Microscopic Structure Properties Research Articles

Influence of assemble patterns on bonding strength of glued bamboo

As a kind of natural composite material, the outer side of bamboo was quite different from its inner side in microscopic structure and mechanical properties. In order to research the effect of these differences on bonding strength of glued bamboo, bamboo strips were bonded by three different forms: outer side to outer side, outer side to inner side and inner side to inner side. Shear strength results indicated that the bamboo sample glued by inner side to inner side has the greatest shear strength value, which is 18.35 MPa, and the other two types have similar shear strength values (approximately 14 MPa). In particular, for the sample glued by outer side to inner side, the broken part is always the outer side. The scanning electron microscope (SEM) images indicated that bamboo fiber cells and parenchyma cells have different failure patterns in compression shear test. For bamboo fiber cells, dominant destruction occurred at the interface between the fibers. And for parenchyma cell, fracture occurred on cell wall and broken the parenchyma cell itself. The interface between bamboo fiber cells was very weak, thus parenchyma cell was the major contributor to shear strength of bamboo. The inner side had higher shear strength because it had higher content of parenchyma cells. The SEM image and shear strength curve also indicated that in the early period of shearing process, the deformed parenchyma cells are in a relax status, and until the later period of shearing process, the parenchyma cells begin to contribute to shear strength.

Community Detection Based on Modularized Deep Nonnegative Matrix Factorization

Community detection is a well-established problem and nontrivial task in complex network analysis. The goal of community detection is to discover community structures in complex networks. In recent years, many existing works have been proposed to handle this task, particularly nonnegative matrix factorization-based method, e.g. HNMF, BNMF, which is interpretable and can learn latent features of complex data. These methods usually decompose the original matrix into two matrixes, in one matrix, each column corresponds to a representation of community and each column of another matrix indicates the membership between overall pairs of communities and nodes. Then they discover the community by updating the two matrices iteratively and learn the shallow feature of the community. However, these methods either ignore the topological structure characteristics of the community or ignore the microscopic community structure properties. In this paper, we propose a novel model, named Modularized Deep NonNegative Matrix Factorization (MDNMF) for community detection, which preserves both the topology information and the instinct community structure properties of the community. The experimental results show that our proposed models can significantly outperform state-of-the-art approaches on several well-known dataset.

Macroscopic Differentiators for Microscopic Structural Nonideality in Binary Ionic Liquid Mixtures.

Combining two ionic liquids to form a binary ionic liquid mixture is a simple yet effective strategy to not only expand the number of ionic liquids but also precisely control various physicochemical properties of resultant ionic liquid mixtures. From a fundamental thermodynamic point of view, it is not entirely clear whether such mixtures can be classified as ideal solutions. Given a large number of binary ionic liquid mixtures that emerge, the ability to predict the presence of nonideality in such mixtures a priori without the need for experimentation or molecular simulation-based calculations is immensely valuable for their rational design. In this research report, we demonstrate that the difference in the molar volumes (ΔV) of the pure ionic liquids and the difference in the hydrogen-bonding ability of anions (Δβ) are the primary determinants of nonideal behavior of binary ionic liquid mixtures containing a common cation and two anions. Our conclusion is derived from a comparison of microscopic structural properties expressed in terms of radial, spatial, and angular distributions for binary mixtures and those of the corresponding pure ionic liquids. Molecular dynamics simulations of 16 binary ionic liquid mixtures, containing a common cation 1-n-butyl-3-methylimidazolium [C4mim]+ and combinations of (less basic) fluorinated {trifluoromethylacetate [TFA]-, trifluoromethanesulfonate [TFS]-, bis(trifluoromethanesulfonyl)imide [NTf2]-, and tris (pentafluoroethyl) trifluorophosphate [eFAP]-} versus (more basic) nonfluorinated {chloride Cl-, acetate [OAC]-, methylsulfate [MeSO4]-, and dimethylphosphate [Me2PO4]-} anions, were conducted. The large number of binary ionic liquid mixtures examined here enabled us to span a broad range of ΔV and Δβ values. The results indicate that binary mixtures of two ionic liquids for which ΔV > 60 cm3/mol and Δβ > 0.4 are expected to be microscopically nonideal. On the other hand, ΔV < 60 cm3/mol and Δβ < 0.4 will lead to molecular structures that are not differentiated from those of their pure ionic liquid counterparts.

Quantitative Delineation of the Low Energy Decomposition Pathway for Lithium Peroxide in Lithium-Oxygen Battery.

Identification of a low‐potential decomposition pathway for lithium peroxide (Li2O2) in nonaqueous lithium–oxygen (Li–O2) battery is urgently needed to ameliorate its poor energy efficiency. In this study, experimental data and theoretical calculations demonstrate that the recharge overpotential (η RC) of Li–O2 battery is fundamentally dependent on the Li2O2 crystallization pathway which is intrinsically related to the microscopic structural properties of the growing crystals during discharge. The Li2O2 grown by concurrent surface reduction and chemical disproportionation seems to form two discrete phases that have been deconvoluted and the amount of Li2O2 deposited by these two routes is quantitatively estimated. Systematic analyses have demonstrated that, regardless of the bulk morphology, solution‐grown Li2O2 shows higher η RC (>1 V) which can be attributed to higher structural order in the crystal compared to the surface‐grown Li2O2. Presumably due to a cohesive interaction between the electrode surface and growing crystals, the surface‐grown Li2O2 seems to possess microscopic structural disorder that facilitates a delithiation induced partial solution‐phase oxidation at lower η RC (<0.5 V). This difference in η RC for differently grown Li2O2 provides crucial insights into necessary control over Li2O2 crystallization pathways to improve the energy efficiency of a Li–O2 battery.

Influence of Al2O3 Addition on Structure and Mechanical Properties of Borosilicate Glasses

Alkali-borosilicate glasses are one of the most used types of glasses with a high technological importance. In order to optimize glasses for diverse applications, an understanding of the correlation between microscopic structure and macroscopic properties is of central interest in materials science. It has been found that the crack initiation in borosilicate glasses can be influenced by changes in network interconnectivity. In the NBS2 borosilicate glass system (74.0SiO2-20.7B2O3-4.3Na2O-1.0Al2O3 in mol%) two subnetworks are present, i.e., a silicate and a borate network. Increasing cooling rates during processing were found to improve glasses crack resistance. Simultaneously, an increase in the network interconnectivity accompanied by an increasing capacity for densification were noticed. Their individual contribution to the mechanic response, however, remained unclear. In the present study the borosilicate glasses were systematically modified by addition of up to 4.0 mol% Al2O3. Changes in the network connectivity as well as the short- and medium-range order were characterized using Raman and NMR spectroscopy. Both the Raman and the 11B NMR results show that four-fold-coordinated boron is converted into three-fold-coordination as the Al2O3 content increases. Additionally, 27Al NMR experiments show that aluminum is dominantly present in four-fold coordination. Aluminum-tetrahedra are thus charge balanced by sodium ions and incorporated into the silicate network. Finally, nanoindentation testing was employed to link the inherent glass structure and its network configuration to the mechanical glass response. It was found that the glass softens with increasing Al2O3 content, which enhances the crack resistance of the borosilicate glass.

ZnO as photocatalyst: An approach to waste water treatment

ZnO nanorods having uniform size have been synthesized using hydrothermal method. Different standard analytical techniques were employed to investigate the microscopic structure and optical properties of the prepared sample. The formation of the hexagonal wurtzite structure of ZnO was established by XRD and SEM analyses. UV-visible spectra of the as-synthesized ZnO show absorption band edge in UV region at 373 nm, corresponding to which the calculated band gap of ZnO nanorods is found to be 3.4 eV. Photodegradation of methylene blue (MB) using ZnO as photocatalyst have also been studied. Experiments revealed that ZnO nanorods with high aspect ratio can degrade 65% of initial concentration of MB in only 50 min.

Influence of $$NO_2^ - $$ on the Microscopic Structure and Physical Properties of the Binary Nitrate Salts: a Molecular Dynamics Simulation Study

Molecular dynamics simulation method was used to study the influence of $$NO_2^ - $$ on both the structure and properties of the binary nitrate salts (60 wt.% NaNO3 + 40 wt.% KNO3). The density and viscosity of the mixtures were experimentally measured and the simulation results met well with the experimental ones. The simulation results showed that, with the addition of $$NO_2^ - $$, the ionic clusters tended to loose and the mobilities of all the ions tended to increase. The density, viscosity, and heat capacity decreased while the thermal conductivity increased with the increase of +++ concentration. The correlation between the microscopic structure and physical properties of the mixtures were discussed and revealed.

Bond additivity model for anisotropic second-harmonic generation from two-dimensional honeycomb lattices

We provide an analytical method for extracting detailed structural information about two-dimensional (2D) honeycomb lattices from optical second-harmonic generation (SHG) anisotropy patterns. When the lattice deviates from the ideal honeycomb structure, we relate the microscopic structural properties, such as bond length and bonding angle, to the macroscopic nonlinear susceptibility tensor based on the molecular bond additivity model. Our method will help quantitative studies of 2D materials with SHG and is readily applied to more general cases.

Investigation of in Vivo Human Cardiac Diffusion Tensor Imaging Using Unsupervised Dense Encoder-Fusion-Decoder Network

Diffusion tensor imaging (DTI) is currently the unique imaging technique that can detect the structure of in-vivo human myocardium without invasivity and radiation. However, it is particularly sensitive to motions, especially respiratory motion that results in serious signal loss in diffusion-weighted (DW) images. This makes it impossible to accurately measure cardiac microscopic structural properties. To cope with such problem, this paper proposes an unsupervised dense-encoder-fusion-decoder network (DEFD-net) to compensate for signal loss in cardiac DW images, which allows investigating in-vivo myocardium structure more accurately. The DEFD-net consists of three modules, namely dense-encoder, fusion module and decoder module. The dense-encoder and decoder are trained firstly with DW images acquired at different trigger delays in an unsupervised manner for extracting local and global features. A fusion strategy is then designed to fuse the extracted features. Finally, the well-trained decoder is used to reconstruct the fused DW image from the fused features. To validate the superiority of the proposed method, comparison with existing methods such as PCAMIP, WIF and U2Fusion is performed on both simulated and acquired datasets. The experimental results showed that the proposed method effectively compensates for motion-induced signal loss in DW images, thus leading to much better DW image quality with respect to existing methods. Moreover, the subsequently derived myocardium fiber structure is more regular.

Luminescence and preparation of Dy2O3 doped SrCO3–WO3–SiO2 glass ceramics

In this paper, Dy3+ doped SrCO3–WO3–SiO2 glass ceramics are successfully prepared by melt-quenching method. The microscopic morphology, structure and luminescence properties of Dy3+ doped glass ceramics are investigated through XRD, DSC, SEM, photoluminescence spectra and decay curves etc. It can be determined that the crystalline phase is SrWO4 after comparing with PDF normal card by XRD. Also, combining with the transmission curves, the optimum heat treatment temperature and time are 740 °C/1.5 h. In the emission spectrum, there are three obvious emission peaks at 484 nm, 575 nm and 665 nm, respectively. The optimum concentration of Dy3+ is found to be 1.6 mol, and electric multipole interaction is the main reason for the concentration quenching. The maximum fluorescence lifetime is 796.5 μs.

Enhancing the local conductivity of Cu films using temperature-assisted agglomerated Cu nanostructures

We investigate the structural and electrical properties of Cu film and reveal their changes as a function of post-annealing temperature. Thermal annealing of a Cu film on a dielectric substrate can improve its crystallinity; however, high-temperature annealing also leads to a morphological transformation that hinders the precise measurement of electrical properties. The enhanced crystallinity of the Cu films is verified with x-ray diffraction as the annealing temperature increases. To examine the electrical properties of the Cu film after the dewetting processes, which promotes the formation of voids and agglomerations, we utilize both conventional micro four-point probe method as well as an advanced four-point probe scanning tunneling microscopy (4P-STM) technique to measure the conductance and evolution of the microscopic structural properties. We could eliminate a deceptive effect of voids with 4P-STM technique, and disclosed a significantly reduced resistivity (1.88 ± 0.07 µΩ·cm) of Cu nanostructure after post-annealing at 700 °C. We unveiled impact of crystallinity and imperfections of Cu nanostructure, and discussed the critical role of the twin grain boundaries of single-crystalline Cu (1 1 1) on an Al2O3 substrate. We anticipate that understanding the evolution of the structures and the enhanced electrical properties of the post-annealed Cu nanostructures would be important for nanoscale devices where Cu is used as an interconnecting material and could provide a new route to control the plasmonic applications.

Structural, Thermodynamic, and Transport Properties of Aqueous Reline and Ethaline Solutions from Molecular Dynamics Simulations.

Deep eutectic solvents (DESs) are a new generation of green solvents, which are considered an environmentally friendly alternative to ionic liquids and volatile organic compounds. The addition of controlled amounts of water to DESs has a significant effect on their microscopic structure and thus on their thermodynamic and transport properties. In this way, DESs can be modified, leading to solvents with improved characteristics. In this work, molecular dynamics (MD) simulations are performed to obtain a better understanding of the relation between the microscopic structure, molecular interactions, and thermophysical properties of aqueous reline and ethaline solutions at temperatures ranging from 303.15 to 363.15 K. For both reline and ethaline solutions, the hydrogen bond (HB) networks disappear with increasing mass fraction of water, and the intensity of radial distribution function (RDF) peaks decreases. For a mass fraction of water of 40%, most of the HBs between the compounds of reline and ethaline are broken, and DESs are fully dissolved in water. Consequently, a monotonic decrease in viscosities and an increase in self-diffusion coefficients are observed. Ionic conductivities show a nonmonotonic behavior with increasing water content. Up to 60% water mass fraction, the ionic conductivities increase with increasing water content. A further increase in the mass fraction of water decreases conductivities. For all studied systems, the HB network and the peaks of RDFs show relatively small changes for water mass fractions below 5% and beyond 40%. The MD results show that viscosities decrease with temperature, while diffusivities and ionic conductivities increase. The effect of the temperature on the structure of DES–water mixtures is negligible.

Formulation strategy of nitrofurantoin: co-crystal or solid dispersion?

Poor solubility and bioavailability of drugs are often affected by its microscopic structural properties. Nitrofurantoin (NF), a Biopharmaceutics Classification System class II item, has a low water solubility with low plasma concentrations. To improve its therapeutic efficacy, formulation strategy of solid dispersion (SD) and co-crystallization are compared herein. The co-crystal is prepared with citric acid in 1:1 stoichiometric ratio while SD consists of 30% w/w nitrofurantoin and 70% w/w hydroxypropyl methylcellulose (HPMC) as the carrier system. As a control, the physical mixture of NF and HPMC was prepared. All the preparations were characterized with differential scanning calorimetry (DSC), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), microscopy analysis, solubility, and dissolution studies. The formation of co-crystal, solvent evaporated, and spray-dried SD are confirmed by the ATR-FTIR where peaks shifting of several functional groups indicate the formation of the hydrogen bond. Dissolution studies showed a greater initial dissolution rate in co-crystal than SD despite the possible presence of amorphous content in the SD system. Overall, co-crystal is concluded to be a better approach than SD for an effective dissolution.

Analysis of effects of meso-scale reactions on multiphysics transport processes in rSOFC fueled with syngas

A two-dimensional mathematical model is developed for a single-cell based on the planar configuration and validated by relevant experimental data, with an aim to describe the coupling phenomena of the multiphysics transport processes and the meso-scale elementary reactions. It is revealed that desorption and adsorption reactions in the electrode mostly take place near the electrolyte and the channel, respectively; the distribution of the surface species depends on the gas diffusion in the porous electrode affected by the thickness and microstructure of the electrode. The electrochemical reactions are centralized in about 100 μm thick electrode from the electrolyte. Nis and COs are the major surface species in both fuel cell (FC) and electrolysis cell (EC) modes. Os is higher in the FC mode, particularly near the electrolyte due to the desorption and charge transfer reactions; The microscopic structure properties, including average porosity, tortuosity and particle size, are also influential on the elementary reactions due to the gas diffusion through the tortuous pathways and the active sites on the catalyst surfaces. It is also found that the performance predicted in the global models is often overestimated, because the limitations of the local elementary reactions are not considered in the global model.

Preparation and Characterization of Cationic Water-Soluble Pillar[5]arene-Modified Zeolite for Adsorption of Methyl Orange.

A novel quaternary cationic pillar[5]arene-modified zeolite (WPA5/zeolite) was prepared via charge interaction between the cationic WPA5 and natural zeolite and characterized by scanning electron microscopy (SEM), Fourier transform infrared absorption spectroscopy, X-ray diffraction, solid-state nuclear magnetic resonance, and thermogravimetric (TG) analysis. The effects of zeolite particle size, WPA5 concentration, adsorption time, initial concentration, and pH on the removal of methyl orange (MO) were studied. The SEM and XRD results revealed a strong interaction between WPA5 and natural zeolite, and the modified composites showed novel microscopic morphology and structural properties. TG analysis indicated excellent thermal stability of the composite. MO was removed via electrostatic adsorption, and the removal efficiency was 84% at an initial concentration of 100 mg/L. Increase in the initial dye concentration enhanced the adsorption capacity of WPA5/zeolite and decreased the removal of MO. Based on the adsorption kinetics, the pseudo-second-order model (R2 = 0.998) described the kinetic behavior of MO on WPA5/zeolite. In addition, UV and fluorescence spectra revealed that MO and WPA5 are complexed by a 1:1 complex ratio, and the binding constant between them was 12 595 L·mol–1. NMR and molecular docking also verified their interaction. Therefore, the potential application of the prepared composite includes removal of organic anionic dyes.

A combination of FTIR and DFT to study the microscopic structure and hydrogen-bonding interaction properties of the [BMIM][BF4] and water.

The structure and hydrogen-bond interaction property of water and a model ionic liquid (IL): 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) were studied using the combination of Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. The O‒D stretching vibration region of the deuterated water was an area of special focus. Excess infrared spectroscopy with enhanced resolution was applied to analyse the original infrared spectra of v(O‒D). It is found that: (1) [BMIM][BF4] forms stable hydrogen-bonds with water in the mixture. (2) The hydrogen-bonds are weak strength, closed shell and electrostatic dominant interactions. The preferred interaction site of [BMIM]+ cation is the hydrogen atom at the C2. (3) Cage hexamer water, cyclic tetramer water, cyclic trimer water, ion cluster-water complex, ion pair-water, and anion-water complexes are identified in the mixture. When the mole fraction of D2O (x(D2O)) is larger than 0.9, ion cluster and ion pair were broken apart into individual cations and anions. The cage hexamer water, cyclic tetramer water, and cyclic trimer water disappear at x(D2O) < 0.8, 0.5, and 0.3, respectively. HDO formed by H/D isotope exchange was detected when x(D2O) is less than 0.3.

Electron Properties and Thermal Decomposition Behaviors for HMX/HTPB Plastic-Bonded Explosives

We study the microscopic structure properties and early thermal decomposition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)/hydroxyl-terminated polybutadiene (HTPB) composites on the ba...

Reversible and High-Temperature-Stabilized Strain in (Pb,La)(Zr,Sn,Ti)O3 Antiferroelectric Ceramics.

Antiferroelectric (AFE) materials have a tremendous advantage as smart materials and large-strain actuators due to their unique reversible characteristic electric-field-induced strain (electrostrain) responses in comparison to piezoelectric effect and electrostriction. A key limitation to today's AFE actuators, however, is the poor temperature stability of electrostrain. In this work, a large reversible strain of 0.4% and an excellent thermal stability with a variation within ±5.5% from 20 to 190 °C were achieved for (Pb0.97La0.02)(Zr0.85Sn0.08Ti0.07)O3 (PLZST) AFE ceramics. A room-temperature electrostrain of 0.71% was obtained in virgin PLZST ceramics. It is intriguing to observe inconsistent strain curves between the first and further measured cycles, implying an incomplete reversible field-induced AFE-ferroelectric phase transition. A sharp electrostrain response in milliseconds was realized in the as-prepared PLZST ceramics. In addition, a phenomenological explanation was proposed to explain the extraordinary phenomena. Our results may shed light on the origin of the superior strain behaviors in AFE materials from the view of microscopic structure and macroscopic properties, and probably improve the understanding of the AFE phase transition.

Diffusing wave spectroscopy for investigating emulsions: II. Characterization of a paradigmatic oil-in-water emulsion

We employ Diffusing Wave Spectroscopy (DWS) to characterize microscopic structure, internal dynamics and rheological properties of a paradigmatic emulsion formed by water and dodecane stabilized by the anionic surfactant Sodium Dodecyl Sulfate (SDS).We focus on ageing and stability in the regime of low surfactant concentration, well below the Critical Micellar Concentration (CMC). In the long-time ageing regimes differentiate in stable and unstable, depending on surfactant concentration. For the stable case, ageing affects the dynamics following a power law with an exponent independent on surfactant concentration, presumably related to the late stages of the water drainage process. On the contrary, at constant ageing, the dependence of the dynamics from surfactant concentration shows a slowdown, corresponding to a maximum in the bulk shear mechanical modulus, around [SDS]=2mM which is reminiscent of a similar maximum found by drop tensiometry in the dilational modulus of the single interface.This suggests a consistent picture of the mechanisms (de)stabilizing the emulsion, explained in terms of elementary process at the interface. These results show furthermore that DWS can be a reliable diagnostic for the study of the aging and of the mechanical properties of concentrate emulsions. This might be relevant to control stability of emulsions when a low concentration of surfactant is desired, e.g. for economical or environment reasons.

Hierarchical self-assembly, spongy architecture, liquid crystalline behaviour and phase diagram of Laponite nanoplatelets in alcohol-water binary solvents

Hydrophobicity and solvation of different charged species are among the various key factors that regulate the self-assembly of colloids, and macromolecules in their suspensions. In this paper, we demonstrate a method to tune the interaction potential and the resulting phase behaviour and microstructure of the states that form by using a combination of Laponite nanoplatelets and alcohols in water. This allows us to exquisitely control the self-assembly process of Laponite nanoplatelets. A new class of soft materials, called nanoclay-organogels, is studied systematically for their aging behaviour, microscopic structure and mechanical properties. Real space imaging techniques depicted spongy architecture with nano and micron size pores inside the gel matrix indicating the hierarchical self-assembly of the nanoplatelets in the aqueous solutions of polar organics. We have extensively examined the dispersion stability, aggregation, gelation and liquid crystalline behaviour of Laponite nanoplatelets in different alcohol (methanol, ethanol, 1-proponaol and ethylene glycol, and glycerol)-water binary solvents, thereby proposing a generalized description of nanoclay in alcoholic solutions, which is poorly probed and marginally understood in the literature. A phase diagram of Laponite® in alcohol solutions is proposed, which clearly demarcates regions of isotropic sol, unstable sol, isotropic gel, nematic/birefringent gel, glass, flocculated sedimentation and liquid crystalline structures.