Pore Orientation Research Articles

Electrospun polyacrylonitrile/polyvinyl pyrrolidone composite nanofibrous membranes with high-efficiency PM2.5 filter

Abstract In this research, we successfully fabricated a novel closed pore polyacrylonitrile (PAN)/polyvinyl pyrrolidone (PVP) composite nanofibrous membrane (PCNM) on the substrate of a commercial polypropylene window mesh. First, smooth and uniform PAN/PVP composite nanofibers (PCNs) were manufactured by blending PAN and PVP with a mass ratio of 5:5 during electrospinning. Subsequently, the prepared PCNs were hot pressed in a vacuum drying oven at a given temperature of 90°C. The morphology and filter efficiency of PCN and PCNM were investigated. It was found that hot-pressing treatment significantly affected the pore structure and orientation of PCNM, which contributed to its closed pore structure and good alignment. The filter efficiency results indicated that the hot-pressed PCNMs have excellent removal efficiency of up to 96.8% of fine particulate matter. This research demonstrates that PCNMs have potential as filters for indoor dust removal and will provide a new idea for the development of air filters.

3D rock fabric analysis using micro-tomography: An introduction to the open-source TomoFab MATLAB code

The study of rock fabric properties (orientation, planar, linear, anisotropy) is key to unravelling the geological processes that generated them. With advancements in data acquisition and treatment, X-ray micro-computed tomography (μXCT) represents a powerful method to analyse the shape preferred orientation (SPO) of rock-forming elements, including minerals, aggregates, and pores, in the three-dimensional space. After reconstruction and segmentation of μXCT images, we developed a novel protocol to construct and analyse the fabric tensor, a second-rank symmetric tensor constructed using the orientation and the length of the three characteristic axes of each grain (simplified to a best fit ellipsoid). The analysis of the fabric tensor permits calculation of mean principal directions and associated confidence ellipses, and quantifies the degree of anisotropy (P′) and the shape (T) of the fabric ellipsoid by eigenvalue and eigenvector analysis.We implement this method in the TomoFab open-source MATLAB package. The code integrates a graphical user interface (GUI) that allows the visualisation of the full set of ellipsoid orientation, shape, and size. Density plots and contouring can be utilised to identify fabrics graphically, and a full set of fabric parameters can be calculated based on the analysis of the fabric tensor and/or the analysis of each principal direction orientation tensor.We demonstrate the versatility of TomoFab with synthetic datasets and a field- and laboratory-based investigation of a sample presenting a magmatic foliation and lineation, collected in the Mafic Complex within the lower crustal section of the Ivrea-Verbano Zone (North Italy). In the light of these developments, we stress that μXCT represents a pertinent tool for rock fabric analysis to characterise the SPO of rock components. This approach can be performed parallel or complementary to other rock fabric quantification methods (e.g., AMS, EBSD) and applied to various rock types. TomoFab is freely available for download at https://github.com/benpetri/tomofab.

Microstructures and properties of porous TiAl-based intermetallics prepared by freeze-casting

Abstract Preparation of porous TiAl-based intermetallics with aligned and elongated pores by freeze-casting was investigated. Engineering Ti−43Al−9V−1Y powder (D50=50 μm), carboxymethyl cellulose, and guar gum were used to prepare the aqueous-based slurries for freeze-casting. Results showed that the porous TiAl was obtained by using a freezing temperature of −5 °C and the pore structure was tailored by varying the particle content of slurry. The total porosity reduced from 81% to 62% and the aligned pore width dropped from approximately 500 to around 270 μm, with increasing the particle content from 10 to 30 vol.%. Furthermore, the compressive strength along the aligned pores increased from 16 to 120 MPa with the reduction of porosity. The effective thermal conductivities of porous TiAl were lower than 1.81 W/(m·K) and showed anisotropic property with respect to the pore orientation.

Mesoporous Silica Thin Membrane with Tunable Pore Size for Ultrahigh Permeation and Precise Molecular Separation.

We report on our use of a thin-layered vertical mesoporous silica thin film (MSTF) with tunable pore size overlaid on an anodic aluminum oxide (AAO) membrane for advancing water purification. The features of ultrathin thickness (about 20 nm), a uniform vertical pore orientation, low tortuosity, high porosity, and a hydrophilic surface endow the MSTF membranes with ultrahigh water permeability compared with that of state-of-the-art membranes. The modified E-MSTF membrane with a small pore diameter of 2.1 ± 0.1 nm demonstrates superior nanofiltration performance for dye molecules with a cutoff of 520 Da and ultrahigh water permeability of 310 ± 8 L m-2 h-1 bar-1. Furthermore, the precise molecular sieving of dye/salt mixtures was realized with outstanding salt permeation (97.5% NaCl, 96.0% Na2SO4) and a high retention of dye (99.0%). The water permeance and selectivity of the modified E-MSTF membrane are higher than that of reported membranes with similar dye rejections. This work opens up new avenues for constructing tailor-made membranes with tunable pore size and remarkable separation performance.

Revealing relationships between porosity, microstructure and mechanical properties of laser powder bed fusion 316L stainless steel through heat treatment

The understanding of relationships between processing, microstructure and mechanical properties in laser powder bed fusion is currently incomplete. Microstructure-property relations in 316L stainless steel are revealed in this study using isothermal heat treatments as an investigative tool. As-built material was heat treated to selectively remove microstructural features such as melt pool boundaries, microsegregations and the as-built grain structure to evaluate their influence on yield and failure behaviour. Anisotropic yield behaviour was found to be caused by microstructural features alone and not influenced by porosity. However, ductility and failure were dominated by lack of fusion porosity. The alignment of pores between tracks along layer boundaries was found to cause anisotropic ductility. Three strengthening mechanisms in as-built material were identified as grain boundaries, chemical segregation and dislocation density. Heat treatments were categorised into three regimes: recovery, homogenisation and annealing. The findings of this study show that the shape, size, orientation and distribution of pores are crucial parameters for evaluating the structural integrity of parts produced by laser powder bed fusion.

The effects of stress and fluid on the anisotropy of reservoir rock: case study of a sandstone from the harvey 3 CCS site, Western Australia

In rock physics one of the important purposes of the determination of P- and S-wave velocities is to obtain the elastic constants and anisotropy parameters. This method is standardised in American Society for Testing and Materials (ASTM) by a standard D2845-95. The most challenging yet important part of these experiments is picking the first arrivals correctly and consistently. A sharp, clean first arrival of a wave is not always possible, especially when testing dry, porous sandstones at low pressures. The signal transmitted through such samples is weak due to a high damping effect, and picking the first break introduces uncertainties. Harvey sandstone is a sample type with high porosity and, therefore, some degree of anisotropy is expected. In order to study the anisotropy parameters of the Harvey 3 sandstone which belongs to Lesuer- Wonnerup Member of the Yalgorup Member, three core plugs in directions of horizontal, vertical and diagonal, were experimentally investigated. The laboratory measurements on three different samples which are cut at three different directions with regards to the base deposition system enabled us to calculate the anisotropy parameters using a standard acoustic equipment while applying stress. We concluded that Harvey 3 poses a more complex symmetry axis of anisotropy, and no sign of low-grade anisotropy was observed through the experimental data. To study the anisotropy degree of the Harvey 3 sandstone, a pressure cell, pore fluid injection pump, and ultrasonic system (consisting of P- and S-wave transducers, oscilloscope and pulser/receiver) were used to record the elastic waves passing through the samples. The specimens were fully saturated inside the pressure cell using vacuum injection for the best possible comparison of dry and saturated status. The results confirmed that the sample is far from weak anisotropy and possesses more axes of symmetries than simple layering anisotropy due to the pore orientation and distribution in the matrix of the background rock. The study also confirms that the anisotropy degree decreases under full compaction and full saturation, and the Harvey 3 anisotropy becomes elliptical when it’s fully saturated. Large, stress-dependent changes in the ultrasonic velocities for porous media were observed in this experimental study, which confirms the usefulness of such studies in examining the inner structure change process.

Investigating Liquid Water Transport in Different Pore Structure of Gas Diffusion Layers for PEMFC Using Lattice Boltzmann Method

Proton exchange membrane fuel cells (PEMFC) require a gas diffusion layer (GDL) to aid in the transport of liquid fuel to the catalyst layer. In this work, direct modeling using the Lattice Boltzmann Method (LBM) was applied to X-ray CT scans of four different carbon gas diffusion layers to understand the mass transport properties through the samples. Three injection orientations were used to study local saturation levels, water evolution through the sample, and mass transport behavior at breakthrough conditions. The LBM, combined with computational fluid dynamic modeling techniques, can accurately predict liquid saturation at the macro and micro scale, which provides more insight into the mass transport phenomena through the GDL. The change of pore structure and orientation in both the in-plane and through-plane determines the path that liquid water must take, which could aid or impact PEMFC performance. The outcomes from this work will also benefit any research that needs knowledge of internal mass transport qualities of gas diffusion media.

Control of Porosity in Freeze Casting

Many biologic structural materials have porous microstructures with a distribution and orientation of pores that are challenging to achieve using traditional methods of processing. In this investigation, numerical and experimental methods of evaluation were used to understand effects from the primary processing parameters on the temperature gradients during solidification in freeze casting of ceramics. The location and orientation of the temperature gradients were found to be highly dependent on the geometrical and thermal properties of the mold material used in processing. Furthermore, it was found that careful control of these processing variables can be used to design bioinspired porous materials with graded orientations and distributions of pores.

Deformation of organic matter and its effect on pores in mud rocks

Pores within organic matter (OM) are strongly linked to hydrocarbon generation and primary migration in fine-grained source rocks and are very important for evaluating hydrocarbon storage and flow in shale reservoirs. Thus, it is critical to clarify the features of OM-hosted pores and their evolution in organic-rich mud rocks. The OM in mud rocks, including kerogen and bitumen, is deformed when the original equilibrium stress conditions are altered. The OM deformation at the nano- or microscale has rarely been discussed because of the lack of unequivocal evidence. This research begins with examining the subsurface evolution of kerogen and bitumen, with emphasis on various features of pores hosted by bitumen. Evidence of OM deformation is documented in scanning electron microscope images of seven overmature samples from the lower Silurian Longmaxi Shale, Sichuan Basin. To aid in the understanding and analysis, OM deformation is classified into three types: type I deformation induced by one additional force, type II deformation induced by two additional forces acting on two locations of single OM particles, and type III deformation induced by three or more deforming forces acting at three or more locations of single OM particles. Thus, type I deformation is generally less complex than type II and III deformation. The OM particles subjected to type I deformation were analyzed quantitatively for parameters such as pore size, geometry, and long-axis orientation of elliptical pores. Deformation of OM enhances the robust heterogeneity of OM-hosted pores.

Calculating Components of the Effective Tensors of Elastic Moduli and Biot’s Parameter of Porous Geocomposites

Methods of composite mechanics were used to evaluate the effective elastic moduli and Biot’s parameter of porous media. Natural composites — dolomites and hyaloclastites — were considered as examples, which were also examined experimentally. The microscopic structure of the rocks was studied under a microscope, and their mineral composition was determined by the X-ray diffractometry. A comparison of experimental and calculated elastic moduli of dolomites showed their good agreement, which proved that the averaging method can be used to rapidly evaluate their effective elastic properties. For dolomites, Young’s modulus and Biot’s parameter were determined as functions of porosity using the calculation results and experimental data. The computation method described in this paper allows one to calculate Biot’s tensor in the general case of an anisotropic and inhomogeneous matrix and to evaluate the influence of pore shape on stresses and strains at the microlevel, which is not possible by experimental methods. Using samples of hyaloclastites with round and angular pores, the effect of pore shape on the elastic moduli and the effective stress coefficient was investigated. The effect of pore orientation was also studied using anisotropic dolomite samples with elongated pores.

Comparison of elastic properties of low-density polymeric foams determined by ultrasonic wave propagation and quasi-static mechanical testing

The ability to predict the mechanical performance of materials without sample extraction is of great interest to manufacturers and end-users. The aim of this work was to examine the relationship between the quasi-static measurements (i.e. the typically reported elastic property) and the non-destructive in-line in-situ ultrasonic wave propagation-derived elastic moduli of porous polyurethane foams over a range of densities. It was found that the ratio of moduli was direction-dependent: a factor of 2 when the testing was perpendicular to the pore orientation and a factor of 1.7 when parallel to the pore rising direction. The deviation was explained by ruling mechanisms such as strain rate and amplitude, deviation from orthotropic theory and anisotropy, and degree of density which affected shear wave propagation. The correlations were in agreement with those reported for other porous materials. The quantification of this correlation is a practical tool for estimating elastic properties on heterogeneous, irregularly shaped samples not suitable for bulk testing, or for in-line rapid quality control of parts in production lines.

Micropatterned Poly(ethylene glycol) Islands Disrupt Endothelial Cell-Substrate Interactions Differently from Microporous Membranes.

Porous membranes are ubiquitous in cell co-culture and tissue-on-a-chip studies. These materials are predominantly chosen for their semi-permeable and size exclusion properties to restrict or permit transmigration and cell-cell communication. However, previous studies have shown pore size, spacing and orientation affect cell behavior including extracellular matrix production and migration. The mechanism behind this behavior is not fully understood. In this study, we fabricated micropatterned non-fouling polyethylene glycol (PEG) islands to mimic pore openings in order to decouple the effect of surface discontinuity from potential grip on the vertical contact area provided by pore wall edges. Similar to previous findings on porous membranes, we found that the PEG islands hindered fibronectin fibrillogenesis with cells on patterned substrates producing shorter fibrils. Additionally, cell migration speed over micropatterned PEG islands was greater than unpatterned controls, suggesting that disruption of cell-substrate interactions by PEG islands promoted a more dynamic and migratory behavior, similarly to enhanced cell migration on microporous membranes. Preferred cellular directionality during migration was nearly indistinguishable between substrates with identically patterned PEG islands and previously reported behavior over micropores of the same geometry, further confirming disruption of cell-substrate interactions as a common mechanism behind the cellular responses on these substrates. Interestingly, compared to respective controls, there were differences in cell spreading and a lower increase in migration speed over PEG islands compared prior results on micropores with identical feature size and spacing. This suggests that membrane pores not only disrupt cell-substrate interactions, but also provide additional physical factors that affect cellular response.

Magnetic Pore Fabrics: The Role of Shape and Distribution Anisotropy in Defining the Magnetic Anisotropy of Ferrofluid‐Impregnated Samples

AbstractPore fabrics define physical properties of a rock, such as permeability and elasticity, both of which are important to many geological, hydrological, and environmental applications. Minerals and hence pores are often preferentially aligned, leading to anisotropy of physical properties and preferred flow directions. Preferred flow paths are defined by the shape and arrangement of pores, and a characterization of this pore fabric forms the basis for prediction of fluid flow directions. Magnetic pore fabrics (MPFs), that is, magnetic anisotropy measurements on ferrofluid‐impregnated samples, are a promising and fast way to characterize the pore fabric of connected pores in 3‐D, while analyzing a large number of pores with sizes down to 10 nm, without the need for any a priori knowledge about fabric orientation. Empirical relationships suggest that the MPF is related to the pore shape and orientation and approximates permeability anisotropy. This study uses models including shape and distribution anisotropy to better understand and quantify MPFs, using simple pore shapes and pore assemblies measured in previous studies. The results obtained in this study show that (1) shape anisotropy reliably predicts the MPF of single pores, (2) both shape and distribution anisotropy are needed to predict MPFs of pore assemblies, and (3) the anisotropy parameters P, L, and F are affected by the intrinsic susceptibility of the ferrofluid in addition to pore geometry. These findings can help explain some of the variability in empirical relationships and are an important step toward a quantitative understanding and application of MPFs in geological and environmental studies.

Non-destructive characterization of process-induced defects and their effect on the fatigue behavior of austenitic steel 316L made by laser-powder bed fusion

Additive manufacturing (AM) offers a high potential for light weight applications due to its possibility to generate complex structures with a high freedom of design compared to conventional techniques. However, the mechanical characterization of additively manufactured materials has become an essential topic in research over the last years to use AM parts for structural components especially in the automotive and aerospace industry. In the current research, specimens for fatigue tests made of the austenitic stainless steel AISI 316L processed by laser-powder bed fusion technique with three different building orientations were investigated. The gauge sections of the fatigue specimens were scanned by microfocus computed tomography (µ-CT) to detect and identify process-induced defects. The 3D information about the defects gained by µ-CT were compared with the crack-initiating defect on the fractured surfaces. The fatigue data were used for a model-based description of the fatigue strength based on the √area-parameter model. The results depict that the fatigue life is significantly influenced by the orientation of the inherent pores caused by the building direction causing a significant scatter in fatigue life. The µ-CT data allow to estimate the fatigue strength using the √area-parameter model based on the identified critical defects and are in good accordance with the results from the fatigue tests and the data obtained by fractography. Additionally, it could be shown that the √area-parameter model is applicable for additively manufactured 316L steel. It can also give an explanation for the anisotropic fatigue behavior, which supports the assumption that mainly the orientation of the pores and their √area-parameter are influencing the fatigue strength.

Form and orientation of soil pores as indicators of a structural soil organization

The work is based on the idea that the shape and orientation of soil pores are among the direct indicators of the structural state of the soil. The specific features of the quantitative assessment of the shape of pores in two-dimensional sections by the degree of its difference from the circle are considered. To improve the quality of the evaluation of the pore shape, it was proposed to use a generalized index of the pore shape F, which reflects both roundness and pore isometry. Using the form factor F, the structure of thin macropores was studied in vertical sections from the genetic horizons of the zonal loamy soils of the European territory of Russia. With the help of cluster analysis in the studied soils, 8 types of pore space specific for the main aggregative soil structures were identified. The selected types differ in shape, orientation and size of thin macropores in micromorphological sections. By means of discriminant analysis, a system of automated morphometric diagnostics of the aggregate soil structure based on the structure of the pore space of the soil has been developed. The natural genetic divergence of the aggregate structure in virgin soils and the agrogenic convergence of the structure in the arable horizons of agrosoils are shown. Morphometric criteria for diagnosing the four main stages of the degradation of the physical structure of the soil according to the shape and orientation of the soil pores are proposed.

Tailoring degradation-resistant thermal barrier coatings based on the orientation of spontaneously formed pores: From retardation to self-improvement

Thermal barrier coatings (TBCs) endow metal components with exceptional endure capability to withstand high temperatures over their bearable limits. Thus, TBCs are indispensable in a wide range of applications related to high temperatures. However, the thermal barrier performance degrades by at least 50% during service, which remains a critical challenge for these coatings. Herein, degradation-resistant TBCs were achieved using composited structures. Thermal insulation 2D pores were spontaneously formed during thermal exposure. Moreover, the degree of resistance was optimized from 20% to 50% by tailoring the orientation of the 2D pores. Thus, the thermal barrier performance was self-improved. A detailed examination suggests that scale-progressive healing of the initial pores is primarily responsible for the degradation mechanism. Analysis of the orientation of the spontaneously-formed 2D pores on thermal resistance reveals that this accounts for the self-improved thermal barrier performance. These results will guide the advanced design of TBCs for future applications.

Computational study of clot formation in aneurysms treated with shape memory polymer foam

To prevent aneurysmal rupture, intracranial aneurysms are often treated with endovascular metal coils that fill the aneurysm sac and stimulate thrombus formation, thereby isolating the aneurysm from the arterial flow. Despite its widespread use, this method can result in suboptimal outcomes leading to aneurysm recurrence. Recently, shape memory polymer foam has been proposed as an alternative aneurysm filler. In this work, a computational thrombus model is used to predict the clotting response within idealized 2D aneurysms virtually treated with foam. The results are compared to previously reported clot formation predictions in identical 2D aneurysm geometries filled with simplified endovascular metal coil shapes. Each of the foam-filled aneurysms reached at least 94% thrombus occlusion regardless of foam pore size or orientation, whereas the final thrombus occlusion within the coil-filled aneurysms varied from 80.8 to 92.2% with many of the cases leaving large areas in the aneurysm neck unfilled. Based on the simulations presented here, shape memory polymer foams may be able to produce more predictable, uniform, and complete clotting results than bare metal coils, independent of foam geometry or orientation.

Effects of Pore on Thermal Diffusivity and Thermal Radiation Properties of C/SiC Composites at High Temperatures

The effects of pore in C/SiC composites on thermal diffusivity and thermal radiation properties were investigated systematically. Pores were introduced into C/SiC by oxidizing carbon phase at 700 °C and damaged the thermal properties of C/SiC composites. Because of little changes in the pore shape and the pore orientation in C/SiC, thermal diffusivity of samples increased linearly with porosity. The pores within C/SiC absorbed and reflected the radiated heat, decreasing spectral emissivity. However, the temperature dependence of spectral emissivity didn’t change by the pore. With measurement temperature increasing, the pores weakened the thermal radiation property of samples gradually. A linear relation was suggested to quantify the negative effect of pores on the total emissivity.

Strength assessment of biomaterial models using selective sintering technology

The article presents an innovative method for the assessment of mechanical properties of biomaterials. 3D models were used for this purpose, obtained by selective laser sintering, designed in various spatial configuration (size of pores, orientation of pores ). The Rotational Bridge test stand was used to carry out the tests, which allowed generating of twisting deformations in the tested materials. The values of the moment of torsion forces transferred by the tested models were analyzed and compared, depending on their spatial structure.

Dielectric and optical properties of porous graphenes with uniform pore structures

Chemical synthesis for graphenes with uniform pore structures opens a new way for the precise modulation toward the performances of graphene-based materials. A family of porous graphenes with continuous and ordered pore distributions was designed by tracking the synthetic paths and studied by using density functional theory calculations. Three compounds with different pore sizes and orientations have remarkably different energy band structures. Introduction of pores opens the band gap of graphene. While the valence band maximum (VBM) is subject to small changes, the conduction band minimum (CBM) shifts with pore size and orientation. Furthermore, distinct in-plane anisotropy was noted in electron delocalization for the VBM and CBM bands. Enlargement of pore size alters the electron delocalization between the longitudinal and transverse directions. Confined by the ribbons and bridges that are separated by pores, electric dipoles cost more energy to respond to the applied fields, and electron excitations become more difficult in less conjugated systems. Our calculations reveal that for the graphenes with uniform pore structures, their band structures and optoelectronic properties are expected to be modulated by careful control over pore size and orientation through chemical synthesis.