Nanoscale Hierarchical Structures Research Articles

Solvothermal synthesis of CuS nanosheets loaded porous carbon electrode composites for high performance supercapacitors

In this work, an electrode composite (CuS-NPC) for supercapacitors was synthesized by loading hexagonal nano-sheeted copper sulfide onto porous carbon through a solvothermal reaction using thiourea and copper acetate as the sulfur and copper sources, respectively. The synergistic effect of nanoscale copper sulfide sheet and hierarchical pore structure of porous carbon with high surface area achieves excellent capacitive performance in electrochemical reactions. CuS-NPC exhibited a large specific capacitance of 1298.7F g−1 at current density of 0.5 A/g and 766.3F g−1 at current density of 10 A/g, revealing that the electrode composite of copper sulfide and porous carbon have a great prospect as a supercapacitor electrode material.

Microarchitectured and nanoscale hierarchical structures of carbon in ancient archaeological carburisation slags

The famed Wootz steels are hypothesized to contain carbon nanotubes. However, the primary context of such nanostructures in Wootz steels is not known. In this letter, we present the microarchitectured and nanoscale hierarchical carbon structures in ancient archaeological carburization slags from 400 BCE to 16th century CE. We show that carbon microrods at the micro-scale are composed of finer carbon microrods, which are arranged in a co-axial manner. Carbon microrods are composed of twisted carbon nanotubes at the nanoscale. Such carbon nanostructure formation in the crucible process provides the possible source of carbon nanostructures in crucible steels of antiquity.

Nanoscale Dots, Grids, Ripples, and Hierarchical Structures on PET by UV Laser Processing

Nanostructures can be produced on poly(ethylene terephthalate) (PET) foils by using a krypton fluoride (KrF) excimer laser with a wavelength of 248 nm and a pulse duration of about 20 ns. We show that surface nanoripples, nanodots, nanogrids, and hybrid patterns of ripples with dots or finer ripples on top can be fabricated. The effects of a water layer in front of the PET foil and of cooling during laser processing were investigated. For pattern formation, several irradiation parameters (pulse number, pulse energy, and polarization) were varied systematically. The spatial periods of the ripples were changed by adjusting the angle of incidence of the laser beam. All nanostructures were characterized by scanning electron microscopy, and relevant morphological parameters, such as peak-to-peak distances and spatial periods, were assessed. Shapes and heights of some structures were characterized by using focused ion beam cuts to avoid the tip-sample convolution effects typical of atomic force microscopy images. We further demonstrate nanoripple formation on PET foils as thin as 12 µm, 6 µm, and 1.4 µm. The remarkable variety of nanostructures on PET we present here enables customized fabrication for a wide range of applications.

Nanoscale Hierarchical Structures Formed by Sequence-Defined Polycations and Homopolyanions for High Salt-Tolerance Adhesives

Nanoscale Hierarchical Structures Formed by Sequence-Defined Polycations and Homopolyanions for High Salt-Tolerance Adhesives

Bio-inspired dual-responsive photonic crystal with smart responsive hydrogel for pH and temperature detection

Responsive photonic crystals (PCs) with bio-inspired microstructures and tailorable functionalities are of critical importance for their potential applications in diverse fields such as biological detection, sensing, decoration, anti-counterfeiting, etc. However, limited by preparation technologies and design theories, it is still a challenge to accurately and uniformly deposit smart responsive materials on natural PC structures and achieve dual stimulus response. Herein, a simple and rapid in situ polymerization method is presented for preparing dual-responsive PCs with ultra-precise micro-/nanoscale hierarchical structures. Exposure of the reaction site by deacetylation of Morpho butterfly wings allows in situ polymerisation of poly (N-isopropylacrylamide-co-acrylic acid) (P(NIPAAM-co-AAc)) on the surface of the natural photonic structure. The obtained P(NIPAAM-co-AAc) photonic crystals (P(NIPAAM-co-AAc)-PCs) exhibited a dual response to pH and temperature reversibility. In addition, the synergistic effect of the structures and materials on the optical response of the natural PCs is revealed. This work allows the combination of natural hierarchical PC structures with smart hydrogel to achieve an optical response to pH and temperature, thus opening up the channels for responsive PC to multiple stimulus responses.

Aligned Nanofibrous Net Deposited Perpendicularly on Microridges Supports Endothelium Formation and Promotes the Structural Maturation of hiPSC-Derived Cardiomyocytes.

Cell alignment widely exists in various in vivo tissues and also plays an essential role in the construction of in vitro models, such as vascular endothelial and myocardial models. Recently, microscale and nanoscale hierarchical topographical structures have been drawing increasing attention for engineering in vitro cell alignment. In the present study, we fabricated a micro-/nanohierarchical substrate based on soft lithography and electrospinning to assess the synergetic effect of both the aligned nanofibrous topographical guidance and the off-ground culture environment provided by the substrate on the endothelium formation and the maturation of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). The morphology, proliferation, and barrier formation of human umbilical vein endothelial cells (HUVECs) as well as the alignment, cardiac-specific proteins, and maturity-related gene expression of hiPSC-CMs on the aligned-nanofiber/microridge (AN-MR) substrate were studied. Compared with the glass slide and the single-aligned nanofiber substrate, the AN-MR substrate enhanced the proliferation, alignment, and cell-cell interaction of HUVECs and improved the length of the sarcomere and maturation-related gene expression of hiPSC-CMs. Finally, the response of hiPSC-CMs on different substrates to two typical cardiac drugs (isoproterenol and E-4031) was tested and analyzed, showing that the hiPSC-CMs on AN-MR substrates were more resistant to drugs than those in other groups, which was related to the higher maturity of the cells. Overall, the proposed micro-/nanohierarchical substrate supports the in vitro endothelium formation and enhances the maturation of hiPSC-CMs, which show great potential to be applied in the construction of in vitro models and tissue engineering.

Recent Advancements in Novel Sensing Systems through Nanoarchitectonics.

The fabrication of various sensing devices and the ability to harmonize materials for a higher degree of organization is essential for effective sensing systems. Materials with hierarchically micro- and mesopore structures can enhance the sensitivity of sensors. Nanoarchitectonics allows for atomic/molecular level manipulations that create a higher area-to-volume ratio in nanoscale hierarchical structures for use in ideal sensing applications. Nanoarchitectonics also provides ample opportunities to fabricate materials by tuning pore size, increasing surface area, trapping molecules via host-guest interactions, and other mechanisms. Material characteristics and shape significantly enhance sensing capabilities via intramolecular interactions, molecular recognition, and localized surface plasmon resonance (LSPR). This review highlights the latest advancements in nanoarchitectonics approaches to tailor materials for various sensing applications, including biological micro/macro molecules, volatile organic compounds (VOC), microscopic recognition, and the selective discrimination of microparticles. Furthermore, different sensing devices that utilize the nanoarchitectonics concept to achieve atomic-molecular level discrimination are also discussed.

Fabrication of dual-functional cellulose nanocrystals/fluorinated polyacrylate containing coumarin derivatives by RAFT-assisted Pickering emulsion polymerization for self-healing application

Polymeric coatings are easy to be damaged by harsh environment condition, which causes cracks and loss of function. Inspired by the natural self-healing phenomenon, we successfully synthesized dual-functional cellulose nanocrystals/fluorinated polyacrylate containing coumarin derivatives by RAFT-assisted Pickering emulsion polymerization. The amphiphilic and photo-responsive copolymer, PDMAEMA-b-PGMA-b-P(HFBA-co-VBMC) was synthesized by RAFT process, followed by characterization using FT-IR, SEC, 1H NMR and UV–vis. The cellulose nanocrystals were modified by the copolymer, which were confirmed via XPS, UV–vis and so on. Besides, the droplet size of Pickering emulsion gradually increased and the creaming layer gradually decreased as the pH value increased. The TEM result showed that the modified cellulose nanocrystals were effectively anchored on the outside of latex particles. The size of the spherical-like latex particles increased and the stability of latex particles was worse with increasing pH value. Finally, the finished fabric had excellent water resistance due to the combination of micro- or nanoscale hierarchical structure and low surface energy. Moreover, the latex film exhibited excellent repeatability of self-healing ability. The fabric coating achieved the intrinsic and superficial dual-functional self-healing performance by the reversible [2 + 2] cycloaddition of coumarin groups. This strategy provides a powerful guide for preparing the high-performance waterborne fluorinated polyacrylate coating.

Recent advances in the synthesis of nanoscale hierarchically porous metal–organic frameworks

Nanoscale hierarchically porous metal–organic frameworks (NHP-MOFs) have received unprecedented attention in many fields owing to their integration of the strengths of nanoscale size (<1 ​μm) and hierarchical porous structure (micro-, meso- and/or macro-pores) of MOFs. This review focuses on recent advances in the main synthetic strategies for NHP-MOFs based on different metal ions (e.g., Cu, Fe, Co, Zn, Al, Zr, and Cr), including the template method, composite technology, post-synthetic modification, in situ growth and the grind method. In addition, the mechanisms of synthesis, regulation techniques and the advantages and disadvantages of various methods are discussed. Finally, the challenges and prospects of the commercialisation of promising NHP-MOFs are also presented. The purpose of this review is to provide a road map for future design and development of NHP-MOFs for practical application.

A layered superhydrophobic coating with excellent mechanical robustness and anti-corrosion performances

Lotus-like superhydrophobic coatings play an essential role for the corrosion protection of steel substrates exposed to harsh environments. Thus, improving the mechanical robustness and corrosion resistance of superhydrophobic coatings through macroscopic material matching and microscopic structure manipulation is an important task. In this study, a layered superhydrophobic coating with a “1 + 1” structural mode was successfully prepared using the spinning and spraying techniques. In order to prevent the interface debonding of upper and lower layers, the epoxy resin was introduced as bonding transition zones, and its three-dimensional cross-linking characteristic was used to realize the super stable “welding”. Then, the structure-function design, surface wetting behavior, mechanical robustness and corrosion resistance were systematically investigated. The results showed that the superhydrophobic coating was successfully constructed by designing micro-/nano-scale hierarchical structure and reducing surface energy, achieving a desirable static contact angle of 172.5° and a roll-off angle of 3.4°. Through high-pressure water anti-jetting, high-height sand impacting, and loaded sandpaper shear abrasion tests, the as-prepared coating still showed obvious superhydrophobicity and the shapes of water droplets on the coating surface continued to be nearly spherical. After immersion in 5 wt% NaCl solution for 28 days, an increase of polarization current density was negligible (∼0.0035 μA/cm2), and the impedance values (107 Ω•cm2) of the superhydrophobic coating were approximately three orders of magnitude higher than the control coating in the low-frequency region. This was because the corrosive species (H2O and Cl−) were restricted from entering the coating interior owing to the extreme water-repellence. In addition, the electron-carrying capacity of the superhydrophobic coating was vastly weakened, which impeded the formation of the corrosive conductive circuit and improved the anti-corrosion properties, prolonging the service life of the polymer coating system.

High-Performance Directional Water Transport Using a Two-Dimensional Periodic Janus Gradient Structure.

Numerous materials in micro- or nanoscale hierarchical structures with surface gradients serve as the enablers in directional liquid transportation. However, concurrent high-speed and long-range liquid transport is yet to be fully realized so far. Here, an overall-improved approach is achieved in both water transport distance and velocity aspects using a 2D periodic Janus gradient structure, which is inspired by the Janus-wettable desert beetle back, tapered asymmetric cacti spine, and periodic Nepenthes alata microcavity. This 2D channel can efficiently regulate the kinetics of liquid transport within its confined structure, in which the terminal potential well and periodic Janus topological structure enable sustaining water propelling through a long distance. In addition, the rapidly formed aqueous film facilitates a high initial momentum and fast transport of liquid droplets along the channel, achieving an averaged velocity of over 400mm s-1 and a maximum normalized transport distance of 23.4 for a 3µL droplet, as well as an ultralow liquid volume loss of 6.02% upon high-flux water transport. This scalable, controllable, and easy-fabricable 2D water transport system provides an insightful pathway in realizing high-performance water manipulation and possibly facilitates substantial innovative applications in multidisciplinary fields.

Characterization of Prepared Superhydrophobic Surfaces on AZ31 and AZ91 Alloys Etched with ZnCl2 and SnCl2

Superhydrophobic surfaces were prepared using a two-step method that involved the etching of AZ31 and AZ91 magnesium alloys and then modifying the etched alloys with stearic acid. Magnesium alloys etched with ZnCl2 and SnCl2 exhibited surfaces roughened with micro- and nanoscale hierarchical structures consisting of two chemically distinct regions (Zn/Zn(OH)2 or Sn/SnO2 and Mg(OH)2). An optimum etching time of ten minutes was chosen for both etchants. Superhydrophobic surfaces with the highest contact angle were prepared when stearic acid reacted with the etched alloys at 50 °C for 4 h. Stearic acid was bound as zinc stearate and magnesium stearate on Mg alloys etched with ZnCl2 and SnCl2 solutions, respectively. The superhydrophobic process on AZ31 alloys etched with ZnCl2 and SnCl2 improved the corrosion resistance in phosphate buffered saline (PBS) solution compared to bare AZ31 alloy, with the use of ZnCl2 etchant leading to better results. An improvement in the corrosion resistance of AZ91 alloy was observed when the stearic-acid-modified AZ91 alloy was etched with SnCl2. In contrast, the use of ZnCl2 etchant to pretreat AZ91 alloy resulted in a significant deterioration in corrosion properties compared to bare AZ91 alloy. The microstructure of the Mg alloy had an impact on the etching and modification process. On the basis of the findings, a characterization of the chemistry of etching magnesium alloys and the formation of superhydrophobic surfaces was proposed. Magnesium alloys were prepared with superhydrophobic surfaces, incorporating antibacterial metals, features which may increase their potential for use in medical applications.

Highly transparent and super-wettable nanocoatings hybridized with isocyanate-silane modified surfactant for multifunctional applications

Highly transparent and super-wettable nanocoatings for multifunctional applications with outstanding physical properties are in high demanded. However, such nanocoatings resistant to water invasion and Ultraviolet (UV) weathering remain a significant challenge. In this work, physically durable coatings based on inorganic nanoparticles (NPs) and an organic segment (isocyanate-silane modified surfactant) have been synthesized via a sol-gel approach. It is noteworthy the isocyanate-silane with –NH–CO- functional group creates a strong bonding between the highly hydrophilic surfactant and the inorganic NPs. This in-house synthesized organic segment can render the coating long-lasting wetting properties and resist to be washed away by water, while the inorganic NPs can form sturdy covalent bonds with the nano-scale hierarchical structure on the glazing substrate to improve the durability. This nanocoating demonstrates high transparency with superwetting property (water contact angle, WCA ​= ​4.4 ​± ​0.3°), effective de-frosting performance. Water invasion or UV accelerated weathering tests do not significantly affect the self-cleaning performance of nanocoating. Physical properties, including coating adhesion, hardness, Young's modulus, and abrasion resistance are systematically investigated. Interestingly, this clear coating shows prominent infrared shielding property attributed to Antimony-doped tin oxide (Sb-doped SnO2) NPs. The developed nanocoating process is easy to scale up for larger areas that require multipurpose self-cleaning functions.

Microcellular foams simultaneous reinforcing and toughening strategy of combining nano-fibrillation network and supercritical solid-state foaming

Foams with excellent mechanical performance are extremely valuable, as playing a key role in structural materials. However, it is still a significant challenge to simultaneously strengthen and toughen foam materials. In this work, a novel strategy combining nano-fibrillation network and supercritical carbon dioxide (scCO 2 ) solid-state foaming was proposed as follows: 1) In designing micro-scale cellular structure, chain extension and fibrillation technologies were synergistically adopted to improve the matrix viscoelasticity for cell stability, scCO 2 solid-sate foaming was then adopted to improve cell nucleation and cell growth. The combination of the above technologies helps to obtain a microcellular foam with large expansion ratio and small cell size; 2) In designing nano-scale hierarchical structure of crystalline and multiphase, flexible fibrils were dispersed in cell walls to compensate for matrix's brittleness and hence increased the foam impact strength, the crystals in cell walls improved the bending strength of cell walls and hence increased the foam compression strength. Herein, the obtained microcellular foam has simultaneous improvements in compression strength from 1.7 MPa to 2.7 MPa and impact toughness from 0.26 kJ/m 2 to 0.46 kJ/m 2 while maintaining a low foam density of 0.13 g/cm 3 . • A novel strategy is firstly proposed to simultaneously strengthen and toughen foams. • Micro/nano structure is regulated by in-situ fibrillation and supercritical solid-state foaming. • Nano fibrils facilitate crystallization and hence improve foam compression strength. • Nano fibril network hinders crack propagation and hence improves foam toughness. • Micro cellular structure improves foam compression strength and toughness.

Contact angle of Nepenthes slippery zone: results from measurement and model analysis

The slippery zone of Nepenthes alata depends on its highly evolved morphology and structure to show remarkable superhydrophobicity, which has gradually become a biomimetic prototype for developing superhydrophobic materials. However, the mechanism governing this phenomenon has not been fully revealed through a model analysis. In this paper, the superhydrophobicity of the slippery zone is studied by contact angle measurement, morphology/structure examination and model analysis. The slippery zone causes an ultrapure water droplet to produce a considerably high contact angle (155.11–158.30°) and has micro–nanoscale hierarchical structures consisting of lunate cells and wax coverings. According to the Cassie–Baxter equation and a self-defined infiltration coefficient, a model was established to analyse the effect of a structure characteristic on the contact angle. The analysis, result showed that the calculated contact angle (154.67–159.49°) was highly consistent with the measured contact angle, indicating that the established model can quantitatively characterise the relationship between the contact angle and the structure characteristic. The authors’ study provides some evidences to further reveal the superhydrophobic mechanism of the slippery zone of N. alata, as well as inspiring the biomimetic development of superhydrophobic surfaces.

Enhanced Growth of Broad Beans (Vicia faba L.) through Separating Antagonistic Nutrients Using Nitrogen-Doped Carbon Nanotubes

Iron (Fe) and manganese (Mn) remain intractable in the fertilizer design due to the incompatibility with phosphorus (P). Herein, we proposed a nanoscale hierarchical structure, where traditional io...

Micron-/nano-scale hierarchical structures and hydrogen storage mechanisms in a cast vanadium-based multicomponent alloy

Multicomponent vanadium-based alloys (MVAs), often considered as conventional coarse-grained alloys, have been extensively studied in past decades as important metal hydride electrodes and solid state hydrogen storage materials. A micron-scale microstructure composed of a V-based main phase and a TiNi-based secondary phase has been often used to explain the electrochemical performance of MVAs, where the micron-scale TiNi-based secondary phase with a three-dimensional network is considered as a catalyst for electrochemical reaction and/or a current collector. However, the atomic-scale microstructure of MVAs has been largely unknown to date. Here, using advanced aberration corrected electron microscopy, we have found micron-/nano-scale hierarchical structures in an as-cast MVA, V0.35Cr0.1Ti0.25Ni0.3. The micron-scale TiNi-phase contains VCr nanoprecipitates whereas the micron-scale VCr-phase contains TiNi nanoprecipitates and Ni-rich nanoclusters. In addition, we have found that the nanoprecipitates plays an essential role in the hydrogen storage, namely, TiNi nanoprecipitates with a diameter of approx. 30 nm absorb hydrogen faster than their VCr-matrix. Our studies revise conventional understanding on the microstructures in MVAs and the hydrogen storage mechanism, which may guide the development of nanostructured hydrogen storage materials for practical applications

Eco-friendly and facile fabrication of superhydrophobic aluminum alloy

Synthetic superhydrophobic surfaces have drawn significant interest owing to their water-resistant and self-cleaning applications. However, most of the fabrication practices involve complex processes that are unsustainable to withstand large-scale fabrication to transform into standard industrial practice. The desired durability of these surfaces is another crucial challenge that makes the translation of these products difficult. In this paper, we reported the fabrication of superhydrophobic aluminum alloy with a simpler, low-cost, and eco-friendly technique using the hydrothermal treatment. Subsequently, the surface energy of the processed substrate was modulated using a chemical vapor deposition technique. The developed surface shows an extreme water repellency with a contact angle above 160° and a very low contact angle hysteresis and rolling angle (&lt;5°). Surface morphological characterizations showed the formation of nanoscale hierarchical structures which resulted in a stable Cassie state due to the effective entrapment of air and exhibiting self-cleaning ability. The developed surface showed extreme wetting resilience during exposure to a droplet impingement with an impinging velocity of &gt;2 m/s. Further, these superhydrophobic surfaces were exposed to atmospheric weather conditions to check their robustness. During a rain simulator testing, a developed surface showed low contact angle hysteresis (&lt;10°) after enduring multiple cycles. The processed surface also showed significant de-wetting behavior during condensation experiments and chemical resistance under prolonged exposure. Weathering tests performed under outdoor conditions showed an insignificant influence on the de-wettability of the processed sample. The present study highlights the fabrication of superhydrophobic durable metallic surfaces through a facile and green fabrication route for multifunctional applications.

Superhydrophobic Coating Derived from the Spontaneous Orientation of Janus Particles.

A superhydrophobic surface was achieved using a monolayer of the perpendicularly oriented epoxy-silica@polydivinylbenzene (PDVB) Janus particles (JPs) on an epoxy resin substrate. The epoxy-silica@PDVB JPs were synthesized from the silica@PDVB/polystyrene (PS) JPs through selective etching of the PDVB/PS belly and the surface modification of the silica part. The modified silica parts can be covalently bonded with the epoxy resin to make the perpendicular orientation spontaneous as well as the coating more robust. The outward PDVB bellies can constitute the micro-/nanoscale hierarchical structures for the superhydrophobic property. The superhydrophobic coating exhibits water repellence and self-cleaning properties. Moreover, the coating exhibits good chemical durability that it can keep the superhydrophobic property after long-time immersion in various aqueous solutions and organic solvents. The coating is still superhydrophobic after water flushing and mechanical wearing, showing the perfect mechanical durability.

Wettability improvement of ceramic membrane by intercalating nano-Al2O3 for oil and water separation

The objective of this study is to investigate the spontaneous wettability response of alumina nanocomposites deposited onto hollow fibre ceramic based membrane. Bare membrane was fabricated from kaolin powder using a phase inversion technique and sintering process. The nanocomposites were synthesized by varying alumina nanoparticles composition via a sol-gel method. A dip-coating approach was used to deposit perfluorooctanoate (PFO) with alumina nanoparticles and poly (diallyl dimethylammonium chloride) (PDDA) on the active layer of the hydrolysed bare membrane to improve on the inefficiency of the conventional oil/water separation materials and easy fouling of the bare ceramic membrane. Both the bare membrane and coated membrane were characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and contact angle measurement. The performance of the membrane was tested for oil rejection and oil flux. The results suggest that higher sintering temperature improves the flexural strength of the bare membrane. The oil flux performance showed a decrease from 37.02 L/m2 h to 2.50 L/m2 h when the loadings of alumina nanocomposites (PDADMAC-Al2O3/PFO, PAP) coated onto the bare membrane was increased from 0.1 wt. to 0.6 wt., and in comparison, the oil rejection performance revealed an increase in the oil repellence from 80 to 98%. The oil contact angle was obtained at 125° after the chemical stability test in an acidic medium. The cogent mechanism of oleophobic and hydrophilic character of the coated membrane can be ascribed to the nano-scale hierarchical structure, as a result of alumina intercalated on the PFO. Alumina nanocomposite provides an excellent surface-coating material for ceramic-based hollow fibre membrane for oil-water separation to address the needs of wastewater industries.