Wearable Polyethylene/Polyamide Composite Fabric for Passive Human Body Cooling

A systematic review of Personal Comfort Systems from a post-phenomenological view

Personal Comfort Systems (PCS) are equipments that heat and/or cool occupants without affecting surrounding environments, ranging from commonly used devices to innovative technologies, and that tend to be controlled by people. These systems aim to address energy consumption and occupant satisfaction issues related to centralised air-conditioning. Although there are systematic studies on these systems, there is a lack of documentation regarding mediation characteristics between people and the built environment. This article presents a systematic review of PCS using a search of academic literature and patents, classifying PCS based on thermal categories and device typologies while introducing post-phenomenological mediation categories. The results show that most PCS fall into the thermal categories of 'Heating' and 'Cooling and ventilation'. The review also presents a view of the PCS territory based on mediation attributes and technological complexity. Finally, the PCS' characteristics are discussed based on the post-phenomenological concepts of Embodiment, Hermeneutic, and Background providing insights for future research opportunities and PCS development.

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.

Environmentally responsive hydrogel composites for dynamic body thermoregulation

Hydrogel composites exhibiting dynamic thermo-hydro responsive modulation of infrared radiation (IR) in the 5-15 μm range are designed for personalized body thermoregulation. Fabrication of the proposed system relies on the periodic arrangement of submicron-sized spherical fine silica (SiO₂) particles within poly(N-isopropylacrylamide) (PNIPAM)-based hydrogels. The dependence of the SiO₂ particles content on the IR reflection, followed by its modulation in response to any immediate environmental changes are thereby investigated. The addition of 20 wt% of SiO₂ allowed the hydrogel composites to reflect 20% of the IR emitted by the human body at constant temperature (i.e. T = 20 °C) and relative humidity (i.e. RH = 0%). According to Bragg's law, we found that the smaller the distance between the SiO₂ particles, the higher the IR reflection. The IR reflection further increased to a maximum of 42% when the resulting hydrogel composites are subjected to changes in relative humidity (i.e. RH = 60%) and temperature (i.e. T = 35 °C). Thermography is used to map the IR radiation emitted from the hydrogel composites when placed on the skin of the human body, demonstrating that the composite is actually reflecting IR. The latter results are supported by theoretical models that define the IR reflection profile of the resulting hydrogel composites with respect to the silica content, relative humidity and temperature.

Recent Advances in Nanomaterials Used for Wearable Electronics

In recent decades, thriving Internet of Things (IoT) technology has had a profound impact on people's lifestyles through extensive information interaction between humans and intelligent devices. One promising application of IoT is the continuous, real-time monitoring and analysis of body or environmental information by devices worn on or implanted inside the body. This research area, commonly referred to as wearable electronics or wearables, represents a new and rapidly expanding interdisciplinary field. Wearable electronics are devices with specific electronic functions that must be flexible and stretchable. Various novel materials have been proposed in recent years to meet the technical challenges posed by this field, which exhibit significant potential for use in different wearable applications. This article reviews recent progress in the development of emerging nanomaterial-based wearable electronics, with a specific focus on their flexible substrates, conductors, and transducers. Additionally, we discuss the current state-of-the-art applications of nanomaterial-based wearable electronics and provide an outlook on future research directions in this field.

Personal Cooling Garments: A Review

Thermal comfort is of critical importance to people during hot weather or harsh working conditions to reduce heat stress. Therefore, personal cooling garments (PCGs) is a promising technology that provides a sustainable solution to provide direct thermal regulation on the human body, while at the same time, effectively reduces energy consumption on whole-building cooling. This paper summarizes the current status of PCGs, and depending on the requirement of electric power supply, we divide the PCGs into two categories with systematic instruction on the cooling materials, working principles, and state-of-the-art research progress. Additionally, the application fields of different cooling strategies are presented. Current problems hindering the improvement of PCGs, and further development recommendations are highlighted, in the hope of fostering and widening the prospect of PCGs.

The Role of Sports Clothing in Thermoregulation, Comfort, and Performance During Exercise in the Heat: A Narrative Review

The aims of this review are to (1) summarise the current research of sports clothing as it relates to thermoregulation, comfort, and performance during exercise in the heat, (2) identify methodological limitations and gaps in the knowledge base of sports clothing, and (3) provide recommendations for exercise testing protocols to accurately assess the impact of sports clothing in athletic populations during exercise in the heat. Sports clothing consists of lightweight and breathable fabrics, surface treatments, and various designs which aim to enhance sweat evaporation and comfort during exercise in the heat. Sports clothing comprised of natural, synthetic, and chemically treated fabrics has been investigated during exercise of varying durations (15–120 min), intensities (20–70% VO₂ max) and types (fixed intensity, incremental, self-paced), and in an array of climatic conditions (18–40 °C, 20–60% relative humidity). To date, few studies have identified significant differences in thermo-physiological, perceptual, and performance measures between natural and synthetic fabrics or compared the effect of chemical treatments to their non-treated equivalent on such measures during exercise. Collectively, previous wearer trials have failed to replicate the upper limit of training and competition demands when assessing sports clothing in endurance-trained individuals who regularly train and compete in hot and humid climates. Clothing comfort has also been evaluated using simple scales which fail to capture intricate detail pertaining to psychological and sensorial parameters. The incorporation of protocols using hot and humid climates (≥ 30 °C, ≥ 70% relative humidity) and longer exercise durations (> 45 min) is warranted. Future research should also consider exploring the effect of sports clothing on thermal, physiological, perceptual, and performance measures between males and females, and assessing clothing comfort using a multi-dimensional approach.

Radiative Cooling Nanofabric for Personal Thermal Management

A wearable textile that is engineered to reflect incoming sunlight and allow the transmission of mid-infrared radiation simultaneously would have a great impact on the human body's thermal regulation in an outdoor environment. However, developing such a textile is a tough challenge. Using nanoparticle-doped polymer (zinc oxide and polyethylene) materials and electrospinning technology, we have developed a nanofabric with the desired optical properties and good applicability. The nanofabric offers a cool fibrous structure with outstanding solar reflectivity (91%) and mid-infrared transmissivity (81%). In an outdoor field test under exposure of direct sunlight, the nanofabric was demonstrated to reduce the simulated skin temperature by 9 °C when compared to skin covered by a cotton textile. A heat-transfer model is also established to numerically assess the cooling performance of the nanofabric as a function of various climate factors, including solar intensity, ambient air temperature, atmospheric emission, wind speed, and parasitic heat loss rate. The results indicate that the nanofabric can completely release the human body from unwanted heat stress in most conditions, providing an additional cooling effect as well as demonstrating worldwide feasibility. Even in some extreme conditions, the nanofabric can also reduce the human body's cooling demand compared with traditional cotton textile, proving this material as a feasible solution for better thermoregulation of the human body. The facile fabrication of such textiles paves the way for the mass adoption of energy-free personal cooling technology in daily life, which meets the growing demand for healthcare, climate change, and sustainability.

Recent Progress in Daytime Radiative Cooling: Advanced Material Designs and Applications

Passive daytime radiative cooling (PDRC) is emerging as a promising cooling technology. Owing to the high, broadband solar reflectivity and high mid-infrared emissivity, daytime radiative cooling materials can achieve passive net cooling power under direct sunlight. The zero-energy-consumption characteristic enables PDRC to reduce negative environmental issues compared with conventional cooling systems. In this review, the development of advanced daytime radiative cooling designs is summarized, recent progress is highlighted, and potential correlated applications, such as building cooling, photovoltaic cooling, and electricity generation, are introduced. The remaining challenges and opportunities of PDRCs are also indicated. It is expected that this review provides an overall picture of recent PDRC progress and inspires future research regarding the fundamental understanding and practical applications of PDRC.

Superhydrophobic Silica Aerogels and Their Layer-by-Layer Structure for Thermal Management in Harsh Cold and Hot Environments

Personal thermal management (PTM) materials have recently received considerable attention to improve human body thermal comfort with potentially reduced energy consumption. Strategies include passive radiative cooling and warming. However, challenges remain for passive thermal regulation of one material or structure in both harsh hot and cold environments. In this work, silica aerogels derived from sodium silicate were prepared through a solvent-boiling strategy, where hydrophobization, solvent exchange, sodium purification, and ambient pressure drying (HSSA) proceeded successively and spontaneously in a one-pot process. This strategy leads to the synthesis of superhydrophobic silica aerogels with extremely low energy consumption without out the use of an ion-exchange resin or low surface tension solvents. Silica aerogels possess a high specific surface area (635 m²/g), high contact angle (153°), and low thermal conductivity (0.049 W/m K). A layer-by-layer (LBL) structure including the silica aerogel layer and an extra phase change material layer was designed. The structure demonstrates dual-functional thermal regulation performance in both harsh cold (-30 °C) and hot (70 °C) environments, where the time to reach equilibrium is postponed, and the inner temperature of the LBL structure can be kept above 20 °C in harsh cold environments (-30 °C) and below 31 °C in harsh hot environments (70 °C). A proof-of-concept experimental setup to simulate the illumination of sunlight also proved that the inside temperature of a model car protected by the LBL structure was below 28 °C, while the outside temperature was 70 °C. In addition, these results are well supported by theoretical COMSOL simulation results. The findings of this work not only provide an eco-friendly approach to synthesize silica aerogels but also demonstrate that the LBL structure is a robust dual-functional PTM system for thermal regulation in both harsh hot and cold environments.

Micro/nanofibrous nonwovens with high filtration performance and radiative heat dissipation property for personal protective face mask

The COVID-19 pandemic and airborne particulate matter (PM) pollution have posed a great threat to human health. Personal protective face masks have become an indispensable protective equipment in our daily lives. However, wearing conventional face masks for a long time cause swelter and discomfort on the face. Introducing thermal comfort into personal protective face masks becomes desirable. Herein, face masks that show excellent filtration performance and radiative heat dissipation effect are successfully designed and prepared by electrospining Nylon-6 (PA) nanofibers onto polyethylene (PE) meltblown nonwovens. The resultant PE/PA nonwovens have high PM filtration efficiency (>99%) with a low pressure drop (<100 Pa). Moreover, taking the advantage of the property of PE, the designed face mask posses high mid-infrared (mid-IR) transmittance and brings about high radiative cooling power, resulting in effective heat dissipation performance. This face mask design may provides new insights into the development of thermal comfort materials for personal protection.

Advanced materials for personal thermal and moisture management of health care workers wearing PPE

In recent years, the development of personal protective equipment (PPE) for health care workers (HCWs) attracted enormous attention, especially during the pandemic of COVID-19. The semi-permeable protective clothing and the prolonged working hours make the thermal comfort a critical issue for HCWs. Although there are many commercially available personal cooling products for PPE systems, they are either heavy in weight or have limited durability. Besides, most of the existing solutions cannot relieve the perspiration efficiently within the insolation gowns. To avoid heat strain and ensure a longtime thermal comfort, new strategies that provide efficient personal thermal and moisture management without compromising health protection are required. This paper reviews the emerging materials for protective gown layers and advanced technologies for personal thermal and moisture management of PPE systems. These materials and strategies are examined in detail with respect to their fundamental working principles, thermal and mechanical properties, fabrication methods as well as advantages and limitations in their prospective applications, aiming at stimulating creative thinking and multidisciplinary collaboration to improve the thermal comfort of PPEs.

Scalable and Flexible Electrospun Film for Daytime Subambient Radiative Cooling

Daytime radiative cooling materials reflect solar light and dissipate heat directly to outer space without any energy consumption, and thus, have attracted much attention due to the potential applications in many fields. Recently, elaborately designed photonic crystal and metamaterials have been reported for daytime subambient radiative cooling. However, such materials and structures have the drawbacks of complex shapes, inflexibility, high cost, and limitation in scaling up. It is also extremely difficult to apply such materials to buildings, vehicles, and other objects having complex surfaces. Here, a scalable and flexible hybrid film for daytime subambient radiative cooling was fabricated by a facile electrospinning method. The hybrid film consists of poly(vinylidene fluoride)/alumina (PVDF/Al2O3) fibers with diameters of 0.5-2.5 μm. Owing to the efficient scattering by fibers and Al2O3 nanoparticles, the hybrid film exhibits an extremely high average solar reflectance of 0.97. A high average atmospheric window emittance of 0.95 is simultaneously achieved due to the molecular vibrations of PVDF and the phonon polariton resonance of Al2O3 nanoparticles. The composite film delivers an average net radiative cooling power of 82.7 W/m2, and a temperature drop of up to 4.0 °C under direct sunlight. The hybrid film exhibits remarkable radiative cooling performance under different weather conditions including sunny, cloudy, overcast, and rainy. It can be used not only for cooling buildings and vehicles but also for delaying the melting of glaciers. This work demonstrates a promising method for scale-up production of the radiative cooling film with high performance.

Multilayered graphene/boron nitride/thermoplastic polyurethane composite films with high thermal conductivity, stretchability, and washability for adjustable-cooling smart clothes

Polymers having high filler loading levels are not able to meet the increasing requirements of thermal interface materials by themselves; therefore, fillers and structures with unique advantages have been developed. In this study, mechanical mixing was used to disperse graphene nanoplatelets (GNPs) and boron nitride (BN) fillers inside thermoplastic polyurethane (TPU)-based films, which were then compounded into a multilayered structure. The multilayered BN-GNP/TPU composite film created during this study exhibited a high thermal conductivity of 6.86 W m^-1 K^-1 at a low filler loading of 20 wt% BN with 20 wt% GNP, which was significantly higher (2844%) than that of the neat TPU film. The composite film also had good durability to flexural fatigue and laundering. This was exhibited by maintaining thermal conductivity values of 6.25 W m^-1 K^-1 after 5000 cycles of the flexural fatigue test, and 6.85 W m^-1 K^-1 after 10 cycles of laundering, respectively. Furthermore, enhanced thermal stability, cooling, and hydrophobic properties of the multilayered BN-GNP/TPU composite films were also observed with the resulting composite film. Overall, such a system provides a facile approach that is applicable for the fabrication of multifunctional materials as thermal interface materials within smart cooling garments.

Multifunctional Membrane for Thermal Management Applications

Space cooling and heating consume a large proportion of global energy, so passive thermal management materials (i.e., without energy input), especially dual-mode materials including cooling and heating bifunctions, are becoming more and more attractive in many areas. Herein, a function-switchable Janus membrane between cooling and heating consisting of a multilayer structure of polyvinylidene fluoride nanofiber/zinc oxide nanosheet/carbon nanotube/Ag nanowire/polydimethylsiloxane was fabricated for comprehensive thermal management applications. In the cooling mode, the high thermal radiation emissivity (89.2%) and sunlight reflectivity (90.6%) of the Janus membrane resulted in huge temperature drops of 8.2-12.6, 9.0-14.0, and 10.9 °C for a substrate, a closed space, and a semiclosed space, respectively. When switching to the heating mode, temperature rises of 3.8-4.6, 4.0-4.8, and 12.5 °C for the substrate, closed space, and semiclosed space, respectively, were achieved owing to the high thermal radiation reflectivity (89.5%) and sunlight absorptivity (74.1%) of the membrane. Besides, the Janus membrane has outstanding comprehensive properties of the membrane, including infrared camouflaging/disguising, electromagnetic shielding (53.1 dB), solvent tolerance, waterproof properties, and high flexibility, which endow the membrane with promising application prospects.

Knit Architecture for Water-Actuating Woolen Knitwear and Its Personalized Thermal Management

Personalized thermal management using water-actuated woolen knitwear has great potential for smart textile production. However, woolen knitwear exists in a wide range of forms with different derivatives. Manufacturing of smart woolen structures with excellent cooling properties is linked to certain parameters such as changes in loop formation, loop shape, and yarn arrangement upon stimulation of body fluids. To address this issue, textile knit structures with different physical and mechanical properties have been prepared using water-responsive descaled wool fibers and their smart heat and moisture regulation behavior have been investigated and compared to detect the fabric architectural effect on water actuation and cooling performance of woolen garments. The evidence suggests that the technical structure of the fabrics plays a crucial role in pore actuation and fabric cooling performance. The water actuation and thermal management abilities of single jersey were greatly enhanced because of unbalanced structures with lower mechanical stress among the loops and yarns. The experimental data is also in line with the theoretical analysis. Hence, the unbalanced structures control fast heat and mass transfer from the human body, which may offer a promising year-round clothing material to the wearer. This material can have a similar response upon contact with body sweat and humid environments and hence can act as a skinlike fabric. Their possible applications can lie in different fields, such as thermoregulation, functional clothing, sportswear, and medical care.

Multifunctional Daytime Radiative Cooling Devices with Simultaneous Light-Emitting and Radiative Cooling Functional Layers

In this study, multifunctional light-emitting and passive radiative cooling (LEPC) materials and devices are designed by embedding chemically designed perovskite nanocrystals (NCs) into the radiative polymer layer. Lead halide perovskite NCs are chosen as the light-emitting material, owing to their high photon radiation rate and low phonon generation. To integrate the perovskite NCs into the radiative polymer layers, a surface passivation is achieved by coating the NCs with silica. The silica shell synergistically improves the chemical stability and cooling efficiency. Both outdoor experimental and simulation results demonstrate that the fabricated LEPC devices show better cooling performance than conventional cooling devices. The LEPC devices are easily patterned by utilizing pixelating, assembling, and simple cutting or drawing techniques with the LEPC materials. This study also demonstrates the potential applications of these materials as components of smart building systems, in smart window displays, or for anticounterfeiting cooling systems, thus proving the practicality of these multifunctional LEPC devices.

Thermoconductive, Moisture-Permeable, and Superhydrophobic Nanofibrous Membranes with Interpenetrated Boron Nitride Network for Personal Cooling Fabrics

Space cooling occupies a large portion of total building energy consumption, aggravating the energy crisis and restricting human sustainable development, thus an efficient and energy-saving personal cooling technology is in high demand. Recently, thermally conductive fillers, such as boron nitride (BN), are usually enriched to fibrous materials to construct thermal management textiles. However, these fabrication processes are complex and time-consuming, and the resultant materials fail to transmit moisture and resist liquid water. Herein, we develop a facile and scalable methodology to construct highly thermoconductive breathable superhydrophobic nanofibrous membranes to enhance the thermal management of textiles for personal cooling. The strategy causes boron nitride (BN) to be linked with each other along nanofibers, and thus the membranes contain well interpenetrated BN network and remain porous structure simultaneously, improving their thermal conductivity without sacrificing the moisture permeability. In addition, the membranes possess good resistance to water penetration and intriguing superhydrophobicity due to the synergistic effect of the hydrophobic polymeric matrix and improved roughness. As a consequence, the resultant membranes demonstrate outstanding hybrid active-passive cooling performance with ultrahigh in-plane thermal conductivity of 17.9 W m^-1 K^-1, cross-plane thermal conductivity of 0.29 W m^-1 K^-1, and high water vapor transmission (WVT) rate of 11.6 kg m^-2 day^-1, as well as excellent water repellency with water contact angle of 153° and high hydrostatic pressure of 32 kPa, indicating promising utility for the next generation of cooling fabrics.

Polymer photonic crystal membrane for thermo-regulating textile

We study numerically the absorption and scattering properties of a polymer photonic membrane to thermoregulate the human body microclimate which corresponds to the area between the skin and a textile. We first show that the structuration of the absorbing photonic membrane with air holes leads to a modulation of the optical spectrum in the Mid-Infrared range. Indeed, we show that the membrane is able to modulate the transmission amplitude by 28% in benefit or deficit of both the absorption and reflection. We then studied the thermal balance between the human body and the surrounding environment through the photonic membrane. We found that, compared to a regular membrane, the photonic crystal structure behaves as a heating component that offers the possibility to reduce the temperature of the room up to +1 °C. The membrane is flexible, low cost, 3D-printable, free of metallic particles, and can easily be added to usual textiles.

Spectrally Selective Inorganic-Based Multilayer Emitter for Daytime Radiative Cooling

Daytime radiative coolers are used to pump excess heat from a target object into a cold exterior space without energy consumption. Radiative coolers have become attractive cooling options. In this study, a daytime radiative cooler was designed to have a selective emissive property of electromagnetic waves in the atmospheric transparency window of 8-13 μm and preserve low solar absorption for enhancing radiative cooling performance. The proposed daytime radiative cooler has a simple multilayer structure of inorganic materials, namely, Al₂O₃, Si₃N₄, and SiO₂, and exhibits high emission in the 8-13 μm region. Through a particle swarm optimization method, which is based on an evolutionary algorithm, the stacking sequence and thickness of each layer were optimized to maximize emissions in the 8-13 μm region and minimize the cooling temperature. The average value of emissivity of the fabricated inorganic radiative cooler in the 8-13 μm range was 87%, and its average absorptivity in the solar spectral region (0.3-2.5 μm) was 5.2%. The fabricated inorganic radiative cooler was experimentally applied for daytime radiative cooling. The inorganic radiative cooler can reduce the temperature by up to 8.2 °C compared to the inner ambient temperature during the daytime under direct sunlight.

Green Production of Regenerated Cellulose/Boron Nitride Nanosheet Textiles for Static and Dynamic Personal Cooling

Personal cooling technology using functional clothing that could provide localized thermal regulation instead of cooling the entire space is regarded as a highly anticipated strategy to not only facilitate thermal comfort and human health but also be energy-saving and low-cost. The challenge is how to endow textiles with prominent cooling effect whenever the wearer is motionless or sportive. In this study, high content of edge-selective hydroxylated boron nitride nanosheets (BNNSs) up to 60 wt % was added into a biodegradable cellulose/alkaline/urea aqueous solution, and then regenerated cellulose (RCF)/BNNS multifilaments were successfully spun in a simple, low-cost, and environmentally friendly process, which was demonstrated to serve as both static and dynamic personal cooling textile. Typically, excellent axial thermal conductivity of RCF/BNNS filament rendered that body-generated heat could directly escape from skin to the outside surface of the textile by means of thermal conduction, achieving a much better static personal cooling result through continuous thermal radiation. Besides, synergistic effect between excellent heat dissipation capability and good hygroscopicity also resulted in much better dynamic cooling effect once the wearer is doing some sports, whose efficiency was even better than commercial hygroscopic textiles such as cotton and RCF.