Albedo Research Articles

Fabrication of black metal surface for high solar energy absorption by femtosecond laser hybrid technology

Metals are crucial for solar energy applications, but their highly reflective surfaces limit solar energy absorption. The difficulty in manufacturing an ideal light-absorbing structure limits the incorporation of anti-reflective characteristics in metals. In this study, a femtosecond laser method was introduced to form micro-nano structures in metals, enhancing absorption by the application of silver nanoparticles and resulting in solar absorption rates of 97.2%, 98.3%, and 98.9% for aluminum, titanium, and steel, respectively. The solar reflectance was reduced by 82.3%, 62.6%, and 79.2%, respectively, compared to bare metal. Photothermal conversion and deicing tests verified a more efficient photothermal conversion ability in the composite micro-nanostructure surface. Compared to bare metal, the structure has more than twice the solar absorption efficiency and improves the deicing efficiency by 132%. The resultant material exhibits high photothermal conversion and deicing efficiencies, enhancing its potential for solar energy applications, particularly in photothermal, photovoltaic, and thermal solar technologies.

Macro-Nanoporous Film with Cauliflower-Shaped Fibers for Highly Efficient Passive Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) is a simple and effective cooling approach that does not consume any extra energy just by highly reflecting shortwave sunlight and highly radiating infrared heat through the atmospheric windows. In recent years, the application of photonic coolers and metamaterials for PDRC has been studied. However, they usually have complex processes and high precision requirements, which seriously limit large-scale fabrication. In this paper, a high-performance polyvinylidene difluoride-hexafluoropropylene (PVDF-HFP) PDRC fiber film was prepared by a simple and efficient electrospinning method combined with phase separation, and the obtained PVDF-HFP fibers have a cauliflower-shaped macro-nanoporous structure. The cauliflower-shaped structure provides more scattering sites of the fibers, and the fiber film with the macro-nanoporous morphology has a high scattering ability in the solar region, resulting in a high solar reflectivity of 99.65%. The PVDF-HFP porous film possesses an emissivity of 90.44% in the atmospheric window, and it can reach a maximum cooling temperature of 10.2 °C during the daytime. In addition, the excellent mechanical strength provides a guarantee for its large-scale practical application. This study offers an effective improvement strategy for the spectral performance of polymer fiber films, which is meaningful for green cooling management and reduction of carbon emission.

Yarn-Based Degradable Janus PPDO Fabric for Multifunctional Applications.

The growing high standard of people's wear has put forward requirements for fabrics, and multifunctional fabrics have been developed precisely in response to the requirements of the times. However, the incineration of waste fabrics produces a large amount of pollutants, resulting in a massive waste of resources and environmental pollution. Herein, the degradable nanofiber yarns (NYs) with self-cleaning properties were fabricated by in situ growth of SiO2 nanoparticles on the surface of the electrospun poly(p-dioxanone) (PPDO) NYs using the Stöber method. Then, the PPDO NYs were blended with carbon fibers and the PPDO/SiO2 NYs with themselves to form the Janus PPDO fabrics, respectively. The Janus PPDO fabric offered asymmetric wettability and dual personal thermal management properties. The PPDO/C side of the Janus PPDO fabric provided 65.8 °C at 1.5 V or 58.5 °C under one sunlight intensity for radiative heating. The PPDO/SiO2 side exhibited high solar reflectivity (81.8%) and mid-infrared (MIR) emissivity (99.1%), which reduced the skin temperature by 4.6 °C, resulting in radiative cooling. Moreover, the Janus PPDO fabrics display an excellent electromagnetic interference (EMI) shielding performance (53.3 dB). Therefore, yarn-based degradable Janus fabric has a promising future in multifunctional wearable products.

Phase transformation enabled textile triboelectric nanogenerators for wearable energy harvesting and personal thermoregulation

The practical applications of environmentally friendly wearable textile triboelectric nanogenerators (t-TENGs) are constrained by inadequate heat dissipation, moisture permeability, and outdoor durability, particularly in humid and high-temperature environments. This study introduces a novel passive cooling strategy by integrating super-hydrophilic titanium dioxide solvent-free TiO2 nanofluids (TiO2 nfs) into cellulose acetate (CA) fibrous membranes (TiO2 nfs@CA) to achieve human comfort and efficient energy harvesting. Interestingly, the phase transformation of TiO2 nfs around boy temperature range (32-38 °C) effectively regulates the surface temperature of TiO2 nfs@CA fibrous membranes. In comparison with pristine CA fabric, TiO2 nfs@CA textile demonstrates exceptional solar reflectance (93.43%), high infrared emissivity (85%), excellent water vapor transport rate (12.6gm-2 h-1), and a significant cooling effect of 4-8 ℃ for both human skin and indoor environments. TiO2 nfs significantly enhances their ultraviolet resistance as well as mechanical properties and dielectric properties while improving triboelectric output performance with output voltage (66V), current (2.7 μA), and power density (82mWm-2). And TiO2 nfs@CA t-TENGs exhibit superior multifunctionality in terms of energy harvesting capabilities along with pressure sensing abilities for real-time movement monitoring including foot movements assessment as well as recovery evaluation for human body health maintenance purposes. Overall, TiO2 nfs@CA t-TENGs with the skin-friendly, dyeable, and recyclable properties provides a novel approach towards comfortable self-powered wearable devices that enable practical foot movement prediction alongside health monitoring.

Bioinspired smart dual-layer hydrogels system with synchronous solar and thermal radiation modulation for energy-saving all-season temperature regulation

All-season thermal management with zero energy consumption and emissions is more crucial to global decarbonization over traditional energy-intensive cooling/heating systems. However, the static single thermal management for cooling or heating fails to self-regulate the temperature in dynamic seasonal temperature condition. Herein, inspired by the dual-temperature regulation function of the fur color changes on the backs and abdomens of penguins, a smart thermal management composite hydrogel (PNA@H-PM Gel) system was subtly created though an “on-demand” dual-layer structure design strategy. The PNA@H-PM Gel system features synchronous solar and thermal radiation modulation as well as tunable phase transition temperatures to meet the variable seasonal thermal requirements and energy-saving demands via self-adaptive radiative cooling and solar heating regulation. Furthermore, this system demonstrates superb modulations of both the solar reflectance (ΔR = 0.74) and thermal emissivity (ΔE = 0.52) in response to ambient temperature changes, highlighting efficient temperature regulation with average radiative cooling and solar heating effects of 9.6 °C in summer and 6.1 °C in winter, respectively. Moreover, compared to standard building baselines, the PNA@H-PM Gel presents a more substantial energy-saving cooling/heating potentials for energy-efficient buildings across various regions and climates. This novel solution, inspired by penguins in the real world, will offer a fresh approach for producing intelligent, energy-saving thermal management materials, and serve for temperature regulation under dynamic climate conditions and even throughout all seasons.

Study of Roof and Ceiling Surface Temperatures in Coastal Area (Case Study: Pasar Bengkulu Village)

Abstract The majority of residential roofs in Pasar Bengkulu Village are constructed using corrugated iron and galvalum metal. These coastal areas often grapple with high levels of solar heat radiation. Both corrugated zinc and galvalum roofing materials are known for their high heat conductivity and excellent heat-reflecting capabilities. To combat this, solar reflectance paint is often used to reflect solar radiation heat, thereby reducing heat absorption. This research is a qualitative research with a focus on the description and analysis of measured data which aims to compare the surface temperature of the roof and ceiling before and after being coated with reflective solar paint. This research was conducted to determine the difference in roof and ceiling surface temperatures before and after the application of solar reflective paint. The results of the roof surface temperature measurements revealed that galvalum metal roofs exhibited the most significant reduction in roof surface temperature, with a decrease of 9.1°C.

Enhanced NIR reflectance black pigments based on CuCr2-xTixO4: Synthesis and properties

Ti-doped CuCr2O4 is an excellent black cool pigment for preventing surface overheating. Ti was introduced into the precursor in the form of tetrabutyl titanate(C16H36O4Ti) and calcined to obtain a CuCr2-xTixO4 black pigment. XRD, XPS, and EDS results showed that a portion of Ti entered the lattice of CuCr2O4, while the remaining Ti existed in the form of TiO2. The absence of TiO2 reduced the absorption of visible light. As the x value increased, the absorption of visible light by CuCr2-xTixO4 decreased and L* increased. CuCr1.1Ti0.9O4 has a maximum reflectance of 23.0% for NIR solar reflectance, and the mechanism could be determined by the following three reasons: 1) Small particles help to reflect NIR; 2) TiO2 improves the NIR reflectivity of the black pigment; and 3) According to the Drude free-electron theory, the substitution of Ti4+ for Cr3+ increases the concentration of free carriers in CuCr2O4, which increases the NIR reflectance. Application studies indicated that the CuCr1.1Ti0.9O4 coating on an alumina plate was approximately 3 °C lower than the CuCr2O4 coating after 40 minutes of irritation by an IR lamp. Therefore, CuCr1.1Ti0.9O4 pigments exhibited potential applications in insulating materials.

A novel colorless flexible polymer aerogel with stable amine linkage enabled superior formaldehyde removal and multifunctional application

Massive formaldehyde emissions have seriously endangered environment and human health, while predictably polymer aerogel is a promising candidate for formaldehyde (FA) removal, whereas low FA adsorption capacity, high volume shrinkage, and mechanical brittleness restrict its further development. Herein, based on “rigid-soft combination” polycondensation strategy, trifunctional 1,3,5-benzenetricarboxaldehyde (BTC) and polyetheramine Jeffamine T403 are selected as building blocks to construct a novel amine-linked polymer aerogel (rBTA) with hierarchical micro-nano porous structure via mild sol-gel method and freeze-drying process. Stable amine linkages in rBTA are formed by NaBH4 reduction of imine bonds, improving acid/alkali resistance and chemical stability greatly, and creating numerous active amine sites for reaction with FA. Formation of robust 3D covalent network facilitates to simultaneously achieve ultra-low-shrinkage (5.4%), high specific compressive modulus (5.32 kN·m·kg-1), remarkable mechanical durability/fatigue-resistance, flexibility, and machinability. Benefiting from synergistic physical-chemical adsorption effect, FA adsorption capacity and removal ratio of rBTA reach as high as 459.84 mg·g-1 and 97.87%, respectively. Colorless rBTA is further ground into powders for preparing polyoxymethylene (POM)/rBTA composite without affecting its color and formaldehyde emission amount at 60/230°C effectively decreases by 66.87%/79.55%. Furthermore, rBTA exhibits hydrophobicity, low thermal conductivity, and high solar reflectance, being successfully applied in emulsion separation, thermal insulation, and energy-efficient buildings fields.

Bioinspired polylactic acid/polyethylene glycol @ silicon dioxide microfibrous tarpaulin with dual-layer heterogeneous structure for enhanced daytime radiative cooling

Fibrous tarpaulin serves as the core barrier that protects goods, people, or areas from the adverse impacts of the external environment, such as rain, dust, and sunlight. However, conventional tarpaulins exhibit inadequate mechanical properties, a low solar reflectance, and are susceptible to pollution. To address these issues, a bioinspired polylactic acid/polyethylene glycol @silicon dioxide (PLA/PEG@SiO₂) microfibrous tarpaulin with a dual-layer heterogeneous structure was fabricated via in-situ drafting melt-blowing combined with thermal bonding, inspired by the layered structure of shells. This bioinspired dual-layer heterogeneous structure, with an adjustable heterodyne angle and SiO₂ size gradient, significantly improved the mechanical performance of the PLA/PEG@SiO2 microfibrous tarpaulin, and specifically manifested as an increase in the bursting strength of the sample to 25.5 N. Moreover, PLA/PEG@SiO2 microfibrous tarpaulin demonstrated excellent anti-pollution properties, effectively repelling liquids and dust. Additionally, its radiative cooling efficiency was notably enhanced, achieving a temperature reduction of ~9.8 °C compared with conventional fabrics, with reflectance of ~88.6 % and emissivity of ~98.3 %. These findings suggest that dual-layered PLA/PEG@SiO₂ microfibrous tarpaulin with multifunctional capabilities is a promising candidate for radiative cooling in outdoor shelters, wearable cooling devices, and energy-efficient building insulation materials.

A UV-resistant porous composite film for radiative cooling and enhanced hydrophobicity

Passive Daytime Radiative Cooling (PDRC) offers a promising strategy to reduce surface heat by reflecting solar radiation and emitting long-wave infrared radiation into space. However, the widespread application of PDRC is currently limited by challenges such as complex fabrication processes, high costs, and the materials’ susceptibility to outdoor aging. In this work, we fabricated a cost-effective, ultraviolet (UV)-resistant porous composite (UPC) film by phase separation technology. UPC films achieve high solar reflectance (0.92) and outstanding broadband longwave infrared thermal emissivity (0.975) by adjusting particle size and mass fractions of TiO2 particles embedded in Poly (methyl methacrylate) (PMMA). When applied to a drone, the films achieve a cooling effect of 12.6°C. Notably, the mid-infrared emissivity of UPC films remained stable after prolonged exposure to UV radiation (360 hours at an irradiance of 1 W/m2), with the reflectance decreasing by only 1.3 %. Software simulations were employed to evaluate the energy savings performance of UPC films in various urban environments, showing significant energy-saving benefits. Furthermore, after treatment with the modified solution, the surface contact angle of UPC films reaches 152.5°, providing excellent resistance to contamination. This work contributes to the advancement of low-cost, durable, and energy-efficient cooling solutions.

A sustainable and robust Janus film Inspired by the bird’s nest structure for efficient year-round outdoor thermal management

Janus structures combining radiative cooling and heating have attracted considerable interest for providing thermal comfort in dynamic environments. However, most of the strategies ignore the weak interfacial bonding due to the differences in material properties of the cooling and heating sides, which ultimately results in a lack of durability. Herein, inspired by the bird’s nest structure, we demonstrated a dual-mode Janus film with bonded interfaces through a simple vacuum-assisted filtration and PDMS modification. The unique structure of film ensures efficient thermal management including a sub-ambient temperature drop of ∼6.7 °C and a rise of ∼19.8 °C under direct sunlight irradiance. The cooling performance is activated by the synergistic enhancement with BaSO4 and BC porous networks, which exhibits high solar reflectivity (∼95.6 %) and MIR emissivity (∼95.2 %). The heating performance is derived from solar heating (∼71.6 °C at one sun irradiation) and Joule heating (∼88.6 °C at a low voltage of 2.5 V) as a complement, benefiting from the photothermal and electrothermal conversion of MXene. The cooling and heating can be easily obtained by flipping. In addition, the film maintains efficient cooling and heating even after being immersed in water and exposed to sunlight, thereby ensuring outdoor thermal management. Overall, this dual-mode Janus film shows great potential for regulating outdoor thermal comfort and alleviating the energy crisis.

A Camel-Fur-Inspired Micro-Extrusion Foaming Porous Elastic Fiber for All-Weather Dual-Mode Human Thermal Regulation.

Maintaining the stability of human body temperature is the basis of ensuring the normal life activities of witness, and the emergence of various functional clothing is committed to assisting the human body temperature in thermal comfort range in the changeable environment. However, achieve dual-mode thermal regulation for cooling and insulation on an integrated material without energy input and addition of functional particles has thus far been a huge challenge. Herein, a biomimetic camel-fur designed micro-extruded physically foamed porous elastic fiber (MEPF) using thermoplastic polyurethane (TPU) elastomer as raw material is reported, and its dual-layered fabric (MEPFT-d) for effective personal thermal comfortable management at extreme temperature differences. Benefit from its micro-nano-pores structure, MEPFT-d represents radiate cooling capacity by high solar reflectance and emissivity, behaves low thermal conductivity delaying heat scattering, and promotes evaporative cooling by unidirectional water transport. These excellent properties ensure that MEPFT-d reduces heat loss in cold weather (7.2 °C higher than cotton) and blocks outside heat in hot weather (10.2 °C lower than cotton), which is suitable for various complex outdoor scenes. The cost-effectiveness and superior wearing comfort of this work provide innovative pathways for sustainable energy, smart textiles, and personal thermal comfort applications.

An Investigation of Globe Temperature in Street Canyons: A Scaled Model Study Implementing Cool Materials

The measurement of globe temperature (GT) is essential for investigating pedestrian thermal comfort in street canyons. The globe thermometer is the most common instrument used to measure GT; however, its application in scale models has not been thoroughly investigated to date. Therefore, this study explicitly investigates globe thermometer measurements in scale models and analyzes the need for customization of the globe thermometer for more reliable measurements. Scaling down with respect to the size of the globe thermometer and the effect of solar orientation/envelope materials are investigated in this study. The initial experiments were carried out in an outdoor setting using a typical street canyon model (scale 1:100) with an east-west street orientation. The results of the experiment are presented to compare a low solar reflectance street canyon (albedo of 0.4) and a high solar reflectance canyon (albedo of 0.6) in terms of surface temperatures, heat flux, and globe temperature. It is observed that although the wall and road surface temperatures are lower for the high solar reflectance canyon compared to those for the low solar reflectance canyon, the GT (measured at pedestrian height) is higher in a high reflectance canyon during the daytime, which could be due to the combined effect of direct radiation and short-wave reflection. However, for the hours after sunset, a reverse effect is observed, i.e., the GT becomes lower (up to 0.8 °C) in the case of a high reflectance canyon compared to that for the low reflectance canyon. Furthermore, the study emphasizes the impact of solar reflectance of canyon surfaces on GT values, due to the view factors that the globe thermometer on those surfaces.

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.

Chameleon‐Inspired, Dipole Moment‐Increasing, Fire‐Retardant Strategies Toward Promoting the Practical Application of Radiative Cooling Materials

AbstractToward addressing the aesthetic demand, IR emissivity, and fire hazards of radiative cooling materials in the practical application, chameleon‐inspired is tactfully employed, dipole moment‐increasing, and fire‐retardant strategies to manufacture an advanced polyurea‐based composite coating through incorporating thermochromic microcapsules, boron nitride nanosheets, and montmorillonite nanosheets. The chameleon‐inspired thermochromic microcapsules and admirable IR emissivity (supported by the original IR emittance spectra) realized by the increasing dipole moment allow the composite coatings to spontaneously adjust the solar absorption and reflection during hot daytime, while enabling high‐efficiency radiative cooling throughout the day. The IR emissivity higher than most literature is attributed to the strong interfacial interactions within polyurea composite coatings which improve the dipole moment of C─O─C, Si─O, and B─N bonds by increasing the distance between the centers of positive and negative charges, thus producing more IR emissions. Furthermore, the thermally melted montmorillonite nanosheets can form a ceramic protective layer enhanced by boron nitride nanosheets, further suppressing combustion behavior to improve the fire safety performance of polyurea coatings. The integration of thermochromic functionality, high fire safety, and admirable IR emissivity not only contribute to promoting the practical application of radiative cooling materials, but also provide a precious reference route to design high IR emissivity.

Experimental studies on the cooling and heating performance of a highly emissive coating

In this study, the cooling effect below ambient air temperature, heat dissipation properties and heating energy efficacy of a superomniphobic self-cleaning (SSC) highly emissive (HE) coating were systematically investigated. Except at midday, the SSC-HE coating with an extremely high solar reflectance of 0.985 showed a better cooling effect than a 10-cm-thick polyurethane insulation layer. The coating substantially reduced the interior air temperature of a well-insulated system by as much as 6.9 °C. The SSC-HE coating enabled the roof surface and room temperatures of the brick bungalow to be 3.4 and 10.2 °C below the ambient air temperature, respectively. Compared with the sunshade and spray water, the SSC-HE coating exhibited better cooling effect. The SSC topcoat allowed the battery cabinet of an HE-coated distributed telecommunication base station to remain its original sub-ambient cooling effect for a long time. Regardless of the location of the HE-coated metal facility, the ultrahigh emissivity of the coating enabled it to exhibit excellent heat dissipation performance during both day and night, even under adiabatic conditions. Additionally, under identical room temperature settings, the HE-coated electric oil heater not only showed faster heating but also had heating energy efficiency of 5.9 % and 4.4 % relative to heaters coated with aluminium- and black paints, respectively. Under identical heating power consumption levels, compared to black paint-coated heater, the HE-coated heater endowed the surrounding environment with a higher equilibrium air temperature, improving the thermal comfort of the indoor environment.

High-performance, superhydrophobic, durable photonic structure coating for efficient passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is an innovative and energy-free cooling technology that automatically cools the surface of an object by reflecting sunlight and emitting heat into outer space without the need for external energy inputs. However, PDRC materials often face issues such as surface contamination and poor long-term outdoor durability. Herein, a photonic structure coating with high PDRC performance, superhydrophobic property, and high outdoor durability was designed and prepared using a phase separation strategy. The photonic structure coating achieves a solar reflectance ∼97.6 % and an average atmospheric window (AW) emissivity of ∼93 %. Under direct sunlight (800 W/m2), the coating exhibits good PDRC performance, with an average temperature drop of ∼13 °C and a maximum temperature drop of up to ∼20 °C. The rough and porous surface of the coating can adsorb air, reducing the solid-liquid adhesion and endowing the coating with super-hydrophobic properties. The incorporation of a small amount of fluoroalkyl silanes into the coating provides water resistance, resulting in a water contact angle (WCA) of ∼155.1° and sliding angle (SA) of ∼2.3°, meeting the need for self-cleaning. Furthermore, the coating exhibits superior durability, including resistance to acid and alkali, UV aging, abrasion, and scratching. All these merits render this photonic structure coating great potential for real-world applications.

Enhancing Power and Thermal Gradient of Solar Photovoltaic Panels with Torched Fly-Ash Tiles for Greener Buildings

Solar photovoltaic (PV) panels that use polycrystalline silicon cells are a promising technique for producing renewable energy, although research on the cells’ efficiency and thermal control is still ongoing. This experimental research aims to investigate a novel way to improve power output and thermal performance by combining solar PV panels with burned fly-ash tiles. Made from burning industrial waste, torched fly ash has special qualities that make it useful for architectural applications. These qualities include better thermal insulation, strengthened structural integrity, and high energy efficiency. Our test setup shows that when solar PV panels are combined with torched fly-ash tiles, power generation rises by 7% and surface temperature decreases by 3% when compared to standard panels. The enhanced PV efficiency is ascribed to the outstanding thermal insulation properties of fly ash tiles and their capacity to control panel temperature. To ensure longevity and safety in building applications, the tiles employed in this study had a water absorption rate of 5.37%, flexural strength of 2.95 N/mm2, and slip resistance at 38 km/h. Furthermore, we find improved structural resilience and lower cooling costs when up to 30% of the sand in floor tiles is replaced with torched fly ash, which makes this method especially appropriate for sustainable buildings. Key performance indicators that show how effective these tiles are in maximizing energy use in buildings include thermal emissivity (0.874), solar reflectance (0.8), and solar absorption (0.256). While supporting more ecofriendly building techniques, this study highlights the advantages of utilizing burned fly ash in solar PV systems: enhanced power generation and thermal comfort. The main results open a greater potential for fly ash use in different building materials. The use of torched fly ash in building materials enhances thermal insulation and structural integrity while lowering cooling costs, making it an ideal choice for eco-friendly construction and highlighting the potential for further research into environmentally responsible, energy-efficient solutions.

Radiative cooling materials prepared by SiO2 aerogel microspheres@PVDF-HFP nanofilm for building cooling and thermal insulation

Radiative cooling is promising in meeting the current global demand for green sustainable development. However, the effective cooling of the existing radiant cooler will be limited due to the serious solar energy absorption and poor thermal insulation performance on the cold side. To addresss these issues, we propose herein a novel composite material of silicon dioxide (SiO2) aerogel microspheres combined with polyvinylidene fluoride-cohexafluoropropylene (PVDF-HFP) nanofiber membrane, in which SiO2 aerogel microspheres are firstly synthesized by sol-gel method and then incorporated into PVDF-HFP nanofiber membrane to give radiative cooling performance. As we expected, the molecular vibration characteristics of PVDF-HFP nanofiber membrane and the phonon polarization resonance of Si-O-Si bond in the transparent window can enhance the infrared emissivity of the membrane surface. In addition, the high porosity and the mesoporous structure formed by the interconnection of nano-network skeletons of SiO2 aerogel microspheres determine its excellent thermal insulation performance. The as-prepared material displays that the average solar reflectance of the composite membrane is 96.07 % and the average infrared emissivity of the atmospheric window is 94.95 %. Notably, when the average solar radiation intensity is 885.56 W•m−2, the passive radiative cooling temperature during the day can reach 11.2 °C. Furthermore, this material has excellent self-cleaning and thermal insulation performance, making it a potential radiant cooling candidate in many fields.

Experimental study on the thermal performance of non-white near-infrared solar reflective coatings in a permafrost region

Solar reflective coating (SRC) offers a method to reduce surface temperature without the need for additional energy consumption, making it highly applicable in permafrost regions. However, many SRCs with high solar reflectance are white, which can cause glare and not meet the aesthetic pavement requirements of high-grade highways. Herein, we developed two non-white SRCs (black and gray) designed to achieve low reflectance in the visible spectrum while maintaining high reflectance in the near-infrared region. We then evaluated the thermal performance of a white SRC, two non-white SRCs and asphalt (as a control) by analyzing surface temperature, ground temperature, and the heat flux between the soil and pavement in a permafrost region of the Qinghai-Tibet Plateau. The results showed that three SRCs reduced the annual mean surface temperature and surface temperature fluctuation compared to the asphalt. The white SRC exhibited annual heat release, whereas the non-white SRCs (black and gray) reduced heat absorption by 34.53% and 69.44%, respectively, compared to the asphalt. By directly reducing the heat absorption of asphalt, the non-white SRCs can potentially slow permafrost degradation beneath asphalt pavements. This study provides a theoretical foundation and technical support for applying non-white near-infrared SRC on high-grade highways in permafrost regions.