Formation Mechanism Of Structures Research Articles

High hydrogen permselective carbon molecular sieve membrane and its structural formation mechanism

A novel hydroxyl-containing polyetherimide (named BAHPPF-ODPA) with highly aromatic backbone and contorted chain conformation was designed and synthesized as the precursor to fabricate carbon molecular sieve membranes (CMSMs) for H2/N2 separation. The structural evolution from polymeric precursor to carbon during pyrolysis was investigated using characterization techniques combined with pyrolysis simulation. And the relationship between membrane structure formation and their separation performance was explored here. Results indicate that the generation and evolution of pyrolysis products including formed fragments and gases, which depend on the precursor chemistry and pyrolysis conditions, exhibited a significant influence on microstructure and performance of derived CMSMs. Designing precursors with an aromatic backbone and contorted structure and precisely tuning pyrolysis temperature allows the fabrication of CMSMs with controllable micropore structure and excellent H2 separation performance. The BAHPPF-ODPA derived CMSM pyrolyzed at 600 °C exhibited the high H2 permeability of about 3500 Barrer and the superior H2/N2 selectivity of more than 400 were obtained after 750 h of long-term mixed gas (75:25 mixture of H2/N2) testing, showing promising application prospects. The experimental and simulation results obtained here would be beneficial to understand the CMS formation and reasonable to design the precursor molecular structure for fabrication of high-performance CMSMs.

Grain boundary engineering process for nano reinforced aluminum matrix composites

It is challenging to obtain a balance of strength and ductility for alloys and their composites. They are expected to exhibit good comprehensive properties by adjusting the grain boundary character and/or introducing twin structures. However, for coarse grained aluminum with high stacking fault energies, twin structures are rarely found. In this study, a grain boundary engineering process was carried out on coarse grained aluminum containing nano-reinforcements via an alternated compression deformation, followed by an annealing treatment. The effects of the thermo-mechanical process and alloy elements on the microstructures of the composites were analyzed. The mechanical properties and inter-granular corrosion properties of the composites were evaluated. Twin structures could be generated in these alloys. After thermo-mechanical process, the composites exhibited good plasticity as well as higher strength. A Σ3 twin boundary hindered inter-granular corrosion crack propagation. The formation mechanism of the twin structures and the strengthening mechanism are discussed.

INFLUENCE OF STRUCTURAL FACTORS ON THE MECHANICAL STRENGTH OF GLASS-CERAMIC PROPANTS

The results of studying the influence of the chemical composition, material structure, crystallization features and isomorphic substitutions in pyroxene solid solutions of the augite type on the mechanical characteristics of glass ceramics are presented. The mechanism of structure formation is shown, which consists in the crystallization of chromium spinel and subsequent growth on its surface of crystals of a pyroxene solid solution of the augite type in the form of spherical intergrowths, which ensures high mechanical strength of glass-ceramic proppants. It has been established that during the course of isomorphic substitutions in the diopside-augite series, the mechanical strength of glass-ceramic proppants increases, which is associated with a decrease in bond lengths, an increase in their number, and compaction of the unit cell.

Pore-forming mechanisms and sodium-ion-storage performances in a porous Na3V2(PO4)3/C composite cathode.

Na3V2(PO4)3 (NVP) is regarded as one of the most promising cathode materials for sodium-ion batteries (SIBs). However, it suffers from a dense bulk structure and low intrinsic electronic conductivity, which lead to limited electrochemical performances. Herein, we propose a surfactant-assisted molding strategy to regulate the pore-forming process in NVP/C composite cathode materials. More precisely, the forming process of the pores in NVP could be easily controlled by utilizing the huge difference in critical micelle concentration of a surfactant (cetyltrimethylammonium bromide, CTAB) in water and ethanol. By reasonably modulating the ratio of water and ethanol in the solution, the as-synthesized NVP/C sample exhibited a three-dimensional interconnected structure with hierarchical micro/meso/macro-pores. Benefiting from these hierarchical porous structures in NVP/C, the structural stability, contact surface with the electrolyte, and electronic/ionic conductivity were improved simultaneously; whereby the optimized porous NVP/C sample exhibited an excellent high-rate performance (61.3 mA h g-1 at 10 C) and superior cycling stability (90.2% capacity retention after 500 cycles at 10 C).

LOW-TEMPERATURE CATALYZED GROWTH AND PLASMONIC PROPERTIES OF COLUMNAR Au-SiOx NANOCOMPOSITE THIN FILMS

The optical properties of noble metal nanoparticles (NPs) can be efficiently controlled by their incorporation into host matrix films. Here, we report on the fabrication of composite films of gold NPs in a silicon suboxide matrix by a novel approach using a combination of pulsed laser deposition for NP production and gas-jet, electron-beam plasma chemical vapor deposition for low-temperature (300°C) synthesis of a SiO<sub>x</sub> (x = 0.38-1.55) thin film as a matrix for the NPs. The produced nanocomposite exhibits unexpected plasmonic properties, non-monotonically dependent on the matrix thickness, due to a porous columnar matrix structure grown from the NPs with variable oxygen content along the columns. This implies that low-temperature, gold-catalyzed oxidation of silicon occurs during the structure growth. Calculations based on Mie theory show that the refractive index of the obtained SiO<sub>x</sub> matrix can be as low as 1.2 at certain film thicknesses. Mechanisms of the columnar structure formation at different deposition stages are discussed. The synthesis approach can be used for the fabrication of optical thin-film materials with controllable low refractive index.

STATISTICAL ANALYSIS OF GEOLOGICAL AND GEOPHYSICAL PARAMETERS OF THE MONGOLIAN-BAIKAL REGION

The origins and formation mechanisms of neotectonic structures in a part of the Mongolian-Siberian region were identified by geodynamic zoning based on multidimensional statistical analysis of numerical arrays describing geological-geophysical and geological-geomorphological processes. These processes in the regional lithosphere were described by a set of 11 geological and geophysical parameters, divided into three main groups using the hierarchical method of cluster analysis. The first group includes the seismic moment, the density of active faults, the rates of current horizontal deformations, and the magnitude of the deep heat flow. The second group involves the thicknesses of the earth’s crust and exogenous active layer, the velocities of current horizontal movements, and the amplitudes of vertical neotectonic movements. The third group includes gravity anomalies and the lithosphere thickness. The spatial grouping of parameters by cluster analysis (K-means method) yields seven clusters, whose spatial position and composition are determined by the geological history, geological structure, geodynamic evolution of the region, and the current deformation rates. Some clusters characterize large rigid lithospheric blocks, while other clusters describe large active fault systems in the given area. The search for latent factors that make the greatest contribution to the dispersion of the geological and geophysical parameter values was carried out using the principal component method, which makes it possible to minimize the number of factors. Four main factors were identified for areas that differ in the morphology and origin of neotectonic structures: (i) higher horizontal compressive and tensile strains, (ii) dynamic effect of mantle anomalies, manifested in uplifts and arching, (iii) activation of thinned lithosphere within the boundaries of lithospheric plates and large blocks, and (iv) active shear deformation of the earth’s crust. The results of clustering and factor analysis of numerical arrays describing the geological-geophysical and geological-geomorphological processes within the Mongolian-Siberian region can be interpreted in the framework of physical mesomechanics.

Structural characteristics and formation mechanism of global cross-border M&A networks: Based on the exponential random graph model

Structural characteristics and formation mechanism of global cross-border M&A networks: Based on the exponential random graph model

Structural measures, multidimensional effects and formation mechanisms of workplace fear of missing out

Structural measures, multidimensional effects and formation mechanisms of workplace fear of missing out

Phase Equilibria, Diffusion and Structure in the Epoxypolycaprolactone System

Currently, there is no quantitative approach for the phase structure of cured thermoplastic systems modified with thermoplastic predicting. To solve this problem, we carried out the first stage of the study on a model polycaprolactone-epoxy oligomer (PCL-DGEBA) system. Using differential scanning calorimetry (DSC), refractometry and optical interferometry, a phase diagram for PCL-DGEBA mixtures was constructed, and the Flory-Huggins interaction parameters of PCL-DGEBA mixtures were calculated. The structure of PCL-DGEBA mixtures with different PCL content was analyzed by optical microscopy. The change in the structure formation mechanism with increasing PCL concentration was shown. The diffusion coefficients are calculated by the Motano-Boltzmann method. The values of the apparent activation energy of the viscous flow PCL and of self-diffusion of DGEBA are determined. The obtained data will be used for the in situ curing kinetics and phase equilibria in the diffusion zone investigations in order to develop a quantitative method for predicting the phase structure of cured systems.

Two Novel Pyrene Tetra-Sulfonate Europium Coordination Polymers: Structure Formation Mechanism Analysis and Sequential Modulation Strategy

For the purpose of broadening the understanding of the sulfonic acid coordination mechanism, a coordination system consisting of Eu(III) ion and 1,3,6,8-pyrene tetra-sulfonate (1,3,6,8-PTS) ligand was chosen as the typical research object. By step regulating the volume ratio of mixed solvents and the molar ratio of metal salts to ligands, two pyrene tetra-sulfonate europium coordination polymers, Eu6(μ6-O)(μ3-OH)8(NO3)6(1,3,6,8-H2PTS)(H2O)10 (1) and Eu(NO3)(1,3,6,8-PTS)0.5(H2O)3·0.5bipy (2), were obtained in sequence. Compound 1 shows a 1D chain-like structure interconnected with 1,3,6,8-PTS bridging ligands and rare [Eu6(μ6-O)(μ3-OH)8(NO3)6]2+ cluster nodes, while compound 2 shows a 2D layered structure. Further structural comparison with compound Eu(1,3,6,8-PTS)(H2O)7·4H2O·Hbipy (EuPTSbp-1) was discussed in detail and the structure formation mechanism was analyzed. On this basis, a sequential modulation strategy for pyrene tetra-sulfonate europium coordination polymers was proposed.

Perspectives on MOVPE-grown (100) β-Ga2O3 thin films and its Al-alloy for power electronics application

Beta gallium oxide (β-Ga2O3) is a promising ultra-wide bandgap semiconductor with attractive physical properties for next-generation high-power devices, radio frequency electronics, and solar-blind ultraviolet radiation detectors. Here, we present an overview and perspective on the development of MOVPE-grown (100) β-Ga2O3 thin films and its role in supplementing high-power electronics. We review the development path of the growth process on (100) β-Ga2O3 thin films with a discussion regarding the solved and remaining challenges. The structural defect formation mechanism, substrate treatment strategies, and different growth windows are analyzed to optimize the grown film to fulfill the requirements for device fabrication. Toward industrial applications, MOVPE-grown β-Ga2O3 thin films are evaluated in two aspects: thick layers with smooth surface roughness and the electrical properties in terms of high carrier mobility and low doping concentration. Based on the reviewed results, we propose strategies in substrate preparation treatments and supportive tools such as the machine learning approaches for future growth process optimization and envision the rising interest of the β-Ga2O3-related alloy, β-(AlxGa1−x)2O3.

Characterization of dislocation microstructures in near-[formula omitted] single crystal copper using high-voltage scanning transmission electron microscopy

Metallic structures are prone to failure caused primarily by fatigue-related damage to the structural material. Fatigue behavior is strongly correlated with dislocation structures in metals. Therefore, investigating the formation of dislocation structures is essential for understanding the fatigue process. The dislocation structure in face-centered cubic crystals has a strong orientation dependence. However, the detailed characteristics and evolution process of dislocation structures of fatigued [1‾11] single crystal copper are still insufficient. This study investigated dislocation structures in near-[1‾11] single crystal copper cyclically deformed at room temperature under different constant plastic shear strain amplitude (γpl) to analyze the formation mechanism of dislocation structures and their relationship with fatigue behavior. Characteristic dislocation structures were characterized by adopting multiple planes using a high-voltage scanning transmission electron microscope. With increasing shear strain amplitude, a vein-like structure along the (1‾11) plane gradually developed into a wall structure. When γpl ≥ 1 × 10−3, deformation bands and cell bands were formed to accommodate the higher plastic strain. The state of cell-band development significantly affected the cyclic softening of the single crystal copper. A positive linear relationship existed between the shear stress amplitude and the reciprocal of the cell width.

Self-Propagating High-Temperature Synthesis of the Heterophase Materials in the Zr–Mo–Si–B System: Kinetics and Mechanisms of Combustion and Structure Formation

Self-Propagating High-Temperature Synthesis of the Heterophase Materials in the Zr–Mo–Si–B System: Kinetics and Mechanisms of Combustion and Structure Formation

Large amplitude oscillatory shear behavior of thermoresponsive hydrogels: Single versus double network

Double network (DN) hydrogels have been recognized as new tough materials for several industries due to their precise structural platforms and significant properties. However, a comprehensive understanding of microstructural changes of DN hydrogels under large deformations is required to extend their applications. In this work, we use the large amplitude oscillatory shear (LAOS) technique to study the nonlinear response of a thermoresponsive κ-carrageenan/polyacrylamide DN system and its nanocomposite containing graphene oxide (GO) in comparison to its single network components. The results show a combination of strain stiffening and shear thickening nonlinear responses. The elastic intracycle strain stiffening was mainly attributed to the shear-induced increase in the elasticity of network chains and non-Gaussian stretching of individual chains. In addition, the orientation of the κ-carrageenan double helix segments and their enhancing effect on molecular orientation could be proposed as another possible mechanism of strain stiffening. The viscous intracycle shear thickening is also interpreted by two mechanisms of shear-induced temporary structure formation and reformation of dissociated physical interactions. It is also found that the GO nanosheets could contribute to the viscoelastic response by increasing the molecular interactions and, thus, amplification of energy dissipation. Furthermore, temperature dependency of the DN hydrogel owing to the conformational changes of the κ-carrageenan network at sufficiently high temperatures is used to investigate the effect of temperature on nonlinear behaviors. Increasing the temperature is found to have a significant decreasing effect on viscous nonlinearity, while its effect on the elastic nonlinearity was strongly dependent on the strain amplitude. This study provides a better understanding of the correlation between the microstructure and viscoelastic properties for designing tough hydrogels.

Effect of Acetone as Co-Solvent on Fabrication of Polyacrylonitrile Ultrafiltration Membranes by Non-Solvent Induced Phase Separation.

For the first time, the presence of acetone in the casting solutions of polyacrylonitrile (PAN) in dimethylsulfoxide or N-methyl-2-pyrrolidone was studied with regards to thermodynamical aspects of phase separation of polymeric solutions induced by contact with non-solvent (water), formation and performance of porous membranes of ultrafiltration range. The positions of the liquid equilibrium binodals on the phase diagrams of these three-component and pseudo-three-component mixtures were determined. For PAN-N-methyl-2-pyrrolidone-water glass transition curve on a ternary phase diagram was plotted experimentally for the first time. The real-time evolution of the structure of mixtures of PAN with solvents (co-solvents) upon contact with a non-solvent (water) has been studied. The thermodynamic analysis of the phase diagrams of these mixtures, together with optical data, made it possible to propose a mechanism of structure formation during non-solvent induced phase separation of different mixtures. The addition of acetone promotes the formation of a spongy layer on the membrane surface, which decreases the probability of defect formation on the membrane surface and keeps finger-like macrovoids from the underlying layers of the membrane. It was shown that the molecular weight cut-off (MWCO) of the membranes can be improved from 58 down to 1.8 kg/mol by changing the acetone content, while polymer concentration remained the same.

Circular RNAs as diagnostic biomarkers for gastric cancer: A comprehensive update from emerging functions to clinical significances.

The incidence and mortality of gastric cancer ranks as a fouth leading cause of cancer death worldwide, especially in East Asia. Due to the lack of specific early-stage symptoms, the majority of patients in most developing nations are diagnosed at an advanced stage. Therefore, it is urgent to find more sensitive and reliable biomarkers for gastric cancer screening and diagnosis. Circular RNAs (circRNAs), a novel type of RNAs with covalently closed loops, are becoming a latest hot spot in the field of. In recent years, a great deal of research has demonstrated that abnormal expression of circRNAs was associated with the development of gastric cancer, and suggested that circRNA might serve as a potential biomarker for gastric cancer diagnosis. In this review, we summarize the structural characteristics, formation mechanism and biological function of circRNAs, and elucidate research progress and existing problems in early screening of gastric cancer.

Mechanism of high-moisture extruded protein fibrous structure formation based on the interactions among pea protein, amylopectin, and stearic acid

During high-moisture extrusion (HME) processing for plant protein texturization, the interactions among proteins, starch and lipids should determine the formation of fibrous structures, which has not been confirmed systematically. In this study, the mechanism of protein fibrous structure formation during HME processing (58% moisture) was investigated based on the intermolecular interactions among the pea protein, amylopectin and stearic acid. Results suggested that the amylopectin and stearic acid synergistically contributed to improve the fibrous structures such as the hardness and fibrous degree in pea protein extrudate. In the extruder barrel, the complexation among the protein with amylopectin and stearic acid gave rise to the formation of aggregates with higher thermal stability and delayed the formation of protein gel network. In the die, the amylopectin and stearic acid weakened the hydrogen bonds between proteins and hindered the aggregation of legumin and vicilin subunits. In the cooling zone and extrudate, the amylopectin and stearic acid promoted the formation of fibrous structures through an “anchor orientation and flexible cross-linking” mechanism. Namely, the stearic acid as anchors hindered the refolding of protein molecular chains, while the amylopectin promoted the rearrangement, cross-linking and aggregation of protein molecules. The amylopectin and stearic acid synergistically weakened the interaction forces between proteins and led to the formation of more flexible structures in aggregates, which was favorable for the orientation and formation of anisotropic fibrous structures in extrudates. This study provided a theoretical basis for the development and improvement of the plant-based meat substitutes.

Self-propagating high-temperature synthesis of heterophase materials in the Zr–Mo–Si–B system. Kinetics and mechanisms of combustion and structure formation

The paper focuses on the study of the combustion kinetics and mechanisms of elemental mixtures in the Zr–Mo–Si–B system, as well as the analysis of phase and structural transformation stages in the combustion wave. A thermodynamic analysis of potential chemical reactions occurring in the combustion wave was carried out. The reaction of ZrB2 formation is preferred in the range of 298–2500 K. Above 2200 K, the formation of MoB becomes more thermodynamically advantageous as compared to MoSi2. Phase stability estimates of combustion products showed that ZrB2, MoSi2 and MoB phases are in equilibrium. Experimental dependences Тc(Т0) and Uc(Т0) are linear, which implies an unchanged combustion mechanism at T0 = 298÷800 K. Preheating leads to an increase in Uc. Similarly, an increase in the proportion of Zr and B in the mixture has a similar effect, i.e. an increase in heat emission and Tc. With a minimum content of Zr and B, the interaction between Mo and Si with the formation of MoSi2 by the reaction diffusion mechanism is decisive. As the proportion of Zr and B increases, the rise of T0 to 750 K does not affect the Tc. Eeff values (50–196 kJ/mol) confirm the significant influence of liquid-phase processes on the combustion kinetics. The mechanism of structure formation was studied. A Si–Zr–Mo melt is formed in the combustion front. The primary grains of ZrB2 and MoB crystallize from this melt as it is saturated with boron. At the same time, the melt spreads over the surface of Zr and Mo particles. This leads to the formation of ZrSix, MoSix films. Core-shell structures are formed behind the combustion front, which disappear as they move towards the post-combustion zone. The phase composition of products is formed in the combustion front in less than 0.25 s.

3D Printing Using Ti-Al Nanopowders: Mechanisms of Structure Formation

In the presented research work, 3D materials were fabricated by additive moulding by means of extrusion of a mixture of high filled polymers and nanopowders of Ti-Al intermetallides with subsequent sintering at 1100 ± 20 °C, 1200 ± 20 °C and 1250 ± 20 °C (MEAM-HP process). Nanopowders of Ti-Al intermetallides were obtained by the electrical explosion of intertwined aluminium and titanium wires. It was found that the structure of the materials comprises an AlTi matrix with Ti2AlN MAX-phase particles distributed within it, surrounded by a composite layer of Ti3Al-Ti2AlN. Sintering temperature increases led to changes in the concentration of TiAl, Ti3Al and Ti2AlN phases in the samples. Besides that, aluminium oxide particles were discovered in the structure of the materials. It was found that as the sintering temperature was increased from 1100 ± 20 °C to 1250 ± 20 °C, the average microhardness of the samples increased from 193 to 690 HV0.1.

Scalable Multi-Material Additive Manufacturing of Bioinspired Polymeric Material With Metallic Structures Via Electrically Assisted Stereolithography

Abstract Heterogeneous material systems consisting of metallic structures and polymer matrixes are of significance for applications such as integrated circuits, microelectromechanical devices, antennas, sensors, actuators, and metamaterials. Scaly-foot snail which lives in the deep ocean exhibits high strength and temperature resistance due to unique shells made of metal and polymer. Recently, different multi-material structures have been fabricated with metal deposition using multiple manufacturing processes. However, using these complicated hybrid processes is challenging to construct complexthree-dimensional (3D) structures of heterogeneous material with enhanced properties, high resolution, and time efficiency. Here, we establish a novel manufacturing strategy to build bioinspired hierarchical structures with heterogeneous material systems using electrically assisted stereolithography. The photocurable printing solution that can act as an electrolyte for charge transfer was developed, and the curing characteristic of the printing solution was further investigated. A fundamental understanding of the formation mechanism of metallic structures on the polymer matrix was studied through physics-based multi-scale modeling and simulations. The correlation between metallic structures morphology, printing solution properties, and printing process parameters, and their effects in building bioinspired hierarchical structures with heterogeneous materials were identified. Demonstrative test cases were built to verify the printing performance of the proposed approach. This research work will deliver a scalable additive manufacturing (AM) process that can facilitate various interesting applications based on bioinspired heterogeneous material and structures.