Personal Thermal Management by Radiative Cooling and Heating.

Maintaining thermal comfort within the human body is crucial for optimal health and overall well-being. By merely broadening the set-point of indoor temperatures, we could significantly slash energy usage in building heating, ventilation, and air-conditioning systems. In recent years, there has been a surge in advancements in personal thermal management (PTM), aiming to regulate heat and moisture transfer within our immediate surroundings, clothing, and skin. The advent of PTM is driven by the rapid development in nano/micro-materials and energy science and engineering. An emerging research area in PTM is personal radiative thermal management (PRTM), which demonstrates immense potential with its high radiative heat transfer efficiency and ease of regulation. However, it is less taken into account in traditional textiles, and there currently lies a gap in our knowledge and understanding of PRTM. In this review, we aim to present a thorough analysis of advanced textile materials and technologies for PRTM. Specifically, we will introduce and discuss the underlying radiation heat transfer mechanisms, fabrication methods of textiles, and various indoor/outdoor applications in light of their different regulation functionalities, including radiative cooling, radiative heating, and dual-mode thermoregulation. Furthermore, we will shine a light on the current hurdles, propose potential strategies, and delve into future technology trends for PRTM with an emphasis on functionalities and applications.

Soft Robotic Textiles for Adaptive Personal Thermal Management.

Thermal protective textiles are crucial for safeguarding individuals, particularly firefighters and steelworkers, against extreme heat, and for preventing burn injuries. However, traditional firefighting gear suffers from statically fixed thermal insulation properties, potentially resulting in overheating and discomfort in moderate conditions, and insufficient protection in extreme fire events. Herein, an innovative soft robotic textile is developed for dynamically adaptive thermal management, providing superior personal protection and thermal comfort across a spectrum of environmental temperatures. This unique textile features a thermoplastic polyurethane (TPU)-sealed actuation system, embedded with a low boiling point fluid for reversible phase transition, resembling an endoskeleton that triggers an expansion within the textile matrix for enhanced air gap and thermal insulation. The thermal resistance improves automatically from 0.23 to 0.48 Km2 W-1 by self-actuating under intense heat, exceeding conventional textiles by maintaining over 10 °C cooler temperatures. Additionally, the knitted substrate incorporated into the soft actuators can substantially mitigate convective heat transfer, as evidenced by the thermal resistance tests and the temperature mapping derived from numerical simulations. Moreover, it boasts significantly increased moisture permeability. The thermoadaptation and breathability of this durable all-fabric system signify considerable progress in the development of protective clothing with high comfort for dynamic and extreme temperature conditions.

Thermoresponsive Skin-like Fabric for Personal Comfort and Protection.

Acting as a "second skin", clothing plays an indispensable role in providing comfort and protection in the wide range of environments in which we live. However, comfort and protection are often competing requirements and are difficult to improve simultaneously. By mimicking the exceptional thermoresponsive one-way liquid transport property of human skin, here we developed a scalable and ecofriendly skin-like fabric that has a tunable directional water transport rate while having excellent water repellency. The water transport rate is also temperature-responsive, just like skin. As the temperature increases, the wettability gradient in the spatially distributed channels (acting like "sweat glands") increases, promoting sweat transport and evaporative heat dissipation. As the temperature decreases, on the other hand, the wettability gradient diminishes, reducing liquid transport and evaporative heat loss, thereby promoting heat retention. The fabric is highly suitable for sportswear and functional clothing and can have wider applications, such as oil-water separation, fog harvesting, etc.

Molecular Mechanisms of the Generation and Accumulation of Gas at the Interface.

Gas-evolving reactions are widespread in chemical and energy fields. However, the generated gas will accumulate at the interface, which reduces the rate of gas generation. Understanding the microscopic processes of the generation and accumulation of gas at the interface is crucial for improving the efficiency of gas generation. Here, we develop an algorithm to reproduce the process of catalytic gas generation at the molecular scale based on the all-atom molecular dynamics simulations and obtain the quantitative evolution of the gas generation, which agrees well with the experimental results. In addition, we demonstrate that under an external electric field, the generated gas molecules do not accumulate at the electrode surface, which implies that the electric field can significantly increase the rate of the gas generation. The results suggest that the external electric field changes the structure of the water molecules near the electrode surface, making it difficult for gas molecules to accumulate on the electrode surface. Furthermore, it is found that gas desorption from the electrode surface is an entropy-driven process, and its accumulation at the electrode surface depends mainly on the competition between the entropy and the enthalpy of the water molecules under the influence of the electric field. These results provide deep insight into gas generation and inhibition of gas accumulation.

3D Cellular Solar Crystallizer for Stable and Ultra-Efficient High-Salinity Wastewater Treatment.

Recent developed interfacial solar brine crystallizers, which employ solar-driven water evaporation for salts crystallization from the near-saturation brine to achieve zero liquid discharge (ZLD) brine treatment, are promising due to their excellent energy efficiency and sustainability. However, most existing interfacial solar crystallizers are only tested using NaCl solution and failed to maintain high evaporation capability when treating real seawater due to the scaling problem caused by the crystallization of high-valent cations. Herein, an artificial tree solar crystallizer (ATSC) with a multi-branched and interconnected open-cell cellular structure that significantly increased evaporation surface is rationally designed, achieving an ultra-high evaporation rate (2.30 kg m-2  h-1 during 2 h exposure) and high energy efficiency (128%) in concentrated real seawater. The unit cell design of ATSC promoted salt crystallization on the outer frame rather than the inner voids, ensuring that salt crystallization does not affect the continuous transport of brine through the pores inside the unit cell, thus ATSC can maintain a stable evaporation rate of 1.94 kg m-2  h-1 on average in concentrated seawater for 80 h continuous exposure. The design concept of ATSC represents a major step forward toward ZLD treatment of high-salinity brine in many industrial processes is believed.

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.

2D and 3D Electrospinning of Nanofibrous Structures by Far-Field Jet Writing.

Electrospinning offers remarkable versatility in producing superfine fibrous materials and is hence widely used in many applications such as tissue scaffolds, filters, electrolyte fuel cells, biosensors, battery electrodes, and separators. Nevertheless, it is a challenge to print pre-designed 2D/3D nanofibrous structures using electrospinning due to its inherent jet instability. Here, we report on a novel far-field jet writing technique for precisely controlling the polymer jet in nanofiber deposition, which was achieved through a combination of reducing the nozzle voltage, adjusting the electric field, and applying a set of passively focusing electrostatic lenses. By optimizing the applied voltage, the circular aperture of lenses, and the distance between the adjacent lenses, the best precision achieved using this technique was approximately 200 µm, similar to that of a conventional polymer-based 3D printer. This development makes it possible for printing 2D/3D nanofibrous structures by far-field jet writing for different applications with enhanced performance.

Wetting-State-Induced Turning of Water Droplet Moving Direction on the Surface.

The spontaneous directional movement of water droplets on a wedge-shaped groove has gained extensive attention due to the advantage of not requiring energy input and its potential wide applications. However, manipulating the direction of movement of water droplets on a wedge-shaped groove has been not fully achieved, and the fundamental understanding of its underlying mechanism remains unclear. Here, molecular dynamics simulations and theoretical analyses are combined to reveal the mechanism of movement in opposite directions of a water droplet at the same position on the wedge-shaped groove interface. It is shown that the moving direction of the water droplet is related to its wetting state on the surface, i.e., the Wenzel and the Cassie states. A water droplet initially in the Wenzel and Cassie states will move toward the diverging and the converging ends, respectively. This phenomenon is attributed to the opposite roles played by the groove substrate and the upper layers in the two wetting states. Moreover, it is found that the water droplet is likely to move faster on a surface with a higher groove, larger opening angle and stronger hydrophobicity. These findings are expected to be of benefit for fully understanding droplet movement and shedding light on the regulation of the direction of movement of the droplets on the groove surface.

Design and evaluation of multifunctional protective clothing for tunnel workers.

By examining the requirements of tunnel workers, multifunctional tunnel protective clothing was proposed in this study. The traditional tunnel protective clothing was redesigned from the perspective of improving clothing structure and fabric. A safe and protective clothing system, incorporating a harmful gas detection module, position monitoring module and data transmission module, was developed. Objective evaluation tests were carried out to verify the effectiveness of the proposed protective clothing. During the medium-intensity exercise phase, the average skin temperature and humidity of the participants who wore the new protective clothing were 1.0725 °C and 2.6% lower, respectively, than those who wore the conventional protective clothing (p < 0.05). Furthermore, the new protective clothing system exhibited a highly sensitive and complete feedback mechanism. The positioning error could be controlled within ±10 cm, when the horizontal spacing distance of the base station was set to 200 m.

Enhanced In Vitro Biocompatible Polycaprolactone/Nano-Hydroxyapatite Scaffolds with Near-Field Direct-Writing Melt Electrospinning Technology.

Polycaprolactone (PCL) scaffold is a common biological material for tissue engineering, owing to its good biocompatibility, biodegradability and plasticity. However, it is not suitable for osteoblast adhesion and regeneration of bone tissue due to its non-biological activity, poor mechanical strength, slow degradation speed, smooth surface and strong hydrophobicity. To improve the mechanical properties and biocompatibility of PCL scaffold, the PCL/nHA scaffolds were prepared by melting and blending different proportions of nano-hydroxyapatite (nHA) with PCL by the near-field direct-writing melt electrospinning technology in this study. The morphology, porosity, mechanical properties and in vitro biocompatibility of the PCL/nHA scaffolds were studied. The results showed that when the proportion of nHA was less than or equal to 25%, PCL/nHA composite scaffolds were easily formed in which bone marrow mesenchymal stem cells proliferated successfully. When the proportion of nHA was 15%, the PCL/nHA composite scaffolds had excellent structural regularity, good fiber uniformity, outstanding mechanical stability and superior biocompatibility. The PCL/nHA composite scaffolds were ideal scaffold materials, which would broaden their applications for bone tissue engineering.

Influences of Process Parameters of Near-Field Direct-Writing Melt Electrospinning on Performances of Polycaprolactone/Nano-Hydroxyapatite Scaffolds.

In this paper, near-field direct-writing melt electrospinning technology was employed to fabricate a polycaprolactone/nano-hydroxyapatite (PCL/nHA) scaffold for future applications in tissue engineering. The influences of different fabrication parameters on the structural characteristics, mechanical properties, and thermal stability of the scaffolds were discussed. It was found that the moving speed of the receiving plate had the most significant effect on the scaffold performance, followed by the receiving distance and spinning voltage. The results also showed that these process parameters affected the fiber diameter, corresponding coefficient of variation, porosity of the composite scaffolds, and mechanical properties of the samples, including the tensile strength and fiber peeling strength. Moreover, the process parameters could influence the thermal degradation performance and melting process. Although the mass loss of the composite scaffolds was not obvious after degradation, the mechanical performance degraded severely. It was concluded that the more appropriate process parameters for preparing PCL/nHA scaffolds were a spinning voltage of -4 kV, receiving distance of 4 mm, moving speed of receiving plate of 5 mm/s, and melt temperature of 130 °C. This study proved that near-field direct-writing melt electrospinning technology is a good method to obtain PCL/nHA composite scaffolds with an excellent mechanical properties and desired morphology for future tissue engineering applications.

Photothermal Nanoconfinement Reactor: Boosting Chemical Reactivity with Locally High Temperature in a Confined Space.

A photothermal nanoconfinement reactor (PNCR) system is proposed and demonstrated by using hollow carbon nanospheres (HCNs) to enhance the performance of the chemical reaction. Under light irradiation, the local temperature of the HCN inner void space was much higher than the bulk solution temperature because the confined space concentrates heat and inhibits heat loss. Using the temperature-sensitive model reaction, peroxydisulfate (PDS) activation to oxidize micropollutant, it is shown that the degradation rate of sulfamethoxazole in the PNCR system is 7.1 times of that without nanoconfinement. It is further discovered that the high-quality local heat inside the nanoconfined space shifted the model reaction from an otherwise non-radical pathway to a radical-based pathway. This work provides an interesting strategy to produce a locally high temperature, which has a wide range of applications to energy and environmental fields.

Effects of body positions and garment design on the performance of a personal air cooling/heating system.

Heating and cooling efficiencies of a personal air thermoregulatory system are not only determined by the physics of energy conversion efficiency but also influenced by the interactions between human body and clothing microenvironment. It was found that for a wearable air ventilating system, sedentary position can lead to higher heating and cooling power than standing position. Also, leaning on the chair backrest during sitting can further improve the air cooling performance in hot condition compared with a non-leaning position. These improvements are mainly attributed to the change of clothing microclimate at chest and back areas, where cooling/heating air is directed. It was also found locations of air outlets in a wearable air ventilating system can affect the cooling/heating performance. With the improved understanding of the influence of human and design factors, the study provides a guideline for the design of personal air thermoregulatory systems used for different body positions.

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.

Development of wearable air-conditioned mask for personal thermal management.

A mask that creates a physical barrier to protect the wearer from breathing in airborne bacteria or viruses, reducing the risk of infection in polluted air and potentially contaminated environments, has become a daily necessity for the public especially as COVID-19 has exploded around the world. However, the use of masks often causes soaring temperatures and thick humid air, leading to thermal and wear discomfort and breathing difficulties for a number of people, and further increasing the elevated risk of heat illnesses including heat stroke and heat exhaustion. When wearers become highly active or work under high tension, the excess sweat generated negatively affects the functionality of masks. Here, we report on an innovative design of an air-conditioned mask (AC Mask) system, facilitating thermoregulation in the mask microclimate, ease of breathing, and wear comfort. The AC Mask system is developed by integrating a cost-effective and lightweight thermoelectric (TE) and ventilation unit in a wearable 3D printed mask device, compatible with existing disposable masks, to protect end users safely against toxic particles such as viruses. A wind-guided tunnel has been developed for quick and efficient ventilation of cooling air. Based on a human trial, reductions in the apparent microclimate temperature and the humidity by 3.5 °C and 50%, respectively, have been achieved under a low voltage. With the excellent thermal management properties, the AC Mask will find also wide application among professional end-users such as construction workers, firefighters, and medical personnel.

Electrical Resistance of Stainless Steel/Polyester Blended Knitted Fabrics for Application to Measure Sweat Quantity.

Skin wetness and body water loss are important indexes to reflect the heat strain of the human body. According to ISO 7933 2004, the skin wetness and sweat rate are calculated by the evaporative heat flow and the maximum evaporative heat flow in the skin surface, etc. This work proposes the soft textile-based sensor, which was knitted by stainless steel/polyester blended yarn on the flat knitting machine. It investigated the relationship between electrical resistance in the weft/warp directions and different water absorption ratio (0-70%), different sample size (2 cm × 2 cm, 2 cm × 4 cm, 2 cm × 6 cm and 2 cm × 8 cm). The hydrophilic treatment effectively improved the water absorption ratio increasing from 40% to 70%. The weft and warp direction exhibited different electrical behaviors when under dry and wet conditions. It suggested the weft direction of knitted fabrics was recommended for detecting the electrical resistance due to its stable sensitivity and linearity performance. It could be used as a flexible sensor integrated into a garment for measuring the skin wetness and sweat rate in the future instead of traditional measurements.

Electric field-induced gas dissolving in aqueous solutions.

Gas dissolution or accumulation regulating in an aqueous environment is important but difficult in various fields. Here, we performed all-atom molecular dynamics simulations to study the dissolution/accumulation of gas molecules in aqueous solutions. It was found that the distribution of gas molecules at the solid-water interface is regulated by the direction of the external electric field. Gas molecules attach and accumulate to the interface with an electric field parallel to the interface, while the gas molecules depart and dissolve into the aqueous solutions with a vertical electric field. The above phenomena can be attributed to the redistribution of water molecules as a result of the change of hydrogen bonds of water molecules at the interface as affected by the electric field. This finding reveals a new mechanism of regulating gas accumulation and dissolution in aqueous solutions and can have tremendous applications in the synthesis of drugs, the design of microfluidic device, and the extraction of natural gas.

Effect of material property, surface temperature and contact duration on the thermal sensation when contacting shell materials of electronic devices.

Heat generated in electronic devices is generally unevenly distributed across the casing. Contacting the hot areas may cause thermal discomfort and possibly skin burn. This study aims at better understanding the interrelationship between the thermal sensation, material properties and surface temperature for enhancing the user experience of electronic devices. A Thermal Simulation System was developed in this study to precisely control the surface temperature of shell materials to simulate various end-use conditions. Seventeen participants were asked to contact the plates with their fingers and rate their thermal sensation using the magnitude estimation approach. Results showed that thermal sensation magnitude and plate temperature followed a power function. The differences in sensation magnitude can be attributed to the thermal inertias of different materials. The findings suggested that laminated plate was generally perceived cooler when heated. Given that the surface temperature of plate is higher than skin, the thermal sensation magnitude increases with contact duration.

Correction: Nanoporous two-dimensional MoS2 membranes for fast saline solution purification.

Correction for 'Nanoporous two-dimensional MoS2 membranes for fast saline solution purification' by Jianlong Kou et al., Phys. Chem. Chem. Phys., 2016, 18, 22210-22216.

Designing wearable computing devices for improved comfort and user acceptance.

This study identified acceptable range of physical attributes (form factors, weight, volume and contact area) of wearable computing devices (WCD) on different body areas in relation to human factors, through human performance tests with 41participants. Findings of this study discovered that there is a different level of threshold to discomfort on each part of the body; forearm has the smallest estimated mean of acceptable maximum weight of WCD followed by shirt pocket and collar area. On the other hand, front waist and back waist, when placed on one side, showed significantly higher estimated means of acceptable maximum weight of WCD than any other areas. Similar data trend was found in acceptable maximum volume and contact area of WCD. Body movement and posture influence the users' comfort, as the weight of WCD can cause unhealthy posture over time, and increased energy expenditure, which may cause orthopaedic problems and discomfort. Practitioner summary: This study discovered that in carrying wearable computing devices (WCD), there is a different level of threshold to discomfort on each part of the body, as evidenced by significantly different acceptable maximum weight, volume and contact area of WCD on different body part. Abbreviations: WCD: wearable computing devices.