Matrix Inhomogeneity Research Articles

Hydrophilic 2D composite LDHs-MXene pervaporation membrane for highly efficient ethanol dehydration

Mixed matrix membranes (MMMs) demonstrate significant potential for pervaporation applications. Nevertheless, single lamella 2D materials are prone to stacking problems in membranes, resulting in unforeseen matrix inhomogeneity and defects. Here, we propose a wafer-like membrane structure designed for ethanol dehydration. This structure features a surface modification of transition metal carbides (MXenes) with layered dihydroxides (LDHs), which effectively enlarges the interlayer spacing and ameliorates the stacking issue. The LDHs-modified MXenes were then incorporated into the sodium alginate (SA) layer. The hydrophilicity, stability and morphology of the MMM were evaluated by water contact angle measurements, swelling tests and scanning electron microscopy. The experiment results indicated the hydrophilicity and stability of the MMM were effectively improved. The novel L-M@CS MMM exhibited outstanding dehydration performance for ethanol solution, with the membrane containing 0.4 wt % LDHs-modified MXenes achieving the highest permeation flux of 1377 g/(m2·h) and the optimal separation factor up to 1650.

Nanoscale magnetic phase competition throughout the Ni50−xCoxMn40Sn10 phase diagram: Insights from small-angle neutron scattering

The $\mathrm{N}{\mathrm{i}}_{2}\mathrm{MnSn}$-derived $\mathrm{N}{\mathrm{i}}_{50\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x}\mathrm{M}{\mathrm{n}}_{25+y}\mathrm{S}{\mathrm{n}}_{25\ensuremath{-}y}$ alloys are premier examples of a class of off-stoichiometric Heusler alloys recently discovered to exhibit attractive magnetic properties in tandem with extraordinarily reversible martensitic phase transformations. Multiferroicity, magnetic phase competition and separation, field-induced martensitic transformations, magnetic shape memory behavior, and sizable magneto-, elasto-, and barocaloric effects result, generating substantial interest and application potential. In this work we expand on a prior small-angle neutron scattering (SANS) study at a single composition $(\mathrm{N}{\mathrm{i}}_{44}\mathrm{C}{\mathrm{o}}_{6}\mathrm{M}{\mathrm{n}}_{40}\mathrm{S}{\mathrm{n}}_{10})$ by exploring all three main regions of the recently established $\mathrm{N}{\mathrm{i}}_{50\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x}\mathrm{M}{\mathrm{n}}_{40}\mathrm{S}{\mathrm{n}}_{10}$ phase diagram, i.e., at the representative $y=15$ composition. Wide temperature and scattering wave-vector range $(20\ensuremath{-}500\phantom{\rule{0.16em}{0ex}}\mathrm{K},0.004\ensuremath{-}0.2\phantom{\rule{0.16em}{0ex}}{\AA{}}^{\ensuremath{-}1})$ SANS data on $x=2$, 6, and 14 polycrystals provide a detailed picture of the evolution in magnetic order and inhomogeneity. Consistent with recent studies with a variety of techniques, phase separation into short-range coexisting ferromagnetic and antiferromagnetic regions is deduced below the martensitic transformation at $x=2$ and 6, with average ferromagnetic cluster spacing of \ensuremath{\sim}13 nm. Remarkably, at $x=14$, where the martensitic transformation is suppressed and ferromagnetic austenite is stabilized to low temperatures, nanoscopic magnetic inhomogeneity nevertheless persists. Distinct ferromagnetic clusters (\ensuremath{\sim}36-nm average spacing) in a ferromagnetic matrix are observed at intermediate temperatures, homogenizing into a uniform long-range ordered ferromagnet only at low temperatures. This unusual ferromagnet cluster/ferromagnet matrix inhomogeneity, as well as $x$-dependent subtleties of the superparamagnetic freezing of ferromagnetic clusters, are discussed in light of $^{55}\mathrm{Mn}$ nuclear magnetic resonance data, and the recent observation of annealing-induced core/shell nanoprecipitates. The origins of nanoscale magnetic inhomogeneity are discussed in terms of statistical variations in local composition and structure, tendency to chemical phase separation, and other forms of disorder.

Three-dimensional pore-scale numerical simulation of methane-air combustion in inert porous media under the conditions of upstream and downstream combustion wave propagation through the media

Abstracts Porous media combustion of lean and ultra-rich methane-air mixtures was numerically studied using the approach when the process is simulated at the pore scale with explicit consideration of the three-dimensional porous structure and interstitial flow with thermal interaction between fluid and solid phases including the detailed chemical kinetics model and solid-to-solid radiation. The geometrical model of the packed bed was generated synthetically by simulation of particles falling under gravity force. A novel workflow for a randomly packed bed meshing at the pore scale was used to avoid the point contact problem. The results demonstrate that the model predicts a thermal nonequilibrium and heat recuperation mechanism in the combustion wave in the low-velocity regime correctly. The inhomogeneous structure of the porous media leads to large spatial variation of the process parameters such as velocity and temperature. It was shown that radiation makes a significant contribution to heat transfer in the region of a large temperature gradient. Radiative heat flux is transferred through the bed via radiation layer-by-layer due to restricted mutual visibility of the opaque particles. The mixture composition has a significant impact on the heat release rate and wave velocity and direction as well as thermal flame thickness and exhaust gas composition. At the macro scale, the mode of combustion wave propagation is quasi-steady whereas at the pore scale with little time steps the unsteady effects can be observed. Different subregions of the flame front propagate with not equal velocity, stand or accelerate depending on the local flow and porous matrix inhomogeneity. For the lean mixture the oscillatory regime of propagation was detected and analyzed.

Applicability of the interface spring model for micromechanical analyses with interfacial imperfections to predict the modified exterior Eshelby tensor and effective modulus

Closed-form solutions for the modified exterior Eshelby tensor, strain concentration tensor, and effective moduli of particle-reinforced composites are presented when the interfacial damage is modeled as a linear-spring layer of vanishing thickness; the solutions are validated against finite element analyses. Based on the closed-form solutions, the applicability of the interface spring model is tested by calculating those quantities using finite element analysis augmented with a matrix–inhomogeneity non-overlapping condition. The results indicate that the interface spring model reasonably captures the characteristics of the stress distribution and effective moduli of composites, despite its well-known problem of unphysical overlapping between the matrix and inhomogeneity.

Biological and nano-indentation properties of polybenzoxazine-based composites reinforced with zirconia particles as a novel biomaterial.

The biological and mechanical properties of substances are relevant to their application as biomaterials and there are many efforts to enhance biocompatibility and mechanical properties of bio-medical materials. In this study, to achieve a low rate of shrinkage during polymerization, good mechanical properties, and excellent biocompatibility, benzoxazine based composites were synthesized. Benzoxazine monomer was synthesized using a solventless method. FTIR and DSC analysis were carried out to determine the appropriate polymerization temperature. The low viscosity of the benzoxazine monomer at 70°C attract us to use in situ polymerization after high speed ball milling of the benzoxazine and it mixture with different weight fractions of zirconia particles. Dispersion and adhesion between the ceramic and polymer components were evaluate by SEM. To evaluate the biological properties and toxicity of the polybenzoxazine-based composite samples reinforced with zirconia particles, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay was conducted. The micromechanical properties of each composite were evaluated by more than 20 nanoindentation tests and 3 nanoscratching tests. Surface topography of scratched regions was investigated using Atomic Force Microscopy. Shrinkage was simulated by Materials Studio software. SEM images showed good dispersion and adhesion between the ceramic and polymer components. Biocompatibility assay showed excellent in vitro biocompatibility. Nano-indentation force-displacement curves showed matrix, reinforcement and interphase regions in specimens and excellent homogeneity in mechanical properties. The nanoindentation results showed that the addition of zirconia particles to the polybenzoxazine matrix increased the modulus and hardness of the neat polybenzoxazine; however, by adding more than an optimum level of reinforcement particles, the mechanical properties decreased due to the agglomeration of reinforcement particles and weak interphase that cause inappropriate load transferring between matrix and reinforcement particles. Results of nano-scratching tests showed effects of zirconia particles as reinforcement on the coeffiecient of friction of the synthesized composites. Shrinkage simulation showed a low rate of shrinkage for polybenzoxazine in comparison with other low shrinkage polymers, such as Bis-GMA. Polybenzoxazine based composites that reinforced with an optimum amount of zirconia particles (60% wt micro and 10% wt nano-particles) could be used as a novel biomaterial duo to its excellent biocompatibility, good mechanical properties, appropriate viscosity and low rate of polymeization shrinkage.

Influence of mixed gel structuring with different degrees of matrix inhomogeneity on oral residence time

The aim of this study was to examine the influence of structuring mixed biopolymer gels with different degrees of inhomogeneity on oral residence time. Ten model gels with varying mechanical and structural properties were prepared using κ-carrageenan and sodium alginate at concentrations ranging from 0 to 4 wt%. In few of the mixed gel systems, structural inhomogeneity was introduced by incorporation of calcium alginate beads of different sizes, later made by syringe extrusion or spraying techniques. The gels were characterized by dynamic oscillation, fracture behaviour and the structural details were evidenced in different length scales by cryo-scanning electron microscopy (cryo-SEM) and transmission electron microscopy (TEM). In parallel, gels were characterized by quantitative descriptive analysis (QDA™). Oral processing behaviour was assessed in terms of oral residence time, number of chews and difficulty perceived by eleven young participants. A decrease in the gel fracture point with the addition of calcium alginate beads was attributed to the interruption of the continuous κ-carrageenan gel network, as revealed in the Cryo-SEM and TEM images and with narrower linear viscoelastic region. When the mixed gel network included κ-carrageenan with sodium alginate, the linear viscoelastic range was extended, but the gel strength was lower than κ-carrageenan alone highlighting the incompatibility between the biopolymers. Oral residence time was highly dependent on the number of chews and to a certain extent on the difficulty perceived. Oral residence time and number of chews were positively correlated with gel strength, degree of network inhomogeneity in terms of particle size of the beads.

Microstructural evolution of Fe[sbnd]22%Cr model alloy under thermal ageing and ion irradiation conditions studied by atom probe tomography

Nanostructure evolution during ion irradiation of two thermally aged binary Fee22Cr alloys has been investigated using atom probe tomography. Specimens aged at 500 °C for 50 and 200 h were irradiated by 5.6 MeV Fe ions at room temperature up to fluences of 0.3 × 1015 ions/cm2 and 1 × 1015 ions/cm2. The effect of irradiation on the material nanostructure was examined at a depth of 1 μm from the irradiated surface. The analysis of Cr radial concentration functions reveals that dense α′-phase precipitates in the 200 h aged alloy become diffuse and thereby larger when subjected to irradiation. On the other hand, less Cr-enriched precipitates in the alloy aged for 50 h are less affected. The CreCr pair correlation function analysis shows that matrix inhomogeneity decreases under irradiation. Irradiation leads to a decrease in the number density of diffuse clusters, whereas in the case of well-developed precipitates it remains unchanged.

Application of GUM Supplement 1 to uncertainty of Monte Carlo computed efficiency in gamma-ray spectrometry

The uncertainty of quantities relevant in gamma-ray spectrometry (efficiency, transfer factor, self-attenuation FA and coincidence summing FC correction factors) is realistically evaluated by Monte Carlo propagation of the distributions characterizing the parameters on which these quantities depend. Probability density functions are constructed and summarized as recommended in the GUM Supplement 1 and compared with the values obtained using the traditional approach (GUM uncertainty framework). Special cases when this approach encounters difficulties (FC uncertainty due to the uncertainty of decay scheme parameters, effect of activity and matrix inhomogeneity on efficiency) are also discussed.

Influence of matrix inhomogeneity on the rheological properties of emulsion-filled gels

The aim of this work was to determine the effect and magnitude of matrix inhomogeneity on the rheological properties of emulsion-filled gels. To this end, we have investigated the rheological properties in casein gels containing different volume fractions of dispersed fat droplets with varying hardness. Rheological properties of the filled gels were investigated by uniaxial compression. Matrix inhomogeneity was controlled by changing the casein concentration, and was quantified by confocal laser scanning microscopy (CLSM) and image analysis. CLSM images showed that the matrix becomes more inhomogeneous when the protein concentration decreases and image analysis was used to quantify this inhomogeneity. As the dispersed fat droplets bind to the proteins (active droplets), the droplets are located more in the casein-rich areas. The inhomogeneous distribution of the casein micelles led to an accumulation of the dispersed fat droplets in the gelled micellar casein regions, thereby increasing the effective volume fraction of the droplets. This increase in the effective volume fraction of the droplets was higher for lower casein concentrations, due to a higher degree of inhomogeneity, resulting in a larger effect in reinforcing the gel compared to more homogeneous systems. These results may be used for designing structures to decrease the fat content or replace solid fat by liquid oil.

Elastohydrodynamic Lubrication Analysis of Point Contacts With Consideration of Material Inhomogeneity

Inhomogeneities in matrix may significantly affect the performance of mechanical elements, such as possible fatigue life reduction for rolling bearing due to stress concentration induced by inhomogeneities; on the other hand, most components operate under lubrication environment. So far the numerical algorithms to solve lubrication problems without the consideration of inhomogeneities or inclusions are well developed. In this paper, the combination of elastohydrodynamic lubrication (EHL) and inclusion problem is realized to consider the effect of material inhomogeneity on the lubrication performance and subsurface stress distribution, etc. The matrix inhomogeneity will induce disturbed displacement, which will modify the film thickness and consequently result in the change of lubricated contact pressure distribution, etc. The matrix inhomogeneity is treated as the homogeneous inclusion with equivalent eigenstrain according to equivalent inclusion method (EIM), and the disturbed displacement is calculated by semi-analytical method (SAM). While the pressure and film thickness distributions are obtained by solving Reynolds equation. The iterative process is realized to consider the interaction between lubrication behavior and material response. The results show the inhomogeneity in contacting body will greatly influence the lubricated contact performance. The influences are different between compliant and stiff inhomogeneity. It is also found that different sizes and positions of inhomogeneity can significantly affect the contact characteristic parameters.

An integral equation formulation of anti-plane inhomogeneities

Abstract In this paper, a boundary integral equation formulation for anti-plane shear inhomogeneous medium is presented to study the interaction between the inhomogeneities and cracks. The proposed boundary integral equation formulation only contains out-of-plane interface displacements and out-of-plane discontinuous displacements over cracks. Numerical implementation is simple since the present formulation has considered the shear equilibrium condition over the interfaces between the matrix and inhomogeneities. Out-of-plane interface displacements and out-of-plane traction integral equations are collocated respectively on the matrix–inhomogeneity interfaces and on one side of the crack surface. Numerical examples are given to show the validity and numerical accuracy of the present method.

Comparison of Mechanical Properties of Mn-Cr-Mo Steels Sintered in Different Conditions

The present work discussed the development of statistical analysis as a reproducibility assistance method for evaluation of advanced Fe-3%Mn-(Cr)-(Mo)-C sintered steel for high performance structural parts. Factors contributing to the reliability and reproducibility of these structural steels include advanced metal matrix with consistent purity and concentration of chemical constituents, as well as mix homogeneity and processing uniformity. Matrix inhomogeneity was found to play an important role in these materials. In this paper the statistical dependence between properties and processing variables of PM Mn-Cr-Mo steels is presented. The investigations of sintered steels were based on commercial powders: pre-alloyed Höganäs iron powders Astaloy CrM and Astaloy CrL and graphite C-UF. As a manganese donor low-carbon ferromanganese powder was used. Sintering was carried out in different atmospheres at 1120°C and 1250°C. After sintering, investigated steels were subsequently tempered at 200°C for 60 min in air. The results of statistical analysis show, there is the relationship between mechanical properties versus processing parameters.

Inhomogeneity effects on HPGe gamma spectrometry detection efficiency using Monte Carlo technique

This work deals with the inhomogeneity effects on the full energy peak efficiency determination with HPGe gamma spectrometry . The inhomogeneity of the sample was defined in this work as being the fraction of its volume, which does not contain gamma emitters. We applied the Monte Carlo technique based on the GEANT4 code of CERN to study these effects for soil samples for the case of high density (1.54 g/cm 3 ) where the attenuation effects are expected to increase the errors on the activity measurement due to the inhomogeneity. The correction of the efficiency against these effects using Monte Carlo method has been applied in two cases. The first is between samples with different homogeneity values and a calibration standard, which is perfectly homogeneous, and the second is between a sample and a calibration standard with different imperfect homogeneities. ► We study inhomogeneity effects on HPGe gamma spectrometry efficiency determination. ► Monte Carlo method has been used (through GEANT4 code of CERN). ► Sample matrix inhomogeneity was modelled. ► Correction of the efficiency against inhomogeneity effects was performed. ► This correction is systematic for high density matrices.

Modeling the influence of grain-level matrix inhomogeneity on strain localization in the presence of hard particles

The influence of grain-level matrix inhomogeneity on strain localization in sheet metals has been studied using a two-dimensional plane stress model containing two hard particles by finite element analysis. When the matrix material is treated as a homogeneous continuum, the localization strain decreases with interparticle spacing for particles aligned along the loading direction. In the case of an inhomogeneous matrix, consisting of grains of different Taylor factors corresponding to different crystallographic orientations, the position of the localization band and the value of localization strain seem to be insensitive to the interparticle spacing. Instead, localization forms preferentially in the softer grains within the matrix. The amount of post-localization deformation decreases significantly when the two particles straddle the shear band. It is concluded that the stress concentration that develops between two closely spaced particles does influence the shear localization process but the matrix inhomogeneity dominates localization behavior during sheet metal deformation.

Understanding Effects of Matrix Protease and Matrix Organization on Directional Persistence and Translational Speed in Three-Dimensional Cell Migration

Recent studies have shown significant differences in migration mechanisms between two- and three-dimensional environments. While experiments have suggested a strong dependence of in vivo migration on both structure and proteolytic activity, the underlying biophysics of such dependence has not been studied adequately. In addition, the existing models of persistent random walk migration are primarily based on two-dimensional movement and do not account for the effect of proteolysis or matrix inhomogeneity. Using lattice Monte Carlo methods, we present a model to study the role of matrix metallo-proteases (MMPs) on directional persistence and speed. The simulations account for a given cell's ability to deform as well as to digest the matrix as the cell moves in three dimensions. Our results show a bimodal dependence of speed and persistence on matrix pore size and suggest high sensitivity on MMP activity, which is in very good agreement with experimental studies carried out in 3D matrices.

Densification Rates of Ceramic Matrix Composites with Initial Matrix Inhomogeneity

Abstract A viscoelastic finite element method is developed to analyze the effect of non-homogeneous matrix compaction on densification of ceramic matrix composites. The heterogeneous matrix of the composite is represented by a system of two or more co-axial cylinders of different initial matrix density. The sintering potential can be expressed in terms of a free strain rate. The free strain rate is derived from the relationship of relative density versus sintering time, measured from the neat matrix sample. The knowledge of free strain rate is a prerequisite for conducting the finite element analysis. For the heterogeneous matrix, two different density-time relationships are assumed, based on the concepts of neck formation and neck growth between contacting particles, and pore coarsening. The results of the finite element analysis show that a nonuniform compaction of the composite generally has a detrimental effect on the densification process.

Matrix inhomogeneity in crosslinked rubber and rubber emulsions

The radiation induced crosslinking of a polymer can be greatly affected by its environment and morphology. This is examined for rubber of identical source, but irradiated as (1) nonpurified, (2) purified rubber and (3) as an emulsion where the rubber particles are separated. Measurements include solubility, swelling and ESR studies using spin probe whose penetration into the denser parts of rubber network can be inhibited in the more crosslinked form. An apparent discrepancy between solubility and swelling data in irradiated emulsion is ascribed to a bimodal structure in the rubber emulsion, with dense rubber particles linked together by more extended chains. The use of spin probe technique allows an estimate of the penetrability of these small molecules in both irradiated latex emulsion and dry latex. The slow component of the ESR spectra is ascribed to spin probes in regions of high crosslink density, whereas the fast component is identified with spin probes in lightly crosslinked regions. According to the ratio of slow and fast ESR component latex irradiated in emulsion reveals different morphology as compared with the irradiated dry latex.

Study of matrix inhomogeneity of natural rubber and synthetic polyisoprenes by a spin probe method

Nitroxide spin probes have been used to investigate the matrix morphology of natural rubber (NR), deproteinized natural rubber (DPNR), synthetic polyisoprene (PI) and modified synthetic polyisoprene (PI-M). Composite electron spin resonance spectra with broad and narrow components appear in NR, DPNR and PI-M, above the glass transition temperature. The slow component is attributed to the spin probes in regions of higher density or gel phase, whereas the narrow component is identified with the nitroxides located in the sol phase. The intensity of the slow component depends both on the amount of gel phase and on the specific gel structure. The restricted spin probe motion above the glass transition is considered to be a measure of the participation of naturally occurring protein components or modifiers in the formation of gel and its structure. Several spin probes differing in size and shape are used in order to assess the free volume distribution.

Polyisoprene matrix inhomogeneity studied by nitroxide spin probe motion

The spin probe ESR method was applied to study natural rubber and synthetic polyisoprenes with different content of cis-configuration over a wide temperature range. The ESR spectra of natural rubber near and above the glass transition indicate the existence of two distinctly different mobilities as a consequence of the spin probe distribution in sol and gel phase. The results show that the spin probe method can yield information about the inhomogeneity of the polyisoprene matrix and the character of gel phase.