A Janus Textile Capable of Radiative Subambient Cooling and Warming for Multi-Scenario Personal Thermal Management

Textiles with radiative cooling/warming capabilities provide a green and effective solution to personal thermal comfort in different climate scenarios. However, developing multiple-mode textiles for wearing in changing climates with large temperature variation remains a challenge. Here a Janus textile is reported, comprising a polyethersulfone (PES)-Al₂O₃ cooling layer optically coupled with a Ti₃C₂T_x warming layer, which can realize sub-ambient radiative cooling, solar warming, and active Joule heating. Owing to the intrinsically high refractive index of PES and the rational design of the fiber topology, the nanocomposite PES textile features a record high solar reflectance of 0.97. Accompanied by an infrared (IR) emittance of 0.91 in the atmospheric window, sub-ambient cooling of 0.5–2.5 °C is achieved near noontime in humid summer under ≈1000 W m⁻² solar irradiation in Hong Kong. The simulated skin covered with the textile is ≈10 °C cooler than that with white cotton. The Ti₃C₂T_x layer provides a high solar-thermal efficiency of ≈80% and a Joule heating flux of 66 W m⁻² at 2 V and 15 °C due to its excellent spectral selectivity and electrical conductivity. The switchable multiple working modes enable effective and adaptive personal thermal management in changing environments.     

Aramid fibers reinforced silica aerogel composites with low thermal conductivity and improved mechanical performance

Aramid fibers reinforced silica aerogel composites (AF/aerogels) for thermal insulation were prepared successfully under ambient pressure drying. The microstructure showed that the aramid fibers were inlaid in the aerogel matrix, acting as the supporting skeletons, to strengthen the aerogel matrix. FTIR revealed AF/aerogels was physical combination between aramid fibers and aerogel matrix without chemical bonds. The as prepared AF/aerogels possessed extremely low thermal conductivity of 0.0227 ± 0.0007 W m⁻¹ K⁻¹ with the fiber content ranging from 1.5% to 6.6%. Due to the softness, low density and remarkable mechanical strength of aramid fibers and the layered structure of the fiber distribution, the AF/aerogels presented nice elasticity and flexibility. TG–DSC indicated the thermal stability reaching approximately 290 °C, can meet the general usage conditions, which was mainly depended on the pure silica aerogels. From mentioned above, AF/aerogels present huge application prospects in heat preservation field, especially in piping insulation.     

Asymmetrical Emissivity and Wettability in Stitching Treble Weave Metafabric for Synchronous Personal Thermal-Moisture Management

Developing textiles with passive thermal management is an effective strategy to maintain the human body healthy as well as decrease energy consumption. Personal thermal management (PTM) textiles with engineered constituent element and fabric structure have been developed, however the comfortability and robustness of these textiles remains a challenge due to the complexity of passive thermal-moisture management. Here a metafabric with asymmetrical stitching treble weave based on woven structure design and yarn functionalization is developed, in which the thermal radiation regulation and moisture-wicking can be achieved simultaneously throughout the dual-mode metafabric due to its optically regulated property, multi-branched through-porous structure and surface wetting difference. With simply flipping, the metafabric enables high solar reflectivity (87.6%) and IR emissivity (94%) in the cooling mode, and a low IR emissivity of 41.3% in the heating mode. When overheating and sweating, the cooling capacity reaches to ≈9 °C owing to the synergistic effect of radiation and evaporation. Moreover, the tensile strengths of the metafabric are 46.18 MPa (warp direction) and 37.59 MPa (weft direction), respectively. This work provides a facile strategy to fabricate multi-functional integrated metafabrics with much flexibility and thus has great potential for thermal management applications and sustainable energy.     

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.     

Silica-based aerogels as aggregates for cement-based thermal renders

Subcritically dried silica-based aerogels were synthesized by design to be used as aggregates for lightweight cement-based thermal renders. The molecular and pore structure of the aerogels and of the corresponding renders were correlated with their thermal conductivities. A subcritical hybrid aerogel proved to have advantages over a supercritical commercial one, since the particle size distribution may be controlled, it is more hydrophobic, and imparts higher specific surface areas and total pore volumes to the renders. Good stabilization of the hybrid aerogels within the aqueous cement paste, without affecting the final renders’ structure, was accomplished by using an anionic surfactant. The efficient range of aerogel contents for thermal insulation purposes (above 60 vol% of total aggregate) was optimized using an inorganic subcritical aerogel. Thermal conductivities as low as ∼0.085 W.m⁻¹.K⁻¹ and densities of 410 kg.m⁻³ were achieved by total replacement of silica sand with a designed hybrid aerogel.     

Synthesis of sustainable silica xerogels/aerogels using inexpensive steel slag and bean pod ash: A comparison study

Low cost silica xerogels/aerogels were synthesized from steel slag and bean pod ash by sol–gel method. Comparison study showed differences between structural, morphological, textural, thermal and physical properties of the silica xerogels and aerogels. Formation of amorphous structure and silica network was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses, respectively. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses revealed that silica xerogels had smaller interlinked network in contrast to silica aerogels. Typical type IV isotherm was observed for all samples in N₂ adsorption-desorption isotherms. The highest surface area was determined as 371 m² g⁻¹ for silica aerogel synthesized from steel slag. Particle size of silica aerogels was lower than that of the silica xerogels. The more porous structure made silica aerogels desirable materials with lower bulk density and thermal conductivity when compared to silica xerogels. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) exhibited high thermal stability of the silica xerogels/aerogels. Although silica xerogels had highly hydrophilic structure, contact angle of silica aerogels synthesized from steel slag and bean pod ash was 60° and 74°, respectively. The comparison study will give a new point of view about differences between silica xerogels and aerogels synthesized from by-products or inorganic/organic waste instead of silicon alkoxides.     

Nanoengineering Natural Leather for Dynamic Thermal Management and Electromagnetic Interference Shielding

Unpredictable and extreme weather conditions, along with increasing electromagnetic pollution, have resulted in a significant threat to human health and productivity, causing irreversible damage to society's well-being and economy. However, existing personal temperature management and electromagnetic protection materials lack adaptability to dynamic environmental changes. To address this, a unique asymmetric bilayer leather/a-MWCNTs/CA fabric is developed by vacuum-infiltrating interconnected a-MWCNTs networks into natural leather's microfiber backbone and spraying porous acetic acid (CA) on the reverse side. Such fabric achieves simultaneous passive radiation cooling, heating, and anti-electromagnetic interference functions without external energy input. The fabric's cooling layer has high solar reflectance (92.0%) and high infrared emissivity (90.2%), providing an average subambient radiation cooling effect of 10 °C, while the heating layer has high solar absorption (98.0%), enabling excellent passive radiative heating and effective compensation for warming via Joule heating. Additionally, the fabric's 3D conductive a-MWCNTs network provides electromagnetic interference shielding effectiveness of 35.0 dB mainly through electromagnetic wave absorption. This multimode electromagnetic shielding fabric can switch between cooling and heating modes to adapt to dynamic cooling and heating scenarios, providing a new avenue for sustainable temperature management and electromagnetic protection applications.     

Strong, low density, hexylene- and phenylene-bridged polysilsesquioxane aerogel–polycyanoacrylate composites

Nanocomposite aerogels were prepared by chemical vapor deposition and polymerization of cyanoacrylate on the surface of bridged polysilsesquioxane aerogels. Phenylene- and hexylene-bridged aerogels were prepared by sol–gel polymerizations and supercritical carbon dioxide drying. Hydrophobic organic bridging groups in the polysilsesquioxane aerogels reduced the amount of adsorbed water available for initiating polymerizations and led to higher molecular weight polycyanoacrylate than was observed with silica aerogels. Densities increased as much as 65% due to the addition of the organic polymer, but the nanocomposite aerogels remained highly porous with surface areas between 440 and 750 m²/g. Polycyanoacrylate–phenylene-bridged aerogel composites were the strongest with flexural strengths up to 780 kPa or 16-fold stronger than the untreated phenylene-bridged aerogels and fivefold stronger than a silica aerogel of the same density. The strongest polycyanoacrylate–hexylene-bridged aerogel composites had flexural strength of 285 kPa or ninefold stronger than the untreated hexylene-bridged aerogels and twice as strong as a silica aerogel of comparable density. The greater strength of the new composites is, in part, due to the greater strength of the bridged aerogels. However, higher molecular weight polycyanoacrylate, due to less surface water on the hydrophobic bridged aerogels, also contributes to the greater nanocomposite strengths.     

Ratio-Tuning of Silica Aerogel Co-Hydrolyzed Precursors Enables Broadband,Angle-Independent,Deformation-Tolerant,Achieving 99.7% Reflectivity

The super-white body might be defined as its reflectivity exceeding 98% at any angle in the visible light spectrum, which can be used in a variety of emerging fields including optics, energy, environment, aerospace, etc. However, elaborate synthesis of a light-weight, highly reflective super-white aerogel body remains a great challenge. In this work, fine-tuning of silica aerogel co-hydrolyzed precursor ratios, 99.7% reflectivity with angle-independence in the visible light spectrum has been successfully achieved when the areal density is only 0.129 g cm⁻², which breaks through the theoretical bandwidth limit of photonic crystals as well as the measured reflectivity limit of conventional porous materials. Furthermore, the reflectivity of super-white silica aerogel remains unchanged after various harsh deformations including compression and bending 1000 times, solar (≈800 W m⁻²), ultraviolet (≈0.68 W m⁻²), and humidity (100%) aging for 100 days, liquid nitrogen (−196 °C) and high-temperature (300 °C) thermal shock 100 times. As proofs of performance, the resulting super-white silica aerogels have been used as the novel standard white plate  for better spectrum calibration, as the flexible projector curtains for optical display, as well as the transmitted light reflective layer in the photovoltaic cell for improving the relative power conversion efficiency of 5.6%.     

Carbon fiber reinforced carbon aerogel composites for thermal insulation prepared by soft reinforcement

To overcome the brittleness and the pyrolysis shrinkage of carbon aerogels, carbon fiber reinforced composites were prepared by copyrolysis of polyacrylonitrile fiber reinforced resorcinol-formaldehyde aerogel composites (PAN/RFs). The PAN/RFs were obtained by impregnating the PAN fiber felt with RF sol and then supercritical drying. Upon carbonization the PAN fiber shrinks with the RF aerogel, thus reducing the shrinkage differences between the fiber and the aerogel, and results in crack-free carbon fiber reinforced carbon aerogel composites, with a thermal conductivity of 0.073 W/m K at 25 °C in air. Our new method may greatly expand the usage of carbon aerogels in general applications.     

Investigation of the effect of rice husk derived Si/SiC on the morphology and thermal stability of carbon composite aerogels

Highly porous carbon aerogels were prepared by pyrolyzing the novolac–silica aerogels. The silica phase was extracted from rice husk ash (RHA). The polymer aerogel was synthesized via the novel method of sol–gel polymerization in solvent vapor-saturated atmosphere. This method removes the need for supercritical drying and reduces the shrinkage of aerogels during drying stage and also has much lower process time compared to the conventional sol–gel method. In the next step, polymer composite aerogels become carbon/silica and carbon/silica/silicon carbide composites in pyrolysis (800 °C) and carbothermal reduction (1500 °C) stages, respectively. The characterization of the prepared composite aerogels was performed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses, respectively. Thermal and mechanical properties of the samples were investigated by differential scanning calorimetry (DSC) and compressive strength analysis. The resultant composite aerogels show a nanostructure with high porosity (above 82%) and low density (below 0.3 g cm^− 3). Si mapping images showed the good distribution of silica phase throughout the carbon matrix. Also the rate of oxidation for carbon composites decreased by silica incorporation and oxidation temperature increased about 20% by adding RHA silica. Compressive strength of composite samples increased about 25% by increasing RHA silica phase content.     

耐高温氧化铝气凝胶隔热复合材料研究进展

氧化铝气凝胶是一种高孔隙率、低密度、高比表面积、耐高温和低热导的纳米多孔材料,在高温隔热领域(如航天飞行器热防护系统、工业窑炉保温材料等)具有广阔的应用前景.但是,纯氧化铝气凝胶因耐温性(1000℃以上)、力学性能和高温隔热性能相对较差难以直接应用,需要引入增强相和遮光组分制备成气凝胶复合材料以进行改善.本文对耐高温氧...     

夏热冬冷地区能源总线系统的区域能源规划方法

本文提出一种适于夏热冬冷地区、采用能源总线进行区域能源规划的普遍方法。利用分布式变频水泵的水力解耦特性,通过冷、热线将多个冷(热)源和多个用户(楼宇)连接成能源网。在冷(热)源处采用制冷或供热设备控制总线供水温度,在用户处采用制冷机组和热泵等为用户提供冷水、热水或生活热水。该能源总线组态方式具有热力解耦能力,源和用户都可根据本地负荷变化灵活调整设备运行。本文建立了一整套水力、热力数学模型,用于规划冬季供暖且夏季供冷的区域供能场合,以实际案例说明了能源总线的区域能源规划的具体方法。结果表明:结合地源热泵、水源热泵及蒸气型溴化锂等供能设备,该方法具有良好的低品位能源利用率,在夏季和冬季的系统综合性能系数COP分别为3.85和3.17。     

多功能热泵热水机的原理及其应用研究

多功能热泵热水机具有制冷、制热、制热水兼制冷、独立制热水的四种功能,可以在任何季节和不同冷、热量需求时,选择满足需求的最佳节能模式运行。本文介绍多功能热泵各种模式运行原理及其应用研究,对夏热冬冷地区的建筑节能改造有着积极意义。     

Structural Engineering of Hierarchical Aerogels Hybrid Networks for Efficient Thermal Comfort Management and Versatile Protection

In recent years, growing concerns regarding energy efficiency and heat mitigation, along with the critical goal of carbon neutrality, have drawn human attention to the zero-energy-consumption cooling technique. Passive daytime radiative cooling (PDRC) can be an invaluable tool for combating climate change by dispersing ambient heat directly into outer space instead of just transferring it across the surface. Although significant progress has been made in cooling mechanisms, materials design, and application exploration, PDRC faces challenges regarding functionality, durability, and commercialization. Herein, a silica nanofiber aerogels (SNAs) functionalized poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) membrane (SFP membrane), inspired by constructional engineering is constructed. As-prepared membranes with flexible network structure combined hierarchical structure design and practicability principal. As the host material for thermal comfort management (TCM) and versatile protection, the SFP membrane features a large surface area, porous structure, and a robust skeleton that can render excellent mechanical properties. Importantly, the SFP membrane can keep exceptional solar reflectivity (0.95) and strong mid-infrared emittance (0.98) drop the temperature to 12.5 °C below ambient and 96 W m⁻² cooling power under typical solar intensities over 910 W m⁻². This work provides a promising avenue for high performance aerogel membranes that can be created for use in a wide variety of applications.     

Ultralight and Superelastic Curly Micro/Nanofibrous Aerogels by Direct Electrospinning Enable High-Performance Warmth Retention

Extremely low temperature has posed huge burden on the public safety concerns and global economics, thereby calling for high-performance warmth retention materials to resist harsh environment. However, most present fibrous warmth retention materials are limited by their large fiber diameter and simple stacking structure, leading to heavy weight, weak mechanical property, and limited thermal insulation performance. Herein, an ultralight and mechanically robust polystyrene/polyurethane fibrous aerogel by direct electrospinning for warmth retention is reported. Manipulation of charge density and phase separation of charged jet allows for the direct assembly of fibrous aerogels consisting of interweaved curly wrinkled micro/nanofibers. The resultant curly wrinkled micro/nanofibrous aerogel possesses low density of 6.8 mg cm⁻³ and nearly full recovery from 1500-cycle deformations, exhibiting both ultralight feature and superelastic property. The aerogel also shows low thermal conductivity of 24.5 mW m⁻¹ K⁻¹, making synthetic warmth retention materials superior to down feather possible. This work may shed light on developing versatile 3D micro/nanofibrous materials for environmental, biological, and energy applications.     

Experimental investigation of solar driven desiccant air conditioning system based on silica gel coated heat exchanger

A silica gel coated heat exchanger based air conditioning system driven by the evacuated tube solar water heater has been experimentally investigated. The system has been operated for two different modes namely cooling with dehumidification mode and heating with humidification mode in summer and winter season respectively. The system performance is analyzed in terms of regeneration rate, dehumidification rate and thermal coefficient of performance (COP_th). Experimental results demonstrated that, for cooling and dehumidification mode, the process air is cooled by an average temperature of 8.5 °C. A better dehumidification rate can be achieved by using pre-cooling before dehumidification process. Post-cooling after dehumidification process is found to be advantageous for cooling capacity and COP_th. For heating with humidification mode, the process air is heated by an average temperature of 13.3 °C with an average increment in humidity ratio of 1.9 g/kg. It is found that the average COP_th of the system is 0.45 and 0.87 for cooling and heating mode respectively.     

聚氨酯基气凝胶隔热材料研究进展

聚氨酯基气凝胶隔热材料是一类新型隔热材料。聚氨酯分子结构的可设计性和气凝胶独特纳米多孔三维网络结构的有机结合能使聚氨酯基气凝胶材料具有更好的隔热性能。本文介绍了聚氨酯气凝胶、聚脲气凝胶和聚氨酯增强无机物气凝胶材料的研究现状,重点介绍其在隔热性能方面的研究进展。     

Agglomeration Dynamics of 1D Materials: Gas‐Phase Collision Rates of Nanotubes and Nanorods

The agglomeration and self‐assembly of gas‐phase 1D materials in anthropogenic and natural systems dictate their resulting nanoscale morphology, multiscale hierarchy, and ultimate macroscale properties. Brownian motion induces collisions, upon which 1D materials often restructure to form bundles and can lead to aerogels. Herein, the first results of collision rates for 1D nanomaterials undergoing thermal transport are presented. The Langevin dynamic simulations of nanotube rotation and translation demonstrate that the collision kernels for rigid nanotubes or nanorods are ≈10 times greater than spherical systems. Resulting reduced order equations allow straightforward calculation of the physical parameters to determine the collision kernel for straight and curved 1D materials from 10² to 10⁶ nm length. The collision kernels of curved 1D structures increase ≈1.3 times for long (>10² nm), and ≈5 times for short (≈10² nm) relative to rigid materials. Applications of collision frequencies allow the first kinetic analysis of aerogel self‐assembly from gas‐phase carbon nanotubes (CNTs). The timescales for CNT collision and bundle formation (0.3–42 s) agree with empirical residence times in CNT reactors (3–15 s). These results provide insights into the CNT length, number, and timescales required for aerogel formation, which bolsters our understanding of mass‐produced 1D aerogel materials.     

Fatigue Resistant Aerogel/Hydrogel Nanostructured Hybrid for Highly Sensitive and Ultrabroad Pressure Sensing

Achieving high sensitivity over a broad pressure range remains a great challenge in designing piezoresistive pressure sensors due to the irreconcilable requirements in structural deformability against extremely high pressures and piezoresistive sensitivity to very low pressures. This work proposes a hybrid aerogel/hydrogel sensor by integrating a nanotube structured polypyrrole aerogel with a polyacrylamide (PAAm) hydrogel. The aerogel is composed of durable twined polypyrrole nanotubes fabricated through a sacrificial templating approach. Its electromechanical performance can be regulated by controlling the thickness of the tube shell. A thicker shell enhances the charge mobility between tube walls and thus expedites current responses, making it highly sensitive in detecting low pressure. Moreover, a nucleotide-doped PAAm hydrogel with a reversible noncovalent interaction network is harnessed as the flexible substrate to assemble the aerogel/hydrogel hybrid sensor and overcome sensing saturation under extreme pressures. This highly stretchable and self-healable hybrid polymer sensor exhibits linear response with high sensitivity (S_min > 1.1 kPa^?1), ultrabroad sensing range (0.12–≈400 kPa), and stable sensing performance over 10 000 cycles at the pressure of 150 kPa, making it an ideal sensing device to monitor pressures from human physiological signals to significant stress exerted by vehicles.