Absorption Performance Research Articles

Infrared Ultralow‐Emissivity Polymeric Metafabric Conductors Enabling Remarkable Electromagnetic and Thermal Management

AbstractInfrared ultralow‐emissivity fabric has garnered significant interest for applications in infrared stealth and personal thermal management. However, reconciling the competing demands of low emissivity, breathability, and mechanical strength poses a formidable challenge. Here, an air‐permeable polymeric metafabric distinguished by a unique non‐through‐hole structure is presented. This design is achieved through the electroless plating of silver nanoparticles onto commercially available nylon fabric, supplemented by an intermediate layer of hot‐processed nylon porous mesh. This metafabric demonstrates an ultralow emissivity of 0.044, an exceptional electrical conductivity of 51 315 S m−1, an impressive electromagnetic interference shielding efficiency of 78 dB, and a high tensile strength of 110 MPa. The emissivity, conductivity, and strength of the metafabric are among the highest values reported for infrared low‐emissivity fabrics. The metafabric also exhibits an air permeability that conforms to Grade 2 of international standards. The metafabric facilitates personal precision heating across diverse environments through its integrated capabilities of passive radiative and active solar/Joule heating. Additionally, the metafabric displays antibacterial properties, flame retardancy, sweat absorption, quick‐drying, and washability performance, thereby significantly enhancing its wearability. This high‐performance, multifunctional, infrared ultralow‐emissivity polymeric metafabric holds great promise for applications in infrared camouflage, electromagnetic protection, and personal thermal management.

Improvement in Compatibility and Drug Release Performance of Hot-Melt Pressure-Sensitive Adhesives by Physical Blending Technique

Background: Hot-melt Pressure-sensitive Adhesives (HMPSA) are eco-friendly pressuresensitive adhesives, with the potential of being used as substrates for transdermal patches. However, due to the low hydrophilicity of HMPSA, the application is limited in the field of Traditional Chinese Medicine (TCM) plasters. Methods: Three modified HMPSA were prepared with acrylic resin EPO, acrylic resin RL100, and Polyvinylpyrrolidone (PVP) as the modifying materials. The physical compatibility between HMPSA and the modifying materials was investigated through in vitro release performance, viscosity, softening point, cohesion, and fluidity, so as to determine the most effective modifying material. The impact of the modified HMPSA on the release properties of different TCM ingredients was elucidated by the performance of water absorption and contact angle behavior. Results: With the addition of the modifying materials, both the viscosity and the softening point of HMPSA were improved, with the flowability reduced and the cohesion maintained. The morphological and structural changes reflected the physical compatibility between HMPSA and the three modifying materials. According to the results of in vitro release experiments, PVP effectively improved the release performance of paeoniflorin, ephedrine hydrochloride, and cinnamaldehyde in HMPSA, with no significant impact on the release performance of eugenol. The changes in the drug release performance of HMPSA may be attributed to the improved hydrophilicity of HMPSA after physical modification. Conclusion: The compatibility and the drug release performance of HMPSA were effectively enhanced after the addition of the modifying materials by the physical blending technique. Among the three modifying materials, PVP has been found to be an ideal modifying material for HMPSA in the field of TCM plasters due to its effects on drug release performance.

Bamboo-Inspired Hierarchically Hollow Aerogel MXene Fibers with Ultrafast Ionic Channels and Multiple Electromagnetic Wave Attenuation Routes Toward High-Performance Supercapacitors and Microwave Absorption.

2D materials feature large specific surface areas and abundant active sites, showing great potential in energy storage and conversion. However, the dense, stacked structure severely restricts its practical application. Inspired by the structure of bamboo in nature, hollow interior and porous exterior wall, hollow MXene aerogel fiber (HA-Ti3C2TX fiber) is proposed. Owing to continuous porous microstructure and optimized hollow cavity, this fiber possesses large accessible area to ions and abundant structural defects, leading to a fast charge transfer kinetics and high faradic activity. Consequently, the HA-Ti3C2TX fiber exhibits exceptional gravimetric capacitance of 355 F g-1. Besides, the solid-state asymmetric fiber-shaped supercapacitors (FSCs) display a high capacitance of 276 F g-1 and energy density of 9.58 Wh kg-1. Additionally, the HA-Ti3C2TX fiber delivers outstanding electromagnetic wave (EMW) absorption performance with a minimum reflection loss of -52.39 dB and the effective absorption bandwidth up to 4.6 GHz, which is attributed to multiple reflection paths, strong dielectric loss from this hollow and porous structure. This novel design of hollow fiber provides a new reference for the construction of advanced fibers for energy storage and EMW absorption materials.

Monolayer Interfacial Assembly toward Two‐Dimensional Mesoporous Heterostructure for Boosting Wave Absorption

AbstractMicrowave absorption materials play a key role in various fields, including military stealth, human safety protection, and so on. Construction of 2D mesoporous heterostructures is an attractive approach to enhance wave‐absorbing ability, while it is still a great challenge. Herein, 2D mesoporous carbon‐MXene‐carbon heterostructures (MCMCH) with channels parallel to surface are successfully prepared via a monolayer interfacial assembly strategy. Through the precise adjustment and polymerization, cylindrical micelles orderly monolayered assemble on both surfaces of 2D MXene nanosheets, resulting in 2D switch‐like polydopamine‐MXene‐polydopamine nanosheets, and 2D MCMCH are finally generated by further calcination. Due to the excellent dielectric polarization relaxation and conductive loss, MCMCH achieves the strongest reflection loss of −54.2 dB at a thickness of only 1.5 mm. The presence of mesochannels not only introduces air with a low permittivity for optimal impedance matching, but also further extends the attenuation path of the incident electromagnetic wave. The maximum radar cross‐section reduction of 26.9 dB m2 is achieved for the MCMCH compared to the perfect electric conductor. This work provides a reference for surface engineering based on 2D mesoporous heterostructures to enhance the microwave absorption performance.

Underwater sound absorption characteristics of the acoustic metamaterials with multiple coupling substructure

The lateral plates are usually used in the field of structural design of acoustic metamaterials (AMs), which can realize the control of AMs on sound waves. Presently, researches on the application of AMs with lateral plates mainly focus on the regulation of sound waves in air media, and rarely involve the research on their underwater acoustic properties. Therefore, a composite acoustic structure is designed by inserting regularly distributed lateral plates into the viscoelastic rubber, and then, the AMs with multiple coupling substructure (AMs-MCS) can be obtained through combining the local resonance structure and functional gradient structure. Based on underwater acoustic calculation model for the functional gradient acoustic structure established by grade finite element method (G-FEM), the underwater sound absorption characteristics of the AMs-MCS are studied, and the influence of each substructure on the acoustic performance of the AMs-MCS is explored. Numerical results indicate inserting gradient-distributed multiple lateral plates inside the homogeneous acoustic structure can improve the sound absorption performance of the acoustic structure in the mid-and high-frequency ranges and the sound absorption frequency band of the acoustic structure can be effectively broadened. Moreover, the sound absorption coefficient of the AMs-MCS is greater than 0.8 at 500Hz-10 kHz, and the average sound absorption coefficient reaches 0.893, thus achieving low-frequency and broadband sound absorption performance.

Evaluation of Impact Energy Absorption by Natural Fiber Composites in Motorcycle Helmets

In response to the growing concerns regarding motorcyclists’ safety and advancements in the motorcycle industry, this study investigated the potential of natural fibers as a sustainable approach for enhancing helmet protection, thus replacing the traditional use of expanded polystyrene. Utilizing statistical tools such as the Shapiro–Wilk test, Chauvenet’s criterion, and the interquartile range, we compared the impact energy absorption of composites reinforced with natural fibers, including sugarcane bagasse, coconut, and sisal, added to expanded polyurethane prototypes. The results, evaluated through confidence intervals, indicated that composites reinforced with 5% sugarcane bagasse, 5% and 10% coconut, and 10% and 15% sisal exhibited significantly superior impact absorption performance compared to pure expanded polyurethane. Composites with agave sisalana fibers exhibited low variability and reliable performance, with the 10% concentration showing the best results. Sugarcane bagasse fiber demonstrated strong stability, especially at a 5% concentration. Coconut fiber performed well at both 5% and 10% concentrations but showed the greatest variability among the fibers tested. These findings underscore the potential of natural fibers in enhancing helmet safety and suggest promising directions for future research into the ideal composite materials for motorcycle helmets, an inquiry that is currently underway.

Optimization of parallel coiled cavities of different depths in microperforated panel sound absorbers

This paper presents a microperforated panel (MPP) sound absorber with parallel coiled-up-cavities of different-depths (PCD) and the corresponding optimization on their cavities. In this study, an analytical model is initially proposed for estimating the cavity depths of the PCD-MPP absorber upon normal incidence absorption coefficient evaluation at given resonance frequencies. Cavity effective depths and normal incidence absorption coefficient are evaluated after coiling up cavities for a compact structure. Numerical simulations with the finite element method and experiments are conducted for validations. Subsequently, a design process is suggested on the basis of the proposed model for sound absorption optimization. Results show that, absorption coefficient from the proposed analytical model agrees well with finite element simulations and experiments. It is also shown that, for the effective depth evaluation of the coiled-up cavities of PCD-MPP absorbers, the diagonal lines of subchannels of coiled-up cavities with a coiled-up angle of 180° can accurately represent the effective depths, while the combination of centerlines of subchannels and quarter arc inside the coiled-up area is more suitable for those with a coiled-up angle of 90°. Optimization investigation shows that, PCD-MPP absorbers can have high absorption performance with the averaged and maximum absorption coefficient of 0.91 and 0.98 within the target bandwidth of 400–1600 Hz, where the absorber thickness can stay below 65 mm. This work can provide valuable guidelines for the design of sound absorbers for broadband absorption.

Ordered Mesoporous Multishell Composite Microspheres with Controlled Loading of Magnetic Particles for Enhanced Electromagnetic Wave Absorption Performance

Ordered Mesoporous Multishell Composite Microspheres with Controlled Loading of Magnetic Particles for Enhanced Electromagnetic Wave Absorption Performance

Dual-cell composite acoustic covering layer with broadband absorption characteristics

A dual-cell combined acoustic covering layer has been designed and optimized, consisting of a viscoelastic rubber matrix, metal vibrators, cavities, and a steel backing. By parallel coupling the sound absorption characteristics of each cell across different frequency bands, the structural size parameters were optimized using finite element methods and genetic algorithms. The optimized covering layer exhibits an average sound absorption coefficient exceeding 0.98 in the range of 561 Hz to 15000 Hz. When adopting 0.8 as the standard for the sound absorption coefficient, an absorption range of 14439 Hz is achieved, demonstrating its wide frequency band and high sound absorption capabilities. The sound absorption mechanism of the covering layer is further revealed by analyzing the displacement and energy power dissipation distribution cloud diagrams. When the angle of sound wave incidence is 60°, the average sound absorption coefficient of the covering layer is above 0.8; even under a hydrostatic pressure of 5 MPa, the sound absorption coefficient of the covering layer remains stable above 0.8 after 595 Hz, confirming its structural stability and the durability of its sound absorption performance.

Solar-Thermal Performance of Sparked Stainless Steel-based Solar Absorber under Solar Concentration

Solar absorbers are indispensable components in concentrated solar-thermal (CST) energy systems. Material selection is crucial in optimizing the performance of these systems. Traditional fabrication methods for solar absorbers often rely on chemical processes, which can be both costly and environmentally detrimental. This study presents the first investigation of the solar-thermal performance of a stainless steel absorber fabricated through a non-chemical sparking process in a tip-substrate configuration. Stainless steel, recognized for its cost-effectiveness and high-temperature thermal stability, emerges as a promising candidate for solar absorber applications. The sparked stainless steel exhibited enhanced solar absorptivity of 84.0% and thermal emissivity of 47.3%, representing increases of approximately 33% and 13.7%, respectively, compared to bare stainless steel. Raman spectroscopy and atomic force microscopy confirmed the formation of a random nanotexture of magnetite on the sparked surface, contributing to the improved optical properties. The solar-thermal performance of the sparked stainless steel is maximized at 84.0% when the absorber temperature aligns with the ambient temperature or under conditions of extreme optical concentration. To maintain a solar-thermal performance exceeding 70% at elevated absorber temperatures of 150 °C, 250 °C, 350 °C, and 450 °C, optical concentrations of 5, 13, 28, and 52, respectively, are required.

Preparation and performance of porous carbon microwave absorber with high porosity from carbonized natural plant fibers

Herein, we present a novel fabrication approach to synthesize lightweight, highly porous, high-frequency microwave absorbers via temperature-induced manufacturing of 1D helical/chiral porous carbon fibers (HPCFs). This approach is unmatched in its effectiveness. Furthermore, this unique fabrication approach does not require pre-treatments such as activation, complex stripping-off processes, or harmful chemicals to generate the microwave absorber (MA). The MA with nanoscale/microscale structures, multidimensional 0 or 1D integration, helical/chiral configuration, and assorted loss mechanisms endow the absorber with exemplary microwave absorption capabilities. The maximum reflection loss (RLmax) of HPCFs-700-22.5% (700 and 22.5% correspond to the temperature at which biomass fiber get carbonized and the amount of filler material present) achieves -57.40dB RLmax at 15.20GHz with the wide effective absorbing bandwidth (EAB, RLmax ≤ -10 dB) of 5.40GHz (12.60-18.00GHz) and 2.47mm thickness. Notably, at a matching thickness of 2.60mm, the EAB improved to cover 12.00-18.00GHz (6.00GHz). Moreover, HPCFs-800-22.5 exhibit ultrawide EAB covers of 14.60-18.00GHz (3.40GHz), while RLmax surpasses -57.80dB at the matching thickness of 1.51mm. HPCFs-900-22.5% achieve RLmax of just -51.00dB with EAB of 5.40GHz (12.60-18.00GHz) at 14.90GHz, while the matching thickness of absorber is 2.22mm. The HPCFs with such exceptional microwave absorption properties shed light on the development economical and environmentally friendly MA with comparable microwave performances over exceptional EAB.

First-principles investigation of the photocatalytic properties of two-dimensional CdO/ZrSSe heterojunctions.

Two-dimensional van der Waals heterojunction materials have demonstrated significant potential for photocatalytic water splitting in hydrogen production, owing to their distinct electronic and optical properties. Among these materials, direct Z-scheme heterojunctions have attracted considerable attention in recent research. In this study, a novel CdO/ZrSSe heterojunction is designed using first-principles calculations. The structural stability, electronic properties, carrier mobility, optical absorption, and photocatalytic performance of this heterojunction are systematically investigated, with a particular focus on the influence of strain on the band structure. The results reveal that both type-I and type-II heterojunctions exhibit staggered, indirect bandgap structures, with bandgap values of 0.80 eV and 0.60 eV, respectively. A built-in electric field is established from the CdO layer to the ZrSSe layer, facilitating oxidation in the ZrSSe layer and reduction in the CdO layer. The highest carrier mobilities are calculated to be 462 cm2 V-1 s-1 and 2738 cm2 V-1 s-1, respectively. Under compressive strain, the bandgap widths of both I-CdO/ZrSSe and II-CdO/ZrSSe heterojunctions decrease, whereas tensile strain results in an increase in the bandgap width. Correspondingly, the optical absorption peaks of both heterojunctions are enhanced under compressive strain and diminished under tensile strain. These findings suggest that the performance of both type-I and type-II CdO/ZrSSe heterojunctions surpasses that of their individual monolayers, exhibiting a typical Z-scheme photocatalytic mechanism, and thus positioning them as promising high-efficiency catalysts for water splitting.

Barrier materials integrated with gas regulation function are used to reduce the explosion risk of battery systems

Large-capacity lithium iron phosphate batteries are widely used in energy storage stations and electric vehicles due to their high cost-effectiveness and long lifespan. However, research shows that the gases generated during thermal runaway are mainly combustible, which may lead to fires or even explosions. Nevertheless, within the millimeter-scale confined space of a battery pack, effective solutions are scarce, making it challenging to simultaneously suppress kilowatt-level heat transfer and dilute the accumulated combustible gases. This research has developed a multifunctional fire shield with capabilities of “low-temperature heat conduction, medium-temperature heat absorption, high-temperature thermal insulation, and gas regulation.” The material is composed of hydrogel, aluminum hydroxide, ceramic fiber, and ammonium bicarbonate. In the low-temperature range, it exhibits an excellent thermal conductivity (0.58 W·m−1·K−1), capable of maintaining the battery module’s operating temperature within a reasonable range. In the medium to high-temperature range, its thermal conductivity rapidly decreases (0.04 W·m−1·K−1), and with its high phase change enthalpy (1727 J/g), the material can suppress the thermal propagation of a 100 Ah lithium iron phosphate battery module. This material starts to release CO2 at 90℃. In a confined space, the CO2 mixes uniformly with the gases generated during the thermal runaway process of the battery, reducing the risk of these gases (increasing the lower explosion limit by 44 % and reducing the maximum laminar flame speed by 58 %). Therefore, the multifunctional fire shield demonstrates exceptional heat conduction, heat absorption, thermal insulation, and gas regulation performance. This research provides new insights for the safety design of battery systems.

Effect of freeze-thaw processes on the water-absorption ability and mechanical properties of hydrogel pads with chitosan/poly(vinyl alcohol) based on citrate crosslinks.

In this study, the effect of freeze-thaw (F-T) processes on the mechanical and water absorption performance of citrate cross-linked chitosan/poly(vinyl alcohol) hydrogel pads was evaluated. An excellent cross-linking of 4% (w/w) citrate was indicated by enhanced peak strength in Fourier-transform infrared spectroscopy and X-ray diffraction patterns, which was applied to the subsequent F-T process. The results in the deswelling rate, water contact angle, and relaxation time of samples exhibited a tendency to decrease and then increase with increasing F-Tcycles, reaching a minimum of 0.08, 16.48°, and 3.92ms in the third cycle, respectively. The swelling rate showed opposite trends with a maximum of 5.92. In addition, scanning electron microscopy observation and mechanical testing confirmed homogeneous pore structure and excellent mechanical properties during the third cycle. This study can provide technical support for fabricating hydrogel absorbent pads and their application in meat products.

Tailoring Yb2Si2O7/TiO2 ceramic structures for enhanced electromagnetic wave absorption performance

Tailoring Yb2Si2O7/TiO2 ceramic structures for enhanced electromagnetic wave absorption performance

Hollow conductive polypyrrole microtubes as microwave absorbents with good seawater corrosion resistance

Conductive polymers materials with hollow micro/nanostructure due to their special electrical properties and corrosion resistance have potential applications in microwave absorption, especially in marine environment. Herein, one-dimensional hollow conductive polypyrrole microtubes (H-PPyM) were prepared by in-situ polymerization of pyrrole monomer with methyl orange (MO) as soft template and FeCl3 as oxidant based on structural regulation strategy. The morphology and conductivity of H-PPyM can be easily controlled by adjusting the content proportion of MO. The results indicated that the surface morphology of polypyrrole changed from random granular to microtubular and the conductivity also gradually rose with the content increase of MO. When the content proportion of MO was 0.25 g, the obtained H-PPyM-0.25 composites possed notable microwave absorption capacity, simultaneously achieving ultrabroad effective absorption bandwidth (EAB, 6.7 GHz) and strong reflection loss value (RL, -33.6 dB) at a thickness of 2.6 mm with the filling content of only 10 wt.%, respectively. Furthermore, the corresponding H-PPyM-0.25 products soaked in corrosive medium (3.5 wt% NaCl solution) for one month still displayed stable tubular hollow structure and excellent microwave absorption performance with RLmin of -43.8 dB and EAB of 6.2 GHz. The research results can not only help to understand the relationship among the morphology and microwave absorption of PPy, but also open a new avenue for preparing excellent seawater corrosion resistant microwave absorption materials.

Hierarchical multi-cell hexagonal tubes under oblique crushing

Bio-inspired structures have been extensively studied under axial compression; however, limited studies investigating their crushing performance under oblique compression. In this paper, the oblique crushing performance of three types of hierarchical hexagonal tubes, bio-inspired hierarchical multi-cell hexagonal tubes (BHMH), hierarchical multi-cell hexagonal tubes (HMHA and HMHB) have been investigated. The effects of loading angle and hierarchical order are investigated. It has been found that BHMH tubes display the superior energy absorption performance compared with HMHA and HMHB tubes. In addition, BHMH, HMHA and HMHB tubes show the excellent crushing performance than that of single tubes. For example, the SEA of BHMH-3 tube at angles of 0°, 10°, 20° and 30° is 146%, 116%, 75% and 42% higher than that of single ones.

Enhanced, broad and thin low-frequency microwave absorption induced by proper magnetic anisotropy in polyhedral SmFeO3-encapsulated Sm2Fe17 nanoparticles

High permeability accompanied with large magnetic loss is considered as an effective strategy for achieving efficient low-frequency absorption. However, it remains a considerable challenge for synergistically improving the permeability and magnetic loss at low frequency range due to the proper magnetic anisotropy. In this study, arc discharge method is proposed to fabricate polyhedral core-shell structured Sm2Fe17 nanoparticles with averaged size of 160nm, in which SmFeO3 with averaged thickness of ~3.5nm works as dielectric shell. The frequency dependence of electromagnetic parameters of 20wt.% Sm2Fe17@SmFeO3 nanoparticles-paraffin composites have been studied at 2-18GHz. Natural resonance frequency reaches 6.64GHz. The real part and imaginary part of initial permeability is up to 2.42 and 0.76, respectively. The composite delivers the minimal reflection loss of -45.36dB at 3.2GHz with 3.0mm and the optimal effective absorption bandwidth of 2GHz (5.84-7.84GHz) with only matching thickness of 1.5mm. The superior low-frequency absorption performances are ascribed to the planar anisotropy field for providing high permeability and the polyhedral structure for suppressing natural resonance movement to mid-high frequencies. Furthermore, radar cross section simulations verify the great potential for practical applications. This work provides a valuable reference for designing microwave absorbers with merits of strong absorption, wide bandwidth and thin thickness in the low frequency range.

PVP-assisted MOF-derived Fe3O4/C powders for microwave absorption applications.

Metal-organic framework (MOF) derived porous Fe3O4/C powders were applied for absorption of microwaves in the frequency range of 1-18GHz. The effects of the polyvinylpyrrolidone (PVP) additive on the synthesis of MIL101-(Fe) precursor were studied by various characterization methods. By adding PVP, the impure hematite phase (α-Fe2O3) with magnetite phase (Fe3O4) was disappeared and the particular morphology was transformed to the porous rod-like, leading to the increase of specific surface area from 150 to 282m2/g. Furthermore, the saturation magnetization (Ms) of Fe3O4/C powders reached a maximum value of 47 emu/g at a proper amount of PVP. A thin absorber (2.6mm) made of 50wt% Fe3O4/C powders and 50wt % paraffine absorbed the whole of X frequency band (8-12GHz) with a minimum reflection loss of -20 dB at a matching frequency of 10GHz. Adjusting the permittivity and permeability parameters of the Fe3O4/C powders via adding PVP was responsible for their better microwave absorption performance.

Direct synthesis of bimetallic Co/Zn-MOF-derivative@mica composite for high microwave absorption performance and pearlescent properties

Direct synthesis of bimetallic Co/Zn-MOF-derivative@mica composite for high microwave absorption performance and pearlescent properties