Transformation Of Nanostructures Research Articles

Microstructural Evolution of Quaternary AlCoCrNi High-Entropy Alloys during Heat Treatment.

This study examines the microstructural evolution and mechanical properties of quaternary AlCoCrNi high-entropy alloys after heat treatment at 873 K for 72 and 192 h. The changes in nanostructure and phase transformation based on the heat treatment duration were as follows: B2 dendrite + BCC interdendrite and sigma phases after 72 h; B2 dendrite and interdendritic sigma phases + BCC after 192 h. After annealing, the morphology of the dendritic region shifted from spherical to needle-like, and the interdendritic region transformed from a spinodal-like to a plate-like morphology. Additionally, a phase transformation was observed in the dendritic regions of the annealed alloys at the nano-scale. The presence of the sigma phase in AlCoCrNi high-entropy alloys significantly improved the yield strength to around 1172 MPa; nevertheless, it decreased the compressive strain rapidly to 0.62%.

Multi-sensor-based process monitoring and quality assessment during laser forming of novel titanium foam to prevent cellular structure damage

Titanium foam finds its application in different fields like battery electrodes, heat exchangers, biological prosthetics, and lightweight structures for aeronautical parts. However, the inherent property of the foam to fail during mechanical loading conditions poses a challenge in providing final shape to these materials for practical applications. The present work investigates forming of Titanium foam (Ti Foam) using inline process monitoring for achieving controlled foam deformation while maintaining its quality without failure. Infrared (IR) pyrometer and laser-based displacement sensor were used to monitor the foam deformation behavior and thermal signature. The monitoring data were used to understand the process mechanism of laser forming. The bending mechanism within the foam was analysed with respect to solid sheet bending process. The correlation of the achieved bending angles, was attempted with the process parameters for surface, microstructural, elemental, and phase transformation. A critical analysis of Ti foam behavior, like surface melting, in situ oxidation, phase transformation, and formation of nano-structures on foam surface was addressed based on process parameter combinations. Micro-computed tomography (μCT) was carried out to investigate the pore deformation mechanism. Metallurgical characterisations for foam surface and phase analysis were carried out using X-ray photoelectron spectroscopy (XPS) and tunneling electron microscopy (TEM) to determine the chemical and crystallographic states of the laser-formed surface.

Green synthesis of selenium nanoparticles capped by Tithonia diversifolia pectin for anti‐inflammation activity

AbstractThis work reports a green method to synthesize pectin‐capped selenium nanoparticles (PT‐SeNPs) using ascorbic acid as a reductant under mild conditions. Pectin was extracted from Tithonia diversifolia (Hemsley) A. Gray plant. Pectin played the role of a capping agent preventing the agglomeration of selenium nanoparticles. The synthesized PT‐SeNPs were characterized by UV–Vis spectrophotometry, EDX spectroscopy, TEM, DLS, FT‐IR, XRD, and TG‐DTA. The TEM and DLS techniques revealed monodispersed spherical selenium nanoparticles with sizes range of 100–200 nm. The amorphous PT‐SeNPs showed a phase transformation of nanostructure at 132 °C and a sublimation at 486 °C. The anti‐inflammatory of the obtained PT‐SeNPs was investigated in ethyl phenylpropiolate (EPP)‐induced rats. Rats treated with PT‐SeNPs exhibited ear edema inhibitions of 34.8%, 43.3%, and 46.7%, respectively at 30, 60 and 90 min after EPP injection.

Thermally stimulated structural evolution of bimetallic nanoplatelets - Changing from core-shell to alloyed to Janus nanoplatelets

Gold-based bimetallic nanostructures exhibit unique optical and catalytic properties that are strongly dependent on their composition and nanoscale geometry. Here we show the nano-structural transformation of mesoporous-silica-coated Au-M (Ag, Pd, Pt) core-shell nanoplatelets (NPLs) with a triangular shape to alloyed platelets at temperatures at least 300 °C below the lowest melting point of the metals while still retaining the out-of-equilibrium triangular shape and intact mesoporous shell. Before the alloying started the rough core-shell morphology of the Au–Pd and Au–Pt NPL systems were first observed to relax into a much smoother core-shell morphology. The alloying temperature was found to be related to the melting points and atom fractions of the shell metals; the higher the melting point and atomic fraction of the shell metal, the higher the temperature required for alloying. The highest alloying temperature was found for the Au–Pt system (650 °C), which is still hundreds of degrees below the bulk melting points. Surprisingly, a phase separation of Au and Pt, and of Au and Pd, was observed at 1100 °C while both systems still had an anisotropic plate-like shape, which resulted in Janus-like morphologies where the pure Pt and pure Pd ended up on the tips of the NPLs as revealed via in-situ heating in the scanning transmission electron microscope (STEM). The Janus-type morphologies obtained at elevated temperatures for the NPLs composed of combinations of Au–Pt and Au–Pd, and the smooth core-shell morphologies before alloying, are very interesting for investigating how differences in the bi-metallic morphology affect plasmonic, catalytic and other properties.

Dominant role of laser-generated nano-structures on enhancement of interfacial bonding strength by laser surface modification

Laser surface modification has been widely applied to the pre-treatment of material surfaces for interface bonding, however, laser-treated surfaces face an inevitable risk of environmental exposure during engineering application, and it remains unclear how laser-induced modifications change under environmental exposure. This study investigates the robustness of laser-treated aluminum surface under typical atmospheric and aqueous environments at different temperature from −40 °C to 80 °C. Although the carbon elemental content and water contact angle greatly fluctuate with exposure environments from 23 at.% to 33 at.%, and from 0° to 148°, respectively, laser-treated surfaces exhibit stable improvement of ∼25 % in bonding strength compared to untreated condition even after 30 days exposure. Notably, hygrothermal exposure of 80 °C and 95 %RH significantly declines bonding strength by ∼45 %, and this strength degradation is accompanied by 1.8 % increase of carbon elemental content and water contact angle of ∼150°. Results reveal that laser-generated nano-structures play crucial role in strength improvement, instead of carbonaceous contaminants and surface polarity, and nanostructure transformation causes an apparent strength degradation and change of fracture mode from cohesive to interface. This work uncovers the dominant role of laser-generated nano-structures in enhancing interfacial bonding strength, and provides supports for engineering application of laser surface modification.

Nanostructural phase transformations in eutectoid reactions of binary alloys

It is shown that eutectoid reactions of binary alloys are nanostructural processes. The main phase, which decays during the eutectoid reaction, is formed during the crystallization of a metal melt of eutectoid composition. This process is nanostructured. In it, the main elements of microcrystals are the nanocrystals of the alloy components. During the eutectoid reaction, the microcrystals of the main phase disintegrate into nanocrystals. Microcrystals of the other two phases are formed from them.

Intrinsic and Dynamic Heterogeneity of Nonlamellar Lyotropic Liquid Crystalline Nanodispersions.

Nonlamellar lyotropic liquid crystalline (LLC) nanoparticles are a family of versatile nano-self-assemblies, which are finding increasing applications in drug solubilization and targeted drug delivery. LLC nanodispersions are heterogeneous with discrete nanoparticle subpopulations of distinct internal architecture and morphology, frequently coexisting with micelles and/or vesicles. Diversity in the internal architectural repertoire of LLC nanodispersions grants versatility in drug solubilization, encapsulation, and release rate. However, drug incorporation contributes to the heterogeneity of LLC nanodispersions, and on exposure to biological media, LLC nanodispersions often undergo nanostructural and morphological transformations. From a pharmaceutical perspective, coexistence of multiple types of nanoparticles with diverse structural attributes, together with media-driven transformations in colloidal characteristics, brings challenges in dissecting biological and therapeutic performance of LLC nanodispersions in a spatiotemporal manner. Here, we outline innate and acquired heterogeneity of LLC nanodispersions and discuss technological developments and alternative approaches needed to improve homogeneity of LLC formulations for drug delivery applications.

Monolayer Borophene Formation on Cu(111) Surface Triggered by Step Edge.

Borophene, a promising material with potential applications in electronics, energy storage, and sensors, is successfully grown as a monolayer on Ag(111), Cu(111), and Au(111) surfaces using molecular beam epitaxy. The growth of two-dimensional borophene on Ag(111) and Au(111) is proposed to occur via surface adsorption and boron segregation, respectively. However, the growth mode of borophene on Cu(111) remains unclear. To elucidate this, scanning tunneling microscopy in conjunction with theoretical calculations is used to study the phase transformation of boron nanostructures under post-annealing treatments. Results show that by elevating the substrate temperature, boron nanostructures undergo an evolution from amorphous boron to striped-phase borophene (η = 1/6) adhering to the Cu step edge, and finally to irregularly shaped β-type borophene (η = 5/36) either on the substrate surface or embedded in the topmost Cu layer. dI/dV spectra recorded near the borophene/Cu lateral interfaces indicate that the striped-phase borophene is a metastable phase, requiring more buckling and electron transfer to stabilize the crystal structure. These findings offer not only an in-depth comprehension of the β-type borophene formation on Cu(111), but also hold potential for enabling borophene synthesis on weakly-binding semiconducting or insulating substrates with 1D active defects.

Grapefruit juice containing rich hydroxyl and oxygenated groups capable of transforming 1D structure of NiCo2O4 into 0D with excessive surface vacancies for promising energy conversion and storage applications

Fabrication of an efficient electrode material is highly demanded for obtaining high energy conversion electrochemical system. In this study, we describe a green and innovative approach of using grape fruit juice as a high carrier of reducing and surface modifying agents for manipulating the surface properties of nickel‑cobalt bimetallic oxide NiCo2O4 nanostructures. Different amounts of grape fruit juice were used to discern its role on the morphological and surface vacancies of NiCo2O4 nanostructures during oxygen evolution reaction (OER). Importantly, the physical characterization revealed the morphological transformation of NiCo2O4 nanostructures from 1D nanorods to short range 0D nanoparticles. Furthermore, the surface studies have shown that NiCo2O4 nanostructures prepared with grapefruit juice have high density of surface vacancies and higher amount of Ni2+ and a Co2+ metallic ions on the surface of NiCo2O4 compare to pure NiCo2O4 nanostructures. The OER of electrodes modified with NiCo2O4 nanostructures, particularly (sample-2, 2 mL of grape fruit juice) gave rise to an overpotential value of 260 mV at 10 mAcm−2 in 1.0 M KOH aqueous solution along with high durability/stability for 40 h. Additionally, the obtained electrochemical impedance spectroscopy value of 80 Ω and active surface area of 18.1 μFcm−2 attested for the excellent OER performance of NiCo2O4 nanostructures (sample-2). Eventually, the proven enhancement in surface vacancies, alternation in the mixed oxidation states of both Ni and Co together with the morphological transformation that have been accomplished via the green, simple, and low-cost strategy of using grape juice make it a suitable option for large scale production of wide range of multifunctional metal oxides and related nanostructured materials for plethora of energy conversion and storage applications.

Nanostructure transformation as a signature of oxygen redox in Li-rich cathodes

Nanostructure transformation as a signature of oxygen redox in Li-rich cathodes

PH-Triggered Size-Transformable and Bioactivity-Switchable Self-Assembling Chimeric Peptide Nanoassemblies for Combating Drug-Resistant Bacteria and Biofilms.

Drug-resistant bacteria and biofilm-associated infections are prominent problems in the field of antibacterial medicine, seriously affecting human and animal health. Despite the great potential of nanomaterials in the antibacterial field, overcoming the paradox of size and charge, efficient penetration, and retention within biofilms remain a formidable challenge. Here, self-assembling chimeric peptide nanoassemblies composed of multiple functional fragments are designed for the treatment of drug-resistant bacteria and biofilm-associated infections. Notably, the chimeric peptide self-assembles into nanofibers at pH 7.4 and is transformable into nanoparticles in the acidic biofilm-infected microenvironment at pH 5.0, and thus achieves a size reduction and charge increase, improving the penetration into the bacterial biofilms and killing drug-resistant bacteria by a mechanism dominated by membrane cleavage. In vivo mouse and piglet infection models confirm the ability of chimeric peptide nanoassemblies to reduce bacterial load within biofilms. Collectively, this research on pathological-environment-driven nanostructural transformations may provide a theoretical basis for designing high-performance antibacterial nanomaterials and advance the application of peptide-based nanomaterials in medicine and animal husbandry.

Utilizing in-situ construction of tailored block copolymer nanostructures to enhance CF/epoxy composites compressive properties

The imbalance in the compressive strength to tensile strength ratio of carbon fiber reinforced polymer (CFRP) composites is a key factor that limits its lightweight application. Increasing the tenacity and strength of resin matrix has been evidenced as an effective method to address this problem. In this work, an interesting strategy that block copolymer nanostructures built in-situ in epoxy to simultaneously increase its tensile strength and fracture toughness, is provided. Benefitting from the nanostructures, the tensile strength and fracture toughness of epoxy matrix are increased by 19% and 236%, respectively, without lowering its Tg. Block copolymers’ impact on the morphologies and transformation of nanostructures, the relationship between nanostructures and epoxy properties, and the strengthening and toughening mechanism are systematically studied. Meanwhile, these epoxy resins with excellent tensile properties and toughness are selected for the verification of the CFRP composite performance. The compression properties and interfacial properties of CFRP composites were 34.5% and 17.8% improved, demonstrating that in-situ constructing nanostructures in resin matrix is an effective strategy to enhance the compressive and interfacial properties of composites. Our research is anticipated to offer some fresh suggestions for creating high-performance CFRP composites.

An Accelerated Method for Investigating Spectral Properties of Dynamically Evolving Nanostructures

The discrete-dipole approximation (DDA) is widely applied to study the spectral properties of plasmonic nanostructures. However, the high computational cost limits the application of DDA in static geometries, making it impractical for investigating spectral properties during structural transformations. Here we developed an efficient method to simulate spectra of dynamically evolving structures by formulating an iterative calculation process based on the rank-one decomposition of matrices and DDA. By representing structural transformation as the change of dipoles and their properties, the updated polarizations can be computed efficiently. The improvement in computational efficiency was benchmarked, demonstrating up to several hundred times acceleration for a system comprising ca. 4000 dipoles. The rank-one decomposition accelerated DDA method (RD-DDA) can be used directly to investigate the optical properties of nanostructural transformations defined by atomic- or continuum-scale processes, which is essential for understanding the growth mechanisms of nanoparticles and algorithm-driven structural optimization toward enhanced optical properties.

Construction and Structural Transformation of Metal-Organic Nanostructures Induced by Alkali Metals and Alkali Metal Salts.

Metal-organic nanostructures are attractive in a variety of scientific fields, such as biomedicine, energy harvesting, and catalysis. Alkali-based metal-organic nanostructures have been extensively fabricated on surfaces based on pure alkali metals and alkali metal salts. However, their differences in the construction of alkali-based metal-organic nanostructures have been less discussed, and the influence on structural diversity remains elusive. In this work, from the interplay of scanning tunneling microscopy imaging and density functional theory calculations, we constructed Na-based metal-organic nanostructures by applying Na and NaCl as sources of alkali metals and visualized the structural transformations in real space. Moreover, a reverse structural transformation was achieved by dosing iodine into the Na-based metal-organic nanostructures, revealing the connections and differences between NaCl and Na in the structural evolutions, which provided fundamental insights into the evolution of electrostatic ionic interactions and the precise fabrication of alkali-based metal-organic nanostructures.

Twin-induced transformation strengthening of CoCrNi-based medium-entropy alloy with a gradient nanostructure

Single-phase face-centered cubic (fcc) medium-entropy alloys (MEAs) generally exhibit good ductility but insufficient room temperature strength that limits their potential application. Here, a deformation mechanism of twin-induced transformation was achieved to strength the CoCrNi-base alloy with gradient nanostructure obtained by surface mechanical rolling treatment (SMRT) technique. Significantly, the SMRT processed CoCrNi-based alloy exhibits a substantial improvement in the mechanical property comparing with the wrought counterpart by increasing the yield strength from 964 to 1664 MPa and the ultimate tensile strength from 1210 to 1883 MPa, while maintaining a uniform elongation of 11.3%. The enhanced combination of strength and ductility attributes to the extra hardening from the synergistic effect of nanostructure and phase transformation.

3D Flower-like TiO2 Nanostructures: Anatase-To-Rutile Phase Transformation and Photoelectrochemical Application

Flower-like TiO2 nanostructures were obtained by chemical oxidation of Ti foil using H2O2 combined with subsequent annealing. This paper offers an analysis of the phase transformation of 3D flower-like titanium dioxide nanostructures. The role of the annealing atmosphere, sample thickness, grain shape, and nanoflower size are discussed. The nanostructures were examined using SEM, XRD, and Raman spectroscopy. Due to the nature of these two processes, the morphology of these nanomaterials is complex, and is obtained through a reaction involving Ti foil and H2O2 at 80°C. A distinction is made between the layer composed of small grains at the substrate/oxide interface, elongated crystal-like structures, and outer spongle-like film. The annealing parameters, such as atmosphere (air or argon) and temperature (450 or 600 °C), affect phase composition. The photoelectrochemical performance of the anode based on flower-like TiO2 has been shown. The thickness and phase composition of the anodes are factors that strongly affect the photocurrent. The multiphase heterojunctions proposed for 3D flower-like TiO2 photoanodes in photoelectrochemical (PEC) cells suppose that the conduction band of anatase should be above rutile. The highest photoelectrochemical performance was obtained for a photoanode composed of 20–40% anatase and an associated thickness of 0.75–1.5 µm.

Iron Nanoparticles to Catalyze Graphitization of Cellulose for Energy Storage Applications

The production of highly graphitic carbon from bioresources is an environmentally friendly approach to synthesize graphene for energy storage applications. Iron catalytic graphitization of cellulose, the most abundant biopolymer on earth, is an alternative approach as until now, cellulose has been classified as poorly graphitizable material. In this study, the impact of processing temperature and iron impregnation on the extent of graphitization of the cellulose-derived graphitic carbon nanostructure is uncovered by combining Raman spectroscopy, X-ray diffraction, transmission electron microscopy, and X-ray pair distribution function analysis. Raman spectroscopy is used in an innovative way to describe the evolution of the average graphitic phase size where the ash content misguides the X-ray diffraction analysis. A correlation was established between (i) the in-plane crystallite size La and the ID″/IG first-order ratio, (ii) the out-of-plane Lc crystallite size and the IG/Itot′ second-order ratio, and (iii) the second-order Raman IG′/Itot′ ratio and the average number of carbon layers per carbon crystallite. For iron-impregnated cellulose, phase quantification and analysis of the spatial distribution reveal highly crystalline rhombohedral graphite surrounded by a nanocrystalline carbon matrix. We explicitly show that traditionally non-graphitizable carbons can be used to form a graphite-like structure with multilayers of graphene sheets by careful addition of widely available nontoxic metal as catalysts. The study also shows that the impact of the catalyst is much more effective than the temperature in the nanostructure transformation. The proposed approach and the results obtained provide interesting insights that should stimulate further works aimed at extending the knowledge in the field.

Wettability transition of metallic surfaces from laser-generated superhydrophilicity to water-induced superhydrophobicity via a facile and eco-friendly strategy

Superhydrophobic metallic surfaces exhibit superior self-cleaning and anti-corrosion properties, but facile and pollution-free preparation of such surfaces remains a challenge. Herein, we propose an eco-friendly strategy by using ns-laser treatment followed by simple hygrothermal treatment (95%RH @ 80 °C), and this strategy is applicable to facilely preparing superhydrophobicity for various metals. Immediately after ns-laser treatment, ultra-porous nano-fibers composed of amorphous Al-Al2O3 mixture were produced, and rendered aluminum surface superhydrophilic via local capillary forces. Counterintuitively, subsequent hydrothermal treatment accelerated wettability transition to superhydrophobicity, and comparative analysis and theoretical modelling strongly suggest that the mechanism of accelerated transition is deeply dominated by nanostructure transformation. A roughened but compact surface layer of spherical AlOOH nanocrystals was reconstructed to enable water droplet in Wenzel wetting state. Our results shed new insights into the origin of wettability evolution commonly reported at various processing/service stages, and demonstrate a novel method to construct superhydrophobic metallic surfaces.

Dynamic Assembly of Cascade Enzymes by the Shape Transformation of a DNA Scaffold

AbstractWithin cells, the close spatial arrangement of cascade enzymes facilitates the channeling of intermediates and enhances cascade reaction efficiency. Reconfigurable DNA nanostructures, owing to their structural controllability and precise spatial addressability, are promising tools for mimicking such processes. In this study, a 3D DNA origami scaffold, with a dynamic shape transformation from its open boat form to a closed hexagonal prism induced by toehold‐mediated strand displacement, is designed to investigate the enzyme cascade reaction of xylose reductase and xylitol dehydrogenase from D‐xylose metabolic pathway. Enzymes are assembled on the DNA scaffold in its open state, which is subsequently closed by the assistance of DNA sequence‐specific closing keys. The enzyme cascade efficiency is much higher in the static encapsulated closed state than in the open state due not only to the enzyme proximity but also the environmental factors of 3D DNA structure. These results provide novel insights into controlling enzyme cascade reactions by inducing the shape transformation of DNA nanostructures and how environmental factors affect the action of multi‐enzyme complexes in the cell.

Annealing atmospheres induced structural and morphological transformation of zinc tin hydroxide nanostructures

The variation in crystallinity, morphology and phase of zinc tin hydroxide nanostructures are investigated after annealing at different (oxidizing, non-oxidizing and reducing) atmospheres. The zinc tin hydroxide nanostructures are prepared using hydrolysis assisted co-precipitation method. Annealing in oxidizing (oxygen and air) and non-oxidizing (nitrogen and argon) atmospheres do not have a significant effect on morphological and structural properties. However, the annealing in the reducing (ammonia) atmosphere converts the cubic nanostructures into nanorods and spherical particles. The zinc tin hydroxide forms three new phases (ZnON, SnO2 and Sn) after annealing in reducing atmosphere. The formation of ZnON and SnO2 phases are evident in Raman and XPS analysis. The reducing atmosphere (ammonia) changes the reaction kinetics leading to diffusion control crystal growth that could be responsible for such structural and morphological transformation. The bandgap is significantly changed after morphological and structural transformation with notable variation in photocurrent density, charge transfer resistance, and charge carrier concentration.