Multiscale Hierarchical Structures Research Articles

Magneto-Dielectric Synergy and Multiscale Hierarchical Structure Design Enable Flexible Multipurpose Microwave Absorption and Infrared Stealth Compatibility

HighlightsA multiscale hierarchical structure design, integrating wrinkled MXene radar-infrared shielding layer and flexible Fe3O4@C/PDMS microwave absorption layerThe assembled stealth devices realize a near-perfect stealth capability in both X-band (8-12 GHz) and long-wave infrared (8-14 µm) wavelength ranges.The optimal device demonstrates exceptional curved surface conformability, self-cleaning capability (contact angle ≈ 129°), and abrasion resistance (recovery time ≈ 5 s).

Formation of hierarchically structured martensites in pure iron with ultrahigh strength and stiffness

Strong steels are primarily fabricated by introducing spatial obstacles (e.g., stacking faults and precipitates) that inhibit dislocation slips under stress to achieve high strength. However, for most low-carbon steels, such obstacles are difficult to form mainly because the martensitic transition is kinetically unfavorable by conventional methods, which precludes the attainment of high-strength materials in these steels with low solute contents. Here, we report an innovative high-pressure preparation of martensitic pure Fe with involving nano-effect, which leads to the formation of ultrastrong bulk iron with exceptionally high yield strength, ultimate strength, and hardness of 2.9 GPa, 3.7 GPa, and 9.0 GPa, respectively, exceeding those of high-speed steels. Such extraordinary mechanical properties are closely attributed to its high-density martensites with unique multiscale hierarchical structures formed due to complex phase transitions under pressure.

Biomimetic multiscale structure with hierarchically entangled topologies of cellulose-based hydrogel sensors for human-computer interaction

The development of high-performance cellulose-based sensors with superior interfacial compatibility, flexibility, and strength has always been challenging. Drawing inspiration from the intricate multiscale hierarchy found in resilient natural materials, the incorporation of this structure into cellulose-based hydrogels using biomimetic strategies is anticipated to enhance their properties. Therefore, the cellulose/polyacrylamide (PAM) hybrid hydrogels are fabricated using the aqueous AlCl3/ZnCl2 system through an all-green one-pot method at room temperature, achieving efficient dissolution of cellulose at multiple scales and in-situ polymerization of polyacrylamide. The multiscale cellulose/PAM hydrogels achieve good interfacial compatibility, with the reinforcing mechanism being confirmed through a combination of experimental validation and atomic simulations. The findings underscore the key elements that drive the multiscale behavior of hydrogels, encompassing a range of factors such as multiple interfacial interactions, hierarchical molecular entanglements, and microskeleton reinforcement. The hydrogels exhibit satisfactory stretchability (412 %), compressive strength (1.2 MPa), conductivity (1.65 S m−1), and ultralong circulability (> 12,000 cycles), rendering them suitable for various scenarios of human-computer interaction. This work establishes a comprehensive interpretation of the strengthening mechanism in cellulose-based multiscale hierarchical structures, thereby providing novel insights for the advanced design strategies of other promising hierarchical materials.

Bioinspired Bouligand-Structured Cellulose Nanocrystals/Poly(vinyl alcohol) Composite Hydrogel for Enhanced Impact Resistance.

Impact-protective materials are gaining importance because of the widespread occurrence of impact damage. Hydrogels have emerged as promising candidates owing to their lightweight and flexible nature. However, achieving soft impact-resistant hydrogels with exceptional stiffness, strength, and toughness remains a challenge. Inspired by the Bouligand structure found in the smasher dactyl club of stomatopods, we propose a straightforward multiscale hierarchical structural design strategy. This strategy integrates self-assembly and salting-out techniques to enhance the impact resistance of soft hydrogels. Rigid cellulose nanocrystals (CNCs) self-assemble into Bouligand-like structures within soft poly(vinyl alcohol) (PVA) matrix via supramolecular interactions. This rational structural design combines the CNC Bouligand structure with a cross-linked network of soft PVA crystalline domains, resulting in a composite hydrogel with impressive mechanical properties: high tensile fracture strength (30.2 MPa), elastic modulus (62.7 MPa), and fracture energy (75.6 kJ m-2), surpassing those of other tough hydrogels. Moreover, the multiscale hierarchical structure facilitates various energy dissipation mechanisms, including crack twisting, tortuous crack paths, and PVA chain orientation, resulting in notable force attenuation (80.4%) in the composite hydrogel. This biomimetic design strategy opens new avenues for developing soft and lightweight impact-resistant materials.

Chitin/Chitosan Nanofibers Toward a Sustainable Future: From Hierarchical Structural Regulation to Functionalization Applications.

Owing to its multiple fascinating properties of renewability, biodegradability, biocompatibility, and antibacterial activity, chitin is expected to become a green cornerstone of next-generation functional materials. Chitin nanofibers, as building blocks, form multiscale hierarchical structures spanning nano- and macrolevels in living organisms, which pave the way for sophisticated functions. Therefore, from a biomimetic perspective, exploiting chitin nanofibers for use in multifunctional, high-performance materials is a promising approach. Here, we first summarize the latest advances in the multiscale hierarchical structure assembly mode of chitin and its derivative nanofibers, including top-down exfoliation and bottom-up synthesis. Subsequently, we emphasize the environmental impacts of these methods, which are crucial for whether chitin nanofibers can truly contribute to a more eco-friendly era. Furthermore, the latest progress of chitin nanofibers in environmental and medical applications is also discussed. Finally, the potential challenges and tailored solutions of chitin nanofibers are further proposed, covering raw material, structure, function, manufacturing, policies, etc.

A one-stone-three-birds strategy to construct Mo-FeS2/Ni3S2@C electrocatalyst with strong interfacial coupling effect to achieve efficient oxygen evolution reaction

The development of high-performance oxygen evolution reaction (OER) electrocatalysts is quite pivotal to facilitate hydrogen production. In this work, we integrate the synergistic effects of heterogeneous interface engineering, multiscale engineering and doping engineering to greatly improve the catalytic activity of the electrocatalyst. Specifically, with a Anderson-type polymetallic oxonate (NH4)3[NiMo6O24H6]·7H2O as a precursor, the Mo-FeS2/Ni3S2@C nanowire arrays that uniformly grown on nickel foam (NF) surfaces were prepared by a simple hydrothermal process followed by calcination. The as-prepared Mo-FeS2/Ni3S2@C exhibits excellent alkaline OER performance with a low overpotential of 196 mV to achieve a current density of 10 mA cm−2 and maintain high stability for over 100 h at 100 mA cm−2. Theoretical calculations and experimental results indicate that the high activity of Mo-FeS2/Ni3S2@C is mainly attributed to the charge interaction at the multiple interfaces of FeS2, Ni3S2 and porous carbon layers. The Mo facilitates inducing the formation of high-valent Ni, Fe, thus forming of the Ni(Fe)OOH phase that contributes to the intrinsic OER active site of the Mo-FeS2/Ni3S2@C electrode. In addition, the surface of Mo-FeS2/Ni3S2@C nanowire is composed of ordered nanosheets, exhibiting a unique hierarchical multi-scale structure, which is conducive to exposing more active sites. This hierarchical structure gives it superhydrophilic and superoxyphobic properties, ensuring the stability during continuous electrolysis. This study showcases the importance of multi-engineering synergies and foresees the avenue of designing novel OER electrocatalysts.

Additive manufacturing of heterogeneous combinatorial functional surface by plasmonic hierarchical sintering of silicon particles for active manipulation of rheological liquid motion

We present a sustainable and efficient additive manufacturing method of silicon-based heterogeneous combinatorial functional surfaces designed to actively manipulate liquid droplet motion dynamics to address advanced rheological engineering challenges and applications. This additive manufacturing enables the instantaneous formation and control of hierarchical multiscale structures with tunable wettability through instantaneous plasmonic thermophysical sintering between laser and Si particles, eliminating the need for additional masks and subsequent processing steps. Furthermore, this fabrication approach can selectively implement heterogeneous combinatorial functional surfaces in a single domain by reversibly switching extreme wettability modes (e.g., from superhydrophobic to superhydrophilic) upon laser irradiation. Continuous superhydrophilic channels in a superhydrophobic background created by selective laser re-irradiation provide sufficient local attraction to manipulate droplet motion along the channel due to van der Waals forces and Laplace pressure fields generated by the difference in wettability. Active manipulation of droplet dynamic motion, such as trajectory tracking and antigravity self-propulsion, can be realized by simply designing a laser scanning path that determines the geometry of the local channel. The manipulation platform for liquid motion dynamics can be applied to active microfluidic channels with no cavity, without the need for an external power source. This advancement has important implications for broad fluid and rheological engineering applications.

Lotus leaf and shark skin-inspired micro-, nano-, hierarchical superhydrophobic surfaces for anti-fouling applications

Fouling, the accumulation and adhesion of unwanted contaminants, is a serious issue around the world in many aspects including industrial transport, marine ecological environment, maintenance of infrastructures, etc. which costs hundreds of millions of dollars and lots of manpower and material resources. Multiscale hierarchical surface structures of superhydrophobic surfaces possess various intriguing properties which provides new platforms for fabricating artificial anti-fouling surfaces. In particular, lotus leaf and shark skin with their unique micro-, nano-, hierarchical surfaces structures are highlighted as emerging tools for anti-bacterial, anti-dust, anti-corrosion, anti-icing, drag reduction applications and so on. In this review, we first provide basic information on two famous superhydrophobic states. After that we outlined the biological models and applications of lotus leaf and shark skin respectively. The self-cleaning effect of superhydrophobic lotus leaf due to their multiscale hierarchical surface structures is discussed after which anti-bacterial applications with three kinds of mechanisms and self-cleaning properties are outlined. Biological models of superhydrophobic shark skin are presented followed by their real-life applications in aircrafts and turbine blades. In addition, we discuss the potential drawbacks of recent biomimetic anti-fouling superhydrophobic surfaces like the loss of anti-fouling hydrophobic materials, adaptability to extreme environments, production and use costs and other problems as well as the possibilities of combine superhydrophobic structures and materials with high temperature resistance, oxidation resistance and other characteristics in order to be applied in more industries fields.

Mobile User Traffic Generation Via Multi-Scale Hierarchical GAN

Mobile user traffic facilitates diverse applications, including network planning and optimization, whereas large-scale mobile user traffic is hardly available due to privacy concerns. One alternative solution is to generate mobile user traffic data for downstream applications. However, existing generation models cannot simulate the multi-scale temporal dynamics in mobile user traffic on individual and aggregate levels. In this work, we propose a multi-scale hierarchical generative adversarial network (MSH-GAN) containing multiple generators and a multi-class discriminator. Specifically, the mobile traffic usage behavior exhibits a mixture of multiple behavior patterns, which are called micro-scale behavior patterns and are modeled by different pattern generators in our model. Moreover, the traffic usage behavior of different users exhibits strong clustering characteristics, with the co-existence of users with similar and different traffic usage behaviors. Thus, we model each cluster of users as a class in the discriminator’s output, referred to as macro-scale user clusters. Then, the gap between micro-scale behavior patterns and macro-scale user clusters is bridged by introducing the switch mode generators, which describe the traffic usage behavior in switching between different patterns. All users share the pattern generators. In contrast, the switch mode generators are only shared by a specific cluster of users, which models the multi-scale hierarchical structure of the traffic usage behavior of massive users. Finally, we urge MSH-GAN to learn the multi-scale temporal dynamics via a combined loss function, including adversarial loss, clustering loss, aggregated loss, and regularity terms. Extensive experiment results demonstrate that MSH-GAN outperforms state-of-art baselines by at least 118.17% in critical data fidelity and usability metrics. Moreover, observations show that MSH-GAN can simulate traffic patterns and pattern switch behaviors.

Bioinspired multiscale hierarchical structure enables solar-thermal conversion for low-temperature aqueous electrochromic device

Solar-thermal conversion can mitigate the inadequate electrochemical performance in extreme cold environment for aqueous electrochromic devices (AEDs). However, the limited intrinsic absorptance of electrochromic materials impedes a satisfying solar-thermal conversion. Herein, bioinspired by the Paradisaeidae’s super black feathers, multiscale hierarchical structure is purposely made to compose of WO3-x nanowires (WNWs) and silver nanowires (AgNWs), where WNWs are grown on AgNWs in different orientations (denoted as WAg). Our ray tracing simulation reveals its underlying absorption mechanism, demonstrating both an increased optical path and a concentrated energy distribution. Comparably, the WAg-AED exhibits much enhanced absorption (87.0 vs. 68.5 % across the entire solar spectrum) and a broader surface temperature change (51.2 vs. 39.7 °C within 8 min) under 1 solar illumination. This leads to a rapid recovery of electrochromic/electrochemical performance even conducted at −20 °C. Notably, upon irradiation for 12 min, the areal capacities of WAg-AED at 0.5mA cm−2 increase by 3.8 and 1.7 times, when compared to the device operating at −20 °C and room temperature, respectively. The WAg-AED establishes a close connection between the photo-thermal conversion and electrochemistry, proving a new pathway in the development of sustainable electronics.

New insights into chitosan-induced biomimetic mineralization of hierarchical spherical nesquehonite: Characterization, DFT calculations and construction mechanism

Recently, CO2 mineralization with magnesium salts is a cost-effective method for CO2 utilization and sequestration. The obtained hydrated magnesium carbonate can serve as high-value added functional materials. Inspired by biomineralization, nesquehonite (NSQ) was prepared via chitosan-induced mineralization of MgCl2-(NH4)2CO3, achieving indirect mineralization of CO2. The effects of chitosan (CTS) addition, reaction temperature, and reaction time on the phase composition and micromorphology of the products were systematically investigated. When the chitosan addition was 2%, the reaction temperature was 60℃, and the reaction time was 300 min, the obtained product was hierarchical spherical NSQ with an average diameter of 10 μm. The construction mechanism of the hierarchical spherical NSQ was elucidated. Zeta potential and 1H NMR analyses indicated the interaction of CTS with Mg2+, binding Mg2+ through –OH and –NH2 groups, thereby prolonging the nucleation and growth process of NSQ. FT-IR, XPS, TEM, and AFM analyses revealed that CTS induced directional growth of nanosheets by chemisorption on the crystal surface. Ultimately, through CTS bridging, the nanosheets aggregated and assembled into NSQ sphere. DFT calculations further indicated that CTS forms Mg-O and Mg-N bonds with Mg2+ and that there are Mg-O, Mg-N bonds and hydrogen bonding interactions between CTS and NSQ. This work provides new insights into the preparation of hierarchical NSQ via a biomimetic mineralization mechanism. Additionally, NSQ with a multiscale hierarchical structure has a promising future in the fields of adsorbents, templating agents, and drug carriers.

Bottom-Up Assembling Hierarchical Enamel-Like Bulk Materials with Excellent Optical and Mechanical Properties for Tooth Restoration.

Enamel has good optical and mechanical properties because of its multiscale hierarchical structure. Biomimetic construction of enamel-like 3D bulk materials at nano-, micro-, mesh- and macro-levels is a challenge. A novel facile, cost-effective, and easy large-scale bottom-up assembly strategy to align 1D hydroxyapatite (HA) nanowires bundles to 3D hierarchical enamel structure with the nanowires bundles layer-by-layer interweaving orientation, is reported. In the strategy, the surface of oleate templated ultralong HA nanowires with a large aspect ratio is functionalized with amphiphilic 10-methacryloyloxydecyl dihydrogen phosphate (MDP). Furtherly, the MDP functionalized HA nanowire bundles are assembled layer-by-layer with oriented fibers in a single layer and cross-locked between layers at a certain angle at mesoscale and macroscale in the viscous bisphenol A-glycidyl methacrylate (Bis-GMA) ethanol solution by shear force induced by simple agitation and high-speed centrifugation. Finally, the excessive Bis-GMA and ethanol are removed, and (Bis-GMA)-(MDP-HA nanowire bundle) matrix is densely packed under hot pressing and polymerized to form bulk enamel-like materials. The composite has superior optical properties and comparable comprehensive mechanic performances through a combination of strength, hardness, toughness, and friction. This method may open new avenues for controlling the nanowires assembly to develop hierarchical nanomaterials with superior properties for many different applications.

Polymeric monolithic columns based on natural wood for rapid purification of targeted protein

With multiscale hierarchical structure, wood is suitable for a range of high-value applications, especially as a chromatographic matrix. Here, we have aimed to provide a weak anion-exchange polymeric monolithic column based on natural wood with high permeability and stability for effectively separating the targeted protein. The wood-polymeric monolithic column was synthesized by in situ polymerization of glycidyl methacrylate and ethylene glycol dimethacrylate in wood, and coupled with diethylaminoethyl hydrochloride. The wood-polymeric monolithic column can be integrated with fast-protein liquid chromatography for large-scale protein purification. According to the results, the wood-polymeric monolithic column showed high hydrophilicity, permeability and stability. Separation experiments verified that the wood-polymeric monolithic column could purify the targeted protein (spike protein of SARS-COV-2 and ovalbumin) from the mixed proteins by ion exchange, and the static adsorption capacity was 33.04 mg mL−1 and the dynamic adsorption capacity was 24.51 mg mL−1. In addition, the wood-polymerized monolithic column had good stability, and a negligible decrease in the dynamic adsorption capacity after 20 cycles. This wood-polymerized monolithic column can provide a novel, efficient, and green matrix for monolithic chromatographic columns.

Superhydrophobic Non-Metallic Surfaces with Multiscale Nano/Micro-Structure: Fabrication and Application.

Multiscale nano/micro-structured surfaces with superhydrophobicity are abundantly observed in nature such as lotus leaves, rose petals and butterfly wings, where microstructures typically reinforce mechanical stability, while nanostructures predominantly govern wettability. To emulate such hierarchical structures in nature, various methods have been widely applied in the past few decades to the manufacture of multiscale structures which can be applied to functionalities ranging from anti-icing and water-oil separation to self-cleaning. In this review, we highlight recent advances in nano/micro-structured superhydrophobic surfaces, with particular focus on non-metallic materials as they are widely used in daily life due to their lightweight, abrasion resistance and ease of processing properties. This review is organized into three sections. First, fabrication methods of multiscale hierarchical structures are introduced with their strengths and weaknesses. Second, four main application areas of anti-icing, water-oil separation, anti-fog and self-cleaning are overviewed by assessing how and why multiscale structures need to be incorporated to carry out their performances. Finally, future directions and challenges for nano/micro-structured surfaces are presented.

Multiscale characterization of polymer electrolyte fuel cells elucidated by quantum beam analysis

Abstract Polymer electrolyte fuel cells (PEFCs) offer promising alternatives to conventional gasoline engines in automobiles and have been commercialized over the past decade. This progress can be attributed to state-of-the-art materials with high performance, long-term durability, and robust manufacturing technologies. The multiscale hierarchical structure inherent in PEFCs facilitates the transfer of protons, electrons, oxygen, and water. As various phenomena in PEFCs occur at different scales, multiscale analysis, including quantum beam analysis, is of great interest for materials development and for understanding the processes that take place in PEFCs. In particular, advancements in this field have enabled the further tailoring of properties in a controlled manner and the design of nanostructures processing superior material properties. Additionally, the expansion of quantum beam sources has facilitated the study of manufacturing protocols. This review presents the achievements in the use of synchrotron x-ray and neutron sources in the field of PEFCs, while also addressing remaining issues for the widespread commercialization of fuel cell electric vehicles.

Role of Multi-scale Hierarchical Structures in Regulating Wetting State and Wetting Properties of Structured Surfaces

Role of Multi-scale Hierarchical Structures in Regulating Wetting State and Wetting Properties of Structured Surfaces

Flexible, hierarchical MXene@SWNTs transparent conductive film with multi-source thermal response for electromagnetic interference shielding

Flexible transparent electromagnetic interference (EMI) shielding films in visual windows are crucial for the innovation of optoelectronic devices, but the challenge of balancing light transmittance and EMI shielding effectiveness (SE) still exists. Herein, this work described a flexible transparent MXene@SWNTs/PC film with a hierarchical conductive layer that was fabricated via an alternating rotation spraying method. The multi-scale hierarchical structure configured with 1D SWNTs and 2D MXene endow the obtained film with good comprehensive properties, i. e, low sheet resistance of 32.8 Ω/sq at 56.1% light transmittance, thus causing a satisfactory EMI SE of 20.8 dB. Moreover, the transparent shielding films exhibit remarkable flexibility, which can maintain steady EMI SE after 1000 continuous bending cycles. More importantly, the low sheet resistance and high light absorption capacity of hybrid conductive layer facilitate the transparent shielding film with low-voltage-driven electric heating effect and outstanding photothermal conversion ability, respectively, ensuring the normal operation under extreme cold condition. The combination of good light transmittance, satisfactory EMI shielding performance, and multi-source thermal response enables MXene@SWNTs/PC film to have great potential as a transparent shielding film in emerging optoelectronic devices.

Multiscale Synergetic Bandgap/Structure Engineering to Construct Full-Spectrum Responsive Heterostructured MoS2/SnS2 Photocatalysts

A 2D-MoS2/2D-SnS2 photocatalyst with van der Waals (vdW) heterojunction has been prepared by self-assembling MoS2 nanosheets on SnS2 microflake surface. A reasonable multi-scale micro-nano hierarchical structure with a narrow bandgap...

Engineering self-assembled 2D nano-network membranes through hierarchical phase separation for efficient air filtration

Air pollution has garnered significant worldwide attention; however, the existing air filtration materials still suffer from issues related to monotonous structure and the inherent trade-off between PM rejection and air permeability. Herein, a spider web-inspired composite membrane with continuous monolayer structured 2D nano-networks tightly welded on nanofibers in the electrospun membrane scaffold is designed via a hierarchical phase separation strategy. The resultant biomimetic hierarchical-structured membranes possess the integrated features of hierarchical multiscale structures of 2D ultrafine networks composed of nanowires with a diameter of 31 nm self-assembled by nanoparticles, exceptional characteristics involving small average aperture, extremely low network thickness, high porosity and promising pore channel connectivity, combined with rich surface polar functional groups (3.02D dipole moment). Consequently, the composite membrane exhibits a high PM0.3 capture efficiency of 99.6 % and low pressure drop of 58.8 Pa, less than 0.06 % of atmosphere pressure, with outstanding long-term PM2.5 recycling filtration performance. The hierarchical phase separation–driven 2D nano-networks construction strategy, by virtue of their feasibility and tunability, holds great promise for widespread application across diverse membrane-related domains for air filtration.

Hierarchically Structured Bioinspired Fibers Shaped by Liquid Droplets

AbstractNature has a remarkable ability to create multifunctional fibers, such as spider silk, by precisely controlling structures across various scales. However, replicating this in high‐speed spun synthetic fibers is challenging due to the absence of life‐specific forces and interactions required for manipulating composition, gradients, and structures. Here, a novel droplet‐coupled pultrusion spinning technique is demonstrated for industrial‐scale production of microfibers with hierarchical structures. Droplets spontaneously form on the surface of high‐speed spun fibers to tailor multiscale hierarchical structures, resulting in a nonlinear viscoelastic core embedded with anharmonic nanosprings consisting of amorphous and crystalline domains and a periodically reinforced nanofiber skin. These structural hierarchies enable unique mechanical property combinations including nonlinear viscoelasticity, large extensibility (613%), record‐high toughness (536 MJ m−3), highly efficient impact energy absorption, vibration damping and wide temperature adaptability (−67.4 to 278.9 °C). Additionally, the structured bioinspired fibers exhibit low‐frequency phononic bandgap and anomalous dispersion of mechanical waves. The droplet‐based approach allows precise control over heterogeneity at multiple scales within the identical components leading to impressive mechanical performance and additional functionalities, and is consider that it could be applied to the design of the next era of hierarchically structured nanocomposites for a wide range of applications.