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A superhydrophobic textile inspired by polar bear hair for both in air and underwater thermal insulation
Abstract
Polar bears have special hairs with porous microstructure and hydrophobic surface, which help them keep warm in both cold air and water. Due to the large difference in temperature and heat transfer process of aquatic and terrestrial environments, it is quite difficult for typical thermal insulating materials to maintain ideal insulation in air and underwater at the same time. To tackle this problem, we report here a superhydrophobic porous textile mimicking the outstanding thermal insulating properties of polar bear hairs. Fibers used to weave this textile are fabricated by a freeze-spinning method, providing them aligned porous microstructure. After a superhydrophobic surface treatment, the obtained textile with porous microstructure and superhydrophobic surface is capable of capturing air in its multi-scale porous structure, promising an excellent thermal insulating ability in both air and water environments. Our study paves a way for the bioinspired engineering of thermal insulation textiles both in air and underwater.
... We can see the scale pattern on the rough surface of polar bear hairs presented in Fig. 2a. Figure 2b, c exhibits the special core-shell structure. The porous core layer has obvious lamellar structure, and the shell layer is formed by microfibril aggregation (Fig. 2c) [30,51]. ...
... Macrofibril is also composed of microfibrils with microfibrils with a diameter of about 7-8 nm. Subcortical cells are directly composed of microfibrils, which are also Fig. 2 Microstructures of polar bear hairs [30,51] composed of protofibrils with a diameter of about 2 nm [58,59]. ...
... properties and weaving. Freeze-spinning is a combination of solution spinning and directional freezing technology, which can realise continuous large-scale production [14,24,51]. In addition, there are other methods, such as chemical deposition, template method, etc. [40,42,43] (see Table 1). ...
Some living organisms with hierarchical structures in nature have received extensive attention in various fields. The hierarchical structure with multiple pores, a large number of solid–gas interfaces and tortuous conduction paths provide a new direction for the development of thermal insulation materials, making the living creatures under these extreme conditions become the bionic objects of scientific researchers. In this review, the research progress of bionic hierarchical structure in the field of heat insulation is highlighted. Polar bears, cocoons, penguin feathers and wool are typical examples of heat preservation hierarchy in nature to introduce their morphological characteristics. At the same time, the thermal insulation mechanism, fractal model and several preparation methods of bionic hierarchical structures are emphatically discussed. The application of hierarchical structures in various fields, especially in thermal insulation and infrared thermal stealth, is summarised. Finally, the hierarchical structure is prospected.
... [2] Moreover, their excellent knittability and processability make them suitable for intelligent sensing, [3] electromagnetic shielding, [4] biological antimicrobials, [5] and multimedia thermal insulation. [6] Contemporary fibers with novel structures and functions (such as hollow fibers, [7] microfibers, [8] and down [9] ) are the preferred choice for warm fabrics due to their high surface area and high air retention between/within the fibers. These features can surpass the performance limits of animal, plant, or nonporous fibers produced using traditional manufacturing methods. ...
... Aerogel fibers prepared by freezing spinning possess abundant pore counts due to the www.advancedsciencenews.com www.advmat.de growth of ice crystals, [6,25,26] but their low preparation efficiency presents a challenge for large-scale production. Direct wet spinning to obtain aerogel fibers does not consider the reaction rate matching relationship between the precursor and the coagulation bath, [27,28] resulting in poor insulation performance and a limited application range, especially for rigid polymers. ...
The exceptional lightweight, highly porous, and insulating properties of aerogel fibers make them ideal for thermal insulation. However, current aerogel fibers face limitations due to their low resistance to harsh environments and a lack of intelligent responses. Herein, a universal strategy for creating polymer aerogel fibers using crosslinked nanofiber building blocks is proposed. This approach combines controlled proton absorption gelation spinning with a heat‐induced crosslinking process. As a proof‐of‐concept, we designed and synthesized Zylon aerogel fibers that exhibited robust thermal stability (up to 650°C), high flame retardancy (limiting oxygen index of 54.2%), and extreme chemical resistance. These fibers possess high porosity (98.6%), high breaking strength (8.6 MPa), and low thermal conductivity (0.036 W∙m ⁻¹ ∙K ⁻¹ ). These aerogel fibers can be knotted or woven into textiles, utilized in harsh environments (‐196 ∼ 400°C), and demonstrate sensitive self‐powered sensing capabilities. This method of developing aerogel fibers expands the applications of high‐performance polymer fibers and holds great potential for future applications in wearable smart protective fabrics.
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... The programmable form of the hairy SMP allows the irreversible and adaptable reconfiguration of the hair morphology in response to external environments, resulting in more than 61.4% dynamic control of thermal insulation [82]. Superhydrophobic surface treatment of the textile with porous microstructure (Fig. 4d-e) allows for promising a superior thermal insulation in both air and water ambient, paving the way for the bioinspired thermal insulating materials in both air and underwater [83]. In addition, biomimetic thermalregulation textiles can also have stretchability, high strength, flame retardancy, and acid and alkali resistance [84]. ...
... Besides, the anti-reflection properties of hollow cylinders are superior than shell/hollow and solid cylinder structures (Fig. 5d). Moreover, the white scales with gradient refractive [83]. f-g Thermal stealth properties biomimetic textiles. ...
The structural evolutions of the organisms during the development of billions of years endow them with remarkable thermal-regulation properties, which have significance to their survival against the outer versatile environment. Inspired by the nature, there have been extensive researches to develop thermoregulating materials by mimicking and utilizing the advantages from the natural organisms. In this review, the latest advances in thermal regulation of bioinspired microstructures are summarized, classifying the researches from dimension. The representative materials are described with emphasis on the relationship between the structural features and the corresponding thermal-regulation functions. For one-dimensional materials, wild silkworm cocoon fibers have been involved, and the reasons for unique optical phenomena have been discussed. Pyramid cone structure, grating and multilayer film structure are chosen as typical examples of two-dimensional bionics. The excellent thermal performance of the three-dimensional network frame structures is the focus. Finally, a summary and outlook are given.
... The thermal insulating performance and schematic illustration of the thermal insulating mechanism of hydrophilic textile, and superhydrophobic porous textile in air and underwater. Reproduced with permission from ref. [144]. Copyright: 2020, Elsevier. ...
... Keeping warm in various harsh environments is crucial for both humans' and other mammals' health, and can make it possible to expand our activity range and explore unknown regions. By mimicking the polar bears, which can maintain their body temperature at around 37°C in extremely cold regions, Shao et al. [144] developed a special superhydrophobic textile with multiscale porous structure by a freeze-spinning process. In air, the porous structure could effectively capture the air inside the cores and this air could reduce the heat transfer as it has much smaller thermal conductivity than solid surface. ...
Superhydrophobic surfaces with expanded wetting behaviors, like tunable adhesion, hybrid surface hydrophobicity and smart hydrophobic switching have attracted increasing attention due to their broad applications. Herein, the construction methods, mechanisms and advanced applications of special superhydrophobicity are reviewed, and hydro/superhydrophobic modifications are categorized and discussed based on their surface chemistry, and topographic design. The formation and maintenance of special superhydrophobicity in the metastable state are also examined and explored. In addition, particular attention is paid to the use of special wettability in various applications, such as membrane distillation, droplet‐based electricity generators and anti‐fogging surfaces. Finally, the challenges for practical applications and future research directions are discussed.
... By applying the concept of bioinspiration to surface engineering, a new generation of materials has been created. In the wilderness exists a large panel of wonderful properties such as iridescence [6], self-healing [7], self-cleaning [8], anti-adhesive [9], anti-fouling [10], anti-icing [11], thermal insulation [12], energy efficiency [13], hydrophilicity or hydrophobicity [14] and has been exploited to enhance the surface performances. ...
Superhydrophobic surfaces have low water wetting due to their chemical nature and/or surface state structured at multiple scales (micro and nano). Additive manufacturing (AM) processes using stainless steel are expensive due to the cost of stainless steel powder. Additionally, the precision of these technologies rarely goes below 200 μm. The presented work combines two technologies, namely polymer 3D printing and vacuum casting (lost-wax casting), to create various bio-inspired microtextured surfaces in 316L stainless steel from stainless steel waste. Casting micrometric details in stainless steel foundry is a technical challenge due to high surface tension, high dynamic viscosity, and high working temperature (1600°C). Various bioinspired microtextured surfaces (fish scales, drops, honeycomb, etc.) have been successfully manufactured. A nanoscale coating was then applied through atmospheric pressure plasma polymerization to nanotexture the surface, leading to an ultrahydrophobic behavior. Finally, various potential applications for these surfaces, such as anti-fouling, anti-icing, or impregnation with vegetable oil for the development of slippery liquid-infused porous surfaces (SLIPS), are explored and discussed.
... Effective thermal regulation is crucial in complex low-temperature environments. [14,15] To address this, advanced flexible self-healing fabrics, including thermal insulating fabrics, [16,17] radiative cooling fabrics, [18][19][20] evaporative cooling fabrics, [21,22] and heat transfer fabrics have been developed. [23,24] However, fabrics that provide additional heat sources are essential in cold weather conditions. ...
Energy harvesting and storage at extreme temperatures are significant challenges for flexible wearable devices. This study innovatively developed a dynamic‐bond‐cross–linked spinnable azopolymer‐based smart fabric (PAzo‐M/PVA, M = Mg, Ca, Zn) capable of photothermal energy storage, light‐induced self‐heating, mechanical energy harvesting, and self‐powered motion sensing under cold conditions, overcoming issues like low energy density and poor structural stability when azopolymers are combined with other fabrics via impregnation or spraying. PAzo‐Mg, operating without solvents, demonstrated high energy density (264.8 J g⁻¹) and long‐term stability (14 days). Upon light excitation at −20 °C, this fabric achieved the highest temperature increase (9.3 °C) and sustained self‐heating for 45 minutes. A triboelectric nanogenerator based on this fabric achieved a maximum output power density of 3.43 W m⁻² and demonstrated excellent durability (≈10 000 cycles) at −20 °C, with light‐induced trans/cis isomerization and dynamic bond formation/dissociation affected the electrical output, a phenomenon not previously reported. Moreover, a self‐powered motion sensor embedded with this fabric successfully detected subtle pulse variations during outdoor human activities at −18 to −21 °C. This smart fabric combines energy storage, self‐heating, and triboelectric power generation at low temperatures, providing a feasible solution for creating flexible wearable devices for complex environments.
... They further applied a superhydrophobic fluorinated SiO 2 nanoparticle coating to the fabric, mirroring the water-repellent properties of polar bear hair. [144] This treatment effectively reduces heat loss and thermal conductivity, making the fabric versatile for thermal insulation in both air and water environments. Most recently, the team designed an encapsulated aerogel fiber with thermal insulation mechanisms similar to those of polar bear hair. ...
In chemistry, biology, and materials science, ice‐mediated reactions and ice‐template assembly techniques are garnering increasing attention due to their unique advantages. Such approaches not only offer deep insights into the fundamental roles of ice in nature but also pave new avenues for various applications. This review comprehensively explores the mechanisms and applications of ice‐mediated reactions and assembly. It begins by examining the principles of ice‐mediated reactions, particularly how certain chemical reactions are accelerated in the micro‐environment of ice through freeze‐concentration and freeze‐potential effects, and the relationship between the surface structure and properties of ice and chemical reactions. This work then studies significant chemical reactions within the realms of environmental, biological, and materials science engineering, shedding light on the role of ice in these reactions. Furthermore, this work explores the fundamentals of ice templating in material assembly, describe the main ice‐templating methods, and highlight the ice‐templated materials along with their diverse applications. This work concludes by summarizing the prospective challenges and untapped potentials in the field of ice‐mediated reactions and assembly. This review not only accentuates the transformative impact of ice‐mediated techniques in scientific domains but also serves as an useful guide for future research initiatives and practical applications in this burgeoning field.
... As shown in Figure 3f, plenty of air in the pores of the WPUF layer has a lower thermal conductivity than most solids, which enormously reduces the intensity of thermal conduction and the heat transfer by radiation. [50,51] Furthermore, the flexural network of WPUF may lengthen the heat transfer path, thereby decreasing the thermal conduction capacity. [52,53] Due to the low emissivity of the MXene/CNF layer combined with the thermal insulation ability of the WPUF layer, the M-W-M composite exhibits excellent IR stealth performance. ...
Electromagnetic interference (EMI) shielding and infrared (IR) stealth materials have attracted increasing attention owing to the rapid development of modern communication and military surveillance technologies. However, to realize excellent EMI shielding and IR stealth performance simultaneously remains a great challenge. Herein, a facile strategy is demonstrated to prepare high‐efficiency EMI shielding and IR stealth materials of sandwich‐structured MXene‐based thin foam composites (M‐W‐M) via filtration and hot‐pressing. In this composite, the conductive Ti3C2Tx MXene/cellulose nanofiber (MXene/CNF) film serves as the outer layer, which reflects electromagnetic waves and reduces the IR emissivity. Meanwhile, the middle layer is composed of a porous waste polyurethane foam (WPUF), which not only improves thermal insulation capacity but also extends electromagnetic wave propagation paths. Owing to the unique sandwich structure of “film‐foam‐film”, the M‐W‐M composite exhibits a high EMI shielding effectiveness of 83.37 dB, and in the meantime extremely low emissivity (22.17%) in the wavelength range of 7–14 µm and thermal conductivity (0.19 W m⁻¹ K⁻¹), giving rise to impressive IR stealth performance at various surrounding temperatures. Remarkably, the M‐W‐M composite also shows excellent Joule heating properties, capable of maintaining the IR stealth function during Joule heating.
... In recent years, advancements in equipment and deepening research have given rise to new methods for fabricating porous fibers, garnering significant attention. Notably, high internal phase emulsion template methods [50][51][52], coaxial wet spinning [25,53], freeze spinning [6,13,54], and microfluidic spinning [37,55] have gained prominence. Among them, wet spinning refers to a molding method where the spinning solution is extruded into a coagulation bath through a syringe, resulting in the solidification of the polymer into porous fibers through a double-diffusion process. ...
This review introduces an innovative technology termed “Micro-Extrusion Foaming (MEF)”, which amalgamates the merits of physical foaming and 3D printing. It presents a groundbreaking approach to producing porous polymer fibers and parts. Conventional methods for creating porous materials often encounter obstacles such as the extensive use of organic solvents, intricate processing, and suboptimal production efficiency. The MEF technique surmounts these challenges by initially saturating a polymer filament with compressed CO2 or N2, followed by cell nucleation and growth during the molten extrusion process. This technology offers manifold advantages, encompassing an adjustable pore size and porosity, environmental friendliness, high processing efficiency, and compatibility with diverse polymer materials. The review meticulously elucidates the principles and fabrication process integral to MEF, encompassing the creation of porous fibers through the elongational behavior of foamed melts and the generation of porous parts through the stacking of foamed melts. Furthermore, the review explores the varied applications of this technology across diverse fields and imparts insights for future directions and challenges. These include augmenting material performance, refining fabrication processes, and broadening the scope of applications. MEF technology holds immense potential in the realm of porous material preparation, heralding noteworthy advancements and innovations in manufacturing and materials science.
... Here, D represents the instantaneous height of the air layer, and D m represents the maximum height reached by the air layer, as shown in Fig. 6. At t = 0 ms, the silver mirror phenomenon [45,52] caused by the air layer on the surface of the porous copper can be observed. The bubble reaches its maximum volume at t = 1.00 ms, with an equivalent radius of R m = 6.59 mm. ...
This paper aims to apply experimental methods to investigate the effect of the thickness of gas layers on the wall on the collapse direction of spark-induced bubbles. In the experiment, two high-speed cameras synchronously record the time evolution of the bubbles and the corresponding parameters such as the normalized collapse position and bubble collapse time. Experiments yielded results for individual bubbles over a range of normalized distances from 0 to 4.0 for different air layer thicknesses. Based on the morphology of the bubbles, the experimental jets were visualized into six different modes, namely, forward jet (FJ), merging jet (MJ), bidirectional jet (BJ), reversing jet (RJ), forward followed by reversing jet (FRJ), and non-directional jet (NDJ). The height of the air layer on the wall is affected by the fluctuation of the bubble volume and shows the opposite trend to the change of the bubble volume. The air film reaches its maximum height when the bubble collapses, which affects the final jet pattern. In addition, as the thickness of the air layer increases, the center of the bubble gradually migrates away from the wall. The different collapse modes and the migration of the bubble centers have positive significance for reducing cavitation erosion in engineering.
... [2] To solve the above problems, passive anti-icing technology based on the superhydrophobic surfaces is proposed. [10][11][12] The superhydrophobic surface can form an air cushion at the solid-liquid interface, so that the water droplets directly bounce back or roll off and cannot stay on the surface, effectively reducing the contact time between the water droplets and the surface. This facilitates avoidance of ice nucleation by heat conduction. ...
Glass fiber‐reinforced polymer (GFRP) is formed with glass fiber as the reinforcing material and resin as the matrix. It is widely used in wind turbine blades because of its lightweight, high strength, and corrosion resistance properties. Herein, a method to prepare superhydrophobic GFRP surfaces by femtosecond laser direct writing combined with fluoroalkylsilane modification is demonstrated. The prepared GFRP surface has excellent superhydrophobicity with contact angle of 163.9° and sliding angle of 3.8°. In the ice resistance tests, the icing delay time is extended from 33 to 273 s at −5 °C. The ice adhesion strength is reduced from 217.4 to 40.3 kPa. The surface still has superhydrophobicity and ice adhesion strength of less than 100 kPa after ten cycles of the test. The laser exposure conditions are optimized for water/ice repelling and are at high intensity of 4 TW cm⁻² pulse⁻¹ and 2.5 m s⁻¹ beam travel speed, which make the presented approach efficient for fabrication over industrially large areas.
... The SHS possesses low surface energy and micro-nanostructures, which can effectively decrease the contact area between the sample surfaces and water. Meanwhile, the air stratum formed between the water and solid surface acts as a thermal insulation layer, 16 which can delay the crystallization time (Td) of water droplet and decrease the ice adhesion strength (τ ice ). [17][18][19] Thus, SHS is considered as promising anti-icing materials. ...
Undesired ice accumulation can lead to serious negative impacts on daily life and equipment safety. Slippery liquid-infused surfaces (SLISs) have been widely studied for their low ice adhesion strength (τice). However, the lack of durability, weak robustness, and complex preparation process hinder the application of SLISs. In this work, robust oil-infused porous surface (RIPS) was obtained by a facile one-step method, which used epoxy resin (E44) as a substrate and contained fumed silica and silicone oil. The RIPS-6 displays outstanding anti-icing/deicing ability, superior liquid repellency, good self-cleaning performance, and excellent mechanical robustness. At −5 °C, the water droplet remained unfrozen after 7200 s. τice was only 6.9 kPa at −20 °C and remained below 15 kPa during 10 icing cycles. Furthermore, the mixture of E44 and fumed silica enhanced the mechanical properties including the hardness (4 H) and abrasion resistance of RIPS-6. The icephobicity can be remained (τice < 40 kPa) even after 150 cycles of sandpaper abrasion at 2.5 kPa. The anti-icing and deicing coating with excellent mechanical stability and durability significantly improves the practical application possibility of the coating in harsh environments.
... Inspired by special hairs of polar bears with porous microstructure and hydrophobic surface for keeping warm in both cold air and water, Bai's group developed a series of thermoregulation fibers with their aligned porous structure via a "freeze-spinning" technique. [349][350][351] Such biomimetic textiles were woven into a textile showing excellent thermal insulation and good wearability (Figure 9d). Recently, the utilization of moisture-sensitive feature of natural cotton yarn smart muscles with expansion-contraction behavior has been proposed for the fabrication of thermoregulatory clothing. ...
Benefiting from inherent lightweight, flexibility, and good adaptability to human body, functional textiles are attracting tremendous attention to cope with wearable issues in sustainable applications around human beings. In this feature article, a comprehensive and thoughtful review is proposed regarding research activities of functional textiles with smart properties. Specifically, a brief exposition of highlighting the significance and rising demands of novel textiles throughout the human society is begun. Next, a systematic review is provided about the fabrication of functional textiles from 1D spinning, 2D modification, and 3D construction, their diverse functionality as well as sustainable applications, showing a clear picture of evolved textiles to the readers. How to engineer the compositions, structures, and properties of functional textiles is elaborated to achieve different smart properties. All these tunable, upgraded, and versatile properties make the developed textiles well suited for extensive applications ranging from environmental monitoring or freshwater access to personal protection and wearable power supply. Finally, a simple summary and critical analysis is drawn, with emphasis on the insight into remaining challenges and future directions. With worldwide efforts, advance and breakthrough in textile functionalization expounded in this review will promote the revolution of smart textiles for intelligence era.
... Wu et al. [15] studied the thermal insulation performance of silver ants from the aspects of spectrum, wave transmission and thermal conductivity. Some researchers have studied the infrared radiation properties of the porous hair structure of polar bear [16][17][18] and penguin [19], and prepared the fiber structure based on its structure. However, hair materials have superior performance in heat insulation, but the soft hair cannot meet the requirements of labyrinth seal in terms of load-bearing performance. ...
Labyrinth seals are widely used in turbomachinery devices to prevent the leakage of fluid medium in seal structures. Under high parametrical environments, the heat generated by frictional resistance of the turbulence between the stator and rotor walls not only increases the temperature of the fluid and the solid, but also reduces the operation efficiency of the device. Therefore, it is necessary to implement the fluid-solid-thermal multi-field analysis of labyrinth seals and propose a comprehensive optimization design of the load-bearing and heat insulation. In the present study, inspired by a bionic snail shell, a sandwich structure with load-bearing material on both upper and lower surfaces and the heat insulation material in the middle is obtained through the genetic algorithm optimization. Then, the luid-solid-thermal multi-field analysis of the labyrinth seal with the sandwich structure is carried out. It is verified that the layer arrangement and layer thickness ratio of the bionic structure ensured the optimal performance of load-bearing and heat insulation. After changing the layer arrangement or layer thickness ratio, the comprehensive performance of load-bearing and heat insulation is obviously weakened. The result shows that the bionic multilayer sandwich structure can be applied to the labyrinth seal to achieve optimal comprehensive performance of load-bearing and heat insulation.
Chitin and keratin are naturally abundant biopolymers. They hold significant potential for sustainable applications due to their chemical structure, (nano)structural properties, biodegradability and nontoxicity. Chitin, a polysaccharide contained in exoskeletons of arthropods and the cell walls of fungi, forms strong hydrogen bonds that confer mechanical stability, which is ideal for use in protective structures and lightweight composites. Keratin, a fibrous protein found in vertebrate epithelial tissues such as wool, feathers and hair, is characterized by its high sulfur content and the formation of disulfide bonds, which provide both mechanical strength and flexibility. Utilizing chitin and keratin waste materials from the food industry, such as shrimp shells, chicken feathers and sheep wool, offers an eco-friendly alternative to synthetic materials and leverages their inherent biocompatibility. Additionally to the common macroscale reuse of chitin and keratin waste as fertilizer or livestock feed, using chitin and keratin as functional materials adds further uses for these versatile materials. The waste is increasingly being utilized specifically for its superior structural properties resulting from nanoscale functionalities. Chitin and keratin exhibit excellent thermal insulation properties, making them suitable for energy-efficient building materials. Their structural colours (e.g., in butterflies and birds), arising from micro- and nanoscale arrangements, offer non-fading colouration for textiles and coatings without the need for potentially harmful dyes. Additionally, these biopolymers provide lightweight yet strong materials ideal for packaging, consumer products, and – when smartly structured – even passive radiative cooling applications. Biomimetic designs based on chitin and keratin promise advancements across multiple fields by harnessing their natural properties and converting waste into high-value products, thereby addressing recycling issues and promoting sustainability.
Personal thermal management (PTM) is an important topic that holds great potential for enhancing human thermal comfort and optimizing energy efficiency, that typically relies on clothing and textiles. However, traditional textiles fail to adjust human thermal loss at low and high temperatures, no longer satisfy the soaring needs of dynamic heat dissipation due to diversified environmental operation. Recent research has seen significant advancements in smart thermal radiative textiles, which are driven by the booming progress in material-oriented and energy-oriented science and technology. These textiles endow the PTM systems with the efficient modulation of human body temperature and wearable comfortability, demonstrating considerable promise due to their rapid conversion efficiency of radiant heat. Here, we primarily introduce the fundamental concepts of heat transfer as well as the radiant heat regulating principles based on smart textiles. Subsequently, different regulation functionalities of smart textiles, consisting of radiative cooling, radiative heating, and smart textile systems for radiative heating and cooling are demonstrated in detail. Finally, the current obstacles and prospective solutions for smart radiation-controlled textiles are proposed to enhance future thermal management technologies, giving prominence to functional innovations and commercial incubation.
Graphical Abstract
With the continuously increasing awareness of energy conservation and the intensifying impacts of global warming, Personal Thermal Management (PTM) technologies are increasingly recognized for their potential to ensure human thermal comfort in extreme environments. Biomimetic structures have emerged as a novel source of inspiration for PTM applications. This review systematically summarizes the biomimetic structures, phase change materials, manufacturing methods, and the performance of multifunctional PTM wearables. Firstly, it analyzes the biomimetic structures with thermal regulation and encapsulated phase change material functionalities from different dimensions, highlighting their applications in PTM. Subsequently, it outlines the conventional manufacturing methods incorporating various biomimetic structures, offering strategies for the production of PTM wearables. The review also discusses the typical performance characteristics of multifunctional PTM wearables, addressing the current demands in thermal management. Finally, opportunities and challenges in PTM field are proposed, proposing new directions for future research.
In extremely cold environments, maintaining body temperature and reducing heat dissipation is essential for maintaining human health and life safety, but the field of thermal insulation shoe upper fabric has not been deeply studied. In this paper, based on the dual-scale structure of the yarn and shoe upper fabric, a composite yarn with a core-sheath structure is designed, and a using plating stitch pattern weft-knitted whole garment thermal insulation shoe upper fabric with double-layer structure is proposed. By testing the mechanical properties and thermal and moisture performance of the shoe upper fabric and the thermal insulation performance of the whole shoe, the thermal insulation mechanism of the weft-knitted whole garment shoe upper fabric with a double-layer structure and dual-scale structure design was systematically studied. The results show that the shoes made of polyimide/hollow polyester composite yarn with core-sheath structure yarn have good thermal insulation performance. The use of core-sheath yarns can improve the thermal insulation performance of the shoe, and, with the increase of the ratio of core-sheath yarn, the thermal insulation performance of the shoe is better. Starting from the dual-scale shoe fabric structure, this article proposes a novel method for the industrial production of thermal insulation shoe upper fabrics, which is expected to provide guidance for the further development of thermal insulation shoe upper fabric in the future.
The crucial point of solar thermal utilization makes solar heat collector gathering much attention. In this study, imitating polar bears' fur structure, fluorescent materials are modified into a solar heat collector, and the photothermal conversion is evaluated to examine the influence of polyvinyl alcohol concentration, fluorescent luminescence type and fluorescence concentration. The test results indicate that fluorescent materials that has a greater Stokes shift show the greater photothermal effect. Moreover, when composed of a PVA concentration being 5.0% and a fluorescent concentration being 0.50%, the composites exhibit the maximal photothermal conversion temperature (99.4°C) that is 17.9% higher than that of the solar heat collectors without fluorescent materials. This study proposes creating solar heat collector with modified fluorescent materials, and the new perspective of which demonstrates that the composites have a great potential and application prospect in the solar photothermal field.
Hair shape affects the frictional properties and tactile sensation of hair. In this study, we evaluated the friction associated with the rubbing of straight, curly, or wavy hair by a contact probe equipped in a sinusoidal motion friction evaluation system. This system provides dynamic information such as the velocity dependence and hysteresis of the frictional force. In the case of hair fibers fixed at 1 mm intervals on a glass plate, a stable friction pattern was observed, in which the friction coefficient was almost constant during the dynamic friction process. The friction coefficients in the inward direction toward the hair root for straight, curly, and wavy hair were 0.47 ± 0.04, 0.51 ± 0.02, and 0.54 ± 0.04, respectively. As wavy hair is thick and has a larger true contact area with the contact probe, the friction coefficient was larger. When the finger model rubbed the straight or curly hair bundle in the inward direction, an oscillation pattern was observed, with the friction coefficient fluctuating at 20 ms intervals and the kinetic friction coefficient evaluated at 0.67 and 0.64, respectively. For the surface of straight hair, containing densely arranged cuticles, a large oscillation was observed in the direction against the cuticles. Meanwhile, no oscillation phenomenon was observed in wavy hair, which is characterized by a smooth cuticle and complex hair flow. Because wavy hair, which is frizzy, has fewer points of contact between hairs, impeding the occurrence of cooperative fluctuations in the frictional force.
graphical abstract Fullsize Image
The amazing qualities of biomaterials are the result of billions of years of evolution. Normally, biomaterials are formed in moderate environments with a restricted supply of components available for living...
The extreme environment of winter sports significantly impacts the performance of athletes, leading to a need for clothing that meets composite functional requirements such as warmth, comfort, and protection to improve competition performance. Knitted fabrics for ice and snow sports with excellent heat and moisture performance were inspired by the water collection and transmission system used by the Moloch horridus. A bionic design model of multi-state fabric morphology was developed by using a topological derivation method and three-dimensional parametric surface modeling technology. The experimental results showed that the four single-sided three-dimensional fabrics have better moisture management characteristics and it is possible to achieve an excellent thermal insulation performance. The textile design application models based on this new design method can provide a feasible solution for developing high-performance textiles for winter sports.
Aerogels have been considered as an ideal material for thermal insulation. Unfortunately, their application in textiles is greatly limited by their fragility and poor processability. We overcame these issues by encapsulating the aerogel fiber with a stretchable layer, mimicking the core-shell structure of polar bear hair. Despite its high internal porosity over 90%, our fiber is stretchable up to 1000% strain, which is greatly improved compared with that of traditional aerogel fibers (~2% strain). In addition to its washability and dyeability, our fiber is mechanically robust, retaining its stable thermal insulation property after 10,000 stretching cycles (100% strain). A sweater knitted with our fiber was only one-fifth as thick as down, with similar performance. Our strategy for this fiber provides rich possibilities for developing multifunctional aerogel fibers and textiles.
Ceramic materials are widely used in engineering field because of their good physical and chemical properties. The poor mechanical properties of traditional ceramics seriously limit the development of ceramic materials and have attracted extensive attention since its birth. The development of high toughness, light weight, and functional ceramic materials has long been the pursuit of materials scientists. Since ancient times, nature has been the source of all kinds of human technological ideas, engineering principles, and major inventions. The functional structure of biology provides a good research object for the bionic design and preparation of ceramic materials. Therefore, it is necessary to summarize the functional structures and mechanisms in nature and biomimetic preparation technology. The purpose of this review is to provide guidance for the functionalized biomimetic design and efficient preparation of ceramic materials. Some typical functional examples in nature are introduced in detail, and several representative biomimetic preparation methods are listed. Finally, the performance and application status of biomimetic ceramics are summarized, and the future development direction of biomimetic ceramic materials is prospected.
Advantages such as increased comfort and reduced energy requirement can be obtained with passive and active smart
textile structures that can adapt to body and environmental condition changes for personal thermal management. In this study, depending
on the energy constraints that are gaining importance, heating/cooling or dual heating-cooling textile materials to keep the thermal
balance of the body by managing natural radiation energy components (ultraviolet, visible, infrared) and mechanisms (emissivity,
reflectivity, absorptivity, transmissivity) were investigated in the light of effective radiation heat transfer mechanisms. Measurement
methods used for such passive smart structures, the deficiencies of current studies and the direction of progress were evaluated in the
light of the literature. It was concluded that, with the effects of global warming, current studies have focused on personal cooling in
indoor environments with radiation management. Moreover, the complex mechanisms valid for outdoor conditions are thought to make
the design and measurements of these structures difficult. In addition, deficiencies were identified about examination of parameters
which are important for wear ability such as hand, comfort and other heat and mass transfer mechanisms. Studies are progressing in the
direction of designing textile structures that perform heating/cooling with radiation management in a way that can adapt to body and
ambient conditions autonomously
Kişisel termal yönetimin sağlanmasına yönelik, değişen vücut ve çevre şartlarına adapte olabilen pasif ve aktif akıllı tekstil yapıları ile artırılmış konfor ve azalan enerji gereksinimi gibi konularda avantajlar sağlanabilmektedir. Bu çalışmada, dünya için gün geçtikçe önem kazanan enerji kısıtlarına bağlı olarak, ekstra enerji harcanmadan doğal radyasyon enerji bileşenleri (ultraviyole, görünür, infrared) ve mekanizmalarının (yayılım, yansıtma, absorpsiyon, geçirgenlik) yönetimiyle vücudun termal dengesini ısıtma/soğutma veya ısıtma-soğutmayı birlikte sağlayarak koruyan yapılar, etkili radyasyon ısı transfer mekanizmaları ışığında incelenmiştir. Bu tür pasif akıllı yapılar için kullanılan ölçüm yöntemleri, mevcut çalışmaların eksik noktaları ve ilerleme yönü konularında da literatür ışığında değerlendirmeler yapılmıştır. Mevcut çalışmaların son dönemde, küresel ısınmanın etkilerinin de somut olarak hissedilmesiyle birlikte, radyasyonla iç ortamlarda kişisel soğutma konusunda yoğunlaştığı, dış ortamda geçerli olan karmaşık mekanizmaların tasarım ve ölçümleri zorlaştırdığı sonucuna varılmıştır. Ayrıca, çalışmalarda yapıların giyilebilirlikleri açısından önemli olan tutum, konfor ve radyasyon dışındaki ısı ve kütle transfer mekanizmalarının bütüncül olarak incelenmeleri konusunda eksiklikler tespit edilmiştir. Çalışmalar, konfor ve enerji tasarrufu beklentilerinin hızla değiştiği günümüzde radyasyon enerjisi yönetimiyle ısıtma/soğutma yapan yapıların vücut ve ortam koşullarına otonom olarak uyum sağlayabilecek şekilde tasarlanması yönünde ilerlemektedir.
ZrO2 fiber aerogels with robust mechanical strength, low density, and low thermal conductivity can be considered high-temperature thermal insulation materials. However, in harsh environments, both radiative thermal resistance and mechanical properties are hindered, resulting in high thermal conductivity and structural degradation. Here, inspired by weaved sisal sheath fiber and polar bear hairs, we proposed a novel hollow ZrO2 nanofibrous aerogel composited with hollow SiC opacifiers (H–ZrO2@H–SiC composite). The super-insulation performances of the aerogel composite were numerically predicted by coupling the 3-D Finite-Difference Time-Domain (FDTD) method with the Rosseland approximation. The low density ordered nanofiber networks improved the mechanical properties, and the opacifiers with low density suppressed the radiative heat transfer. It exhibits a low effective thermal conductivity of 0.020 W⋅m−1⋅K−1 at 1270 K and an outstanding mechanical property based on the prediction using Finite Element Method, making it a new candidate for thermal insulation in harsh environments.
Personal thermal management is a promising solution to improve human body thermal comfort and reduce building energy consumption. Personal management materials (PTMMs) with zero or near-zero power supply are being developed to effectively regulate heat exchange between human body and the ambient. This chapter provides an in-depth overview of the recent progress on the various advanced PTMMs for thermal management under various ambient conditions, including cooling fabrics, heating fabrics, and due-modes fabrics. The functioning principle, engineering methods as well as the cooling/heating effects of the various PTMMs were discussed. Finally, an outlook discussing the development and research of PTMMs is also presented.KeywordsPersonal management materialThermal comfortCooling fabricsHeating fabricsDue-modes fabrics
The regulation and utilization of thermal energy is increasingly important in modern society due to the growing demand for heating and cooling in applications ranging from buildings, to cooling high power electronics, and from personal thermal management to the pursuit of renewable thermal energy technologies. Over billions of years of natural selection, biological organisms have evolved unique mechanisms and delicate structures for efficient and intelligent regulation and utilization of thermal energy. These structures also provide inspiration for developing advanced thermal engineering materials and systems with extraordinary performance. In this review, we summarize research progress in biological and bioinspired thermal energy materials and technologies, including thermal regulation through insulation, radiative cooling, evaporative cooling and camouflage, and conversion and utilization of thermal energy from solar thermal radiation and biological bodies for vapor/electricity generation, temperature/infrared sensing, and communication. Emphasis is placed on introducing bioinspired principles, identifying key bioinspired structures, revealing structure-property-function relationships, and discussing promising and implementable bioinspired strategies. We also present perspectives on current challenges and outlook for future research directions. We anticipate that this review will stimulate further in-depth research in biological and bioinspired thermal energy materials and technologies, and help accelerate the growth of this emerging field.
Recently, consumers have been demanding lightweightness, favorable hand,
stretch, dynamic breathability, and transfer abilities, besides insulation and heating functions being adaptable to the body or environmental conditions. In this
chapter, starting with a summary of physiological effects of the cold, layers of
extreme cold protective clothing (ECPC) are introduced in cases of both material
and structure, focusing more on functional and smart materials/structures,
enabling survival and comfort under dynamic conditions. Moreover, quality parameters of the ECPC and sustainability issues that should be considered for ECPC are also discussed.
Personal thermal management (PTM) materials have attracted increasing attention owing to their application for personal comfort in an energy‐saving mode. However, they normally work in the same media such as in the air, and little is known about what would be happened in other media like water. In this study, we proposed a system for cross‐media thermal management (CMTM): passive cooling in air and thermal insulation underwater. Hybrid aerogels comprising thermoplastic polyurethane (TPU) matrix and superhydrophobic silica aerogel particle (SSAP) for CMTM are designed and synthesized using a thermally induced phase separation and self‐templating strategy. The TPU matrix endows the aerogels with super stretchability (500%), shape memory, and outstanding healing recovery rate (89.9%), which are ideal characteristics for potential wearable usage. Additionally, the TPU and SSAP endow the aerogel with high solar reflectivity and infrared emissivity, thus achieving a sub‐ambient cooling of 10.6 °C in air. Moreover, the SSAP endows the aerogels with low thermal conductivity (0.052 W·m−1·K−1) and high hydrophobicity (143°), enabling the aerogels for underwater thermal insulation. The CMTM performance of the aerogels makes them for potential uses in cross‐media environments such as reefs and islands where cooling in air and thermal insulation in water are required. This article is protected by copyright. All rights reserved
Hollow porous fibers with low emissivity and conductivity aluminum platelets skin for thermal insulation.
Wettability, as a fundamental property of interface materials, is becoming increasingly prominent in frontier research areas, such as water harvesting, microfluidics, biomedicine, sensors, decontamination, wearables, and micro-electromechanical systems. Taking advantage of biological paradigm inspirations and manufacturing technology advancements, diverse wettability materials with precisely customized micro/nano-structures have been developed. As a result of these achievements, wettability materials have significant technical ramifications in sectors spanning from academics to industry, agriculture, and biomedical engineering. Practical applications of wettability-customized materials in medical device domains have drawn significant scientific interest in recent decades due to the increased emphasis on healthcare. In this review, recent advances of wettability-customized micro/nano-materials for biomedical devices are presented. After briefly introducing the natural wettable/non-wettable phenomena, the fabrication strategies and novel processing techniques are discussed. The study emphasizes the application progress of biomedical devices with customized wettability. The future challenges and opportunities of wettability-customized micro/nano-materials are also provided.
Passive thermal regulation has attracted increasing
interest owing to its zero-energy consumption capacity, which is
expected to alleviate current crises in fossil energy and global
warming. In this study, a biomimetic multilayer structure (BMS)
comprising a silica aerogel, a photothermal conversion material
(PTCM), and a phase change material (PCM) layer is designed
inspired by the physiological skin structure of polar bears for
passive heating with desirable temperature and endurance. The
transparent silica aerogel functions as transparent hairs and allows
solar entry and prevents heat dissipation; the PTCM, a glass plate
coated with black paint, acts as the black skin to convert the
incident sunlight into heat; and the PCM composed of n-octadecane microcapsules stores the heat, regulating temperature and
increasing endurance. Impressively, outdoor and simulated experiments indicate efficient passive heating (increment of 60 °C) of the BMS in cold environments, and endurance of 157 and 92 min is achieved compared to a single aerogel and PTCM layer,
respectively. The uses of the BMS for passive heating of model houses in winter show an increase of 12.1 °C. COMSOL simulation
of the BMSs in high latitudes indicates robust heating and endurance performance in a −20 °C weather. The BMS developed in this
study exhibits a smart thermal regulation behavior and paves the way for passive heating in remote areas where electricity and fossil
energy are unavailable in cold seasons.
Passive thermal management (PTM) materials that can stabilize long-duration temperature are highly desirable in thermal insulation applications such as building insulation, infrared stealth, and protection of electronic devices. Here, we proposed a facile method to prepare PTM materials with improved temperature stabilization performance by foaming a paraffin-based phase change composite with heat-sensitive thermal expansion microspheres (TEMs). For the phase change composite with high paraffin content immobilized by 20 wt% poly(styrene-b-(ethylene-co-butylene)-b-styrene, the addition of 10 wt% TEMs made the porosity up to 92.7% while owned a high energy storage density of 137.8 J/g. The low thermal conductivity (0.045 W m⁻¹K⁻¹) contributed by the high porosity and high phase change enthalpy enabled the resulting materials to exhibit significantly improved PTM performance. The possible applications of our resultant materials in thermal insulation fields such as thermotherapy, infrared shielding and building thermal comfort maintenance were demonstrated through simulation experiments. In view of the low cost, non-toxic raw materials, environmental-friendly and large-scale preparation process as well as the flexible, hydrophobic characteristics, our method and the resultant materials exhibited great potential in thermal insulation applications.
Passive warm‐keeping textiles could reduce carbon emissions by turning down indoor heating in winter. Polar bear hair exhibits a unique structure composed of a hollow core and an aligned porous shell, which extremely helps to resist heat transport. Great interest has arisen in the development of thermo‐insulating textiles with this biomimetic structure. In this work, cellular hollow fibers were made by a large‐scalable wet spinning‐foaming process. This efficient method achieved rapid formation of polar bear hair‐like fiber as well as facile turning properties of the fibers. The structure and properties of biomimetic fibers depended on the content of foaming agent. As‐prepared porous thermoplastic polyurethane (TPU)/polyacrylonitrile (PAN) composited fiber showed excellent ductility. The maximum tensile strength and breaking elongation was 4.31 MPa and 121%, respectively. The corresponding woven textile exhibited excellent thermal insulation properties even under deformation by compression or tension. The temperature difference across the thickness of textile was 17.9 and 34.9°C under a background temperature of 0 and 80°C, respectively. It may pave the way to fabricate new structure–function integrated fiber materials for warm‐keeping textiles.
The adaptability of biological organisms to the environment is reflected in many aspects, especially in their camouflage of appearance. Inspired by biological camouflage strategies, a number of adaptive camouflage materials and devices have been developed to protect soldiers, vehicles, or equipment in the military. Today, the need for adaptive camouflage extends into people’s lives, whose privacy and information security need to be protected in the era of big data. Herein, a review is provided on the recent advancements of adaptive camouflage from the perspective of biological organisms and bio-inspired materials. Firstly, according to different biological mechanisms, we review the typical organisms that use pigmentary color, structural color, and morphological variation for adaptive camouflage, as well as those combine these strategies. Then, we provide an up-to-date review on recent developments in bio-inspired adaptive camouflage materials and devices with an emphasis on visible, infrared, and multispectral camouflage. At last, this review concludes the challenges and prospects for the future development of adaptive camouflage materials. It is noteworthy that there is never the best camouflage. To counter advanced detection techniques, it is necessary to unremittingly develop new materials and technologies to meet the increasing need for adaptive camouflage.
Liquid absorption and recycling play a crucial role in many industrial and environmental applications, such as oil spill cleanup and recovery, hemostasis, astronauts' urine recycling, and so on. Although many liquid absorbing materials have been developed, it still remains a grand challenge to achieve both fast absorption and efficient recycling in a cost-effective and energy-saving manner, especially for viscous liquids such as crude oil. A smart polyurethane-based porous sponge with aligned channel structure is prepared by directional freezing. Compared to common sponges with random porous structure, the as-prepared smart sponge has larger liquid absorption speed due to its lower tortuosity and stronger capillary ("tortuosity effect"). More importantly, the absorbed liquid can be remotely squeezed out due to a thermally responsive shape memory effect when the sponge is heated up. Such smart sponges with well-defined porous structure and thermal responsive self-squeezing capability have great potential in efficient liquid absorption and recycling.
Replicating nacre’s multiscale architecture represents a promising approach to design artificial materials with outstanding rigidity and toughness. It is highly desirable yet challenging to incorporate self-healing and shape-programming capabilities into nacre-mimetic composites due to their rigidity and high filler content. Here, we report such a composite obtained by infiltrating a thermally switchable Diels-Alder network polymer into a lamellar scaffold of alumina. The chemical bond switchability and the physical confinement by the filler endows the composite with sufficient molecular mobility without compromising its thermal dimension stability. Consequently, our composite is capable of self-healing internal damages. Additionally, in contrast to the intractable planar shape of other artificial nacres, precise control of the polymer chain dynamics allows the shape of our composite to be programmed permanently via plasticity and temporarily via shape memory effect. Our approach paves a new way for designing durable multifunctional bioinspired structural materials.
Polymer‐based thermal interface materials (TIMs) with excellent thermal conductivity and electrical resistivity are in high demand in the electronics industry. In the past decade, thermally conductive fillers, such as boron nitride nanosheets (BNNS), were usually incorporated into the polymer‐based TIMs to improve their thermal conductivity for efficient heat management. However, the thermal performance of those composites means that they are still far from practical applications, mainly because of poor control over the 3D conductive network. In the present work, a high thermally conductive BNNS/epoxy composite is fabricated by building a nacre‐mimetic 3D conductive network within an epoxy resin matrix, realized by a unique bidirectional freezing technique. The as‐prepared composite exhibits a high thermal conductivity (6.07 W m−1 K−1) at 15 vol% BNNS loading, outstanding electrical resistivity, and thermal stability, making it attractive to electronic packaging applications. In addition, this research provides a promising strategy to achieve high thermal conductive polymer‐based TIMs by building efficient 3D conductive networks. An anisotropically high thermal conductive boron nitride/epoxy composite is fabricated by building a nacre‐mimetic 3D conductive network within an epoxy resin matrix, realized by a unique bidirectional freezing technique. With a high thermal conductivity (6.07 W m–1 K–1) at 15 vol% boron nitride loading, this composite may find wide applications including as a thermal interface material for advanced electronic packaging technology.
Closed-cell foams are widely applied as insulation and essential for the thermal management of protective garments for extreme environments. In this work, we develop and demonstrate a strategy for drastically reducing the thermal conductivity of a flexible, closed-cell polychloroprene foam to 0.031 ± 0.002 W m⁻¹ K⁻¹, approaching values of an air gap (0.027 W m⁻¹ K⁻¹) for an extended period of time (>10 hours), within a material capable of textile processing. Ultra-insulating neoprene materials are synthesized using high-pressure processing at 243 kPa in a high-molecular-weight gas environment, such as Ar, Kr, or Xe. A Fickian diffusion model describes both the mass infusion and thermal conductivity reduction of the foam as a function of processing time, predicting a 24–72 hour required exposure time for full charging of a 6 mm thick 5 cm diameter neoprene sample. These results enable waterproof textile insulation that approximates a wearable air gap. We demonstrate a wetsuit made of ultra-low thermally conductive neoprene capable of potentially extending dive times to 2–3 hours in water below 10 °C, compared with <1 hour for the state-of-the-art. This work introduces the prospect of effectively wearing a flexible air gap for thermal protection in harsh environments.
Maintaining human body temperature is one of the most basic needs for living, which often consumes a huge amount of energy to keep the ambient temperature constant. To expand the ambient temperature range while maintaining human thermal comfort, the concept of personal thermal management has been recently demonstrated in heating and cooling textiles separately through human body infrared radiation control. Realizing these two opposite functions within the same textile would represent an exciting scientific challenge and a significant technological advancement. We demonstrate a dual-mode textile that can perform both passive radiative heating and cooling using the same piece of textile without any energy input. The dual-mode textile is composed of a bilayer emitter embedded inside an infrared-transparent nanoporous polyethylene (nanoPE) layer. We demonstrate that the asymmetrical characteristics of both emissivity and nanoPE thickness can result in two different heat transfer coefficients and achieve heating when the low-emissivity layer is facing outside and cooling by wearing the textile inside out when the high-emissivity layer is facing outside. This can expand the thermal comfort zone by 6.5°C. Numerical fitting of the data further predicts 14.7°C of comfort zone expansion for dual-mode textiles with large emissivity contrast.
Space heating accounts for the largest energy end-use of buildings that imposes significant burden on the society. The energy wasted for heating the empty space of the entire building can be saved by passively heating the immediate environment around the human body. Here, we demonstrate a nanophotonic structure textile with tailored infrared (IR) property for passive personal heating using nanoporous metallized polyethylene. By constructing an IR-reflective layer on an IR-transparent layer with embedded nanopores, the nanoporous metallized polyethylene textile achieves a minimal IR emissivity (10.1%) on the outer surface that effectively suppresses heat radiation loss without sacrificing wearing comfort. This enables 7.1 °C decrease of the set-point compared to normal textile, greatly outperforming other radiative heating textiles by more than 3 °C. This large set-point expansion can save more than 35% of building heating energy in a cost-effective way, and ultimately contribute to the relief of global energy and climate issues.
Climate change is expected to increase the frequency and duration of long-distance swims by polar bears (Ursus maritimus). The energetic costs of such swims are assumed to be large, however, no estimates of metabolic costs of swimming for polar bears are available. Here, I use data on internal body temperature and external ambient temperature for two swimming polar bears, combined with mathematical modeling of heat production and of heat conduction to the surrounding water, to estimate the metabolic rate of swimming. Using this metabolic rate, I then examine the relative heat production and heat loss for bears of a range of sizes and body conditions. I calculated overall mean metabolic rate for a swimming bear to be 2.75 ml O2 g⁻¹ h⁻¹, which is generally higher than metabolic rates previously reported for walking polar bears. When compared at the same movement rate, the cost of transport for swimming was estimated to be approximately 5× that of walking. I further show that for small bears (less than approx. 145 cm body length or 90 kg) and bears in poor body condition, heat loss while swimming in cold Arctic waters should exceed heat production, and long swims should therefore not be thermodynamically sustainable. These results support previous claims that increasing frequency and duration of long-distance swims in polar bears is energetically stressful. Energetic and thermodynamic costs of long swims may be further exacerbated by recent declines in body condition that have been documented due to climate warming.
Materials combining lightweight, robust mechanical performances, and multifunctionality are highly desirable for engineering applications. Graphene aerogels have emerged as attractive candidates. Despite recent progresses, the bottleneck remains how to simultaneously achieve both strength and resilience. While multiscale architecture designs may offer a possible route, the difficulty lies in the lack of design guidelines and how to experimentally achieve the necessary structure control over multiple length scales. The latter is even more challenging when manufacturing scalability is taken into account. The Thalia dealbata stem is a naturally porous material that is lightweight, strong, and resilient, owing to its architecture with three-dimensional (3D) interconnected lamellar layers. Inspired by such, we assemble graphene oxide (GO) sheets into a similar architecture using a bidirectional freezing technique. Subsequent freeze-drying and thermal reduction results in graphene aerogels with highly tunable 3D architectures, consequently an unusual combination of strength and resilience. With their additional electrical conductivity, these graphene aerogels are potentially useful for mechanically switchable electronics. Beyond such, our study establishes bidirectional freezing as a general method to achieve multiscale architectural control in a scalable manner that can be extended to many other material systems.
Hairs of a polar bear are of superior properties such as the excellent
thermal protection. The polar bears can perennially live in an extremely cold
environment and can maintain body temperature at around 37 °C. Why do polar
bears can resist such cold environment? Its membrane-pore structure plays an
important role. In the previous work, we established a 1-D fractional heat
conduction equation to reveal the hidden mechanism for the hairs. In this
paper, we further discuss solutions and parameters of the equation
established and analyze heat conduction in polar bear hairs.
Motivated by diving semiaquatic mammals, we investigate the mechanism of dynamic air entrainment in hairy surfaces submerged in liquid. Hairy surfaces are cast out of polydimethylsiloxane elastomer and plunged into a fluid bath at different velocities. Experimentally, we find that the amount of air entrained is greater than what is expected for smooth surfaces. Theoretically, we show that the hairy surface can be considered as a porous medium and we describe the air entrainment via a competition between the hydrostatic forcing and the viscous resistance in the pores. A phase diagram that includes data from our experiments and biological data from diving semiaquatic mammals is included to place the model system in a biological context and predict the regime for which the animal is protected by a plastron of air.
Unlike many other mammals spending a considerable amount of time in water, river otters (Lutra canadensis (Schreber, 1777)) do not have a thick layer of body fat. Instead, they have a very densely packed layer of thin underhairs. The structure of river otter hair was examined by scanning electron microscopy and polarizing light microscopy. Guard hairs were hollow and became thicker distally and then tapered to a point and had different cuticle scales in proximal and distal regions. The cuticle of the thin underhairs had a striking pattern of sharply sculpted fins with deep grooves between them; usually there were four fins at each level, rotated 45° with respect to those at an adjacent level. Underhairs varied in diameter and the scales were sometimes petal-shaped. Polarizing light microscopy images showed interlocking arrangements of the underhairs that help to impede the penetration of water. Also, these images showed that the grooves between fins or petals of underhairs entrap air bubbles. The structure of the hairs allows them to interact loosely with each other, despite variations in size and structure. Furthermore, the nature of the interactions between the fins and depressions allows space between the hairs that can trap air bubbles to increase the thermal insulation of the otter's coat.
The purpose of this study was to compare the thermal resistance of a wetsuit fabricated from aerogel-syntactic foam hybrid insulation developed by Bardy et al [1] to a foam neoprene wetsuit. The thermal resistance of the hybrid wetsuit and a foam neoprene wetsuit was measured on a human test subject in water at 0.25 MPa (15.25 msw) of hyperbaric pressure. Measurements showed that although certain body regions of the hybrid wetsuit had a higher thermal resistance than foam neoprene, the overall thermal resistance of the hybrid wetsuit was 41% less than a foam neoprene wetsuit, and 51–88% less than predicted values. This was postulated, based on sample testing in water, to be due, in part, to increased heat flow through the hybrid insulation from water filled surface depressions at higher pressures. Other factors may have included water flow over the skin and the presence of thermal bridges in the insulation. Due to a smooth surface and tighter fit, the measured thermal resistance of the foam neoprene wetsuit was within 2–23% of the values predicted using data from Bardy et al [2]. It was concluded that unless the surface depressions can be eliminated, and alternative methods for a tighter fit achieved, foam neoprene provides more thermal protection.
The purpose of this study was to present a new underwater thermal insulation designed for flexibility and high thermal resistance. The insulation was a hybrid composite of two constituents: syntactic foam and an insulating aerogel blanket. Methods for treating and combining the constituents into a hybrid insulation of several designs are presented. A final configuration was selected based on high thermal resistance and was tested for thermal resistance and compressive strain to a pressure of 1.2 MPa (107 msw, meters of sea water) for five continuous pressure cycles. The thermal resistance and compressive strain results were compared to foam neoprene and underwater pipeline insulation. It was found that the hybrid insulation has a thermal resistance significantly higher than both foam neoprene and underwater pipeline insulation at atmospheric and elevated hydrostatic pressures (1.2 MPa). The total thermal resistance of the hybrid insulation decreased 32% at 1.2 MPa and returned to its initial value upon decompression. It was concluded that the hybrid insulation, with modifications, could be used for wetsuit construction, shallow underwater pipeline insulation, or any underwater application where high thermal resistance, flexibility, and resistance to compression are desired.
The purpose of this study was to show that the thermal properties of foam neoprene under hydrostatic pressure cannot be predicted by theoretical means, and that uni-axial pressure cannot simulate hydrostatic compression. The thermal conductivity and compressive strain of foam neoprene were measured under hydrostatic pressure. In parallel, uni-axial compressive strain data were collected. The experimental set-up and data were put into perspective with past published studies. It was shown that uni-axial compression yielded strains 20–25% greater than did hydrostatic compression. This suggests the need for direct hydrostatic pressure measurement. For comparison to hydrostatic experimental data, a series of thermal conductivity theories of two phase composites based on particulate phase geometry were utilized. Due to their dependence on the porosity and constituent thermal conductivities, a model to predict porosity under hydrostatic pressure was used and an empirical correlation was derived to calculate the thermal conductivity of pure neoprene rubber from experimental data. It was shown that, although some agreement between experimental data and thermal conductivity theories was present, no particular theory can be used because they all fail to model the complex structure of the pores. It was therefore concluded that an experimental programme, such as reported here, is necessary for direct measurement.
A summary of existing passive solar-heat conversion panels provides the basis for a definition of an ideal passive solar-heat converter. Evidence for the existence of a biological greenhouse effect in certain homopolar homeothermic species is reviewed. The thermal and optical properties of homeothermic pelts, in particular those of the polar bear, are described, and a qualitative optical model of the polar bear pelt is proposed. The effectiveness of polar bear and seal pelts as solar-heat converters is discussed, and comparison is made with the ideal converter.
Solar thermal collectors used at present consist of rigid and heavy materials, which are the reasons for their immobility. Based on the solar function of polar bear fur and skin, new collector systems are in development, which are flexible and mobile. The developed transparent heat insulation material consists of a spacer textile based on translucent polymer fibres coated with transparent silicone rubber. For incident light of the visible spectrum the system is translucent, but impermeable for ultraviolet radiation. Owing to its structure it shows a reduced heat loss by convection. Heat loss by the emission of long-wave radiation can be prevented by a suitable low-emission coating. Suitable treatment of the silicone surface protects it against soiling. In combination with further insulation materials and flow systems, complete flexible solar collector systems are in development.
Thermoregulating textiles (or protective clothing) are highly demanded for both human health and labor productivity especially in hot working environments. It is challenging to balance wearability and thermal insulating property as they usually demand for opposite porosity. Here, learning from the porous structure of polar bear hair, we report a polyimide aerogel fiber obtained by a freeze-spinning technique. A textile woven with such polyimide fiber is thermally insulating, strong and highly stretchable, fire-retardant (or self-extinguishing), and temperature-resistant. Additionally, it can be readily incorporated with other functions such as acid alkali resistance and thermoregulation by surface modification and infiltration of phase change material. All these properties indicate its potential in protective clothing in hot environments. With the versatility and scalability, our approach paves a new way for fabricating smart textiles with well-defined microstructure and multifunctionality by learning from nature.
Their hollow, lightweight, and non-wettable hair helps polor bears resist their extremely cold environment. Inspired by the microstructure of polar bear hair, we fabricated the carbon tube aerogel (CTA), which shows all merits of polar bear hair, such as being lightweight, waterproof, and thermally insulating. Briefly, the CTA composed of hollow carbon tube fibers is lightweight with the lowest density of only 8 kg/m3, and is also waterproof with a contact angle of 146°. The lowest thermal conductivity of the CTA is only 23 mW m−1 K−1. Remarkably, the bioinspired CTA materials show better performance than the polar bear hair. The interconnected network structure of the CTA is endowed with super-elasticity and fatigue resistance, which is confirmed by the rebounding speed of 1,434 mm/s and structural integrity after more than 10,000,000 cyclic compressions at 30% strain. The bioinspired design of macroscopic synthesis of CTA opens a window for designing high-performance material.
A cloth that adapts to the heat
Textiles trap infrared radiation, which helps keep us warm in cold weather. Of course, in hot weather, this is less desirable. Zhang et al. constructed an infrared-adaptive textile composed of polymer fibers coated with carbon nanotubes. The yarn itself expanded and collapsed based on heat and humidity, which changed the spacing of the fibers. Wider fiber spacing allowed the textile to breathe but also altered the infrared emissivity of the textile. This allowed for better heat exchange under hot and wet conditions. The self-adjusting emissivity of the textile could help toward wearable thermal-management attire.
Science , this issue p. 619
Infrared (IR) stealth is essential not only in high technology and modern military but also in fundamental material science. However, effectively hiding targets and rendering them invisible to thermal infrared detectors have been great challenges in past decades. Herein, flexible, foldable, and robust Kevlar nanofiber aerogel (KNA) films with high porosity and specific surface area were fabricated first. The KNA films display excellent thermal insulation performance and can be employed to incorporate with phase-change materials (PCMs), such as polyethylene glycol, to fabricate KNA/PCM composite films. The KNA/PCM films with high thermal management capability and infrared emissivity comparable to that of various backgrounds demonstrate high performance in IR stealth in outdoor environments with solar illumination variations. To further realize hiding hot targets from IR detection, combined structures constituted of thermal insulation layers (KNA films) and ultralow IR transmittance layers (KNA/PCM) are proposed. A hot target covered with this combined structure becomes completely invisible in infrared images. Such KNA/PCM films and KNA-KNA/PCM combined structures hold great promise for broad applications in infrared thermal stealth.
High-performance thermally insulating materials is highly desirable for many applications in which heat transfer should be strictly restricted. Traditional organic or inorganic insulation materials are limited by either poor thermal stability or mechanical brittleness. Here, SiO2 nanoparticles crosslinked polyimide aerogels synthesized by one-pot freeze-drying are presented, which show excellent mechanical properties and super-insulating behavior in a wide temperature range. The highly porous structure of the aerogel and nanosized components benefit the significant reduction of thermal conductivity through inhibiting gas conduction and imparting interfacial thermal resistance, respectively. The PI/SiO2 composite aerogel with a density of 0.07 mg cm⁻³ can achieve a low thermal conductivity of 21.8 mW m⁻¹ K⁻¹, which is lower than the most common super-insulating criterion (25 mW m⁻¹ K⁻¹). More importantly, the PI/SiO2 aerogel exhibits good thermal insulation performance at elevated temperatures, with a thermal conductivity still lower than 35 mW m⁻¹ K⁻¹ even at 300 °C. Therefore, the mechanically strong and super-insulating PI/SiO2 composite aerogels are promising candidates for practical thermal insulation applications.
The requirement of energy efficiency demands materials with superior thermal insulation properties. Inorganic aerogels are excellent thermal insulators but are difficult to produce on a large-scale, are mechanically brittle, and their structural properties depend strongly on their density. Here, we report the scalable generation of low-density, hierarchically porous, polypropylene (PP) foams using industrial-scale foam processing equipment, with thermal conductivity lower than commercially available high performance thermal insulators such as superinsulating Styrofoam. The reduction in thermal conductivity is attributed to the restriction of air flow caused by the porous nanostructure in the cell walls of the foam. In contrast to inorganic aerogels, the mechanical properties of the foams are less sensitive to density suggesting efficient load transfer through the skeletal structure. The scalable fabrication of hierarchically porous polymer foams opens up new perspectives for the scalable design and development of novel superinsulating materials.
Wearable devices and systems demand multifunctional units with intelligent and integrative functions. Smart fibers with response to external stimuli, such as electrical, thermal, and photonic signals, etc., as well as offering energy storage/conversion are essential units for wearable electronics, but still remain great challenges. Herein, flexible, strong, and self‐cleaning graphene‐aerogel composite fibers, with tunable functions of thermal conversion and storage under multistimuli, are fabricated. The fibers made from porous graphene aerogel/organic phase‐change materials coated with hydrophobic fluorocarbon resin render a wide range of phase transition temperature and enthalpy (0–186 J g−1). The strong and compliant fibers are twisted into yarn and woven into fabrics, showing a self‐clean superhydrophobic surface and excellent multiple responsive properties to external stimuli (electron/photon/thermal) together with reversible energy storage and conversion. Such aerogel‐directed smart fibers promise for broad applications in the next‐generation of wearable systems. A variety of multiresponsive smart fibers with a wide range of tunable phase transition temperatures and enthalpy are produced through impregnation of different types of organic phase‐change materials into graphene aerogel fibers and finished by coating a fluorocarbon resin layer, showing a self‐clean superhydrophobic surface and excellent multiple‐responsive properties to external stimuli (electron/photon/thermal) together with reversible energy storage and conversion.
Animals living in the extremely cold environment, such as polar bears, have shown amazing capability to keep warm, benefiting from their hollow hairs. Mimicking such a strategy in synthetic fibers would stimulate smart textiles for efficient personal thermal management, which plays an important role in preventing heat loss and improving efficiency in house warming energy consumption. Here, a “freeze-spinning” technique is used to realize continuous and large-scale fabrication of fibers with aligned porous structure, mimicking polar bear hairs, which is difficult to achieve by other methods. A textile woven with such biomimetic fibers shows an excellent thermal insulation property as well as good breathability and wearability. In addition to passively insulating heat loss, the textile can also function as a wearable heater, when doped with electroheating materials such as carbon nanotubes, to induce fast thermal response and uniform electroheating while maintaining its soft and porous nature for comfortable wearing.
Through designing hierarchical structures, particularly optimizing the chemical and architectural interactions at its inorganic/organic interface, nacre has achieved an excellent combination of contradictory mechanical properties such as strength and toughness, which is highly demanded yet difficult to achieve by most synthetic materials. Most techniques applied to develop nacre-mimetic composites have been focused on mimicking the 'brick-and-mortar' structure, but the interfacial architectural features, especially the asperities and mineral bridges of 'bricks', have been rarely concerned, which are of equal importance for enhancing mechanical properties of nacre. Here, we used a modified bidirectional freezing method followed by uniaxial pressing and chemical reduction to assemble a nacre-mimetic graphene/poly(vinyl alcohol) composite film, with both asperities and bridges introduced in addition to the lamellar layers to mimic the interfacial architectural interactions found in nacre. As such, we have developed a composite film which is not only strong (up to ~150.9 MPa), but also tough (up to ~8.50 MJ/m(3)), and highly stretchable (up to ~10.44%), difficult to obtain by other methods. This was all achieved by only interfacial architectural engineering within the traditional 'brick-and-mortar' structure, without introducing a third component or employing chemical cross-linker as in some other nacre-mimetic systems. More importantly, we believe that the design principles and processing strategies reported here can also be applied to other material systems to develop strong and stretchable materials.
Bioinspired materials capable of driving liquid in a directional manner have wide potential applications in many chemical engineering processes, such as heat transfer, separation, microfluidics and so on. Numerous natural materials and systems such as spider silk, cactus, shorebirds, desert beetles, butterfly wing, and Nepenthes alata have been serving as a rich source of inspirations in the area. During the last decades, great efforts have been devoted to design bioinspired smart materials for directional liquid transport. In this review, we will start from introducing several natural materials and systems with surface structural features contributing for their directional liquid transport property, followed by the basic concepts and theories about surface wettability, droplet motion and driving forces with different structural features. Then, we will summarize some typical applications of such bioinspired smart materials in industrial process and chemical engineering, particularly in heat transfer, separation, microfluidic systems. In the end, future perspectives of such bioinspired smart materials for directional liquid transport will be discussed.
Thermal management through personal heating and cooling is a strategy by which to expand indoor temperature setpoint range for large energy saving. We show that nanoporous polyethylene (nanoPE) is transparent to mid-infrared human body radiation but opaque to visible light because of the pore size distribution (50 to 1000 nanometers). We processed the material to develop a textile that promotes effective radiative cooling while still having sufficient air permeability, water-wicking rate, and mechanical strength for wearability. We developed a device to simulate skin temperature that shows temperatures 2.7° and 2.0°C lower when covered with nanoPE cloth and with processed nanoPE cloth, respectively, than when covered with cotton. Our processed nanoPE is an effective and scalable textile for personal thermal management.
Solar thermal technology is a promising key strategy for future renewable energy production. Various concepts exist that use solar collectors and heat mirrors, built from rigid materials, to gather thermal energy from solar radiation. A new approach is the utilization of textile materials to build solar thermal collector systems with flexible material properties, lightweight design and improved material-efficiency. A solar collector, based on a multi-layer arrangement of technical textiles and foil membranes, has been realized by the ITV Denkendorf (Institute of Textile Technology and Process Engineering Denkendorf). The proposed collector system allows transparent insulation in textile-based buildings while gathering thermal energy simultaneously. The system is inspired by the transparent insulation and heat harvesting strategies of polar bear fur and can inform textile-based envelopes of future transparent buildings. In this study, different material arrangements and the influence of different parameters on the temperature distribution along the collector were tested. Air temperatures up to 150 °C (302 °F) could be generated inside the collector system. Furthermore, a closer look at the polar bear fur and other related principles in nature delivered additional concepts for energetic optimization.
Inspired by the surface geometry and composition of lotus leaf with self-cleaning behavior, in this work, a composite TiO2@fabric was prepared via a facile strategy for preparing marigold flower-like hierarchical TiO2 particles through a one-pot hydrothermal reaction on cotton fabric surface. In addition, robust superhydrophobic TiO2@fabric were further constructed by fluoroalkylsilane modification as a versatile platform for self-cleaning, and oil-water separation. The results showed TiO2 particles were distributed uniformly on the fibre surface with a high coating density. In comparison with hydrophobic cotton fabric, the TiO2@fabric exhibited a highly superhydrophobic activity with a contact angle of ~160o and a sliding angle lower than 10o. The robust superhydrophobic fabric had high stability against repeated abrasion without apparent reduction of contact angle. The as-prepared composite TiO2@fabric demonstrated good anti-UV ability. Moreover, the composite fabric demonstrated high efficient oil-water separation due to its highly extreme wettability contrast (superhydrophobicity/superoleophilicity). We expect that this facile process can be readily and widely adopted for the design of multifunctional fabrics for excellent anti-UV, effective self-cleaning, efficient oil-water separation, and microfluidic management applications.
High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m(-1) K(-1), which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.
In the development of next-generation materials with enhanced thermal properties, biological systems in nature provide many examples that have exceptional structural designs and unparalleled performance in their thermal or nonthermal functions. Bioinspired engineering thus offers great promise in the synthesis and fabrication of thermal materials that are difficult to engineer through conventional approaches. In this review, recent progress in the emerging area of bioinspired advanced materials for thermal science and technology is summarized. State-of-the-art developments of bioinspired thermal-management materials, including materials for efficient thermal insulation and heat transfer, and bioinspired materials for thermal/infrared detection, are highlighted. The dynamic balance of bioinspiration and practical engineering, the correlation of inspiration approaches with the targeted applications, and the coexistence of molecule-based inspiration and structure-based inspiration are discussed in the overview of the development. The long-term outlook and short-term focus of this critical area of advanced materials engineering are also presented.
The surprising properties of biomaterials are the results of billions of years of evolution. Generally, biomaterials are assembled under mild conditions with very limited supply of constituents available for living organism, and their amazing properties largely result from the sophisticated hierarchical structures. Following the biomimetic principles to prepare manmade materials has drawn great research interests in materials science and engineering. In this review, we summarize the recent progress in fabricating bioinspired materials with the emphasis on mimicking the structure from one to three dimensions. Selected examples are described with a focus on the relationship between the structural characters and the corresponding functions. For one-dimensional materials, spider fibers, polar bear hair, multichannel plant roots and so on have been involved. Natural structure color and color shifting surfaces, and the antifouling, antireflective coatings of biomaterials are chosen as the typical examples of the two-dimensional biomimicking. The outstanding protection performance, and the stimuli responsive and self-healing functions of biomaterials based on the sophisticated hierarchical bulk structures are the emphases of the three-dimensional mimicking. Finally, a summary and outlook are given.
High-performance thermal insulating materials are desired especially from the viewpoint of saving energy for a sustainable society. Aerogel is the long-awaited material for extended applications due to its excellent thermal insulating ability. These materials are, however, seriously fragile against even small mechanical stress due to their low density, and their poor mechanical properties inhibit their practical use as superinsulators. In this paper, we report relationships between the thermal conductivity, pore size and mechanical properties of organic–inorganic hybrid polymethylsilsesquioxane (PMSQ) aerogels with improved mechanical properties and controllable pore sizes from 50 nm to 3 μm. The dependency of thermal conductivity on gas pressure and pore properties can be well explained by the thermal conduction theory of porous materials. These PMSQ aerogels show improved mechanical properties due to their elastic networks, which enable easier handling compared to conventional aerogels and facile production by simple ambient pressure drying. An aerogel-like “xerogel” monolithic panel has been successfully prepared via ambient pressure drying, which shows a low thermal conductivity (0.015 W m−1 K−1) comparable with those of the corresponding PMSQ aerogel and conventional silica aerogels. These results would open the gate for practical applications of these porous materials.
Aerogel is a kind of synthetic porous material, in which the liquid component of the gel is replaced with a gas. Aerogel has specific acoustic properties and remarkably lower thermal conductivity (≈0.013 W/m K) than the other commercial insulating materials. It also has superior physical and chemical characteristics like the translucent structure. Therefore, it is considered as one of the most promising thermal insulating materials for building applications. Besides its applications in residential and industrial buildings, aerogel has a great deal of application areas such as spacecrafts, skyscrapers, automobiles, electronic devices, clothing etc. Although current cost of aerogel still remains higher compared to the conventional insulation materials, intensive efforts are made to reduce its manufacturing cost and hence enable it to become widespread all over the world. In this study, a comprehensive review on aerogel and its utilization in buildings are presented. Thermal insulation materials based on aerogel are illustrated with various applications. Economic analysis and future potential of aerogel are also considered in the study.
This review is focused on describing the intimate link which exists between aerogels and thermal superinsulation. For long, this applied field has been considered as the most promising potential market for these nanomaterials. Today, there are several indicators suggesting that this old vision is likely to become reality in the near future. Based on recent developments in the field, we are confident that aerogels still offer the greatest potential for non-evacuated superinsulation systems and consequently must be considered as an amazing opportunity for sustainable development. The practical realization of such products however is time-consuming and a significant amount of R&D activities are still necessary to yield improved aerogel-based insulation products for mass markets.
In order to obtain foams possessing flexibility and at the same time heat insulation under high hydrostatic pressure, composite foams with spherical rigid foams filled in flexible rubber foam at certain intervals were prepared and their thermal conductivity and flexural rigidity were studied. The following points were found: (1) With a unit model having a spherical rigid foam in the middle, the thermal conduction of a composite foam was analyzed under the conditions of steady one-dimensional heat flow. Theoretical equations giving overall coefficients of heat transmission under atmospheric and hydrostatic pressures were obtained, and the adequacy of these theoretical equations was confirmed by the measurement of overall coefficients of heat transmission of composite foams in an apparatus so constructed as to allow heat conduction experiments under pressures ranging from atmospheric to the hydrostatic pressure corresponding to 100-m depth in water. (2) The effect of the filled spherical rigid foams on heat insulation is notable under hydrostatic pressures corresponding to a 20-m depth or more in water. Under the hydrostatic pressure corresponding to a 100-m depth in water, the coefficient of heat insulation of the most closely filled composite foam used in the experiment was approximately 35% larger than that of the unfilled foam, while the theoretical most closely filled composite foam gives an approximately 110% increase. (3) Under the hydrostatic pressure corresponding to a 100-m depth in water, the flexural rigidity of the most closely filled composite foam used in the experiment was approximately one half that of an unfilled foam of the same heat insulating property.
A novel superhydrophilic and underwater superoleophobic polyacrylamide (PAM) hydrogel-coated mesh is successfully fabricated in an oil/water/solid three-phase system. Compared to traditional oleophilic materials, the as-prepared hydrogel-coated meshes can selectively separate water from oil/water mixtures with the advantages of high efficiency, resistance to oil fouling, and easy recyclability.
Silk fibroin, derived from Bombyx mori cocoons, is a widely used and studied protein polymer for biomaterial applications. Silk fibroin has remarkable mechanical properties when formed into different materials, demonstrates biocompatibility, has controllable degradation rates from hours to years and can be chemically modified to alter surface properties or to immobilize growth factors. A variety of aqueous or organic solvent-processing methods can be used to generate silk biomaterials for a range of applications. In this protocol, we include methods to extract silk from B. mori cocoons to fabricate hydrogels, tubes, sponges, composites, fibers, microspheres and thin films. These materials can be used directly as biomaterials for implants, as scaffolding in tissue engineering and in vitro disease models, as well as for drug delivery.