermal management. In this study, we design a metamaterial consisting of an array of aluminum disks embedded on a surface of a stretchable elastomeric substrate. Mechanical stretching-induced deformation allows dynamic modification of the surface structure and equivalent optical parameters, thus enabling dynamic control of the emissivity. By utilizing the elastomer polydimethylsiloxane (PDMS) as the substrate, the microstructure interdisk gap can be altered by stretching the PDMS. Through theoretical calculations, the plausibility of this approach is explained by the excitation of plasmon resonance and the variation in the exposed area of highly absorbent PDMS, and the optimal structures for tuning the infrared emissivity are revealed to be 6 μm in diameter and 100 nm in height. Based on this design, we prepare samples with periods of 7 and 7.9 μm and experimentally demonstrate that a change in the period can cause a change in the emissivity and thus tunability in thermal control performance. The temperature difference between the two samples reaches 44.1 °C at a heating power of 0.28 W/cm2 for both samples. Furthermore, we construct a stretching platform that enables in situ mechanical stretching to realize dynamic changes in emissivity. The integral infrared emissivity of the sample increases from 0.32 to 0.5 at a biaxial tensile strain of 13%, achieving a 56% modulation rate of the integral infrared emissivity. The material is expected to enable dynamic thermal management.

Integrated triboelectric nanogenerator and radiative cooler for all-weather transparent glass surfaces

Sustainable energies from weather are the most ubiquitous and non-depleted resources. However, existing devices exploiting weather-dependent energies are sensitive to weather conditions and geographical locations, making their universal applicability challenging. Herein, we propose an all-weather sustainable glass surface integrating a triboelectric nanogenerator and radiative cooler, which serves as a sustainable device, harvesting energy from raindrops and saving energy on sunny days. By systematically designing transparent, high-performance triboelectric layers, functioning as thermal emitters simultaneously, particularly compatible with radiative cooling components optimized with an evolutionary algorithm, our proposed device achieves optimal performance for all-weather-dependent energies. We generate 248.28 Wm-2 from a single droplet with an energy conversion ratio of 2.5%. Moreover, the inner temperature is cooled down by a maximum of 24.1 °C compared to pristine glass. Notably, as the proposed device is realized to provide high transparency up to 80% in the visible range, we are confident that our proposed device can be applied to versatile 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.

Confined Crystallization Polyether-Based Flexible Phase Change Film for Thermal Management

Phase change materials (PCMs) possess the potential to regulate temperature by utilizing their thermal properties to absorb and release heat. Nevertheless, the application of PCMs in thermal management is constrained by issues such as liquid leakage and limited flexibility. In this study, we propose a novel approach to address these challenges by incorporating a pore structure within nanofibers to confine the crystallization of phase change molecules, thereby enhancing the flexibility of the composite material. Additionally, inspired by the adaptive mechanisms observed in plants, we have developed a form stable PCM based on polyether, which effectively mitigates the issue of liquid leakage at higher temperatures. Despite being a solid-liquid PCM at its core, this material exhibits molecular-scale flow and macroscopic shape stability as a result of intermolecular forces. The composite film material possesses remarkable flexibility, efficient thermal management capabilities, adjustable phase transition temperature, and the ability to undergo repeated processing and utilization. Consequently, it holds promising potential for applications in personal thermal energy management.

A photoluminescent hydrogen-bonded biomass aerogel for sustainable radiative cooling

Passive radiant cooling is a potentially sustainable thermal management strategy amid escalating global climate change. However, petrochemical-derived cooling materials often face efficiency challenges owing to the absorption of sunlight. We present an intrinsic photoluminescent biomass aerogel, which has a visible light reflectance exceeding 100%, that yields a large cooling effect. We discovered that DNA and gelatin aggregation into an ordered layered aerogel achieves a solar-weighted reflectance of 104.0% in visible light regions through fluorescence and phosphorescence. The cooling effect can reduce ambient temperatures by 16.0°C under high solar irradiance. In addition, the aerogel, efficiently produced at scale through water-welding, displays high reparability, recyclability, and biodegradability, completing an environmentally conscious life cycle. This biomass photoluminescence material is another tool for designing next-generation sustainable cooling materials.

Photoelectric dual-mode triggered phase change materials for all-weather personal thermal management and shape memory

To cope with the demand of more complex and variable applications, it is urgent to develop dual-mode triggered, breathable, and shape-memory wearable heaters for all-weather personal thermal management of composite phase change materials (PCMs). Herein, after high-temperature carbonization of ZnCo-MOF (metal-organic framework) nanosheet array grown in situ on flexible and breathable carbon cloth (CC) and subsequent encapsulation of polyethylene glycol (PEG), the as-prepared PEG/CC@Co/CNT (carbon nanotube) composite PCMs exhibited good breathability, mechanical strength (tensile strength of 9.15 MPa), thermal energy storage density (114.19 J/g), and shape memory due to the synergy of flexible CC skeleton and rigid PEG. More importantly, composite PCMs possessed excellent solar-thermal (93.7 %, 100 mW/cm2) and electro-thermals (94.5 %, 2.0 V) conversion and storage capacity, benefiting from the conjugation effect of high graphitized carbon/carbon heterostructure with fast electron/photon/phonon transmission and the localized surface plasmon resonance effect of Co nanoparticles. Therefore, the integration of solar heating and Joule heating into breathable composite PCMs can be accurately used for next-generation all-weather, all-season, dual-mode triggered personal thermal management, including indoor/outdoor, daytime/night, rainy/cloudy and other complex and changeable scenarios.

High-Efficiency Thermal-Shock Resistance Enabled by Radiative Cooling and Latent Heat Storage

Radiative cooling technology is well known for its subambient temperature cooling performance under sunlight radiation. However, the intrinsic maximum cooling power of radiative cooling limits the performance when the objects meet the thermal shock. Here, a dual-function strategy composed of radiative cooling and latent heat storage simultaneously enabling the efficient subambient cooling and high-efficiency thermal-shock resistance performance is proposed. The electrospinning and absorption-pressing methods are used to assemble the dual-function cooler. The high sunlight reflectivity and high mid-infrared emissivity of radiative film allow excellent subambient temperature of 5.1 °C. When subjected the thermal shock, the dual-function cooler demonstrates a pinning effect of huge temperature drop of 39 °C and stable low-temperature level by isothermal heat absorption compared with the traditional radiative cooler. The molten phase change materials provide the heat-time transfer effect by converting thermal-shock heat to the delayed preservation. This strategy paves a powerful way to protect the objects from thermal accumulation and high-temperature damage, expanding the applications of radiative cooling and latent heat storage technologies.

Polyethylene fibers containing directional microchannels for passive radiative cooling

Passive radiative cooling (PRC) that realizes thermal management without consuming any energy has attracted increasing attention. Unfortunately, polymer fibers with radiative cooling function fabricated via a facile, continuous, large-scale and eco-friendly method have been scarcely reported. Herein, polyethylene fibers containing directional microchannels (PFCDM) are facilely fabricated via melt extrusion and water leaching. Interestingly, fabric based on such hydrophobic PFCDM shows high sunlight reflectivity (93.6%), and mid-infrared emissivity (93.9%), endowing it with remarkable PRC performance. Compared with other reported examples, the as-prepared PFDCM fabric has the highest cooling power (i.e., 104.285 W m-2) and temperature drop (i.e., 27.71 °C). Furthermore, decent self-cleaning performance can keep the PFCDM fabric away from contamination and enable it to retain an excellent radiative cooling effect. The method proposed to fabricate PFCDM in this paper will widen the potential application of thermoplastic polyolefins in the field of radiative cooling.

Multispectral camouflage and radiative cooling using dynamically tunable metasurface

With the increasing demand for privacy, multispectral camouflage devices that utilize metasurface designs in combination with mature detection technologies have become effective. However, these early designs face challenges in realizing multispectral camouflage with a single metasurface and restricted modes. Therefore, this paper proposes a dynamically tunable metasurface. The metasurface consists of gold (Au), antimony selenide (Sb2Se3), and aluminum (Al), which enables radiative cooling, light detection and ranging (LiDAR) and infrared camouflage. In the amorphous phase of Sb2Se3, the thermal radiation reduction rate in the mid wave infrared range (MWIR) is up to 98.2%. The echo signal reduction rate for the 1064 nm LiDAR can reach 96.3%. In the crystalline phase of Sb2Se3, the highest cooling power is 65.5 Wm-2. Hence the metasurface can reduce the surface temperature and achieve efficient infrared camouflage. This metasurface design provides a new strategy for making devices compatible with multispectral camouflage and radiative cooling.

Ultrahigh Passive Cooling Power in Hydrogel with Rationally Designed Optofluidic Properties

The cooling power of a radiative cooler is more than halved in the tropics, e.g., Singapore, because of its harsh weather conditions including high humidity (84% on average), strong downward atmospheric radiation (∼40% higher than elsewhere), abundant rainfall, and intense solar radiation (up to 1200 W/m2 with ∼58% higher UV irradiation). So far, there has been no report of daytime radiative cooling that well achieves effective subambient cooling. Herein, through integrated passive cooling strategies in a hydrogel with desirable optofluidic properties, we demonstrate stable subambient (4-8 °C) cooling even under the strongest solar radiation in Singapore. The integrated passive cooler achieves an ultrahigh cooling power of ∼350 W/m2, 6-10 times higher than a radiative cooler in a tropical climate. An in situ study of radiative cooling with various hydration levels and ambient humidity is conducted to understand the interaction between radiation and evaporative cooling. This work provides insights for the design of an integrated cooler for various climates.

Thin lamellar films with enhanced mechanical properties for durable radiative cooling

Passive daytime radiative cooling is a promising path to tackle energy, environment and security issues originated from global warming. However, the contradiction between desired high solar reflectivity and necessary applicable performance is a major limitation at this stage. Herein, we demonstrate a "Solvent exchange-Reprotonation" processing strategy to fabricate a lamellar structure integrating aramid nanofibers with core-shell TiO2-coated Mica microplatelets for enhanced strength and durability without compromising optical performance. Such approach enables a slow but complete two-step protonation transition and the formation of three-dimensional dendritic networks with strong fibrillar joints, where overloaded scatterers are stably grasped and anchored in alignment, thereby resulting in a high strength of ~112 MPa as well as excellent environmental durability including ultraviolet aging, high temperature, scratches, etc. Notably, the strong backward scattering excited by multiple core-shell and shell-air interfaces guarantees a balanced reflectivity (~92%) and thickness (~25 μm), which is further revealed by outdoor tests where attainable subambient temperature drops are ~3.35 °C for daytime and ~6.11 °C for nighttime. Consequently, both the cooling capacity and comprehensive outdoor-services performance, greatly push radiative cooling towards real-world applications.

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.