Multifunctional Membrane for Thermal Management Applications

Multifunctional Janus-Coated Metafabric for Personal Thermal Comfort and Energy Efficient Buildings

Space cooling and heating consume huge energy resources globally, while existing cooling/heating equipment can only address indoor temperature control. In this work, we report a multifunctional layered Janus-coated fabric (JCF) with radiative cooling/solar heating/Joule heating, which can utilize space and the sun as a source of cooling and heating. By adjusting the reflectivity, emissivity, and absorptivity of the coating, the fabric performs a thermal management function in a complex and changeable environment without consuming energy. In cooling mode, the cooling layer achieves a high solar reflectivity of 96% and an infrared emissivity of 96%, resulting in a 3.1 °C reduction in ambient temperature without any convective shielding. In addition, it reduces temperatures by 1.6 °C on human arms and by 5.1 °C inside houses, respectively. In the heating mode, the heating layer demonstrates excellent light-to-heat conversion efficiency under direct sunlight, achieving a 13.3 °C radiation warming ability, 16 °C heating effect on the surface of the arm, and a 12.8 °C temperature increase in the house. Furthermore, when switched to active heating for temperature regulation, JCF exhibits fast electrical response, high-efficiency electrical heat conversion capability, and stable electrical heat circulation capability. Building energy simulations indicate that widespread deployment of JCF across China could lead to a reduction in cooling and heating energy consumption by more than 25 MJ/m2 in 80% of cities. This multifunctional Janus-coated fabric not only provides a viable engineering path for the practical application of radiative heat management technology but also demonstrates its potential applications in human thermal comfort, smart wearable and building energy efficiency.

Spectrally selective and thermally insulating hybrid nanofiber aerogel coolers for building energy conservation

With the advancement of worldwide carbon neutralization, passive radiative cooling (PRC) has attracted tremendous interest in energy conservation by dissipating heat into the ultracold outer space without any electricity consumption. Despite some progress has been made in tailoring spectral properties for PRC, it still remains a crucial challenge in fabricating efficient and low-cost coolers for building energy saving. Herein, hierarchical cellulose-based aerogel coolers consisting of beads-on-string structural electrospun nanofibers are manufactured for all-day and all-region energy saving by combining radiative cooling and thermal insulation in one design. The hierarchically porous architectures and well-designed chemical compositions endow the aerogels with strong solar reflectance (∼0.974), high mid-infrared emittance (∼0.985), and ultra-low thermal conductivity (0.0285 W (m K)-1), achieving a sub-ambient cooling of ∼8.24 °C during the daytime and ∼7.41 °C during the nighttime. The aerogels also exhibit exceptional compressive resiliency, anti-aging, and self-cleaning properties, promising for durable cooling under harsh conditions. The building energy simulations show that about 23.1 kWh m-2 of the total energy consumption per year can be saved if the aerogel coolers are widely deployed as building envelopes in China. This work provides new perspectives for the development of advanced aerogel coolers for future energy saving applications.

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.

Emerging Trends of Nanofibrous Piezoelectric and Triboelectric Applications: Mechanisms, Electroactive Materials, and Designed Architectures

Over the past few decades, significant progress in piezo-/triboelectric nanogenerators (PTEGs) has led to the development of cutting-edge wearable technologies. Nanofibers with good designability, controllable morphologies, large specific areas, and unique physicochemical properties provide a promising platform for PTEGs for various advanced applications. However, the further development of nanofiber-based PTEGs is limited by technical difficulties, ranging from materials design to device integration. Herein, the current developments in PTEGs based on electrospun nanofibers are systematically reviewed. This review begins with the mechanisms of PTEGs and the advantages of nanofibers and nanodevices, including high breathability, waterproofness, scalability, and thermal-moisture comfort. In terms of materials and structural design, novel electroactive nanofibers and structure assemblies based on 1D micro/nanostructures, 2D bionic structures, and 3D multilayered structures are discussed. Subsequently, nanofibrous PTEGs in applications such as energy harvesters, personalized medicine, personal protective equipment, and human-machine interactions are summarized. Nanofiber-based PTEGs still face many challenges such as energy efficiency, material durability, device stability, and device integration. Finally, the research gap between research and practical applications of PTEGs is discussed, and emerging trends are proposed, providing some ideas for the development of intelligent wearables.

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.

Reduced Graphene Oxide/Cellulose Sodium Aerogel-Supported Eutectic Phase Change Material Gel Demonstrating Superior Energy Conversion and Storage Capacity toward High-Performance Personal Thermal Management

By virtue of their capacity to absorb and release energy during the phase change process, phase change materials (PCMs) are ideal for personal thermal management (PTM). The combination of reduced graphene oxide/cellulose sodium aerogel (rGCA) and lauric acid/myristic acid binary eutectic phase change gel (LMG) creates a composite phase change material that possesses outstanding photothermal conversion capabilities, electro-thermal conversion capabilities, energy storage capabilities, and shape-stable performance. The results showed that rGCA had a maximum adsorption efficiency of 99.7% with a melting latent heat of 124.6 J g-1. The high absorption rate of rGCA to LMG is a result of the capillary force, pore characteristics, hydrogen bonding, and the π-π interaction. Notably, rGCA and LMG composite material (rGCG) exhibited an excellent photothermal conversion efficiency of 96.5% and electro-thermal conversion of 82.3%. Results indicate that binary eutectic phase change materials are more suitable for temperature regulation than single phase change materials, making them more suitable for PTM. It is anticipated that the innovative thermal comfort solution, which provides thermal shielding, thermal energy storage, self-supporting characteristics, and wearability, will offer new possibilities for the next generation of wearable PTMs.

Wicking assisted condenser platform with patterned wettability for space application

Vapor condensation is extensively used in applications that demand the exchange of a substantial amount of heat energy or the vapor-liquid phase conversion. In conventional condensers, the condensate removal from a subcooled surface is caused by gravity force. This restricts the use of such condensers in space applications or horizontal orientations. The current study demonstrates proof-of-concept of a novel plate-type condenser platform for passively removing condensate from a horizontally oriented surface to the surrounding wicking reservoir without gravity. The condensing surface is engineered with patterned wettabilities, which enables the continuous migration of condensate from the inner region of the condenser surface to the side edges via surface energy gradient. The surrounding wicking reservoir facilitates the continuous absorption of condensate from the side edges. The condensation dynamics on different substrates with patterned wettabilities are investigated, and their condensation heat transfer performance is compared. The continuous migration of condensate drops from a superhydrophobic to a superhydrophilic area can rejuvenate the nucleation sites in the superhydrophobic area, resulting in increased heat transport. The proposed condenser design with engineered wettability can be used for temperature and humidity management applications in space.

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.

Dual-asymmetrically selective interfaces-enhanced poly(lactic acid)-based nanofabric with sweat management and switchable radiative cooling and thermal insulation

All-weather personal thermal regulation has far been challenged by variable environments especially the regulatory failure caused by highly-dense solar radiation, low environmental radiation and the fluctuated epidermal moisture in different seasons. Herein, from the design of interface selectivity, dual-asymmetrically optical and wetting selective polylactic acid-based (PLA) Janus-type nanofabric is proposed to achieve on-demand radiative cooling and heating as well as sweat transportation. Hollow TiO₂ particles are introduced in PLA nanofabric causing high interface scattering (∼99%) and infrared emission (∼91.2%) as well as surface hydrophobicity (CA > 140°). The strictly optical and wetting selectivity help achieve ∼12.8℃ of net cooling effect under > 1500 W/m² of solar power and ∼5℃ of cooling advantage higher than cotton fabric and sweat resistance simultaneously. Contrarily, the semi-embedded Ag nanowires (AgNWs) with high conductivity (0.245 Ω/sq) endows the nanofabric with visible water permeability and excellent interface reflection for thermal radiation from body (>65%) thus causing ∼7℃ of thermal shielding. Through simple interface flipping, synergistical cooling-sweat reducing and warming-sweat resisting can be achieved to satisfy the thermal regulation in all weather. Compared with conventional fabrics, multi-functional Janus-type passive personal thermal management nanofabrics would be of great significance to achieve the personal health maintenance and energy sustainability.

Recent Advances in Electrospun Membranes for Radiative Cooling

Radiative cooling is an approach that maximizes the thermal emission through the atmospheric window in order to dissipate heat, while minimizing the absorption of incoming atmospheric radiation, to realize a net cooling effect without consuming energy. Electrospun membranes are made of ultra-thin fibers with high porosity and surface area, which makes them suitable for radiative cooling applications. Many studies have investigated the use of electrospun membranes for radiative cooling, but a comprehensive review that summarizes the research progress in this area is still lacking. In this review, we first summarize the basic principles of radiative cooling and its significance in achieving sustainable cooling. We then introduce the concept of radiative cooling of electrospun membranes and discuss the selection criteria for materials. Furthermore, we examine recent advancements in the structural design of electrospun membranes for improved cooling performance, including optimization of geometric parameters, incorporation of highly reflective nanoparticles, and designing multilayer structure. Additionally, we discuss dual-mode temperature regulation, which aims to adapt to a wider range of temperature conditions. Finally, we provide perspectives for the development of electrospun membranes for efficient radiative cooling. This review will provide a valuable resource for researchers working in the field of radiative cooling, as well as for engineers and designers interested in commercializing and developing new applications for these materials.

Slippery Passive Radiative Cooling Supramolecular Siloxane Coatings

Polymer coatings with comprehensive properties including passive radiative cooling, anti-fouling, and self-healing constitute a promising energy-saving strategy but have not been well documented yet. Herein, we reported a class of novel multifunctional supramolecular polysiloxane composite coatings showing the combination of these features. The coatings have a hybrid structure with a slippery liquid-infused porous surface and a gradient polymer-Al₂O₃ composite matrix constructed by reversible hydrogen bonding. The gradient matrix consists of a polymer-rich top and a particle-rich bottom favoring coating attachment on rigid substrates. Such a complex structure can be obtained by simply casting the suspending solutions of the polydimethylsiloxane (PDMS)-urea copolymer and Al₂O₃ on substrates followed by swelling silicone oil. Obtained coatings display good passive daytime radiative cooling (a temperature drop of ∼2 °C), self-healing ability, and anti-fouling properties. Since the comprehensive performances and the facile fabrication, the coatings should have application potential for various thermal management purposes.

New focus of the cloud point/Krafft point of nonionic/cationic surfactants as thermochromic materials for smart windows

A nonionic poly(oxyethylene) monoalkyl ether (C12(EO)6) and a cationic hexadecylpyridinium bromide (HPB) were used to achieve warm/cool transparency transition.