Pore invasion dynamics during fluid front displacement in porous media determine functional pore size distribution and phase entrapment

NASA Astrophysics Data System (ADS)

Moebius, F.; Or, D.

2012-12-01

Dynamics of fluid fronts in porous media shape transport properties of the unsaturated zone and affect management of petroleum reservoirs and their storage properties. What appears macroscopically as smooth and continuous motion of a displacement fluid front may involve numerous rapid interfacial jumps often resembling avalanches of invasion events. Direct observations using high-speed camera and pressure sensors in sintered glass micro-models provide new insights on the influence of flow rates, pore size, and gravity on invasion events and on burst size distribution. Fundamental differences emerge between geometrically-defined pores and "functional" pores invaded during a single burst (invasion event). The waiting times distribution of individual invasion events and decay times of inertial oscillations (following a rapid interfacial jump) are characteristics of different displacement regimes. An invasion percolation model with gradients and including the role of inertia provide a framework for linking flow regimes with invasion sequences and phase entrapment. Model results were compared with measurements and with early studies on invasion burst sizes and waiting times distribution during slow drainage processes by Måløy et al. [1992]. The study provides new insights into the discrete invasion events and their weak links with geometrically-deduced pore geometry. Results highlight factors controlling pore invasion events that exert strong influence on macroscopic phenomena such as front morphology and residual phase entrapment shaping hydraulic properties after the passage of a fluid front.

Quantification of soil structure based on Minkowski functions

NASA Astrophysics Data System (ADS)

Vogel, H.-J.; Weller, U.; Schlüter, S.

2010-10-01

The structure of soils and other geologic media is a complex three-dimensional object. Most of the physical material properties including mechanical and hydraulic characteristics are immediately linked to the structure given by the pore space and its spatial distribution. It is an old dream and still a formidable challenge to relate structural features of porous media to their functional properties. Using tomographic techniques, soil structure can be directly observed at a range of spatial scales. In this paper we present a scale-invariant concept to quantify complex structures based on a limited set of meaningful morphological functions. They are based on d+1 Minkowski functionals as defined for d-dimensional bodies. These basic quantities are determined as a function of pore size or aggregate size obtained by filter procedures using mathematical morphology. The resulting Minkowski functions provide valuable information on the size of pores and aggregates, the pore surface area and the pore topology having the potential to be linked to physical properties. The theoretical background and the related algorithms are presented and the approach is demonstrated for the pore structure of an arable soil and the pore structure of a sand both obtained by X-ray micro-tomography. We also analyze the fundamental problem of limited resolution which is critical for any attempt to quantify structural features at any scale using samples of different size recorded at different resolutions. The results demonstrate that objects smaller than 5 voxels are critical for quantitative analysis.

DNA-assisted oligomerization of pore-forming toxin monomers into precisely-controlled protein channels

PubMed Central

Knechtel, Johann

2017-01-01

Abstract We have developed a novel approach for creating membrane-spanning protein-based pores. The construction principle is based on using well-defined, circular DNA nanostructures to arrange a precise number of pore-forming protein toxin monomers. We can thereby obtain, for the first time, protein pores with specifically set diameters. We demonstrate this principle by constructing artificial alpha-hemolysin (αHL) pores. The DNA/αHL hybrid nanopores composed of twelve, twenty or twenty-six monomers show stable insertions into lipid bilayers during electrical recordings, along with steady, pore size-dependent current levels. Our approach successfully advances the applicability of nanopores, in particular towards label-free studies of single molecules in large nanoscaled biological structures. PMID:29088457

Sol-gel derived ceramic electrolyte films on porous substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kueper, T.W.

1992-05-01

A process for the deposition of sol-gel derived thin films on porous substrates has been developed; such films should be useful for solid oxide fuel cells and related applications. Yttria-stabilized zirconia films have been formed from metal alkoxide starting solutions. Dense films have been deposited on metal substrates and ceramic substrates, both dense and porous, through dip-coating and spin-coating techniques, followed by a heat treatment in air. X-ray diffraction has been used to determine the crystalline phases formed and the extent of reactions with various substrates which may be encountered in gas/gas devices. Surface coatings have been successfully applied tomore » porous substrates through the control of substrate pore size and deposition parameters. Wetting of the substrate pores by the coating solution is discussed, and conditions are defined for which films can be deposited over the pores without filling the interiors of the pores. Shrinkage cracking was encountered in films thicker than a critical value, which depended on the sol-gel process parameters and on the substrate characteristics. Local discontinuities were also observed in films which were thinner than a critical value which depended on the substrate pore size. A theoretical discussion of cracking mechanisms is presented for both types of cracking, and the conditions necessary for successful thin formation are defined. The applicability of these film gas/gas devices is discussed.« less

Ion transport in sub-5-nm graphene nanopores.

PubMed

Suk, Myung E; Aluru, N R

2014-02-28

Graphene nanopore is a promising device for single molecule sensing, including DNA bases, as its single atom thickness provides high spatial resolution. To attain high sensitivity, the size of the molecule should be comparable to the pore diameter. However, when the pore diameter approaches the size of the molecule, ion properties and dynamics may deviate from the bulk values and continuum analysis may not be accurate. In this paper, we investigate the static and dynamic properties of ions with and without an external voltage drop in sub-5-nm graphene nanopores using molecular dynamics simulations. Ion concentration in graphene nanopores sharply drops from the bulk concentration when the pore radius is smaller than 0.9 nm. Ion mobility in the pore is also smaller than bulk ion mobility due to the layered liquid structure in the pore-axial direction. Our results show that a continuum analysis can be appropriate when the pore radius is larger than 0.9 nm if pore conductivity is properly defined. Since many applications of graphene nanopores, such as DNA and protein sensing, involve ion transport, the results presented here will be useful not only in understanding the behavior of ion transport but also in designing bio-molecular sensors.

Counting polymers moving through a single ion channel

NASA Astrophysics Data System (ADS)

Bezrukov, Sergey M.; Vodyanoy, Igor; Parsegian, V. Adrian

1994-07-01

THE change in conductance of a small electrolyte-filled capillary owing to the passage of sub-micrometre-sized particles has long been used for particle counting and sizing. A commercial device for such measurements, the Coulter counter, is able to detect particles of sizes down to several tenths of a micrometre1-3. Nuclepore technology (in which pores are etched particle tracks) has extended the lower limit of size detection to 60-nm particles by using a capillary of diameter 0.45 μm (ref. 4). Here we show that natural channel-forming peptides incorporated into a bilayer lipid membrane can be used to detect the passage of single molecules with gyration radii as small as 5-15 Å. From our experiments with alamethicin pores we infer both the average number and the diffusion coefficients of poly(ethylene glycol) molecules in the pore. Our approach provides a means of observing the statistics and mechanics of flexible polymers moving within the confines of precisely defined single-molecule structures.

The phenotype of cancer cell invasion controlled by fibril diameter and pore size of 3D collagen networks.

PubMed

Sapudom, Jiranuwat; Rubner, Stefan; Martin, Steve; Kurth, Tony; Riedel, Stefanie; Mierke, Claudia T; Pompe, Tilo

2015-06-01

The behavior of cancer cells is strongly influenced by the properties of extracellular microenvironments, including topology, mechanics and composition. As topological and mechanical properties of the extracellular matrix are hard to access and control for in-depth studies of underlying mechanisms in vivo, defined biomimetic in vitro models are needed. Herein we show, how pore size and fibril diameter of collagen I networks distinctively regulate cancer cell morphology and invasion. Three-dimensional collagen I matrices with a tight control of pore size, fibril diameter and stiffness were reconstituted by adjustment of concentration and pH value during matrix reconstitution. At first, a detailed analysis of topology and mechanics of matrices using confocal laser scanning microscopy, image analysis tools and force spectroscopy indicate pore size and not fibril diameter as the major determinant of matrix elasticity. Secondly, by using two different breast cancer cell lines (MDA-MB-231 and MCF-7), we demonstrate collagen fibril diameter--and not pore size--to primarily regulate cell morphology, cluster formation and invasion. Invasiveness increased and clustering decreased with increasing fibril diameter for both, the highly invasive MDA-MB-231 cells with mesenchymal migratory phenotype and the MCF-7 cells with amoeboid migratory phenotype. As this behavior was independent of overall pore size, matrix elasticity is shown to be not the major determinant of the cell characteristics. Our work emphasizes the complex relationship between structural-mechanical properties of the extracellular matrix and invasive behavior of cancer cells. It suggests a correlation of migratory and invasive phenotype of cancer cells in dependence on topological and mechanical features of the length scale of single fibrils and not on coarse-grained network properties. Copyright © 2015 Elsevier Ltd. All rights reserved.

Interconnected Porous Polymers with Tunable Pore Throat Size Prepared via Pickering High Internal Phase Emulsions.

PubMed

Xu, Hongyun; Zheng, Xianhua; Huang, Yifei; Wang, Haitao; Du, Qiangguo

2016-01-12

Interconnected macroporous polymers were prepared by copolymerizing methyl acrylate (MA) via Pickering high internal phase emulsion (HIPE) templates with modified silica particles. The pore structure of the obtained polymer foams was observed by field-emission scanning electron microscopy (FE-SEM). Gas permeability was characterized to evaluate the interconnectivity of macroporous polymers. The polymerization shrinkage of continuous phase tends to form open pores while the solid particles surrounding the droplets act as barriers to produce closed pores. These two conflicting factors are crucial in determining the interconnectivity of macroporous polymers. Thus, poly-Pickering HIPEs with high permeability and well-defined pore structure can be achieved by tuning the MA content, the internal phase fraction, and the content of modified silica particles.

Experimental study on pore structure and performance of sintered porous wick

NASA Astrophysics Data System (ADS)

He, Da; Wang, Shufan; Liu, Rutie; Wang, Zhubo; Xiong, Xiang; Zou, Jianpeng

2018-02-01

Porous wicks were prepared via powder metallurgy using NH4HCO3 powders as pore-forming agent. The pore-forming agent particle size was varied to control the pore structure and equivalent pore size distribution feature of porous wick. The effect of pore-forming agent particle size on the porosity, pore structures, equivalent pore size distribution and capillary pumping performance were investigated. Results show that with the particle size of pore-forming agent decrease, the green density and the volume shrinkage of the porous wicks gradually increase and the porosity reduces slightly. There are two types of pores inside the porous wick, large-sized prefabricated pores and small-sized gap pores. With the particle size of pore-forming agent decrease, the size of the prefabricated pores becomes smaller and the distribution tends to be uniform. Gap pores and prefabricated pores inside the wick can make up different types of pore channels. The equivalent pore size of wick is closely related to the structure of pore channels. Furthermore, the equivalent pore size distribution of wick shows an obvious double-peak feature when the pore-forming agent particle size is large. With the particle size of pore-forming agent decrease, the two peaks of equivalent pore size distribution approach gradually to each other, resulting in a single-peak feature. Porous wick with single-peak feature equivalent pore size distribution possesses the better capillary pumping performances.

A mathematical multiscale model of bone remodeling, accounting for pore space-specific mechanosensation.

PubMed

Pastrama, Maria-Ioana; Scheiner, Stefan; Pivonka, Peter; Hellmich, Christian

2018-02-01

While bone tissue is a hierarchically organized material, mathematical formulations of bone remodeling are often defined on the level of a millimeter-sized representative volume element (RVE), "smeared" over all types of bone microstructures seen at lower observation scales. Thus, there is no explicit consideration of the fact that the biological cells and biochemical factors driving bone remodeling are actually located in differently sized pore spaces: active osteoblasts and osteoclasts can be found in the vascular pores, whereas the lacunar pores host osteocytes - bone cells originating from former osteoblasts which were then "buried" in newly deposited extracellular bone matrix. We here propose a mathematical description which considers size and shape of the pore spaces where the biological and biochemical events take place. In particular, a previously published systems biology formulation, accounting for biochemical regulatory mechanisms such as the rank-rankl-opg pathway, is cast into a multiscale framework coupled to a poromicromechanical model. The latter gives access to the vascular and lacunar pore pressures arising from macroscopic loading. Extensive experimental data on the biological consequences of this loading strongly suggest that the aforementioned pore pressures, together with the loading frequency, are essential drivers of bone remodeling. The novel approach presented here allows for satisfactory simulation of the evolution of bone tissue under various loading conditions, and for different species; including scenarios such as mechanical dis- and overuse of murine and human bone, or in osteocyte-free bone. Copyright © 2017 Elsevier Inc. All rights reserved.

Quantification of Soil Pore Structure Based on Minkowski-Functions

NASA Astrophysics Data System (ADS)

Vogel, H.; Weller, U.; Schlüter, S.

2009-05-01

The porous structure in soils and other geologic media is typically a complex 3-dimensional object. Most of the physical material properties including mechanical and hydraulic characteristics are immediately linked to this structure which can be directly observed using non-invasive techniques as e.g. X-ray tomography. It is an old dream and still a formidable challenge to related structural features of porous media to their physical properties. In this contribution we present a scale-invariant concept to quantify pore structure based on a limited set of meaningful morphological functions. They are based on d+1 Minkowski functionals as defined for d-dimensional bodies. These basic quantities are determined as a function of pore size obtained by filter procedures using mathematical morphology. The resulting Minkowski functions provide valuable information on pore size, pore surface area and pore topology having the potential to be linked to physical properties. The theoretical background and the related algorithms are presented and the approach is demonstrated for the structure of an arable topsoil obtained by X-ray micro tomography. We also discuss the fundamental problem of limited resolution which is critical for any attempt to quantify structural features at any scale.

Neutrons measure phase behavior in pores at Angstrom size

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bardoel, Agatha A; Melnichenko, Yuri B

Researchers have measured the phase behavior of green house gases in pores at the Angstrom-level, using small angle neutron scattering (SANS) at the Oak Ridge National Laboratory's High Flux Isotope Reactor. Yuri Melnichenko, an instrument scientist on the General Purpose Small Angle Neutron Scattering (GP SANS) Diffractometer at ORNL's High Flux Isotope Reactor, his postdoctoral associate Lilin He and collaborators Nidia Gallego and Cristian Contescu from the Material Sciences Division (ORNL) were engaged in the work. They were studying nanoporous carbons to assess their attractiveness as storage media for hydrogen, with a view to potential use for on-board hydrogen storagemore » for transportation applications. Nanoporous carbons can also serve as electrode material for supercapacitors and batteries. The researchers successfully determined that the most efficiently condensing pore size in a carbon nanoporous material for hydrogen storage is less than one nanometer. In a paper recently published by the Journal of the American Chemical Society, the collaborators used small angle neutron scattering to study how hydrogen condenses in small pores at ambient temperature. They discovered that the surface-molecule interactions create internal pressures in pores that may exceed the external gas pressure by a factor of up to 50. 'This is an exciting result,' Melnichenko said, 'as you achieve extreme densification in pores 'for free', i.e. without spending any energy. These results can be used to guide the development of new carbon adsorbents tailored to maximize hydrogen storage capacities.' Another important factor that defines the adsorption capacity of sub-nanometer pores is their shape. In order to get accurate structural information and maximize sorption capacity, it is important that pores are small and of approximately uniform size. In collaboration with Drexel University's Yury Gogotsi who supplied the samples, Melnichenko and his collaborators used the GP SANS instrument to study how the size and shape of pores in sub-nanometer porous carbons varies, depending on the manufacturing conditions. While small angle X-ray scattering (SAXS) can do the job too, Melnichenko says, the SANS method broke new ground in analyzing the shape and behavior of pores at subnanometer size, when subjected to varying synthesis temperature. 'We found that these very small pores are in fact spherical, and that when we change the synthesis conditions, they become elongated, even 'slit-like', and all of this on a subnanometer scale,' Melnichenko said.« less

Fast Two-Dimensional Bubble Analysis of Biopolymer Filamentous Networks Pore Size from Confocal Microscopy Thin Data Stacks

PubMed Central

Molteni, Matteo; Magatti, Davide; Cardinali, Barbara; Rocco, Mattia; Ferri, Fabio

2013-01-01

The average pore size ξ0 of filamentous networks assembled from biological macromolecules is one of the most important physical parameters affecting their biological functions. Modern optical methods, such as confocal microscopy, can noninvasively image such networks, but extracting a quantitative estimate of ξ0 is a nontrivial task. We present here a fast and simple method based on a two-dimensional bubble approach, which works by analyzing one by one the (thresholded) images of a series of three-dimensional thin data stacks. No skeletonization or reconstruction of the full geometry of the entire network is required. The method was validated by using many isotropic in silico generated networks of different structures, morphologies, and concentrations. For each type of network, the method provides accurate estimates (a few percent) of the average and the standard deviation of the three-dimensional distribution of the pore sizes, defined as the diameters of the largest spheres that can be fit into the pore zones of the entire gel volume. When applied to the analysis of real confocal microscopy images taken on fibrin gels, the method provides an estimate of ξ0 consistent with results from elastic light scattering data. PMID:23473499

Porous Electrodes I: Numerical Simulation Using Random Network and Single Pore Models.

DTIC Science & Technology

1984-01-31

characteristic of Zn and ZnO ) and scaling them down to the magnitude of a unit pore size- approximately 10i in diameter. We define a characteristic...supported by the Office of Naval Research under contract N00014-81-K-0339. 11 - 15 - REFERENCES 1. R. de Levis in Advances in Electrochemistry and...P. 3. Hendra Dr. C. E. Mueller Department of Chemistry The Electrochemistry Branch University of Southampton Naval Surface Weapons Center

A pore-size classification for peat bogs derived from unsaturated hydraulic properties

NASA Astrophysics Data System (ADS)

Weber, Tobias Karl David; Iden, Sascha Christian; Durner, Wolfgang

2017-12-01

In ombrotrophic peatlands, the moisture content of the acrotelm (vadoze zone) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Thus, variably saturated flow processes determine whether peatlands act as sinks or sources of atmospheric carbon, and modelling these processes is crucial to assess effects of changed environmental conditions on the future development of these ecosystems. We show that the Richards equation can be used to accurately describe the moisture dynamics under evaporative conditions in variably saturated peat soil, encompassing the transition from the topmost living moss layer to the decomposed peat as part of the vadose zone. Soil hydraulic properties (SHP) were identified by inverse simulation of evaporation experiments on samples from the entire acrotelm. To obtain consistent descriptions of the observations, the traditional van Genuchten-Mualem model was extended to account for non-capillary water storage and flow. We found that the SHP of the uppermost moss layer reflect a pore-size distribution (PSD) that combines three distinct pore systems of the Sphagnum moss. For deeper samples, acrotelm pedogenesis changes the shape of the SHP due to the collapse of inter-plant pores and an infill with smaller particles. This leads to gradually more homogeneous and bi-modal PSDs with increasing depth, which in turn can serve as a proxy for increasing state of pedogenesis in peatlands. From this, we derive a nomenclature and size classification for the pore spaces of Sphagnum mosses and define inter-, intra-, and inner-plant pore spaces, with effective pore diameters of > 300, 300-30, and 30-10 µm, respectively.

Universal Spatial Correlation Functions for Describing and Reconstructing Soil Microstructure

PubMed Central

Skvortsova, Elena B.; Mallants, Dirk

2015-01-01

Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification, pore-scale modelling of soil properties, soil degradation monitoring, and description of spatial dynamics of soil microbial activity. PMID:26010779

Universal spatial correlation functions for describing and reconstructing soil microstructure.

PubMed

Karsanina, Marina V; Gerke, Kirill M; Skvortsova, Elena B; Mallants, Dirk

2015-01-01

Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification, pore-scale modelling of soil properties, soil degradation monitoring, and description of spatial dynamics of soil microbial activity.

Bioaccessible Porosity: A new approach to assess residual contamination after bioremediation of hydrophobic organic compounds in sub-surface microporous environments

NASA Astrophysics Data System (ADS)

Akbari, A.; Ghoshal, S.

2016-12-01

We define a new parameter, "bioaccessible porosity", the fraction of aggregate volume accessible to soil bacteria, towards a priori assessment of hydrocarbon bioremediation end points. Microbial uptake of poorly soluble hydrocarbons occurs through direct uptake or micellar solubilzation/emulsification associated with biosurfactant production, and requires close proximity of bacteria and hydrocarbon phase. In subsurface microporous environments, bioremediation rates are attenuated when residual hydrophobic contamination is entrapped in sterically restrictive environments which is not accessible to soil bacteria. This study presents new approaches for characterization of the microstructure of porous media and as well, the ability of indigenous hydrocarbon degraders to access to a range of pore sizes. Bacterial access to poorly soluble hydrocarbons in soil micro pores were simulated with bioreactors with membranes with different pore sizes containing the hydrocarbon degrading bacteria, Dietzia maris. D. maris is Gram-positive, and nonmotile that we isolated as the major hydrocarbon degrader from a fine-grained, weathered, hydrocarbon-contaminated site soil. Under nutritional stress, planktonic D. maris cells were aggregated and accessed 5 µm but not 3 µm and smaller pores. However, when hexadecane was available at the pore mouth, D. maris colonized the pore mouth, and accessed pores as small as 0.4 µm. This suggests bacterial accessibility to different pore sizes is regulated by nutritional conditions. A combination of X-ray micro-CT scanning, gas adsorption and mercury intrusion porosimetry was used to characterize the range of pore sizes of soil aggregates. In case of the studied contaminated soil, the bioaccessible porosity were determined as 25% , 27% and 29% (assuming 4, 1, 0.4 µm respectively as accessibility criteria), and about 2.7% of aggregate volume was attributed to 0.006-0.4 µm pores. The 2% aggregate volume at an assumed saturation of 10% could accommodate 1000 mg/ kg soil of oil. The remediation endpoint after extended biotreatment was at similar order of magnitude of 600 mg/kg. The approach introduced here could be used for qualitative assessment of attainable bioremediation endpoint in soils with different microstructure and hydrocarbon degrading bacterial community.

Investigation of thin/well-tunable liquid/gas diffusion layers exhibiting superior multifunctional performance in low-temperature electrolytic water splitting

DOE PAGES

Kang, Zhenye; Mo, Jingke; Yang, Gaoqiang; ...

2016-10-11

Liquid/gas diffusion layers (LGDLs), which are located between the catalyst layer (CL) and bipolar plate (BP), play an important role in enhancing the performance of water splitting in proton exchange membrane electrolyzer cells (PEMECs). They are expected to transport electrons, heat, and reactants/products simultaneously with minimum voltage, current, thermal, interfacial, and fluidic losses. Here in this study, the thin titanium-based LGDLs with straight-through pores and well-defined pore morphologies are comprehensively investigated for the first time. The novel LGDL with a 400 μm pore size and 0.7 porosity achieved a best-ever performance of 1.66 V at 2 A cm -2 andmore » 80 °C, as compared to the published literature. The thin/well-tunable titanium based LGDLs remarkably reduce ohmic and activation losses, and it was found that porosity has a more significant impact on performance than pore size. In addition, an appropriate equivalent electrical circuit model has been established to quantify the effects of pore morphologies. The rapid electrochemical reaction phenomena at the center of the PEMEC are observed by coupling with high-speed and micro-scale visualization systems. Lastly, the observed reactions contribute reasonable and pioneering data that elucidate the effects of porosity and pore size on the PEMEC performance. This study can be a new guide for future research and development towards high-efficiency and low-cost hydrogen energy.« less

Intrinsic Size Effect in Scaffolded Porous Calcium Silicate Particles and Mechanical Behavior of Their Self-Assembled Ensembles.

PubMed

Hwang, Sung Hoon; Shahsavari, Rouzbeh

2018-01-10

Scaffolded porous submicron particles with well-defined diameter, shape, and pore size have profound impacts on drug delivery, bone-tissue replacement, catalysis, sensors, photonic crystals, and self-healing materials. However, understanding the interplay between pore size, particle size, and mechanical properties of such ultrafine particles, especially at the level of individual particles and their ensemble states, is a challenge. Herein, we focus on porous calcium-silicate submicron particles with various diameters-as a model system-and perform extensive 900+ nanoindentations to completely map out their mechanical properties at three distinct structural forms from individual submicron particles to self-assembled ensembles to pressure-induced assembled arrays. Our results demonstrate a notable "intrinsic size effect" for individual porous submicron particles around ∼200-500 nm, induced by the ratio of particle characteristic diameter to pore characteristic size distribution. Increasing this ratio results in a brittle-to-ductile transition where the toughness of the submicron particles increases by 120%. This size effect becomes negligible as the porous particles form superstructures. Nevertheless, the self-assembled arrays collectively exhibit increasing elastic modulus as a function of applied forces, while pressure-induced compacted arrays exhibit no size effect. This study will impact tuning properties of individual scaffolded porous particles and can have implications on self-assembled superstructures exploiting porosity and particle size to impart new functionalities.

Recent advances of mesoporous materials in sample preparation.

PubMed

Zhao, Liang; Qin, Hongqiang; Wu, Ren'an; Zou, Hanfa

2012-03-09

Sample preparation has been playing an important role in the analysis of complex samples. Mesoporous materials as the promising adsorbents have gained increasing research interest in sample preparation due to their desirable characteristics of high surface area, large pore volume, tunable mesoporous channels with well defined pore-size distribution, controllable wall composition, as well as modifiable surface properties. The aim of this paper is to review the recent advances of mesoporous materials in sample preparation with emphases on extraction of metal ions, adsorption of organic compounds, size selective enrichment of peptides/proteins, specific capture of post-translational peptides/proteins and enzymatic reactor for protein digestion. Copyright © 2011 Elsevier B.V. All rights reserved.

The influence of pore textures on the permeability of volcanic rocks

NASA Astrophysics Data System (ADS)

Mueller, S.; Spieler, O.; Scheu, B.; Dingwell, D.

2006-12-01

The permeability of a porous medium is strongly dependent on its porosity, as a higher proportion of pore volume is generally expected to lead to a greater probability of pore interconnectedness and the formation of a fluid-flow providing pathway. However, the relationship between permeability and porosity is not a unique one, as many other textural parameters may play an important role and substantially affect gas flow properties. Among these parameters are (a) the connection geometry (i.e. intergranular pore spaces in clastic sediments vs. bubble interconnections), (b) the pore sizes, (c) pore shape and (d) pore size distribution. The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rock's permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. It is therefore essential to understand and quantify influences of different pore textures on the degassing properties of volcanic rocks, as well as investigate the effects of permeability on eruptive processes. Using a modified shock-tube-based fragmentation apparatus, we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample in a steel autoclave. A transient 1D filtration code has been developed to calculate permeability using the experimental pressure decay curve within a defined volume below the sample. An external furnace around the autoclave and the use of compressed salt as sealant allows also measurements at high temperatures up to 800 °C. Over 130 permeability measurements have been performed on samples of different volcanic settings, covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Analysis of the samples eruptive origin as well as the pore sizes, shapes and size distribution allow an estimation of the contribution of various textural effects to the overall permeability.

Bottom-up synthesis of multifunctional nanoporous graphene

NASA Astrophysics Data System (ADS)

Moreno, César; Vilas-Varela, Manuel; Kretz, Bernhard; Garcia-Lekue, Aran; Costache, Marius V.; Paradinas, Markos; Panighel, Mirko; Ceballos, Gustavo; Valenzuela, Sergio O.; Peña, Diego; Mugarza, Aitor

2018-04-01

Nanosize pores can turn semimetallic graphene into a semiconductor and, from being impermeable, into the most efficient molecular-sieve membrane. However, scaling the pores down to the nanometer, while fulfilling the tight structural constraints imposed by applications, represents an enormous challenge for present top-down strategies. Here we report a bottom-up method to synthesize nanoporous graphene comprising an ordered array of pores separated by ribbons, which can be tuned down to the 1-nanometer range. The size, density, morphology, and chemical composition of the pores are defined with atomic precision by the design of the molecular precursors. Our electronic characterization further reveals a highly anisotropic electronic structure, where orthogonal one-dimensional electronic bands with an energy gap of ∼1 electron volt coexist with confined pore states, making the nanoporous graphene a highly versatile semiconductor for simultaneous sieving and electrical sensing of molecular species.

Decreasing transmembrane segment length greatly decreases perfringolysin O pore size

DOE PAGES

Lin, Qingqing; Li, Huilin; Wang, Tong; ...

2015-04-08

Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakagemore » assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.« less

Hollow porous-wall glass microspheres for hydrogen storage

DOEpatents

Heung, Leung K.; Schumacher, Ray F.; Wicks, George G.

2010-02-23

A porous wall hollow glass microsphere is provided having a diameter range of between 1 to 200 microns, a density of between 1.0 to 2.0 gm/cc, a porous-wall structure having wall openings defining an average pore size of between 10 to 1000 angstroms, and which contains therein a hydrogen storage material. The porous-wall structure facilitates the introduction of a hydrogen storage material into the interior of the porous wall hollow glass microsphere. In this manner, the resulting hollow glass microsphere can provide a membrane for the selective transport of hydrogen through the porous walls of the microsphere, the small pore size preventing gaseous or liquid contaminants from entering the interior of the hollow glass microsphere.

Permeability changes induced by microfissure closure and opening in tectonized materials. Effect on slope pore pressure regime.

NASA Astrophysics Data System (ADS)

De la Fuente, Maria; Vaunat, Jean; Pedone, Giuseppe; Cotecchia, Federica; Sollecito, Francesca; Casini, Francesca

2015-04-01

Tectonized clays are complex materials characterized by several levels of structures that may evolve during load and wetting/drying processes. Some microstructural patterns, as microfissures, have a particular influence on the value of permeability which is one of the main factors controlling pore pressure regime in slopes. In this work, the pore pressure regime measured in a real slope of tectonized clay in Southern Italy is analyzed by a numerical model that considers changes in permeability induced by microfissure closure and opening during the wetting and drying processes resulting from climatic actions. Permeability model accounts for the changes in Pore Size Distribution observed by Microscopy Intrusion Porosimetry. MIP tests are performed on representative samples of ground in initial conditions ("in situ" conditions) and final conditions (deformed sample after applying a wetting path that aims to reproduce the saturation of the soil under heavy rains). The resulting measurements allow for the characterization at microstructural level of the soil, identifying the distribution of dominant families pores in the sample and its evolution under external actions. Moreover, comparison of pore size density functions allows defining a microstructural parameter that depends on void ratio and degree of saturation and controls the variation of permeability. Model has been implemented in a thermo-hydro-mechanical code provided with a special boundary condition for climatic actions. Tool is used to analyze pore pressure measurements obtained in the tectonized clay slope. Results are analyzed at the light of the effect that permeability changes during wetting and drying have on the pore pressure regime.

Fines classification based on sensitivity to pore-fluid chemistry

USGS Publications Warehouse

Jang, Junbong; Santamarina, J. Carlos

2016-01-01

The 75-μm particle size is used to discriminate between fine and coarse grains. Further analysis of fine grains is typically based on the plasticity chart. Whereas pore-fluid-chemistry-dependent soil response is a salient and distinguishing characteristic of fine grains, pore-fluid chemistry is not addressed in current classification systems. Liquid limits obtained with electrically contrasting pore fluids (deionized water, 2-M NaCl brine, and kerosene) are combined to define the soil “electrical sensitivity.” Liquid limit and electrical sensitivity can be effectively used to classify fine grains according to their fluid-soil response into no-, low-, intermediate-, or high-plasticity fine grains of low, intermediate, or high electrical sensitivity. The proposed methodology benefits from the accumulated experience with liquid limit in the field and addresses the needs of a broader range of geotechnical engineering problems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Qingqing; Li, Huilin; Wang, Tong

Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakagemore » assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.« less

Nondestructive assessment of pore size in foam-based hybrid composite materials

NASA Astrophysics Data System (ADS)

Chen, M. Y.; Ko, R. T.

2012-05-01

In-situ non-destructive evaluation (NDE) during processing of high temperature polymer based hybrids offers great potential to gain close control and achieve the desired level of pore size, with low overall development cost. During the polymer curing cycle, close control over the evolution of volatiles would be beneficial to avoid the presence of pores or at least control their sizes. Traditional NDE methods cannot realistically be expected to evaluate individual pores in such components, as each pore evolves and grows during curing. However, NDE techniques offer the potential to detect and quantify the macroscopic response of many pores that are undesirable or intentionally introduced into these advanced materials. In this paper, preliminary results will be presented for nondestructive assessment of pore size in foam-based hybrid composite materials using ultrasonic techniques. Pore size was evaluated through the frequency content of the ultrasonic signal. The effects of pore size on the attenuation of ultrasound were studied. Feasibility of this method was demonstrated on two types of foams with various pore sizes.

Analysis of Effective Interconnectivity of DegraPol-foams Designed for Negative Pressure Wound Therapy

PubMed Central

Milleret, Vincent; Bittermann, Anne Greet; Mayer, Dieter; Hall, Heike

2009-01-01

Many wounds heal slowly and are difficult to manage. Therefore Negative Pressure Wound Therapy (NPWT) was developed where polymer foams are applied and a defined negative pressure removes wound fluid, reduces bacterial burden and increases the formation of granulation tissue. Although NPWT is used successfully, its mechanisms are not well understood. In particular, different NPWT dressings were never compared. Here a poly-ester urethane Degrapol® (DP)-foam was produced and compared with commercially available dressings (polyurethane-based and polyvinyl-alcohol-based) in terms of apparent pore sizes, swelling and effective interconnectivity of foam pores. DP-foams contain relatively small interconnected pores; PU-foams showed large pore size and interconnectivity; whereas PVA-foams displayed heterogeneous and poorly interconnected pores. PVA-foams swelled by 40 %, whereas DP- and PU-foams remained almost without swelling. Effective interconnectivity was investigated by submitting fluorescent beads of 3, 20 and 45 μm diameter through the foams. DP- and PU-foams removed 70-90 % of all beads within 4 h, independent of the bead diameter or bead pre-adsorption with serum albumin. For PVA-foams albumin pre-adsorbed beads circulated longer, where 20 % of 3 μm and 10 % of 20 μm diameter beads circulated after 96 h. The studies indicate that efficient bead perfusion does not only depend on pore size and swelling capacity, but effective interconnectivity might also depend on chemical composition of the foam itself. In addition due to the efficient sieve-effect of the foams uptake of wound components in vivo might occur only for short time suggesting other mechanisms being decisive for success of NPWT.

Nano-Pore Size Analysis by SAXS Method of Cementitious Mortars Undergoing Delayed Ettringite Formation

NASA Astrophysics Data System (ADS)

Shekar, Yamini

This research investigates the nano-scale pore structure of cementitious mortars undergoing delayed ettringite formation (DEF) using small angle x-ray scattering (SAXS). DEF has been known to cause expansion and cracking during later ages (around 4000 days) in concrete that has been heat cured at temperatures of 70°C or above. Though DEF normally occurs in heat cured concrete, mass cured concrete can also experience DEF. Large crystalline pressures result in smaller pore sizes. The objectives of this research are: (1) to investigate why some samples expand early than later expansion, (2) to evaluate the effects of curing conditions and pore size distributions at high temperatures, and (3) to assess the evolution of the pore size distributions over time. The most important outcome of the research is the pore sizes obtained from SAXS were used in the development of a 3-stage model. From the data obtained, the pore sizes increase in stage 1 due to initial ettringite formation and in turn filling up the smallest pores. Once the critical pore size threshold is reached (around 20nm) stage 2 is formed due to cracking which tends to decrease in the pore sizes. Finally, in stage 3, the cracking continues, therefore increasing in the pore size.

Hydroxyapatite coatings containing Zn and Si on Ti-6Al-4Valloy by plasma electrolytic oxidation

NASA Astrophysics Data System (ADS)

Hwang, In-Jo; Choe, Han-Cheol

2018-02-01

In this study, hydroxyapatite coatings containing Zn and Si on Ti-6Al-4Valloy by plasma electrolytic oxidation were researched using various experimental instruments. The pore size is depended on the electrolyte concentration and the particle size and number of pore increase on surface part and pore part. In the case of Zn/Si sample, pore size was larger than that of Zn samples. The maximum size of pores decreased and minimum size of pores increased up to 10Zn/Si and Zn and Si affect the formation of pore shapes. As Zn ion concentration increases, the size of the particle tends to increase, the number of particles on the surface part is reduced, whereas the size of the particles and the number of particles on pore part increased. Zn is mainly detected at pore part, and Si is mainly detected at surface part. The crystallite size of anatase increased as the Zn ion concentration, whereas, in the case of Si ion added, crystallite size of anatase decreased.

Multiscale pore structure and constitutive models of fine-grained rocks

NASA Astrophysics Data System (ADS)

Heath, J. E.; Dewers, T. A.; Shields, E. A.; Yoon, H.; Milliken, K. L.

2017-12-01

A foundational concept of continuum poromechanics is the representative elementary volume or REV: an amount of material large enough that pore- or grain-scale fluctuations in relevant properties are dissipated to a definable mean, but smaller than length scales of heterogeneity. We determine 2D-equivalent representative elementary areas (REAs) of pore areal fraction of three major types of mudrocks by applying multi-beam scanning electron microscopy (mSEM) to obtain terapixel image mosaics. Image analysis obtains pore areal fraction and pore size and shape as a function of progressively larger measurement areas. Using backscattering imaging and mSEM data, pores are identified by the components within which they occur, such as in organics or the clastic matrix. We correlate pore areal fraction with nano-indentation, micropillar compression, and axysimmetic testing at multiple length scales on a terrigenous-argillaceous mudrock sample. The combined data set is used to: investigate representative elementary volumes (and areas for the 2D images); determine if scale separation occurs; and determine if transport and mechanical properties at a given length scale can be statistically defined. Clear scale separation occurs between REAs and observable heterogeneity in two of the samples. A highly-laminated sample exhibits fine-scale heterogeneity and an overlapping in scales, in which case typical continuum assumptions on statistical variability may break down. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

Measurement of variation in soil solute tracer concentration across a range of effective pore sizes

USGS Publications Warehouse

Harvey, Judson W.

1993-01-01

Solute transport concepts in soil are based on speculation that solutes are distributed nonuniformly within large and small pores. Solute concentrations have not previously been measured across a range of pore sizes and examined in relation to soil hydrological properties. For this study, modified pressure cells were used to measure variation in concentration of a solute tracer across a range of pore sizes. Intact cores were removed from the site of a field tracer experiment, and soil water was eluted from 10 or more discrete classes of pore size. Simultaneous changes in water content and unsaturated hydraulic conductivity were determined on cores using standard pressure cell techniques. Bromide tracer concentration varied by as much as 100% across the range of pore sizes sampled. Immediately following application of the bromide tracer on field plots, bromide was most concentrated in the largest pores; concentrations were lower in pores of progressively smaller sizes. After 27 days, bromide was most dilute in the largest pores and concentrations were higher in the smaller pores. A sharp, threefold decrease in specific water capacity during elution indicated separation of two major pore size classes at a pressure of 47 cm H2O and a corresponding effective pore diameter of 70 μm. Variation in tracer concentration, on the other hand, was spread across the entire range of pore sizes investigated in this study. A two-porosity characterization of the transport domain, based on water retention criteria, only broadly characterized the pattern of variation in tracer concentration across pore size classes during transport through a macroporous soil.

Dependence of Capillary Properties of Contemporary Clinker Bricks on Their Microstructure

NASA Astrophysics Data System (ADS)

Wesołowska, Maria; Kaczmarek, Anna

2017-10-01

Contemporary clinker bricks are applied for outer layers of walls built from other materials and walls which should have high durability and aesthetic qualities. The intended effect depends not only on the mortar applied but also on clinker properties. Traditional macroscopic tests do not allow to predict clinker behaviour in contact with mortars and external environment. The basic information for this issue is open porosity of material. It defines the material ability to absorb liquids: rain water (through the face wall surface) and grout from mortar (through base surface). The main capillary flow goes on in pores with diameters from 300 to 3000nm. It is possible to define pore distribution and their size using the Mercury Intrusion Porosimetry method. The aim of these research is evaluation of clinker brick capillary properties (initial water absorption and capillary rate) and analysis of differences in microstructure of the face and base wall of a product. Detailed results allowed to show pore distribution in function of their diameters and definition of pore amount responsible for capillary flow. Based on relation between volume function differential and pore diameter, a differential distribution curve was obtained which helped to determine the dominant diameters. The results obtained let us state that face wall of bricks was characterized with the lowest material density and open porosity. In this layer (most burnt) part of pores could be closed by locally appearing liquid phase during brick burning. Thus density is lower comparing to other part of the product.

Ectopic osteogenesis and angiogenesis regulated by porous architecture of hydroxyapatite scaffolds with similar interconnecting structure in vivo

PubMed Central

Li, Jinyu; Zhi, Wei; Xu, Taotao; Shi, Feng; Duan, Ke; Wang, Jianxin; Mu, Yandong; Weng, Jie

2016-01-01

The macro-pore sizes of porous scaffold play a key role for regulating ectopic osteogenesis and angiogenesis but many researches ignored the influence of interconnection between macro-pores with different sizes. In order to accurately reveal the relationship between ectopic osteogenesis and macro-pore sizes in dorsal muscle and abdominal cavities of dogs, hydroxyapatite (HA) scaffolds with three different macro-pore sizes of 500–650, 750–900 and 1100–1250 µm were prepared via sugar spheres-leaching process, which also had similar interconnecting structure determined by keeping the d/s ratio of interconnecting window diameter to macro-pore size constant. The permeability test showed that the seepage flow of fluid through the porous scaffolds increased with the increase of macro-pore sizes. The cell growth in three scaffolds was not affected by the macro-pore sizes. The in vivo ectopic implantation results indicated that the macro-pore sizes of HA scaffolds with the similar interconnecting structure have impact not only the speed of osteogenesis and angiogenesis but also the space distribution of newly formed bone. The scaffold with macro-pore sizes of 750–900 µm exhibited much faster angiogenesis and osteogenesis, and much more uniformly distribution of new bone than those with other macro-pore sizes. This work illustrates the importance of a suitable macro-pore sizes in HA scaffolds with the similar interconnecting structure which provides the environment for ectopic osteogenesis and angiogenesis. PMID:27699059

Self-Ordered Nanoporous Alumina Templates Formed by Anodization of Aluminum in Oxalic Acid

NASA Astrophysics Data System (ADS)

Vida-Simiti, Ioan; Nemes, Dorel; Jumate, Nicolaie; Thalmaier, Gyorgy; Sechel, Niculina

2012-10-01

Anodic aluminum oxide (AAO) membranes with highly ordered nanopores serve as ideal templates for the formation of various nanostructured materials. The procedure of the template preparation is based on a two-step self-organized anodization of aluminum. In the current study, AAO templates were fabricated in 0.3 M oxalic acid under the anodizing potential range of 30-60 V at an electrolyte temperature of ~5°C. The AAO templates were analyzed using scanning electron microscopy, x-ray diffraction, Fourier-transform infrared spectroscopy, and differential thermal analysis. The as obtained layers are amorphous; the mean pore size is between 40 nm and 75 nm and increases with the increase of the anodization potential. Well-defined pores across the whole aluminum template, a pore density of ~1010 pores/cm2, and a tendency to form a porous structure with hexagonal symmetry were observed.

Shape-memory polymer foam device for treating aneurysms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortega, Jason M.; Benett, William J.; Small, Ward

A system for treating an aneurysm in a blood vessel or vein, wherein the aneurysm has a dome, an interior, and a neck. The system includes a shape memory polymer foam in the interior of the aneurysm between the dome and the neck. The shape memory polymer foam has pores that include a first multiplicity of pores having a first pore size and a second multiplicity of pores having a second pore size. The second pore size is larger than said first pore size. The first multiplicity of pores are located in the neck of the aneurysm. The second multiplicitymore » of pores are located in the dome of the aneurysm.« less

Size effects of pore density and solute size on water osmosis through nanoporous membrane.

PubMed

Zhao, Kuiwen; Wu, Huiying

2012-11-15

Understanding the behavior of osmotic transport across nanoporous membranes at molecular level is critical to their design and applications, and it is also beneficial to the comprehension of the mechanism of biological transmembrane transport processes. Pore density is an important parameter for nanoporous membranes. To better understand the influence of pore density on osmotic transport, we have performed systematic molecular dynamics simulations on water osmosis across nanoporous membranes with different pore densities (i.e., number of pores per unit area of membrane). The simulation results reveal that significant size effects occur when the pore density is so high that the center-to-center distance between neighboring nanopores is comparable to the solute size. The size effects are independent of the pore diameter and solute concentration. A simple quantitative correlation between pore density, solute size, and osmotic flux has been established. The results are excellently consistent with the theoretical predictions. It is also shown that solute hydration plays an important role in real osmotic processes. Solute hydration strengthens the size effects of pore density on osmotic processes due to the enlarged effective solute size induced by hydration. The influence of pore density, solute size, and solute hydration on water osmosis through nanoporous membranes can be introduced to eliminate the deviations of real osmotic processes from ideal behavior.

Relationship between pore size and reversible and irreversible immobilization of ionic liquid electrolytes in porous carbon under applied electric potential

DOE PAGES

Mahurin, Shannon M.; Mamontov, Eugene; Thompson, Matthew W.; ...

2016-10-04

Transport of electrolytes in nanoporous carbon-based electrodes largely defines the function and performance of energy storage devices. Here, using molecular dynamics simulation and quasielastic neutron scattering, we investigate the microscopic dynamics of a prototypical ionic liquid electrolyte, [emim][Tf 2N], under applied electric potential in carbon materials with 6.7 nm and 1.5 nm pores. The simulations demonstrate the formation of dense layers of counter-ions near the charged surfaces, which is reversible when the polarity is reversed. In the experiment, the ions immobilized near the surface manifest themselves in the elastic scattering signal. The experimentally observed ion immobilization near the wall ismore » fully reversible as a function of the applied electric potential in the 6.7 nm, but not in the 1.5 nm nanopores. In the latter case, remarkably, the first application of the electric potential leads to apparently irreversible immobilization of cations or anions, depending on the polarity, near the carbon pore walls. This unexpectedly demonstrates that in carbon electrode materials with the small pores, which are optimal for energy storage applications, the polarity of the electrical potential applied for the first time after the introduction of an ionic liquid electrolyte may define the decoration of the small pore walls with ions for prolonged periods of time and possibly for the lifetime of the electrode.« less

Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks

PubMed Central

Li, Tianyang; Qiu, Hao; Wang, Feifei

2015-01-01

Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks. PMID:25961729

Electrochemically assisted fabrication of size-exclusion films of organically modified silica and application to the voltammetry of phospholipids.

PubMed

Mehdi, B Layla; Rutkowska, Iwona A; Kulesza, Pawel J; Cox, James A

2013-06-01

Modification of electrodes with nm-scale organically modified silica films with pores diameters controlled at 10- and 50-nm is described. An oxidation catalyst, mixed-valence ruthenium oxide with cyano crosslinks or gold nanoparticles protected by dirhodium-substituted phosophomolybdate (AuNP-Rh 2 PMo 11 ), was immobilized in the pores. These systems comprise size-exclusion films at which the biological compounds, phosphatidylcholine and cardiolipin, were electrocatalytically oxidized without interference from surface-active concomitants such as bovine serum albumin. 10-nm pores were obtained by adding generation-4 poly(amidoamine) dendrimer, G4-PAMAM, to a (CH 3 ) 3 SiOCH 3 sol. 50-nm pores were obtained by modifying a glassy carbon electrode (GC) with a sub-monolayer film of aminopropyltriethoxylsilane, attaching 50-nm diameter poly(styrene sulfonate), PSS, spheres to the protonated amine, transferring this electrode to a (CH 3 ) 3 SiOCH 3 sol, and electrochemically generating hydronium at uncoated GC sites, which catalyzed ormosil growth around the PSS. Voltammetry of Fe(CN) 6 3- and Ru(NH 3 ) 6 3+ demonstrated the absence of residual charge after removal of the templating agents. With the 50-nm system, the pore structure was sufficiently defined to use layer-by-layer electrostatic assembly of AuNP-Rh 2 PMo 11 therein. Flow injection amperometry of phosphatidylcholine and cardiolipin demonstrated analytical utility of these electrodes.

Synthesis and characterization of high surface area TiO 2/SiO 2 mesostructured nanocomposite

NASA Astrophysics Data System (ADS)

Bonne, Magali; Pronier, Stéphane; Can, Fabien; Courtois, Xavier; Valange, Sabine; Tatibouët, Jean-Michel; Royer, Sébastien; Marécot, Patrice; Duprez, Daniel

2010-06-01

Recently titania synthesis was reported using various structuration procedures, leading to the production of solid presenting high surface area but exhibiting moderate thermal stability. The study presents the synthesis of TiO 2/SiO 2 nanocomposites, a solid that can advantageously replace bulk titania samples as catalyst support. The silica host support used for the synthesis of the nanocomposite is a SBA-15 type silica, having a well-defined 2D hexagonal pore structure and a large pore size. The control of the impregnation media is important to obtain dispersed titania crystals into the porosity, the best results have been obtained using an impregnation in an excess of solvent. After calcination at low temperature (400 °C), nanocomposites having titania nanodomains (˜2-3 nm) located inside the pores and no external aggregates visible are obtained. This nanocomposite exhibits high specific surface area (close to that of the silica host support, even with a titania loading of 55 wt.%) and a narrow pore size distribution. Surprisingly, the increase in calcination temperature up to 800 °C does not allow to detect the anatase to rutile transition. Even at 800 °C, the hexagonal mesoporous structure of the silica support is maintained, and the anatase crystal domain size is evaluated at ˜10 nm, a size close to that of the silica host support porosity (8.4 nm). Comparison of their physical properties with the results presented in literature for bulk samples evidenced that these TiO 2/SiO 2 solids are promising in term of thermal stability.

Mesoporous carbon synthesized from different pore sizes of SBA-15 for high density electrode supercapacitor application

NASA Astrophysics Data System (ADS)

Jamil, Farinaa Md; Sulaiman, Mohd Ali; Ibrahim, Suhaina Mohd; Masrom, Abdul Kadir; Yahya, Muhd Zu Azhan

2017-12-01

A series of mesoporous carbon sample was synthesized using silica template, SBA-15 with two different pore sizes. Impregnation method was applied using glucose as a precursor for converting it into carbon. An appropriate carbonization and silica removal process were carried out to produce a series of mesoporous carbon with different pore sizes and surface areas. Mesoporous carbon sample was then assembled as electrode and its performance was tested using cyclic voltammetry and impedance spectroscopy to study the effect of ion transportation into several pore sizes on electric double layer capacitor (EDLC) system. 6M KOH was used as electrolyte at various scan rates of 10, 20, 30 and 50 mVs-1. The results showed that the pore size of carbon increased as the pore size of template increased and the specific capacitance improved as the increasing of the pore size of carbon.

Highly tunable porous organic polymer (POP) supports for metallocene-based ethylene polymerization

NASA Astrophysics Data System (ADS)

Wang, Xiong; Li, Zhenyou; Han, Xiaoyu; Han, Zhengang; Bai, Yongxiao

2017-10-01

Porous organic Polymers (POPs) can not only exhibit high specific surface area and pore volume, but also tunable pore size distribution. Herein, copolymers of 2-hydroxyethylmethylacrylate (HEMA) and divinylbenzene (DVB) with specific pore structure were synthesized via a dispersion polymerization strategy, and then immobilized metallocene catalysts with well-defined pore structure were obtained on the produced POP supports. The nitrogen sorption and Gel permeation chromatography (GPC) results demonstrate that the pore structure of the immobilized metallocene catalyst is highly dependent on the pore structure of the POPs, and the pore structure of metallocene catalysts or the POPs has a significant influence on the molecular chain growth of the produced polyethylene. By tuning the distribution of the active species scattered in the micro- and the narrow meso-pore range (roughly ≤4 nm), the chain growth of the polyolefin can be tailored effectively during the polymerization process, although differential scanning calorimetry (DSC) and temperature rising elution fractionation (TREF) results show that the chemical composition distributions (CCDs) of produced PE from the POPs-supported metallocene catalysts are not determined by polymerization activity or molecule chain length, but mainly by the active site species scattered in the supported catalysts. Scanning electron micrograph (SEM) shows that the produced polyethylene has highly porous fabric which consists of nanofiber and spherical beads of micron dimension.

Permeability-Selectivity Analysis of Microfiltration and Ultrafiltration Membranes: Effect of Pore Size and Shape Distribution and Membrane Stretching.

PubMed

Siddiqui, Muhammad Usama; Arif, Abul Fazal Muhammad; Bashmal, Salem

2016-08-06

We present a modeling approach to determine the permeability-selectivity tradeoff for microfiltration and ultrafiltration membranes with a distribution of pore sizes and pore shapes. Using the formulated permeability-selectivity model, the effect of pore aspect ratio and pore size distribution on the permeability-selectivity tradeoff of the membrane is analyzed. A finite element model is developed to study the effect of membrane stretching on the distribution of pore sizes and shapes in the stretched membrane. The effect of membrane stretching on the permeability-selectivity tradeoff of membranes is also analyzed. The results show that increasing pore aspect ratio improves membrane performance while increasing the width of pore size distribution deteriorates the performance. It was also found that the effect of membrane stretching on the permeability-selectivity tradeoff is greatly affected by the uniformity of pore distribution in the membrane. Stretching showed a positive shift in the permeability-selectivity tradeoff curve of membranes with well-dispersed pores while in the case of pore clustering, a negative shift in the permeability-selectivity tradeoff curve was observed.

Study into the correlation of dominant pore throat size and SIP relaxation frequency

NASA Astrophysics Data System (ADS)

Kruschwitz, Sabine; Prinz, Carsten; Zimathies, Annett

2016-12-01

There is currently a debate within the SIP community about the characteristic textural length scale controlling relaxation time of consolidated porous media. One idea is that the relaxation time is dominated by the pore throat size distribution or more specifically the modal pore throat size as determined in mercury intrusion capillary pressure tests. Recently new studies on inverting pore size distributions from SIP data were published implying that the relaxation mechanisms and controlling length scale are well understood. In contrast new analytical model studies based on the Marshall-Madden membrane polarization theory suggested that two relaxation processes might compete: the one along the short narrow pore (the throat) with one across the wider pore in case the narrow pores become relatively long. This paper presents a first systematically focused study into the relationship of pore throat sizes and SIP relaxation times. The generality of predicted trends is investigated across a wide range of materials differing considerably in chemical composition, specific surface and pore space characteristics. Three different groups of relaxation behaviors can be clearly distinguished. The different behaviors are related to clay content and type, carbonate content, size of the grains and the wide pores in the samples.

Modeling a failure criterion for U-Mo/Al dispersion fuel

NASA Astrophysics Data System (ADS)

Oh, Jae-Yong; Kim, Yeon Soo; Tahk, Young-Wook; Kim, Hyun-Jung; Kong, Eui-Hyun; Yim, Jeong-Sik

2016-05-01

The breakaway swelling in U-Mo/Al dispersion fuel is known to be caused by large pore formation enhanced by interaction layer (IL) growth between fuel particles and Al matrix. In this study, a critical IL thickness was defined as a criterion for the formation of a large pore in U-Mo/Al dispersion fuel. Specifically, the critical IL thickness is given when two neighboring fuel particles come into contact with each other in the developed IL. The model was verified using the irradiation data from the RERTR tests and KOMO-4 test. The model application to full-sized sample irradiations such as IRISs, FUTURE, E-FUTURE, and AFIP-1 tests resulted in conservative predictions. The parametric study revealed that the fuel particle size and the homogeneity of the fuel particle distribution are influential for fuel performance.

Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication

NASA Astrophysics Data System (ADS)

Schmidt, Torsten; Zhang, Miao; Sychugov, Ilya; Roxhed, Niclas; Linnros, Jan

2015-08-01

Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication.

PubMed

Schmidt, Torsten; Zhang, Miao; Sychugov, Ilya; Roxhed, Niclas; Linnros, Jan

2015-08-07

Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

Healing kinetics of microneedle-formed pores in PLGA films.

PubMed

Mazzara, J M; Balagna, M A; Thouless, M D; Schwendeman, S P

2013-10-28

The spontaneous healing of aqueous pores in poly(D,L-lactic-co-glycolic acid) (PLGA) drug delivery systems has been identified to play a key role in terminating the burst release of large molecules, and to provide a means for novel aqueous-based microencapsulation. To examine healing of PLGA, pores were created of defined size and depth on the surface of thin PLGA films by stamping with blunt-tip microneedles. Pore dimensions on the micron-scale were relevant to surface pores of common PLGA microspheres and could be easily monitored by light microscopy. Most pores healed reproducibly at temperatures above the glass-transition temperature (T(g)) of the films, with healing times decreasing sharply with increasing temperature according to Williams-Landel-Ferry (WLF) behavior. It is suggested that healing is driven by high surface tension in the films and occurs through viscoelastic creep. Hydrated films healed at lower temperatures than dry films, consistent with a drop in Tg upon polymer hydration. Larger pores took longer to heal than smaller ones, while pores larger than 20 μm did not heal before significant polymer degradation occurred. Films of a less hydrophobic PLGA showed slower healing kinetics, attributed to a weaker surface tension driving force. Deeper pores showed signs of in-plane stress from spin-coating, and either ruptured or only partially healed when incubated wet and dry, respectively. © 2013.

A USANS/SANS study of the accessibility of pores in the Barnett Shale to methane and water

USGS Publications Warehouse

Ruppert, Leslie F.; Sakurovs, Richard; Blach, Tomasz P.; He, Lilin; Melnichenko, Yuri B.; Mildner, David F.; Alcantar-Lopez, Leo

2013-01-01

Shale is an increasingly important source of natural gas in the United States. The gas is held in fine pores that need to be accessed by horizontal drilling and hydrofracturing techniques. Understanding the nature of the pores may provide clues to making gas extraction more efficient. We have investigated two Mississippian Barnett Shale samples, combining small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) to determine the pore size distribution of the shale over the size range 10 nm to 10 μm. By adding deuterated methane (CD4) and, separately, deuterated water (D2O) to the shale, we have identified the fraction of pores that are accessible to these compounds over this size range. The total pore size distribution is essentially identical for the two samples. At pore sizes >250 nm, >85% of the pores in both samples are accessible to both CD4 and D2O. However, differences in accessibility to CD4 are observed in the smaller pore sizes (~25 nm). In one sample, CD4 penetrated the smallest pores as effectively as it did the larger ones. In the other sample, less than 70% of the smallest pores (4, but they were still largely penetrable by water, suggesting that small-scale heterogeneities in methane accessibility occur in the shale samples even though the total porosity does not differ. An additional study investigating the dependence of scattered intensity with pressure of CD4 allows for an accurate estimation of the pressure at which the scattered intensity is at a minimum. This study provides information about the composition of the material immediately surrounding the pores. Most of the accessible (open) pores in the 25 nm size range can be associated with either mineral matter or high reflectance organic material. However, a complementary scanning electron microscopy investigation shows that most of the pores in these shale samples are contained in the organic components. The neutron scattering results indicate that the pores are not equally proportioned in the different constituents within the shale. There is some indication from the SANS results that the composition of the pore-containing material varies with pore size; the pore size distribution associated with mineral matter is different from that associated with organic phases.

Generation of hierarchical pore systems in the titanosilicate ETS-10 by hydrogen peroxide treatment under microwave irradiation.

PubMed

Pavel, Claudiu C; Schmidt, Wolfgang

2006-02-28

Supermicropores and well-defined mesopores with an average size of 10 nm were created in ETS-10 structure by post-synthesis treatment with H2O2 under microwave irradiation. Macropores were also formed and the external surface area of the material was increased during the treatment.

Optically Defined Multifunctional Patterning of Photosensitive Thin-Film Silica Mesophases

NASA Astrophysics Data System (ADS)

Doshi, Dhaval A.; Huesing, Nicola K.; Lu, Mengcheng; Fan, Hongyou; Lu, Yunfeng; Simmons-Potter, Kelly; Potter, B. G.; Hurd, Alan J.; Brinker, C. Jeffrey

2000-10-01

Photosensitive films incorporating molecular photoacid generators compartmentalized within a silica-surfactant mesophase were prepared by an evaporation-induced self-assembly process. Ultraviolet exposure promoted localized acid-catalyzed siloxane condensation, which can be used for selective etching of unexposed regions; for ``gray-scale'' patterning of refractive index, pore size, surface area, and wetting behavior; and for optically defining a mesophase transformation (from hexagonal to tetragonal) within the film. The ability to optically define and continuously control both structure and function on the macro- and mesoscales is of interest for sensor arrays, nanoreactors, photonic and fluidic devices, and low-dielectric-constant films.

Modeling the Pore Formation Mechanism in UMo/AL Dispersion Fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Yeon Soo; Jamison, L.; Hofman, G.

In UMo/Al dispersion fuel meat, pores formed in the ILs or at IL-Al interfaces tend to increase in size with irradiation, potentially limiting performance of this fuel. There has been no universally accepted mechanism for the formation and growth of this type of pore. However, there is a consensus that the stress state determined by meat swelling and fission- induced creep is one of the determinants, and fission gas availability at the pore site is another. Five dispersion RERTR miniplates that have well defined irradiation conditions and PIE data were selected for examination. Meat swelling and pore volume were measuredmore » in each plate. ABAQUS finite element analysis (FEA) package was utilized to obtain the time-dependent evolution of mechanical states in the plates while matching the measured meat swelling and creep. Interpretation of these results give insights on how to model a failure function – a predictor for large pore formation – using variables such as meat swelling, interaction layer growth, stress, and creep. This model can be used for optimizing fuel design parameters to reach the desired goal: meeting high power and performance reactor demand.« less

Pore size distribution and accessible pore size distribution in bituminous coals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakurovs, Richard; He, Lilin; Melnichenko, Yuri B

2012-01-01

The porosity and pore size distribution of coals determine many of their properties, from gas release to their behavior on carbonization, and yet most methods of determining pore size distribution can only examine a restricted size range. Even then, only accessible pores can be investigated with these methods. Small-angle neutron scattering (SANS) and ultra small-angle neutron scattering (USANS) are increasingly used to characterize the size distribution of all of the pores non-destructively. Here we have used USANS/SANS to examine 24 well-characterized bituminous and subbituminous coals: three from the eastern US, two from Poland, one from New Zealand and the restmore » from the Sydney and Bowen Basins in Eastern Australia, and determined the relationships of the scattering intensity corresponding to different pore sizes with other coal properties. The range of pore radii examinable with these techniques is 2.5 nm to 7 {micro}m. We confirm that there is a wide range of pore sizes in coal. The pore size distribution was found to be strongly affected by both rank and type (expressed as either hydrogen or vitrinite content) in the size range 250 nm to 7 {micro}m and 5 to 10 nm, but weakly in intermediate regions. The results suggest that different mechanisms control coal porosity on different scales. Contrast-matching USANS and SANS were also used to determine the size distribution of the fraction of the pores in these coals that are inaccessible to deuterated methane, CD{sub 4}, at ambient temperature. In some coals most of the small ({approx} 10 nm) pores were found to be inaccessible to CD{sub 4} on the time scale of the measurement ({approx} 30 min - 16 h). This inaccessibility suggests that in these coals a considerable fraction of inherent methane may be trapped for extended periods of time, thus reducing the effectiveness of methane release from (or sorption by) these coals. Although the number of small pores was less in higher rank coals, the fraction of total pores that was inaccessible was not rank dependent. In the Australian coals, at the 10 nm to 50 nm size scales the pores in inertinites appeared to be completely accessible to CD{sub 4}, whereas the pores in the vitrinite were about 75% inaccessible. Unlike the results for total porosity that showed no regional effects on relationships between porosity and coal properties, clear regional differences in the relationships between fraction of closed porosity and coal properties were found. The 10 to 50 nm-sized pores of inertinites of the US and Polish coals examined appeared less accessible to methane than those of the inertinites of Australian coals. This difference in pore accessibility in inertinites may explain why empirical relationships between fluidity and coking properties developed using Carboniferous coals do not apply to Australian coals.« less

Critical parameters in the production of ceramic pot filters for household water treatment in developing countries.

PubMed

Soppe, A I A; Heijman, S G J; Gensburger, I; Shantz, A; van Halem, D; Kroesbergen, J; Wubbels, G H; Smeets, P W M H

2015-06-01

The need to improve the access to safe water is generally recognized for the benefit of public health in developing countries. This study's objective was to identify critical parameters which are essential for improving the performance of ceramic pot filters (CPFs) as a point-of-use water treatment system. Defining critical production parameters was also relevant to confirm that CPFs with high-flow rates may have the same disinfection capacity as pots with normal flow rates. A pilot unit was built in Cambodia to produce CPFs under controlled and constant conditions. Pots were manufactured from a mixture of clay, laterite and rice husk in a small-scale, gas-fired, temperature-controlled kiln and tested for flow rate, removal efficiency of bacteria and material strength. Flow rate can be increased by increasing pore sizes and by increasing porosity. Pore sizes were increased by using larger rice husk particles and porosity was increased with larger proportions of rice husk in the clay mixture. The main conclusions: larger pore size decreases the removal efficiency of bacteria; higher porosity does not affect the removal efficiency of bacteria, but does influence the strength of pots; flow rates of CPFs can be raised to 10-20 L/hour without a significant decrease in bacterial removal efficiency.

Continuously Adjustable, Molecular-Sieving “Gate” on 5A Zeolite for Distinguishing Small Organic Molecules by Size

PubMed Central

Song, Zhuonan; Huang, Yi; Xu, Weiwei L.; Wang, Lei; Bao, Yu; Li, Shiguang; Yu, Miao

2015-01-01

Zeolites/molecular sieves with uniform, molecular-sized pores are important for many adsorption-based separation processes. Pore size gaps, however, exist in the current zeolite family. This leads to a great challenge of separating molecules with size differences at ~0.01 nm level. Here, we report a novel concept, pore misalignment, to form a continuously adjustable, molecular-sieving “gate” at the 5A zeolite pore entrance without sacrificing the internal capacity. Misalignment of the micropores of the alumina coating with the 5A zeolite pores was related with and facilely adjusted by the coating thickness. For the first time, organic molecules with sub-0.01 nm size differences were effectively distinguished via appropriate misalignment. This novel concept may have great potential to fill the pore size gaps of the zeolite family and realize size-selective adsorption separation. PMID:26358480

Continuously adjustable, molecular-sieving “gate” on 5A zeolite for distinguishing small organic molecules by size

DOE PAGES

Song, Zhuonan; Huang, Yi; Xu, Weiwei L.; ...

2015-09-11

Zeolites/molecular sieves with uniform, molecular-sized pores are important for many adsorption-based separation processes. Pore size gaps, however, exist in the current zeolite family. This leads to a great challenge of separating molecules with size differences at ~0.01 nm level. Here, we report a novel concept, pore misalignment, to form a continuously adjustable, molecular-sieving “gate” at the 5A zeolite pore entrance without sacrificing the internal capacity. Misalignment of the micropores of the alumina coating with the 5A zeolite pores was related with and facilely adjusted by the coating thickness. For the first time, organic molecules with sub-0.01 nm size differences weremore » effectively distinguished via appropriate misalignment. Lastly, this novel concept may have great potential to fill the pore size gaps of the zeolite family and realize size-selective adsorption separation.« less

Heat of adsorption, adsorption stress, and optimal storage of methane in slit and cylindrical carbon pores predicted by classical density functional theory.

PubMed

Hlushak, Stepan

2018-01-03

Temperature, pressure and pore-size dependences of the heat of adsorption, adsorption stress, and adsorption capacity of methane in simple models of slit and cylindrical carbon pores are studied using classical density functional theory (CDFT) and grand-canonical Monte-Carlo (MC) simulation. Studied properties depend nontrivially on the bulk pressure and the size of the pores. Heat of adsorption increases with loading, but only for sufficiently narrow pores. While the increase is advantageous for gas storage applications, it is less significant for cylindrical pores than for slits. Adsorption stress and the average adsorbed fluid density show oscillatory dependence on the pore size and increase with bulk pressure. Slit pores exhibit larger amplitude of oscillations of the normal adsorption stress with pore size increase than cylindrical pores. However, the increase of the magnitude of the adsorption stress with bulk pressure increase is more significant for cylindrical than for slit pores. Adsorption stress appears to be negative for a wide range of pore sizes and external conditions. The pore size dependence of the average delivered density of the gas is analyzed and the optimal pore sizes for storage applications are estimated. The optimal width of slit pore appears to be almost independent of storage pressure at room temperature and pressures above 10 bar. Similarly to the case of slit pores, the optimal radius of cylindrical pores does not exhibit much dependence on the storage pressure above 15 bar. Both optimal width and optimal radii of slit and cylindrical pores increase as the temperature decreases. A comparison of the results of CDFT theory and MC simulations reveals subtle but important differences in the underlying fluid models employed by the approaches. The differences in the high-pressure behaviour between the hard-sphere 2-Yukawa and Lennard-Jones models of methane, employed by the CDFT and MC approaches, respectively, result in an overestimation of the heat of adsorption by the CDFT theory at higher loadings. However, both adsorption stress and adsorption capacity appear to be much less sensitive to the differences between the models and demonstrate excellent agreement between the theory and the computer experiment.

Hybrid Filter Membrane

NASA Technical Reports Server (NTRS)

Laicer, Castro; Rasimick, Brian; Green, Zachary

2012-01-01

Cabin environmental control is an important issue for a successful Moon mission. Due to the unique environment of the Moon, lunar dust control is one of the main problems that significantly diminishes the air quality inside spacecraft cabins. Therefore, this innovation was motivated by NASA s need to minimize the negative health impact that air-suspended lunar dust particles have on astronauts in spacecraft cabins. It is based on fabrication of a hybrid filter comprising nanofiber nonwoven layers coated on porous polymer membranes with uniform cylindrical pores. This design results in a high-efficiency gas particulate filter with low pressure drop and the ability to be easily regenerated to restore filtration performance. A hybrid filter was developed consisting of a porous membrane with uniform, micron-sized, cylindrical pore channels coated with a thin nanofiber layer. Compared to conventional filter media such as a high-efficiency particulate air (HEPA) filter, this filter is designed to provide high particle efficiency, low pressure drop, and the ability to be regenerated. These membranes have well-defined micron-sized pores and can be used independently as air filters with discreet particle size cut-off, or coated with nanofiber layers for filtration of ultrafine nanoscale particles. The filter consists of a thin design intended to facilitate filter regeneration by localized air pulsing. The two main features of this invention are the concept of combining a micro-engineered straight-pore membrane with nanofibers. The micro-engineered straight pore membrane can be prepared with extremely high precision. Because the resulting membrane pores are straight and not tortuous like those found in conventional filters, the pressure drop across the filter is significantly reduced. The nanofiber layer is applied as a very thin coating to enhance filtration efficiency for fine nanoscale particles. Additionally, the thin nanofiber coating is designed to promote capture of dust particles on the filter surface and to facilitate dust removal with pulse or back airflow.

A non-contact technique for measuring eccrine sweat gland activity using passive thermal imaging.

PubMed

Krzywicki, Alan T; Berntson, Gary G; O'Kane, Barbara L

2014-10-01

An approach for monitoring eccrine sweat gland activity using high resolution Mid-Wave Infrared (MWIR) imaging (3-5 μm wave band) is described. This technique is non-contact, passive, and provides high temporal and spatial resolution. Pore activity was monitored on the face and on the volar surfaces of the distal and medial phalanges of the index and middle fingers while participants performed a series of six deep inhalation and exhalation exercises. Two metrics called the Pore Activation Index (PAI) and Pore Count (PC) were defined as size-weighted and unweighted measures of active sweat gland counts respectively. PAI transient responses on the finger tips were found to be positively correlated to Skin Conductance Responses (SCRs). PAI responses were also observed on the face, although the finger sites appeared to be more responsive. Results indicate that thermal imaging of the pore response may provide a useful, non-contact, correlate measure for electrodermal responses recorded from related sites. Published by Elsevier B.V.

Template-directed assembly of metal-chalcogenide nanocrystals into ordered mesoporous networks.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vamvasakis, Ioannis; Subrahmanyam, Kota S.; Kanatzidis, Mercouri G.

Although great progress in the synthesis of porous networks of metal and metal oxide nanoparticles with highly accessible pore surface and ordered mesoscale pores has been achieved, synthesis of assembled 3D mesostructures of metal-chalcogenide nanocrystals is still challenging. In this work we demonstrate that ordered mesoporous networks, which comprise well-defined interconnected metal sulfide nanocrystals, can be prepared through a polymer-templated oxidative polymerization process. The resulting self-assembled mesostructures that were obtained after solvent extraction of the polymer template impart the unique combination of light-emitting metal chalcogenide nanocrystals, three-dimensional open-pore structure, high surface area, and uniform pores. We show that the poremore » surface of these materials is active and accessible to incoming molecules, exhibiting high photocatalytic activity and stability, for instance, in oxidation of 1-phenylethanol into acetophenone. We demonstrate through appropriate selection of the synthetic components that this method is general to prepare ordered mesoporous materials from metal chalcogenide nanocrystals with various sizes and compositions.« less

Significant Effect of Pore Sizes on Energy Storage in Nanoporous Carbon Supercapacitors.

PubMed

Young, Christine; Lin, Jianjian; Wang, Jie; Ding, Bing; Zhang, Xiaogang; Alshehri, Saad M; Ahamad, Tansir; Salunkhe, Rahul R; Hossain, Shahriar A; Khan, Junayet Hossain; Ide, Yusuke; Kim, Jeonghun; Henzie, Joel; Wu, Kevin C-W; Kobayashi, Naoya; Yamauchi, Yusuke

2018-04-20

Mesoporous carbon can be synthesized with good control of surface area, pore-size distribution, and porous architecture. Although the relationship between porosity and supercapacitor performance is well known, there are no thorough reports that compare the performance of numerous types of carbon samples side by side. In this manuscript, we describe the performance of 13 porous carbon samples in supercapacitor devices. We suggest that there is a "critical pore size" at which guest molecules can pass through the pores effectively. In this context, the specific surface area (SSA) and pore-size distribution (PSD) are used to show the point at which the pore size crosses the threshold of critical size. These measurements provide a guide for the development of new kinds of carbon materials for supercapacitor devices. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pore structure characterization of Chang-7 tight sandstone using MICP combined with N2GA techniques and its geological control factors

NASA Astrophysics Data System (ADS)

Cao, Zhe; Liu, Guangdi; Zhan, Hongbin; Li, Chaozheng; You, Yuan; Yang, Chengyu; Jiang, Hang

2016-11-01

Understanding the pore networks of unconventional tight reservoirs such as tight sandstones and shales is crucial for extracting oil/gas from such reservoirs. Mercury injection capillary pressure (MICP) and N2 gas adsorption (N2GA) are performed to evaluate pore structure of Chang-7 tight sandstone. Thin section observation, scanning electron microscope, grain size analysis, mineral composition analysis, and porosity measurement are applied to investigate geological control factors of pore structure. Grain size is positively correlated with detrital mineral content and grain size standard deviation while negatively related to clay content. Detrital mineral content and grain size are positively correlated with porosity, pore throat radius and withdrawal efficiency and negatively related to capillary pressure and pore-to-throat size ratio; while interstitial material is negatively correlated with above mentioned factors. Well sorted sediments with high debris usually possess strong compaction resistance to preserve original pores. Although many inter-crystalline pores are produced in clay minerals, this type of pores is not the most important contributor to porosity. Besides this, pore shape determined by N2GA hysteresis loop is consistent with SEM observation on clay inter-crystalline pores while BJH pore volume is positively related with clay content, suggesting N2GA is suitable for describing clay inter-crystalline pores in tight sandstones.

Pore structure characterization of Chang-7 tight sandstone using MICP combined with N2GA techniques and its geological control factors

PubMed Central

Cao, Zhe; Liu, Guangdi; Zhan, Hongbin; Li, Chaozheng; You, Yuan; Yang, Chengyu; Jiang, Hang

2016-01-01

Understanding the pore networks of unconventional tight reservoirs such as tight sandstones and shales is crucial for extracting oil/gas from such reservoirs. Mercury injection capillary pressure (MICP) and N2 gas adsorption (N2GA) are performed to evaluate pore structure of Chang-7 tight sandstone. Thin section observation, scanning electron microscope, grain size analysis, mineral composition analysis, and porosity measurement are applied to investigate geological control factors of pore structure. Grain size is positively correlated with detrital mineral content and grain size standard deviation while negatively related to clay content. Detrital mineral content and grain size are positively correlated with porosity, pore throat radius and withdrawal efficiency and negatively related to capillary pressure and pore-to-throat size ratio; while interstitial material is negatively correlated with above mentioned factors. Well sorted sediments with high debris usually possess strong compaction resistance to preserve original pores. Although many inter-crystalline pores are produced in clay minerals, this type of pores is not the most important contributor to porosity. Besides this, pore shape determined by N2GA hysteresis loop is consistent with SEM observation on clay inter-crystalline pores while BJH pore volume is positively related with clay content, suggesting N2GA is suitable for describing clay inter-crystalline pores in tight sandstones. PMID:27830731

Effective pore size and radius of capture for K(+) ions in K-channels.

PubMed

Moldenhauer, Hans; Díaz-Franulic, Ignacio; González-Nilo, Fernando; Naranjo, David

2016-02-02

Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (r(E)) in several K-channel crystal structures. r(E) was operationally defined as the radius of the biggest sphere able to enter the pore from the cytosolic side. We obtained consistent r(E) estimates for MthK and Kv1.2/2.1 structures, with r(E) = 5.3-5.9 Å and r(E) = 4.5-5.2 Å, respectively. We compared these structural estimates with functional assessments of the internal mouth radii of capture (r(C)) for two electrophysiological counterparts, the large conductance calcium activated K-channel (r(C) = 2.2 Å) and the Shaker Kv-channel (r(C) = 0.8 Å), for MthK and Kv1.2/2.1 structures, respectively. Calculating the difference between r(E) and r(C), produced consistent size radii of 3.1-3.7 Å and 3.6-4.4 Å for hydrated K(+) ions. These hydrated K(+) estimates harmonize with others obtained with diverse experimental and theoretical methods. Thus, these findings validate MthK and the Kv1.2/2.1 structures as templates for open BK and Kv-channels, respectively.

The Influence of Pore Size on the Indentation Behavior of Metallic Nanoporous Materials: A Molecular Dynamics Study

PubMed Central

Esqué-de los Ojos, Daniel; Pellicer, Eva; Sort, Jordi

2016-01-01

In general, the influence of pore size is not considered when determining the Young’s modulus of nanoporous materials. Here, we demonstrate that the pore size needs to be taken into account to properly assess the mechanical properties of these materials. Molecular dynamics simulations of spherical indentation experiments on single crystalline nanoporous Cu have been undertaken in systems with: (i) a constant degree of porosity and variable pore diameter; and (ii) a constant pore diameter and variable porosity degree. The classical Gibson and Ashby expression relating Young’s modulus with the relative density of the nanoporous metal is modified to include the influence of the pore size. The simulations reveal that, for a fixed porosity degree, the mechanical behavior of materials with smaller pores differs more significantly from the behavior of the bulk, fully dense counterpart. This effect is ascribed to the increase of the overall surface area as the pore size is reduced, together with the reduced coordination number of the atoms located at the pores edges. PMID:28773476

Gas Release Behavior of Cu-TiH2 Composite Powder and Its Application as a Blowing Agent to Fabricate Aluminum Foams with Low Porosity and Small Pore Size

NASA Astrophysics Data System (ADS)

Cheng, Ying; Li, Yanxiang; Chen, Xiang; Liu, Zhiyong; Zhou, Xu; Wang, Ningzhen

2018-06-01

Compared to traditional pore structure with high porosity (≥ 80 pct) and large pore size (≥ 3 mm), aluminum foams with low porosity (60 to 70 pct) and small pore size (≤ 2 mm) possess higher compressive property and formability. In order to achieve the goal of reducing pore size, Cu-TiH2 composite powder prepared by ball milling preoxidized TiH2 with Cu powder was used as a blowing agent. Its gas release behavior was characterized by thermogravimetric analysis and differential scanning calorimetry. The results show that the ball milling treatment can advance the gas release process and slow the gas release rate at the same time. All these changes are favorable to the reduction of porosity and pore size. Such Cu-TiH2 composite powder provides an alternative way to fabricate aluminum foams with low porosity and small pore size.

Anomalous or regular capacitance? The influence of pore size dispersity on double-layer formation

NASA Astrophysics Data System (ADS)

Jäckel, N.; Rodner, M.; Schreiber, A.; Jeongwook, J.; Zeiger, M.; Aslan, M.; Weingarth, D.; Presser, V.

2016-09-01

The energy storage mechanism of electric double-layer capacitors is governed by ion electrosorption at the electrode surface. This process requires high surface area electrodes, typically highly porous carbons. In common organic electrolytes, bare ion sizes are below one nanometer but they are larger when we consider their solvation shell. In contrast, ionic liquid electrolytes are free of solvent molecules, but cation-anion coordination requires special consideration. By matching pore size and ion size, two seemingly conflicting views have emerged: either an increase in specific capacitance with smaller pore size or a constant capacitance contribution of all micro- and mesopores. In our work, we revisit this issue by using a comprehensive set of electrochemical data and a pore size incremental analysis to identify the influence of certain ranges in the pore size distribution to the ion electrosorption capacity. We see a difference in solvation of ions in organic electrolytes depending on the applied voltage and a cation-anion interaction of ionic liquids in nanometer sized pores.

Generation of random microstructures and prediction of sound velocity and absorption for open foams with spherical pores.

PubMed

Zieliński, Tomasz G

2015-04-01

This paper proposes and discusses an approach for the design and quality inspection of the morphology dedicated for sound absorbing foams, using a relatively simple technique for a random generation of periodic microstructures representative for open-cell foams with spherical pores. The design is controlled by a few parameters, namely, the total open porosity and the average pore size, as well as the standard deviation of pore size. These design parameters are set up exactly and independently, however, the setting of the standard deviation of pore sizes requires some number of pores in the representative volume element (RVE); this number is a procedure parameter. Another pore structure parameter which may be indirectly affected is the average size of windows linking the pores, however, it is in fact weakly controlled by the maximal pore-penetration factor, and moreover, it depends on the porosity and pore size. The proposed methodology for testing microstructure-designs of sound absorbing porous media applies the multi-scale modeling where some important transport parameters-responsible for sound propagation in a porous medium-are calculated from microstructure using the generated RVE, in order to estimate the sound velocity and absorption of such a designed material.

Exploitation of 3D face-centered cubic mesoporous silica as a carrier for a poorly water soluble drug: influence of pore size on release rate.

PubMed

Zhu, Wenquan; Wan, Long; Zhang, Chen; Gao, Yikun; Zheng, Xin; Jiang, Tongying; Wang, Siling

2014-01-01

The purposes of the present work were to explore the potential application of 3D face-centered cubic mesoporous silica (FMS) with pore size of 16.0nm as a delivery system for poorly soluble drugs and investigate the effect of pore size on the dissolution rate. FMS with different pore sizes (16.0, 6.9 and 3.7nm) was successfully synthesized by using Pluronic block co-polymer F127 as a template and adjusting the reaction temperatures. Celecoxib (CEL), which is a BCS class II drug, was used as a model drug and loaded into FMS with different pore sizes by the solvent deposition method at a drug-silica ratio of 1:4. Characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformation infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), nitrogen adsorption, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) was used to systematically investigate the drug loading process. The results obtained showed that CEL was in a non-crystalline state after incorporation of CEL into the pores of FMS-15 with pore size of 16.0nm. In vitro dissolution was carried out to demonstrate the effects of FMS with different pore sizes on the release of CEL. The results obtained indicated that the dissolution rate of CEL from FMS-15 was significantly enhanced compared with pure CEL. This could be explained by supposing that CEL encountered less diffusion resistance and its crystallinity decreased due to the large pore size of 16.0nm and the nanopore channels of FMS-15. Moreover, drug loading and pore size both play an important role in enhancing the dissolution properties for the poorly water-soluble drugs. As the pore size between 3.7 and 16.0nm increased, the dissolution rate of CEL from FMS gradually increased. © 2013.

Microstructured silicon radiation detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okandan, Murat; Derzon, Mark S.; Draper, Bruce L.

2017-03-14

A radiation detector comprises a silicon body in which are defined vertical pores filled with a converter material and situated within silicon depletion regions. One or more charge-collection electrodes are arranged to collect current generated when secondary particles enter the silicon body through walls of the pores. The pores are disposed in low-density clusters, have a majority pore thickness of 5 .mu.m or less, and have a majority aspect ratio, defined as the ratio of pore depth to pore thickness, of at least 10.

Composition for absorbing hydrogen from gas mixtures

DOEpatents

Heung, Leung K.; Wicks, George G.; Lee, Myung W.

1999-01-01

A hydrogen storage composition is provided which defines a physical sol-gel matrix having an average pore size of less than 3.5 angstroms which effectively excludes gaseous metal hydride poisons while permitting hydrogen gas to enter. The composition is useful for separating hydrogen gas from diverse gas streams which may have contaminants that would otherwise render the hydrogen absorbing material inactive.

Facile synthesis of hydrophilic multi-colour and upconversion photoluminescent mesoporous carbon nanoparticles for bioapplications.

PubMed

Kong, Qinglu; Zhang, Lingxia; Liu, Jianan; Wu, Meiying; Chen, Yu; Feng, Jingwei; Shi, Jianlin

2014-12-25

Hydrophilic mesoporous carbon nanoparticles (MCNs) have been synthesized via an extremely facile precursor carbonization-in-hot solvent route. The synthesized MCNs show well-defined particle and pore size distribution at around 100 nm and 2.7 nm, respectively, and multicolor and upconversion photoluminescence, which endow the MCNs with multicolor/upconversion bioimaging and drug delivery properties.

Modeling a failure criterion for U–Mo/Al dispersion fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oh, Jae-Yong; Kim, Yeon Soo; Tahk, Young-Wook

2016-05-01

The breakaway swelling in U-Mo/Al dispersion fuel is known to be caused by large pore formation enhanced by interaction layer (IL) growth between fuel particles and Al matrix. In this study, a critical IL thickness was defined as a criterion for the formation of a large pore in U-Mo/Al dispersion fuel. Specifically, the critical IL thickness is given when two neighboring fuel particles come into contact with each other in the developed IL. The model was verified using the irradiation data from the RERTR tests and KOMO- 4 test. The model application to full-sized sample irradiations such as IRISs, FUTURE,more » E-FUTURE, and AFIP-1 tests resulted in conservative predictions. The parametric study revealed that the fuel particle size and the homogeneity of the fuel particle distribution are influential for fuel performance.« less

Problems associated with using filtration to define dissolved trace element concentrations in natural water samples

USGS Publications Warehouse

Horowitz, A.J.; Lum, K.R.; Garbarino, J.R.; Hall, G.E.M.; Lemieux, C.; Demas, C.R.

1996-01-01

Field and laboratory experiments indicate that a number of factors associated with filtration other than just pore size (e.g., diameter, manufacturer, volume of sample processed, amount of suspended sediment in the sample) can produce significant variations in the 'dissolved' concentrations of such elements as Fe, Al, Cu, Zn, Pb, Co, and Ni. The bulk of these variations result from the inclusion/exclusion of colloidally associated trace elements in the filtrate, although dilution and sorption/desorption from filters also may be factors. Thus, dissolved trace element concentrations quantitated by analyzing filtrates generated by processing whole water through similar pore-sized filters may not be equal or comparable. As such, simple filtration of unspecified volumes of natural water through unspecified 0.45-??m membrane filters may no longer represent an acceptable operational definition for a number of dissolved chemical constituents.

[Isolation of circulating tumor cells in blood by means of "Isolation by SizE of Tumor cells (ISET)"].

PubMed

Liadov, V K; Skrypnikova, M A; Popova, O P

2014-01-01

There is evidence of the importance of circulating tumor cells in bloodstream as a factor of poor prognosis of cancer. The optimum method for isolating and studying of these cells is not defined. The most common methods are either based on the isolation of tumor genetic material from blood or on immune-mediated isolation of epithelial tumor cells. The first group of methods is characterized by a lack of specificity, while the latter do not allow identifying a pool of cells undergone in bloodstream epithelial-mesenchymal transformation. There is presented an overview of results of clinical trials of a new technique of isolation of tumor cells from bloodstream based on the patients' blood filtration through a membrane with defined pore sizes (ISET-Isolation by SizE of Tumor cells).

Pore architecture and cell viability on freeze dried 3D recombinant human collagen-peptide (RHC)-chitosan scaffolds.

PubMed

Zhang, Jing; Zhou, Aimei; Deng, Aipeng; Yang, Yang; Gao, Lihu; Zhong, Zhaocai; Yang, Shulin

2015-04-01

Pore architecture of 3D scaffolds used in tissue engineering plays a critical role in the maintenance of cell survival, proliferation and further promotion of tissue regeneration. We investigated the pore size and structure, porosity, swelling as well as cell viability of a series of recombinant human collagen-peptide-chitosan (RHCC) scaffolds fabricated by lyophilization. In this paper, freezing regime containing a final temperature of freezing (Tf) and cooling rates was applied to obtain scaffolds with pore size ranging from 100μm to 120μm. Other protocols of RHC/chitosan suspension concentration and ratio modification were studied to produce more homogenous and appropriate structural scaffolds. The mean pore size decreased along with the decline of Tf at a slow cooling rate of 0.7°C/min; a more rapid cooling rate under 5°C/min resulted to a smaller pore size and more homogenous microstructure. High concentration could reduce pore size and lead to thick well of scaffold, while improved the ratio of RHC, lamellar and fiber structure coexisted with cellular pores. Human umbilical vein endothelial cells (HUVECs) were seeded on these manufactured scaffolds, the cell viability represented a negative correlation to the pore size. This study provides an alternative method to fabricate 3D RHC-chitosan scaffolds with appropriate pores for potential tissue engineering. Copyright © 2014 Elsevier B.V. All rights reserved.

A simple shape-free model for pore-size estimation with positron annihilation lifetime spectroscopy

NASA Astrophysics Data System (ADS)

Wada, Ken; Hyodo, Toshio

2013-06-01

Positron annihilation lifetime spectroscopy is one of the methods for estimating pore size in insulating materials. We present a shape-free model to be used conveniently for such analysis. A basic model in classical picture is modified by introducing a parameter corresponding to an effective size of the positronium (Ps). This parameter is adjusted so that its Ps-lifetime to pore-size relation merges smoothly with that of the well-established Tao-Eldrup model (with modification involving the intrinsic Ps annihilation rate) applicable to very small pores. The combined model, i.e., modified Tao-Eldrup model for smaller pores and the modified classical model for larger pores, agrees surprisingly well with the quantum-mechanics based extended Tao-Eldrup model, which deals with Ps trapped in and thermally equilibrium with a rectangular pore.

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix

PubMed Central

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N.; Gao, Shengyan

2015-01-01

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir. PMID:26310236

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix.

PubMed

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N; Gao, Shengyan

2015-08-27

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir.

Determination of pore size distributions of porous chromatographic adsorbents by inverse size-exclusion chromatography.

PubMed

Yao, Yan; Lenhoff, Abraham M

2004-05-28

The macroscopic properties of porous chromatographic adsorbents are directly influenced by the pore structure, with the pore size distribution (PSD) playing a major role beyond simply the mean pore size. Inverse size-exclusion chromatography (ISEC), a widely used chromatographic method for determining the PSD of porous media, provides more relevant information on liquid chromatographic materials in situ than traditional methods, such as gas sorption and mercury intrusion. The fundamentals and applications of ISEC in the characterization of the pore structure are reviewed. The description of the probe solutes and the pore space, as well as theoretical models for deriving the PSD from solute partitioning behavior, are discussed. Precautions to ensure integrity of the experiments are also outlined, including accounting for probe polydispersity and minimization of solute-adsorbent interactions. The results that emerge are necessarily model-dependent, but ISEC nonetheless represents a powerful and non-destructive source of quantitative pore structure information that can help to elucidate chromatographic performance observations covering both retention and rate aspects.

Extreme value statistics analysis of fracture strengths of a sintered silicon nitride failing from pores

NASA Technical Reports Server (NTRS)

Chao, Luen-Yuan; Shetty, Dinesh K.

1992-01-01

Statistical analysis and correlation between pore-size distribution and fracture strength distribution using the theory of extreme-value statistics is presented for a sintered silicon nitride. The pore-size distribution on a polished surface of this material was characterized, using an automatic optical image analyzer. The distribution measured on the two-dimensional plane surface was transformed to a population (volume) distribution, using the Schwartz-Saltykov diameter method. The population pore-size distribution and the distribution of the pore size at the fracture origin were correllated by extreme-value statistics. Fracture strength distribution was then predicted from the extreme-value pore-size distribution, usin a linear elastic fracture mechanics model of annular crack around pore and the fracture toughness of the ceramic. The predicted strength distribution was in good agreement with strength measurements in bending. In particular, the extreme-value statistics analysis explained the nonlinear trend in the linearized Weibull plot of measured strengths without postulating a lower-bound strength.

Photo-patterning of porous hydrogels for tissue engineering.

PubMed

Bryant, Stephanie J; Cuy, Janet L; Hauch, Kip D; Ratner, Buddy D

2007-07-01

Since pore size and geometry strongly impact cell behavior and in vivo reaction, the ability to create scaffolds with a wide range of pore geometries that can be tailored to suit a particular cell type addresses a key need in tissue engineering. In this contribution, we describe a novel and simple technique to design porous, degradable poly(2-hydroxyethyl methacrylate) hydrogel scaffolds with well-defined architectures using a unique photolithography process and optimized polymer chemistry. A sphere-template was used to produce a highly uniform, monodisperse porous structure. To create a patterned and porous hydrogel scaffold, a photomask and initiating light were employed. Open, vertical channels ranging in size from 360+/-25 to 730+/-70 microm were patterned into approximately 700 microm thick hydrogels with pore diameters of 62+/-8 or 147+/-15 microm. Collagen type I was immobilized onto the scaffolds to facilitate cell adhesion. To assess the potential of these novel scaffolds for tissue engineering, a skeletal myoblast cell line (C2C12) was seeded onto scaffolds with 147 microm pores and 730 microm diameter channels, and analyzed by histology and digital volumetric imaging. Cell elongation, cell spreading and fibrillar formation were observed on these novel scaffolds. In summary, 3D architectures can be patterned into porous hydrogels in one step to create a wide range of tissue engineering scaffolds that may be tailored for specific applications.

Permeability-porosity relationships in sedimentary rocks

USGS Publications Warehouse

Nelson, Philip H.

1994-01-01

In many consolidated sandstone and carbonate formations, plots of core data show that the logarithm of permeability (k) is often linearly proportional to porosity (??). The slope, intercept, and degree of scatter of these log(k)-?? trends vary from formation to formation, and these variations are attributed to differences in initial grain size and sorting, diagenetic history, and compaction history. In unconsolidated sands, better sorting systematically increases both permeability and porosity. In sands and sandstones, an increase in gravel and coarse grain size content causes k to increase even while decreasing ??. Diagenetic minerals in the pore space of sandstones, such as cement and some clay types, tend to decrease log(k) proportionately as ?? decreases. Models to predict permeability from porosity and other measurable rock parameters fall into three classes based on either grain, surface area, or pore dimension considerations. (Models that directly incorporate well log measurements but have no particular theoretical underpinnings from a fourth class.) Grain-based models show permeability proportional to the square of grain size times porosity raised to (roughly) the fifth power, with grain sorting as an additional parameter. Surface-area models show permeability proportional to the inverse square of pore surface area times porosity raised to (roughly) the fourth power; measures of surface area include irreducible water saturation and nuclear magnetic resonance. Pore-dimension models show permeability proportional to the square of a pore dimension times porosity raised to a power of (roughly) two and produce curves of constant pore size that transgress the linear data trends on a log(k)-?? plot. The pore dimension is obtained from mercury injection measurements and is interpreted as the pore opening size of some interconnected fraction of the pore system. The linear log(k)-?? data trends cut the curves of constant pore size from the pore-dimension models, which shows that porosity reduction is always accompanied by a reduction in characteristic pore size. The high powers of porosity of the grain-based and surface-area models are required to compensate for the inclusion of the small end of the pore size spectrum.

The effect of scaffold pore size in cartilage tissue engineering.

PubMed

Nava, Michele M; Draghi, Lorenza; Giordano, Carmen; Pietrabissa, Riccardo

2016-07-26

The effect of scaffold pore size and interconnectivity is undoubtedly a crucial factor for most tissue engineering applications. The aim of this study was to examine the effect of pore size and porosity on cartilage construct development in different scaffolds seeded with articular chondrocytes. We fabricated poly-L-lactide-co-trimethylene carbonate scaffolds with different pore sizes, using a solvent-casting/particulate-leaching technique. We seeded primary bovine articular chondrocytes on these scaffolds, cultured the constructs for 2 weeks and examined cell proliferation, viability and cell-specific production of cartilaginous extracellular matrix proteins, including GAG and collagen. Cell density significantly increased up to 50% with scaffold pore size and porosity, likely facilitated by cell spreading on the internal surface of bigger pores, and by increased mass transport of gases and nutrients to cells, and catabolite removal from cells, allowed by lower diffusion barriers in scaffolds with a higher porosity. However, both the cell metabolic activity and the synthesis of cartilaginous matrix proteins significantly decreased by up to 40% with pore size. We propose that the association of smaller pore diameters, causing 3-dimensional cell aggregation, to a lower oxygenation caused by a lower porosity, could have been the condition that increased the cell-specific synthesis of cartilaginous matrix proteins in the scaffold with the smallest pores and the lowest porosity among those tested. In the initial steps of in vitro cartilage engineering, the combination of small scaffold pores and low porosity is an effective strategy with regard to the promotion of chondrogenesis.

Investigation of thermal conduction in symmetric and asymmetric nanoporous structures

NASA Astrophysics Data System (ADS)

Yu, Ziqi; Ferrer-Argemi, Laia; Lee, Jaeho

2017-12-01

Nanoporous structures with a critical dimension comparable to or smaller than the phonon mean free path have demonstrated significant thermal conductivity reductions that are attractive for thermoelectric applications, but the presence of various geometric parameters complicates the understanding of governing mechanisms. Here, we use a ray tracing technique to investigate phonon boundary scattering phenomena in Si nanoporous structures of varying pore shapes, pore alignments, and pore size distributions, and identify mechanisms that are primarily responsible for thermal conductivity reductions. Our simulation results show that the neck size, or the smallest distance between nearest pores, is the key parameter in understanding nanoporous structures of varying pore shapes and the same porosities. When the neck size and the porosity are both identical, asymmetric pore shapes provide a lower thermal conductivity compared with symmetric pore shapes, due to localized heat fluxes. Asymmetric nanoporous structures show possibilities of realizing thermal rectification even with fully diffuse surface boundaries, in which optimal arrangements of triangular pores show a rectification ratio up to 13 when the injection angles are optimally controlled. For symmetric nanoporous structures, hexagonal-lattice pores achieve larger thermal conductivity reductions than square-lattice pores due to the limited line of sight for phonons. We also show that nanoporous structures of alternating pore size distributions from large to small pores yield a lower thermal conductivity compared with those of uniform pore size distributions in the given porosity. These findings advance the understanding of phonon boundary scattering phenomena in complex geometries and enable optimal designs of artificial nanostructures for thermoelectric energy harvesting and solid-state cooling systems.

Pore size engineering applied to starved electrochemical cells and batteries

NASA Technical Reports Server (NTRS)

Abbey, K. M.; Thaller, L. H.

1982-01-01

To maximize performance in starved, multiplate cells, the cell design should rely on techniques which widen the volume tolerance characteristics. These involve engineering capillary pressure differences between the components of an electrochemical cell and using these forces to promote redistribution of electrolyte to the desired optimum values. This can be implemented in practice by prescribing pore size distributions for porous back-up plates, reservoirs, and electrodes. In addition, electrolyte volume management can be controlled by incorporating different pore size distributions into the separator. In a nickel/hydrogen cell, the separator must contain pores similar in size to the small pores of both the nickel and hydrogen electrodes in order to maintain an optimum conductive path for the electrolyte. The pore size distributions of all components should overlap in such a way as to prevent drying of the separator and/or flooding of the hydrogen electrode.

Freezing and melting of water in a single cylindrical pore: The pore-size dependence of freezing and melting behavior

NASA Astrophysics Data System (ADS)

Morishige, Kunimitsu; Kawano, Keiji

1999-03-01

In order to clarify the origin of the hysteresis between freezing and melting of pore water, we performed x-ray diffraction measurements of water confined inside the cylindrical pores of seven kinds of siliceous MCM-41 (a member of ordered mesoporous materials denoted by Mobil Oil researchers) with different pore radii (1.2-2.9 nm) and the interconnected pores of Vycor glass as a function of temperature. The hysteresis effect depends markedly on the size of the cylindrical pores: the hysteresis is negligibly small in smaller pores and becomes remarkable in larger pores. This strongly suggests that the hysteresis is arisen from size-dependent supercooling of water confined to the mesopores. For the water confined to the mesopores with pore radius of 1.2 nm, a continuous transition between a liquid and a solid precedes the first-order freezing transition of the pore water which would occur by the same mechanism as in bulk water.

Scaffold permeability as a means to determine fiber diameter and pore size of electrospun fibrinogen.

PubMed

Sell, Scott; Barnes, Catherine; Simpson, David; Bowlin, Gary

2008-04-01

The purpose of this study was to construct a flowmeter that could accurately measure the hydraulic permeability of electrospun fibrinogen scaffolds, providing insight into the transport properties of electrospun scaffolds while making the measurement of their topographical features (fiber diameter and pore size) more accurate. Three different concentrations of fibrinogen were used (100, 120, and 150 mg/mL) to create scaffolds with three different fiber diameters and pore sizes. The fiber diameters and pore sizes of the electrospun scaffolds were first analyzed with scanning electron microscopy and image analysis software. The permeability of each scaffold was measured with the flowmeter and used to calculate permeability-based fiber diameters and pore sizes, which were compared to values obtained through image analysis. Permeability measurement revealed scaffold permeability to increase with fibrinogen concentration, much like average fiber diameter and pore size. Comparison between the two measurement methods demonstrated the efficacy of the flowmeter as a way to measure scaffold features. Copyright 2007 Wiley Periodicals, Inc.

Mineralogy of the Almahata Sitta Ureilite

NASA Technical Reports Server (NTRS)

Zolensky, Michael E.; Herrin, J.; Friedrich, J. M.; Rumble, D.; Steele, A.; Jenniskens, P.; Shaddad, M. H.; Le, L.; Robinson, G. A.

2009-01-01

Mineralogy & Petrography: Almahata Sitta, deriving from the asteroid 2008 TC3, is a coarse-grained- to porous, fine-grained, fragmental breccia with subrounded mineral fragments and olivine aggregates embedded in a cataclastic matrix of ureilitic material. Mineral fragments include polycrystalline olivine, low-calcium, pigeonite, and augite. Abundant carbonaceous aggregates containing graphite, microdiamonds and aliphatics. Kamacite, Cr-rich troilite, silica and schreibersite are abundant. The compositional range of the silicates is characteristic of the ureilites as a group, but unusually broad for an individual ureilite. The dense lithology is typical for ureilites, but the porous lithology is anomalous. In the porous lithology pore walls are largely coated by crystals of olivine. Classification: Almahata Sitta is an anomalous, polymict eucrite. Anomalous features include large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and fine-grained texture. Tomography reveals that the pores define thin, discontinuous "sheets" connected in three dimensions, suggesting that they outline grains that have been incompletely welded together. The crystals lining the pore walls are probably vapor phase deposits. Therefore Almahata Sitta may represent an agglomeration of coarse- to fine-grained, incompletely reduced pellets formed during impact, and subsequently welded together at high temperature.

Relation between the ion size and pore size for an electric double-layer capacitor.

PubMed

Largeot, Celine; Portet, Cristelle; Chmiola, John; Taberna, Pierre-Louis; Gogotsi, Yury; Simon, Patrice

2008-03-05

The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (approximately 0.7 nm). The capacitance values of TiC-CDC produced at 500 degrees C are more than 160 F/g and 85 F/cm(3) at 60 degrees C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm(3) in ionic liquids. A significant drop in capacitance has been observed in pores that were larger or smaller than the ion size by just an angstrom, suggesting that the pore size must be tuned with sub-angstrom accuracy when selecting a carbon/ion couple. This work suggests a general approach to EDLC design leading to the maximum energy density, which has been now proved for both solvated organic salts and solvent-free liquid electrolytes.

Modelling the influence of pore size on the response of materials to infrared lasers An application to human enamel

NASA Astrophysics Data System (ADS)

Vila Verde, A.; Ramos, Marta M. D.

2005-07-01

We present an analytical model for a ceramic material (hydroxyapatite, HA) containing nanometre-scale water pores, and use it to estimate the pressure at the pore as a function of temperature at the end of a single 0.35 μs laser pulse by Er:YAG (2.94 μm) and CO 2 (10.6 μm) lasers. Our results suggest that the pressure at the pore is directly related to pore temperature, and that very high pressures can be generated simply by the thermal expansion of liquid water. Since the temperature reached in the pores at the end of the laser pulse is a strong function of pore size for Er:YAG lasers, but is independent of pore size for CO 2 lasers, our present results provide a possible explanation for the fact that human dental enamel threshold ablation fluences vary more for Er:YAG lasers than for CO 2 lasers. This suggests that experimentalists should analyse their results accounting for factors, like age or type of tooth, that may change the pore size distribution in their samples.

Effect of pore size of three-dimensionally ordered macroporous chitosan-silica matrix on solubility, drug release, and oral bioavailability of loaded-nimodipine.

PubMed

Gao, Yikun; Xie, Yuling; Sun, Hongrui; Zhao, Qinfu; Zheng, Xin; Wang, Siling; Jiang, Tongying

2016-01-01

To explore the effect of the pore size of three-dimensionally ordered macroporous chitosan-silica (3D-CS) matrix on the solubility, drug release, and oral bioavailability of the loaded drug. 3D-CS matrices with pore sizes of 180 nm, 470 nm, and 930 nm were prepared. Nimodipine (NMDP) was used as the drug model. The morphology, specific surface area, and chitosan mass ratio of the 3D-CS matrices were characterized before the effect of the pore size on drug crystallinity, solubility, release, and in vivo pharmacokinetics were investigated. With the pore size of 3D-CS matrix decreasing, the drug crystallinity decreased and the aqueous solubility increased. The drug release was synthetically controlled by the pore size and chitosan content of 3D-CS matrix in a pH 6.8 medium, while in a pH 1.2 medium the erosion of the 3D-CS matrix played an important role in the decreased drug release rate. The area under the curve of the drug-loaded 3D-CS matrices with pore sizes of 930 nm, 470 nm, and 180 nm was 7.46-fold, 5.85-fold, and 3.75-fold larger than that of raw NMDP respectively. Our findings suggest that the oral bioavailability decreased with a decrease in the pore size of the matrix.

Laser beam melting 3D printing of Ti6Al4V based porous structured dental implants: fabrication, biocompatibility analysis and photoelastic study

PubMed Central

Yang, Fei; Chen, Chen; Zhou, QianRong; Gong, YiMing; Li, RuiXue; Li, ChiChi; Klämpfl, Florian; Freund, Sebastian; Wu, XingWen; Sun, Yang; Li, Xiang; Schmidt, Michael; Ma, Duan; Yu, YouCheng

2017-01-01

Fabricating Ti alloy based dental implants with defined porous scaffold structure is a promising strategy for improving the osteoinduction of implants. In this study, we use Laser Beam Melting (LBM) 3D printing technique to fabricate porous Ti6Al4V dental implant prototypes with three controlled pore sizes (200, 350 and 500 μm). The mechanical stress distribution in the surrounding bone tissue is characterized by photoelastography and associated finite element simulation. For in-vitro studies, experiments on implants’ biocompatibility and osteogenic capability are conducted to evaluate the cellular response correlated to the porous structure. As the preliminary results, porous structured implants show a lower stress-shielding to the surrounding bone at the implant neck and a more densed distribution at the bottom site compared to the reference implant. From the cell proliferation tests and the immunofluorescence images, 350 and 500 μm pore sized implants demonstrate a better biocompatibility in terms of cell growth, migration and adhesion. Osteogenic genes expression of the 350 μm group is significantly increased alone with the ALP activity test. All these suggest that a pore size of 350 μm provides an optimal provides an optimal potential for improving the mechanical shielding to the surrounding bones and osteoinduction of the implant itself. PMID:28350007

Laser beam melting 3D printing of Ti6Al4V based porous structured dental implants: fabrication, biocompatibility analysis and photoelastic study

NASA Astrophysics Data System (ADS)

Yang, Fei; Chen, Chen; Zhou, Qianrong; Gong, Yiming; Li, Ruixue; Li, Chichi; Klämpfl, Florian; Freund, Sebastian; Wu, Xingwen; Sun, Yang; Li, Xiang; Schmidt, Michael; Ma, Duan; Yu, Youcheng

2017-03-01

Fabricating Ti alloy based dental implants with defined porous scaffold structure is a promising strategy for improving the osteoinduction of implants. In this study, we use Laser Beam Melting (LBM) 3D printing technique to fabricate porous Ti6Al4V dental implant prototypes with three controlled pore sizes (200, 350 and 500 μm). The mechanical stress distribution in the surrounding bone tissue is characterized by photoelastography and associated finite element simulation. For in-vitro studies, experiments on implants’ biocompatibility and osteogenic capability are conducted to evaluate the cellular response correlated to the porous structure. As the preliminary results, porous structured implants show a lower stress-shielding to the surrounding bone at the implant neck and a more densed distribution at the bottom site compared to the reference implant. From the cell proliferation tests and the immunofluorescence images, 350 and 500 μm pore sized implants demonstrate a better biocompatibility in terms of cell growth, migration and adhesion. Osteogenic genes expression of the 350 μm group is significantly increased alone with the ALP activity test. All these suggest that a pore size of 350 μm provides an optimal provides an optimal potential for improving the mechanical shielding to the surrounding bones and osteoinduction of the implant itself.

Effective pore size and radius of capture for K+ ions in K-channels

PubMed Central

Moldenhauer, Hans; Díaz-Franulic, Ignacio; González-Nilo, Fernando; Naranjo, David

2016-01-01

Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (rE) in several K-channel crystal structures. rE was operationally defined as the radius of the biggest sphere able to enter the pore from the cytosolic side. We obtained consistent rE estimates for MthK and Kv1.2/2.1 structures, with rE = 5.3–5.9 Å and rE = 4.5–5.2 Å, respectively. We compared these structural estimates with functional assessments of the internal mouth radii of capture (rC) for two electrophysiological counterparts, the large conductance calcium activated K-channel (rC = 2.2 Å) and the Shaker Kv-channel (rC = 0.8 Å), for MthK and Kv1.2/2.1 structures, respectively. Calculating the difference between rE and rC, produced consistent size radii of 3.1–3.7 Å and 3.6–4.4 Å for hydrated K+ ions. These hydrated K+ estimates harmonize with others obtained with diverse experimental and theoretical methods. Thus, these findings validate MthK and the Kv1.2/2.1 structures as templates for open BK and Kv-channels, respectively. PMID:26831782

New general pore size distribution model by classical thermodynamics application: Activated carbon

USGS Publications Warehouse

Lordgooei, M.; Rood, M.J.; Rostam-Abadi, M.

2001-01-01

A model is developed using classical thermodynamics to characterize pore size distributions (PSDs) of materials containing micropores and mesopores. The thermal equation of equilibrium adsorption (TEEA) is used to provide thermodynamic properties and relate the relative pore filling pressure of vapors to the characteristic pore energies of the adsorbent/adsorbate system for micropore sizes. Pore characteristic energies are calculated by averaging of interaction energies between adsorbate molecules and adsorbent pore walls as well as considering adsorbate-adsorbate interactions. A modified Kelvin equation is used to characterize mesopore sizes by considering variation of the adsorbate surface tension and by excluding the adsorbed film layer for the pore size. The modified-Kelvin equation provides similar pore filling pressures as predicted by density functional theory. Combination of these models provides a complete PSD of the adsorbent for the micropores and mesopores. The resulting PSD is compared with the PSDs from Jaroniec and Choma and Horvath and Kawazoe models as well as a first-order approximation model using Polanyi theory. The major importance of this model is its basis on classical thermodynamic properties, less simplifying assumptions in its derivation compared to other methods, and ease of use.

A novel porous scaffold fabrication technique for epithelial and endothelial tissue engineering.

PubMed

McHugh, Kevin J; Tao, Sarah L; Saint-Geniez, Magali

2013-07-01

Porous scaffolds have the ability to minimize transport barriers for both two- (2D) and three-dimensional tissue engineering. However, current porous scaffolds may be non-ideal for 2D tissues such as epithelium due to inherent fabrication-based characteristics. While 2D tissues require porosity to support molecular transport, pores must be small enough to prevent cell migration into the scaffold in order to avoid non-epithelial tissue architecture and compromised function. Though electrospun meshes are the most popular porous scaffolds used today, their heterogeneous pore size and intense topography may be poorly-suited for epithelium. Porous scaffolds produced using other methods have similar unavoidable limitations, frequently involving insufficient pore resolution and control, which make them incompatible with 2D tissues. In addition, many of these techniques require an entirely new round of process development in order to change material or pore size. Herein we describe "pore casting," a fabrication method that produces flat scaffolds with deterministic pore shape, size, and location that can be easily altered to accommodate new materials or pore dimensions. As proof-of-concept, pore-cast poly(ε-caprolactone) (PCL) scaffolds were fabricated and compared to electrospun PCL in vitro using canine kidney epithelium, human colon epithelium, and human umbilical vein endothelium. All cell types demonstrated improved morphology and function on pore-cast scaffolds, likely due to reduced topography and universally small pore size. These results suggest that pore casting is an attractive option for creating 2D tissue engineering scaffolds, especially when the application may benefit from well-controlled pore size or architecture.

Desilication of ZSM-5 zeolites for mesoporosity development using microwave irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, Zubair; Jun, Jong Won; Kim, Chul-Ung

2015-01-15

Highlights: • Microwaves have beneficial effects on desilication of zeolites. • Produced mesopores with microwaves have narrow pore-size distribution. • Advantages and disadvantages of various desilicating agents were also reported. - Abstract: Mesoporous ZSM-5 zeolite was obtained by desilication in alkaline solutions with microwave (MW) and conventional electric (CE) heating under hydrothermal conditions. Both methods were effective in the production of mesoporous zeolites; however, MW was more efficient than CE as it led to well-defined mesopores with relatively small sizes and a narrow size distribution within a short treatment time. Moreover, the mesoporous ZSM-5 obtained through this method was effectivemore » in producing less bulky products from an acid-catalyzed reaction, specifically the butylation of phenol. Finally, various bases were found to have advantages and disadvantages in desilication. NaOH was the most reactive; however, macroporosity could develop easily under a severe condition. Ammonia water was weakly reactive; however, it could be used to precisely control the pore architecture, and no ion exchange is needed for acid catalysis. Organic amines such as ethylenediamine can also be used in desilication.« less

Integrating SANS and fluid-invasion methods to characterize pore structure of typical American shale oil reservoirs.

PubMed

Zhao, Jianhua; Jin, Zhijun; Hu, Qinhong; Jin, Zhenkui; Barber, Troy J; Zhang, Yuxiang; Bleuel, Markus

2017-11-13

An integration of small-angle neutron scattering (SANS), low-pressure N 2 physisorption (LPNP), and mercury injection capillary pressure (MICP) methods was employed to study the pore structure of four oil shale samples from leading Niobrara, Wolfcamp, Bakken, and Utica Formations in USA. Porosity values obtained from SANS are higher than those from two fluid-invasion methods, due to the ability of neutrons to probe pore spaces inaccessible to N 2 and mercury. However, SANS and LPNP methods exhibit a similar pore-size distribution, and both methods (in measuring total pore volume) show different results of porosity and pore-size distribution obtained from the MICP method (quantifying pore throats). Multi-scale (five pore-diameter intervals) inaccessible porosity to N 2 was determined using SANS and LPNP data. Overall, a large value of inaccessible porosity occurs at pore diameters <10 nm, which we attribute to low connectivity of organic matter-hosted and clay-associated pores in these shales. While each method probes a unique aspect of complex pore structure of shale, the discrepancy between pore structure results from different methods is explained with respect to their difference in measurable ranges of pore diameter, pore space, pore type, sample size and associated pore connectivity, as well as theoretical base and interpretation.

Synthesis of mesoporous carbon nanoparticles with large and tunable pore sizes

NASA Astrophysics Data System (ADS)

Liu, Chao; Yu, Meihua; Li, Yang; Li, Jiansheng; Wang, Jing; Yu, Chengzhong; Wang, Lianjun

2015-07-01

Mesoporous carbon nanoparticles (MCNs) with large and adjustable pores have been synthesized by using poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a template and resorcinol-formaldehyde (RF) as a carbon precursor. The resulting MCNs possess small diameters (100-126 nm) and high BET surface areas (up to 646 m2 g-1). By using home-designed block copolymers, the pore size of MCNs can be tuned in the range of 13-32 nm. Importantly, the pore size of 32 nm is the largest among the MCNs prepared by the soft-templating route. The formation mechanism and structure evolution of MCNs were studied by TEM and DLS measurements, based on which a soft-templating/sphere packing mechanism was proposed. Because of the large pores and small particle sizes, the resulting MCNs were excellent nano-carriers to deliver biomolecules into cancer cells. MCNs were further demonstrated with negligible toxicity. It is anticipated that this carbon material with large pores and small particle sizes may have excellent potential in drug/gene delivery.Mesoporous carbon nanoparticles (MCNs) with large and adjustable pores have been synthesized by using poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a template and resorcinol-formaldehyde (RF) as a carbon precursor. The resulting MCNs possess small diameters (100-126 nm) and high BET surface areas (up to 646 m2 g-1). By using home-designed block copolymers, the pore size of MCNs can be tuned in the range of 13-32 nm. Importantly, the pore size of 32 nm is the largest among the MCNs prepared by the soft-templating route. The formation mechanism and structure evolution of MCNs were studied by TEM and DLS measurements, based on which a soft-templating/sphere packing mechanism was proposed. Because of the large pores and small particle sizes, the resulting MCNs were excellent nano-carriers to deliver biomolecules into cancer cells. MCNs were further demonstrated with negligible toxicity. It is anticipated that this carbon material with large pores and small particle sizes may have excellent potential in drug/gene delivery. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02389k

Stochastic theory of size exclusion chromatography by the characteristic function approach.

PubMed

Dondi, Francesco; Cavazzini, Alberto; Remelli, Maurizio; Felinger, Attila; Martin, Michel

2002-01-18

A general stochastic theory of size exclusion chromatography (SEC) able to account for size dependence on both pore ingress and egress processes, moving zone dispersion and pore size distribution, was developed. The relationship between stochastic-chromatographic and batch equilibrium conditions are discussed and the fundamental role of the 'ergodic' hypothesis in establishing a link between them is emphasized. SEC models are solved by means of the characteristic function method and chromatographic parameters like plate height, peak skewness and excess are derived. The peak shapes are obtained by numerical inversion of the characteristic function under the most general conditions of the exploited models. Separate size effects on pore ingress and pore egress processes are investigated and their effects on both retention selectivity and efficiency are clearly shown. The peak splitting phenomenon and peak tailing due to incomplete sample sorption near to the exclusion limit is discussed. An SEC model for columns with two types of pores is discussed and several effects on retention selectivity and efficiency coming from pore size differences and their relative abundance are singled out. The relevance of moving zone dispersion on separation is investigated. The present approach proves to be general and able to account for more complex SEC conditions such as continuous pore size distributions and mixed retention mechanism.

Relation Between Pore Size and the Compressibility of a Confined Fluid

PubMed Central

Gor, Gennady Y.; Siderius, Daniel W.; Rasmussen, Christopher J.; Krekelberg, William P.; Shen, Vincent K.; Bernstein, Noam

2015-01-01

When a fluid is confined to a nanopore, its thermodynamic properties differ from the properties of a bulk fluid, so measuring such properties of the confined fluid can provide information about the pore sizes. Here we report a simple relation between the pore size and isothermal compressibility of argon confined in these pores. Compressibility is calculated from the fluctuations of the number of particles in the grand canonical ensemble using two different simulation techniques: conventional grand-canonical Monte Carlo and grand-canonical ensemble transition-matrix Monte Carlo. Our results provide a theoretical framework for extracting the information on the pore sizes of fluid-saturated samples by measuring the compressibility from ultrasonic experiments. PMID:26590541

Processing and Characterization of Porous Ti2AlC with Controlled Porosity and Pore Size

DTIC Science & Technology

2012-09-11

fabricated by spark plasma sintering , were also characterized. The effects of porosity and/or pore size on the room temperature elastic moduli...pressureless- sintered without NaCl pore former, or fabricated by spark plasma sintering , were also characterized. The effects of porosity and/or pore size...as well as several samples sintered using spark plasma sintering (SPS). Furthermore, we demon- strate that the developed methodology can be implemented

Effect of Processing Parameters on Pore Structure and Thickness of Anodic Aluminum Oxide (AAO) Tubular Membranes.

PubMed

Belwalkar, A; Grasing, E; Van Geertruyden, W; Huang, Z; Misiolek, W Z

2008-07-01

Nanoporous anodic aluminum oxide (AAO) tubular membranes were fabricated from aluminum alloy tubes in sulfuric and oxalic acid electrolytes using a two-step anodization process. The membranes were investigated for characteristics such as pore size, interpore distance and thickness by varying applied voltage and electrolyte concentration. Morphology of the membranes was examined using light optical and scanning electron microscopy and characterized using ImageJ software. Results showed that membranes having narrow pore size and uniform pore distribution with parallel channel arrays were obtained. The pore sizes were ranging from 14 to 24 nm and the wall thicknesses as high as 76 microm. It was found that the pore size increased in direct proportion with the applied voltage and inversely with the electrolyte concentration while the interpore distance increased linearly with the applied voltage. It was also observed that increase in acid concentration increased tubular membrane wall thickness that improved mechanical handling. By using anodic alumina technology, robust ceramic tubes with uniformly distributed pore-structure and parallel nano-channels of lengths and sizes practical for industrial applications were reliably produced in quantity.

Effect of Processing Parameters on Pore Structure and Thickness of Anodic Aluminum Oxide (AAO) Tubular Membranes

PubMed Central

Belwalkar, A.; Grasing, E.; Huang, Z.; Misiolek, W.Z.

2008-01-01

Nanoporous anodic aluminum oxide (AAO) tubular membranes were fabricated from aluminum alloy tubes in sulfuric and oxalic acid electrolytes using a two-step anodization process. The membranes were investigated for characteristics such as pore size, interpore distance and thickness by varying applied voltage and electrolyte concentration. Morphology of the membranes was examined using light optical and scanning electron microscopy and characterized using ImageJ software. Results showed that membranes having narrow pore size and uniform pore distribution with parallel channel arrays were obtained. The pore sizes were ranging from 14 to 24 nm and the wall thicknesses as high as 76 µm. It was found that the pore size increased in direct proportion with the applied voltage and inversely with the electrolyte concentration while the interpore distance increased linearly with the applied voltage. It was also observed that increase in acid concentration increased tubular membrane wall thickness that improved mechanical handling. By using anodic alumina technology, robust ceramic tubes with uniformly distributed pore-structure and parallel nano-channels of lengths and sizes practical for industrial applications were reliably produced in quantity. PMID:19578471

Nuclear fuel elements and method of making same

DOEpatents

Schweitzer, Donald G.

1992-01-01

A nuclear fuel element for a high temperature gas nuclear reactor that has an average operating temperature in excess of 2000.degree. C., and a method of making such a fuel element. The fuel element is characterized by having fissionable fuel material localized and stabilized within pores of a carbon or graphite member by melting the fissionable material to cause it to chemically react with the carbon walls of the pores. The fissionable fuel material is further stabilized and localized within the pores of the graphite member by providing one or more coatings of pyrolytic carbon or diamond surrounding the porous graphite member so that each layer defines a successive barrier against migration of the fissionable fuel from the pores, and so that the outermost layer of pyrolytic carbon or diamond forms a barrier between the fissionable material and the moderating gases used in an associated high temperature gas reactor. The method of the invention provides for making such new elements either as generally spherically elements, or as flexible filaments, or as other relatively small-sized fuel elements that are particularly suited for use in high temperature gas reactors.

AAVSO Solar Observers Worldwide

NASA Astrophysics Data System (ADS)

Howe, R.

2013-06-01

(Abstract only) For visual solar observers there has been no biological change in the "detector" (human eye) - at century scales (eye + visual cortex) does not change much over time. Our capacity to "integrate" seeing distortions is not just simple averaging! The visual cortex plays an essential role, and until recently only the SDO-HMI (Solar Dynamics Observatory, Helioseismic and Magnetic Imager) has had the capacity to detect the smallest sunspots, called pores. Prior to this the eye was superior to photography and CCD. Imaged data are not directly comparable or substitutable to counts by eye, as the effects of sensor/optical resolution and seeing will have a different influence on the resulting sunspot counts for images when compared to the human eye. Also contributing to the complex task of counting sunspots is differentiating between a sunspot (which is usually defined as having a darker center (umbra) and lighter outer ring (penumbra)) and a pore, made even more complex by the conflicting definitions of the word "pore" in the solar context: "pore" can mean a small spot without penumbra or "pore" can mean a random intergranular blemish that is not a true sunspot. The overall agreement is that the smallest spot size is near 2,000 km or ~3 arc sec, (Loughhead, R. E. and Bray, R. J. 1961, Australian J. Phys., 14, 347). Sunspot size is dictated by granulation dynamics rather than spot size (cancellation of convective motion), and by the lifetime of the pore, which averages from 10 to 30 minutes. There is no specific aperture required for AAVSO observers contributing sunspot observations. However, the detection of the smallest spots is influenced by the resolution of the telescope. Two factors to consider are the theoretical optical resolution (unobstructed aperture), Rayleigh criterion: theta = 138 / D(mm), and Dawes criterion: theta = 116 / D(mm) (http://www.telescope-optics.net/telescope_resolution.htm). However, seeing is variable with time; daytime range will be similar for all low-altitude sites, within the range of 1.5 to 3 arc sec, (typically = 2 arc sec equivalent diameter D = 45-90 mm, the typical solar scope = 70 mm aperture). Where large apertures are more affected by size of turbulent eddies ~8-12 cm, small-aperture telescopes reduce these differences, i.e. large aperture is not always beneficial.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Hongcai J

In the past decades, there has been an escalation of interest in the study of MOFs due to their fascinating structures and intriguing application potentials. Their exceptionally high surface areas, uniform yet tunable pore sizes, and well-defined adsorbate-MOF interaction sites make them suitable for hydrogen storage. Various strategies to increase the hydrogen capacity of MOFs, such as constructing pore sizes comparable to hydrogen molecules, increasing surface area and pore volume, utilizing catenation, and introducing coordinatively unsaturated metal centers (UMCs) have been widely explored to increase the hydrogen uptake of the MOFs. MOFs with hydrogen uptake approaching the DOE gravimetric storagemore » goal under reasonable pressure but cryo- temperature (typically 77 K) were achieved. However, the weak interaction between hydrogen molecules and MOFs has been the major hurdle limiting the hydrogen uptake of MOFs at ambient temperature. Along the road, we have realized both high surface area and strong interaction between framework and hydrogen are equally essential for porous materials to be practically applicable in Hydrogen storage. Increasing the isosteric heats of adsorption for hydrogen through the introduction of active centers into the framework could have great potential on rendering the framework with strong interaction toward hydrogen. Approaches on increasing the surface areas and improving hydrogen affinity by optimizing size and structure of the pores and the alignment of active centers around the pores in frameworks have been pursued, for example: (a) the introduction of coordinatively UMC (represents a metal center missing multiple ligands) with potential capability of multiple dihydrogen-binding (Kubas type, non-dissociative) per UMC, (b) the design and synthesis of proton-rich MOFs in which a + H3 binds dihydrogen just like a metal ion does, and (c) the preparation of MOFs and PPNs with well aligned internal electric fields. We believe the accomplishments of this DOE supported research will greatly benefit the future pursuit of hydrogen storage materials. The ultimate goal to increase the gravimetric and volumetric hydrogen storage capacity to meet DOE targets for Light-Duty Vehicles is achievable.« less

Porous glasses as a matrix for incorporation of photonic materials. Pore determination by positron annihilation lifetime spectroscopy

NASA Astrophysics Data System (ADS)

Reisfeld, Pore determination by positron annihilation lifetime spectroscopy R.; Saraidarov, T.; Jasinska, B.

2004-07-01

Porous glasses prepared by the sol-gel technique have a variety of applications when incorporated by photonic materials: tunable lasers, sensors, luminescence solar concentrators, semiconductor quantum dots, biological markers. The known methods of pore size determinations, the nitrogen adsorption and mercury porosimetry allow to determine the sizes of open pores. Positron annihilation lifetime spectroscopy (PALS) allows to determine pore sizes also of closed pores. As an example we have performed measurements of non-doped zirconia-silica-polyurethane (ZSUR) ormocer glasses and the same glasses doped with lead sulfide quantum dots. The pore radii range between 0.25-0.38 nm, total surface area 15.5-23.8 m 2/g.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, K.; Tonks, M.; Zhang, Y.

A detailed phase field model for the effect of pore drag on grain growth kinetics was implemented in MARMOT. The model takes into consideration both the curvature-driven grain boundary motion and pore migration by surface diffusion. As such, the model accounts for the interaction between pore and grain boundary kinetics, which tends to retard the grain growth process. Our 2D and 3D simulations demonstrate that the model capture all possible pore-grain boundary interactions proposed in theoretical models. For high enough surface mobility, the pores move along with the migrating boundary as a quasi-rigid-body, albeit hindering its migration rate compared tomore » the pore-free case. For less mobile pores, the migrating boundary can separate from the pores. For the pore-controlled grain growth kinetics, the model predicts a strong dependence of the growth rate on the number of pores, pore size, and surface diffusivity in agreement with theroretical models. An evolution equation for the grain size that includes these parameters was derived and showed to agree well with numerical solution. It shows a smooth transition from boundary-controlled kinetics to pore-controlled kinetics as the surface diffusivity decreases or the number of pores or their size increases. This equation can be utilized in BISON to give accurate estimate for the grain size evolution. This will be accomplished in the near future. The effect of solute drag and anisotropy of grain boundary on grain growth will be investigated in future studies.« less

Prediction of Hydraulic Conductivity as Related to Pore Size Distribution in Unsaturated Soils

USDA-ARS?s Scientific Manuscript database

Soil pore volume as well as pore size, shape, type (i.e. biopore versus crack), continuity, and distribution in soil affect soil water and gas exchange. Vertical and lateral drainage of water by gravitational forces occurs through large, non-capillary soil pores, but redistribution and upward moveme...

Electrochemically-Driven Insertion of Biological Nanodiscs into Solid State Membrane Pores as a Basis for "Pore-In-Pore" Membranes.

PubMed

Farajollahi, Farid; Seidenstücker, Axel; Altintoprak, Klara; Walther, Paul; Ziemann, Paul; Plettl, Alfred; Marti, Othmar; Wege, Christina; Gliemann, Hartmut

2018-04-13

Nanoporous membranes are of increasing interest for many applications, such as molecular filters, biosensors, nanofluidic logic and energy conversion devices. To meet high-quality standards, e.g., in molecular separation processes, membranes with well-defined pores in terms of pore diameter and chemical properties are required. However, the preparation of membranes with narrow pore diameter distributions is still challenging. In the work presented here, we demonstrate a strategy, a "pore-in-pore" approach, where the conical pores of a solid state membrane produced by a multi-step top-down lithography procedure are used as a template to insert precisely-formed biomolecular nanodiscs with exactly defined inner and outer diameters. These nanodiscs, which are the building blocks of tobacco mosaic virus-deduced particles, consist of coat proteins, which self-assemble under defined experimental conditions with a stabilizing short RNA. We demonstrate that the insertion of the nanodiscs can be driven either by diffusion due to a concentration gradient or by applying an electric field along the cross-section of the solid state membrane. It is found that the electrophoresis-driven insertion is significantly more effective than the insertion via the concentration gradient.

Estimating Pore Properties from NMR Relaxation Time Measurements in Heterogeneous Media

NASA Astrophysics Data System (ADS)

Grunewald, E.; Knight, R.

2008-12-01

The link between pore geometry and the nuclear magnetic resonance (NMR) relaxation time T2 is well- established for simple systems but is poorly understood for complex media with heterogeneous pores. Conventional interpretation of NMR relaxation data employs a model of isolated pores in which each hydrogen proton samples only one pore type, and the T2-distribution is directly scaled to estimate a pore-size distribution. During an actual NMR measurement, however, each proton diffuses through a finite volume of the pore network, and so may sample multiple pore types encountered within this diffusion cell. For cases in which heterogeneous pores are strongly coupled by diffusion, the meaning of the T2- distribution is not well understood and further research is required to determine how such measurements should be interpreted. In this study we directly investigate the implications of pore coupling in two groups of laboratory NMR experiments. We conduct two suites of experiments, in which samples are synthesized to exhibit a range of pore coupling strengths using two independent approaches: (a) varying the scale of the diffusion cell and (b) varying the scale over which heterogeneous pores are encountered. In the first set of experiments, we vary the scale of the diffusion cell in silica gels which have a bimodal pore-size distribution comprised of intragrannular micropores and much larger intergrannular pores. The untreated gel exhibits strong pore coupling with a single broad peak observed in the T2-distribution. By treating the gel with varied amounts of paramagnetic iron surface coatings, we decrease the surface relaxation time, T2S, and effectively decrease both the size of the diffusion cell and the degree of pore coupling. As more iron is coated to the grain surfaces, we observe a separation of the broad T2-distribution into two peaks that more accurately represent the true bimodal pore-size distribution. In the second set of experiments, we vary the scale over which heterogeneous pores are encountered in bimodal grain packs of pure quartz (long T2S) and hematite (short T2S). The scale of heterogeneity is varied by changing the mean grain size and relative mineral concentrations. When the mean grain size is small and the mineral concentrations are comparable, the T2-distribution is roughly monomodal indicating strong pore coupling. As the grain size is increased or the mineral concentrations are made increasingly uneven, the T2- distribution develops a bimodal character, more representative of the actual distribution of pore types. Numerical simulations of measurements in both experiment groups allow us to more closely investigate how the relaxing magnetization evolves in both time and space. Collectively, these experiments provide important insights into the effects of pore coupling on NMR measurements in heterogeneous systems and contribute to our ultimate goal of improving the interpretation of these data in complex near-surface sediments.

Fabrication, pore structure and compressive behavior of anisotropic porous titanium for human trabecular bone implant applications.

PubMed

Li, Fuping; Li, Jinshan; Xu, Guangsheng; Liu, Gejun; Kou, Hongchao; Zhou, Lian

2015-06-01

Porous titanium with average pore size of 100-650 μm and porosity of 30-70% was fabricated by diffusion bonding of titanium meshes. Pore structure was characterized by Micro-CT scan and SEM. Compressive behavior of porous titanium in the out-of-plane direction was studied. The effect of porosity and pore size on the compressive properties was also discussed based on the deformation mode. The results reveal that the fabrication process can control the porosity precisely. The average pore size of porous titanium can be tailored by adjusting the pore size of titanium meshes. The fabricated porous titanium possesses an anisotropic structure with square pores in the in-plane direction and elongated pores in the out-of-plane direction. The compressive Young's modulus and yield stress are in the range of 1-7.5 GPa and 10-110 MPa, respectively. The dominant compressive deformation mode is buckling of mesh wires, but some uncoordinated buckling is present in porous titanium with lower porosity. Relationship between compressive properties and porosity conforms well to the Gibson-Ashby model. The effect of pore size on compressive properties is fundamentally ascribed to the aspect ratio of titanium meshes. Porous titanium with 60-70% porosity has potential for trabecular bone implant applications. Copyright © 2015 Elsevier Ltd. All rights reserved.

Synthesis and characterization of pore size-tunable magnetic mesoporous silica nanoparticles.

PubMed

Zhang, Jixi; Li, Xu; Rosenholm, Jessica M; Gu, Hong-chen

2011-09-01

Magnetic mesoporous silica nanoparticles (M-MSNs) are emerging as one of the most appealing candidates for theranostic carriers. Herein, a simple synthesis method of M-MSNs with a single Fe(3)O(4) nanocrystal core and a mesoporous shell with radially aligned pores was elaborated using tetraethyl orthosilicate (TEOS) as silica source, cationic surfactant CTAB as template, and 1,3,5-triisopropylbenzene (TMB)/decane as pore swelling agents. Due to the special localization of TMB during the synthesis process, the pore size was increased with added TMB amount within a limited range, while further employment of TMB lead to severe particle coalescence and not well-developed pore structure. On the other hand, when a proper amount of decane was jointly incorporated with limited amounts of TMB, effective pore expansion of M-MSNs similar to that of analogous mesoporous silica nanoparticles was realized. The resultant M-MSN materials possessed smaller particle size (about 40-70 nm in diameter), tunable pore sizes (3.8-6.1 nm), high surface areas (700-1100 m(2)/g), and large pore volumes (0.44-1.54 cm(3)/g). We also demonstrate their high potential in conventional DNA loading. Maximum loading capacity of salmon sperm DNA (375 mg/g) was obtained by the use of the M-MSN sample with the largest pore size of 6.1 nm. Copyright © 2011 Elsevier Inc. All rights reserved.

Drug release through liposome pores.

PubMed

Dan, Nily

2015-02-01

Electrical, ultrasound and other types of external fields are known to induce the formation of pores in cellular and model membranes. This paper examines drug release through field induced liposome pores using Monte Carlo simulations. We find that drug release rates vary as a function of pore size and spacing, as well as the overall fraction of surface area covered by pores: The rate of release from liposomes is found to increase rapidly with pore surface coverage, approaching that of the fully ruptured liposome at fractional pore areas. For a given pore surface coverage, the pore size affects the release rate in the limit of low coverage, but not when the pores cover a relatively high fraction of the liposome surface area. On the other hand, for a given pore size and surface coverage, the distribution of pores significantly affects the release in the limit of high surface coverage: The rate of release from a liposome covered with a regularly spaced array of pores is, in this limit, higher than the release rate from (most) systems where the pores are distributed randomly on the liposome surface. In contrast, there is little effect of the pore distribution on release when the pore surface coverage is low. The simulation results are in good agreement with the predictions of detailed diffusion models. Copyright © 2014 Elsevier B.V. All rights reserved.

Confinement Correction to Mercury Intrusion Capillary Pressure of Shale Nanopores

PubMed Central

Wang, Sen; Javadpour, Farzam; Feng, Qihong

2016-01-01

We optimized potential parameters in a molecular dynamics model to reproduce the experimental contact angle of a macroscopic mercury droplet on graphite. With the tuned potential, we studied the effects of pore size, geometry, and temperature on the wetting of mercury droplets confined in organic-rich shale nanopores. The contact angle of mercury in a circular pore increases exponentially as pore size decreases. In conjunction with the curvature-dependent surface tension of liquid droplets predicted from a theoretical model, we proposed a technique to correct the common interpretation procedure of mercury intrusion capillary pressure (MICP) measurement for nanoporous material such as shale. Considering the variation of contact angle and surface tension with pore size improves the agreement between MICP and adsorption-derived pore size distribution, especially for pores having a radius smaller than 5 nm. The relative error produced in ignoring these effects could be as high as 44%—samples that contain smaller pores deviate more. We also explored the impacts of pore size and temperature on the surface tension and contact angle of water/vapor and oil/gas systems, by which the capillary pressure of water/oil/gas in shale can be obtained from MICP. This information is fundamental to understanding multiphase flow behavior in shale systems. PMID:26832445

1H and 2H NMR studies of benzene confined in porous solids: melting point depression and pore size distribution.

PubMed

Aksnes, D W; Kimtys, L

2004-01-01

The pore size distributions of four controlled pore glasses and three silica gels with nominal diameters in the range 4-24 nm were determined by measuring the 1H and 2H NMR signals from the non-frozen fraction of confined benzene and perdeuterated benzene as a function of temperature, in steps of ca. 0.1-1 K. The liquid and solid components of the adsorbate were distinguished, on the basis of the spin-spin relaxation time T2, by employing a spin-echo sequence. The experimental intensity curves of the liquid component are well represented by a sum of two error functions. The mean melting point depression of benzene and perdeuterated benzene confined in the four controlled pore glasses, with pore radius R, follows the simplified Gibbs-Thompson equation DeltaT=kp/R with a kp value of 44 K nm. As expected, the kp value mainly determines the position of the pore size distribution curve, i.e., the mean pore radius, while the transition width determines the shape of the pore size distribution curve. The excellent agreement between the results from the 1H and 2H measurements shows that the effect of the background absorption from protons in physisorbed water and silanol groups is negligible under the experimental conditions used. The overall pore size distributions determined by NMR are in reasonable agreement with the results specified by the manufacturer, or measured by us using the N2 sorption technique. The NMR method, which is complementary to the conventional gas sorption method, is particularly appropriate for studying pore sizes in the mesoporous range.

Fabrication and characterization of poly(propylene fumarate) scaffolds with controlled pore structures using 3-dimensional printing and injection molding.

PubMed

Lee, Kee-Won; Wang, Shanfeng; Lu, Lichun; Jabbari, Esmaiel; Currier, Bradford L; Yaszemski, Michael J

2006-10-01

Poly(propylene fumarate) (PPF) is an injectable, biodegradable polymer that has been used for fabricating preformed scaffolds in tissue engineering applications because of in situ crosslinking characteristics. Aiming for understanding the effects of pore structure parameters on bone tissue ingrowth, 3-dimensional (3D) PPF scaffolds with controlled pore architecture have been produced in this study from computer-aided design (CAD) models. We have created original scaffold models with 3 pore sizes (300, 600, and 900 microm) and randomly closed 0%, 10%, 20%, or 30% of total pores from the original models in 3 planes. PPF scaffolds were fabricated by a series steps involving 3D printing of support/build constructs, dissolving build materials, injecting PPF, and dissolving support materials. To investigate the effects of controlled pore size and interconnectivity on scaffolds, we compared the porosities between the models and PPF scaffolds fabricated thereby, examined pore morphologies in surface and cross-section using scanning electron microscopy, and measured permeability using the falling head conductivity test. The thermal properties of the resulting scaffolds as well as uncrosslinked PPF were determined by differential scanning calorimetry and thermogravimetric analysis. Average pore sizes and pore shapes of PPF scaffolds with 600- and 900-microm pores were similar to those of CAD models, but they depended on directions in those with 300-microm pores. Porosity and permeability of PPF scaffolds decreased as the number of closed pores in original models increased, particularly when the pore size was 300 microm as the result of low porosity and pore occlusion. These results show that 3D printing and injection molding technique can be applied to crosslinkable polymers to fabricate 3D porous scaffolds with controlled pore structures, porosity, and permeability using their CAD models.

Understanding the role of pore size homogeneity in the water transport through graphene layers.

PubMed

Su, Jiaye; Zhao, Yunzhen; Fang, Chang

2018-06-01

Graphene is a versatile 2D material and attracts an increasing amount of attention from a broad scientific community, including novel nanofluidic devices. In this work, we use molecular dynamics simulations to study the pressure driven water transport through graphene layers, focusing on the pore size homogeneity, realized by the arrangement of two pore sizes. For a given layer number, we find that water flux exhibits an excellent linear behavior with pressure, in agreement with the prediction of the Hagen-Poiseuille equation. Interestingly, the flux for concentrated pore size distribution is around two times larger than that of a uniform distribution. More surprisingly, under a given pressure, the water flux changes in an opposite way for these two distributions, where the flux ratio almost increases linearly with the layer number. For the largest layer number, more distributions suggest the same conclusion that higher water flux can be attained for more concentrated pore size distributions. Similar differences for the water translocation time and occupancy are also identified. The major reason for these results should clearly be due to the hydrogen bond and density profile distributions. Our results are helpful to delineate the exquisite role of pore size homogeneity, and should have great implications for the design of high flux nanofluidic devices and inversely the detection of pore structures.

Understanding the role of pore size homogeneity in the water transport through graphene layers

NASA Astrophysics Data System (ADS)

Su, Jiaye; Zhao, Yunzhen; Fang, Chang

2018-06-01

Graphene is a versatile 2D material and attracts an increasing amount of attention from a broad scientific community, including novel nanofluidic devices. In this work, we use molecular dynamics simulations to study the pressure driven water transport through graphene layers, focusing on the pore size homogeneity, realized by the arrangement of two pore sizes. For a given layer number, we find that water flux exhibits an excellent linear behavior with pressure, in agreement with the prediction of the Hagen–Poiseuille equation. Interestingly, the flux for concentrated pore size distribution is around two times larger than that of a uniform distribution. More surprisingly, under a given pressure, the water flux changes in an opposite way for these two distributions, where the flux ratio almost increases linearly with the layer number. For the largest layer number, more distributions suggest the same conclusion that higher water flux can be attained for more concentrated pore size distributions. Similar differences for the water translocation time and occupancy are also identified. The major reason for these results should clearly be due to the hydrogen bond and density profile distributions. Our results are helpful to delineate the exquisite role of pore size homogeneity, and should have great implications for the design of high flux nanofluidic devices and inversely the detection of pore structures.

A general diagram for estimating pore size of ultrafiltration and reverse osmosis membranes

NASA Technical Reports Server (NTRS)

Sarbolouki, M. N.

1982-01-01

A slit sieve model has been used to develop a general correlation between the average pore size of the upstream surface of a membrane and the molecular weight of the solute which it retains by better than 80%. The pore size is determined by means of the correlation using the high retention data from an ultrafiltration (UF) or a reverse osmosis (RO) experiment. The pore population density can also be calculated from the flux data via appropriate equations.

Effects of Porous Polystyrene Resin Parameters on Candida antarctica Lipase B Adsorption, Distribution, and Polyester Synthesis Activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen,B.; Miller, M.; Gross, R.

2007-01-01

Polystyrene resins with varied particle sizes (35 to 350-600 {mu}m) and pore diameters (300-1000 {angstrom}) were employed to study the effects of immobilization resin particle size and pore diameter on Candida antarctica Lipase B (CALB) loading, distribution within resins, fraction of active sites, and catalytic properties for polyester synthesis. CALB adsorbed rapidly (saturation time {<=}4 min) for particle sizes 120 {mu}m (pore size = 300 {angstrom}). Infrared microspectroscopy showed that CALB forms protein loading fronts regardless of resin particle size at similar enzyme loadings ({approx}8%). From the IR images, the fractions of total surface area available to the enzyme aremore » 21, 33, 35, 37, and 88% for particle sizes 350-600, 120, 75, 35 {mu}m (pore size 300 {angstrom}), and 35 {mu}m (pore size 1000 {angstrom}), respectively. Titration with methyl p-nitrophenyl n-hexylphosphate (MNPHP) showed that the fraction of active CALB molecules adsorbed onto resins was {approx}60%. The fraction of active CALB molecules was invariable as a function of resin particle and pore size. At {approx}8% (w/w) CALB loading, by increasing the immobilization support pore diameter from 300 to 1000 {angstrom}, the turnover frequency (TOF) of {var_epsilon}-caprolactone ({var_epsilon}-CL) to polyester increased from 12.4 to 28.2 s{sup -1}. However, the {var_epsilon}-CL conversion rate was not influenced by changes in resin particle size. Similar trends were observed for condensation polymerizations between 1,8-octanediol and adipic acid. The results herein are compared to those obtained with a similar series of methyl methacrylate resins, where variations in particle size largely affected CALB distribution within resins and catalyst activity for polyester synthesis.« less

Micelle-Template Synthesis of Nitrogen-Doped Mesoporous Graphene as an Efficient Metal-Free Electrocatalyst for Hydrogen Production

NASA Astrophysics Data System (ADS)

Huang, Xiaodan; Zhao, Yufei; Ao, Zhimin; Wang, Guoxiu

2014-12-01

Synthesis of mesoporous graphene materials by soft-template methods remains a great challenge, owing to the poor self-assembly capability of precursors and the severe agglomeration of graphene nanosheets. Herein, a micelle-template strategy to prepare porous graphene materials with controllable mesopores, high specific surface areas and large pore volumes is reported. By fine-tuning the synthesis parameters, the pore sizes of mesoporous graphene can be rationally controlled. Nitrogen heteroatom doping is found to remarkably render electrocatalytic properties towards hydrogen evolution reactions as a highly efficient metal-free catalyst. The synthesis strategy and the demonstration of highly efficient catalytic effect provide benchmarks for preparing well-defined mesoporous graphene materials for energy production applications.

Micelle-template synthesis of nitrogen-doped mesoporous graphene as an efficient metal-free electrocatalyst for hydrogen production.

PubMed

Huang, Xiaodan; Zhao, Yufei; Ao, Zhimin; Wang, Guoxiu

2014-12-19

Synthesis of mesoporous graphene materials by soft-template methods remains a great challenge, owing to the poor self-assembly capability of precursors and the severe agglomeration of graphene nanosheets. Herein, a micelle-template strategy to prepare porous graphene materials with controllable mesopores, high specific surface areas and large pore volumes is reported. By fine-tuning the synthesis parameters, the pore sizes of mesoporous graphene can be rationally controlled. Nitrogen heteroatom doping is found to remarkably render electrocatalytic properties towards hydrogen evolution reactions as a highly efficient metal-free catalyst. The synthesis strategy and the demonstration of highly efficient catalytic effect provide benchmarks for preparing well-defined mesoporous graphene materials for energy production applications.

Micelle-Template Synthesis of Nitrogen-Doped Mesoporous Graphene as an Efficient Metal-Free Electrocatalyst for Hydrogen Production

PubMed Central

Huang, Xiaodan; Zhao, Yufei; Ao, Zhimin; Wang, Guoxiu

2014-01-01

Synthesis of mesoporous graphene materials by soft-template methods remains a great challenge, owing to the poor self-assembly capability of precursors and the severe agglomeration of graphene nanosheets. Herein, a micelle-template strategy to prepare porous graphene materials with controllable mesopores, high specific surface areas and large pore volumes is reported. By fine-tuning the synthesis parameters, the pore sizes of mesoporous graphene can be rationally controlled. Nitrogen heteroatom doping is found to remarkably render electrocatalytic properties towards hydrogen evolution reactions as a highly efficient metal-free catalyst. The synthesis strategy and the demonstration of highly efficient catalytic effect provide benchmarks for preparing well-defined mesoporous graphene materials for energy production applications. PMID:25523276

Physics Applied to Oil and Gas Exploration

NASA Astrophysics Data System (ADS)

Schwartz, Larry

2002-03-01

Problems involving transport in porous media are of interest throughout the fields of petroleum exploration and environmental monitoring and remediation. The systems being studied can vary in size from centimeter scale rock or soil samples to kilometer scale reservoirs and aquifers. Clearly, the smaller the sample the more easily can the medium's structure and composition be characterized, and the better defined are the associated experimental and theoretical modeling problems. The study of transport in such geological systems is then similar to corresponding problems in the study of other heterogeneous systems such as polymer gels, catalytic beds and cementitious materials. The defining characteristic of porous media is that they are comprised of two percolating interconnected channels, the solid and pore networks. Transport processes of interest in such systems typically involve the flow of electrical current, viscous fluids or fine grained particles. A closely related phenomena, nuclear magnetic resonance (NMR), is controlled by diffusion in the pore network. Also of interest is the highly non-linear character of the stress-strain response of granular porous media. We will review the development of two and three dimensional model porous media, and will outline the calculation of their physical properties. We will also discuss the direct measurement of the pore structure by synchrotron X-ray microtomography.

Diurnal hydrological physicochemical controls and sampling methods for minor and trace elements in an Alpine glacial hydrological system

NASA Astrophysics Data System (ADS)

Mitchell, Andrew C.; Brown, Giles H.

2007-01-01

SummaryWe present diurnal (i) 0.45 and 0.1 μm pore-size filtered and (ii) operationally defined labile particulate-associated major, minor and trace element concentrations and fluxes in glacial outflow waters draining Haut Glacier d'Arolla, Switzerland. We use speciation modelling (PHREEQCi) and water-suspended sediment interaction experiments are utilised under conditions analogous to the subglacial channellised hydrological system, in order to assess controls on, and the most suitable sampling methods to investigate short-term variations in the mode of major, minor and trace element species export from a glacierised headwater catchment. 0.45 μm pore-size filtered major ions, Sr and U are exported in glacial outflow waters predominately as mobile monovalent or divalent ions or as carbonate complexes, and are controlled by hydrological variations over diurnal cycles, exhibiting an inverse concentration with increasing meltwater discharge. Conversely, 0.45 μm pore-size filtered concentrations of most minor and trace elements ( e.g. Fe, Mn, Co, Ba and Pb) exhibit variations that are not strongly inter-correlated with meltwater discharge or suspended sediment concentrations (SSC) over diurnal periods. The use of 0.45 and 0.1 μm pore-size filter membranes indicates that significant colloidal material is not passing through the 0.45 μm pore-size filters, and these unsystematic variations are not a result of colloid measurement. Speciation modelling applied to meltwaters and observations during water-rock interaction experiments suggest that these unsystematic temporal variations reflect physicochemical controls. This includes sorption, and the oversaturation and precipitation of Fe and Al (oxi)hydroxides, and the co-precipitation of other species. Diurnal pH variations appear important in controlling such short-term physicochemical controls, which limits such species use for hydrological investigations. The percentage of total elemental fluxes exported as the labile particulate-associated flux (%PAF) for each minor and trace element changes dramatically between and during the diurnal cycles, reflecting species-specific sensitivity to hydrological and physicochemical controls. Hydrological interpretations of hydrochemical data must be made carefully when using chemical determinations by ICP-MS, since we demonstrate that measurements will comprise of any material that passes through the filter. This can lead to higher concentration measurements than if determined by ion chromatography, which measures truly ionic dissolved species.

Influence of pore structure on compressive strength of cement mortar.

PubMed

Zhao, Haitao; Xiao, Qi; Huang, Donghui; Zhang, Shiping

2014-01-01

This paper describes an experimental investigation into the pore structure of cement mortar using mercury porosimeter. Ordinary Portland cement, manufactured sand, and natural sand were used. The porosity of the manufactured sand mortar is higher than that of natural sand at the same mix proportion; on the contrary, the probable pore size and threshold radius of manufactured sand mortar are finer. Besides, the probable pore size and threshold radius increased with increasing water to cement ratio and sand to cement ratio. In addition, the existing models of pore size distribution of cement-based materials have been reviewed and compared with test results in this paper. Finally, the extended Bhattacharjee model was built to examine the relationship between compressive strength and pore structure.

Influence of Pore Structure on Compressive Strength of Cement Mortar

PubMed Central

Zhao, Haitao; Xiao, Qi; Huang, Donghui

2014-01-01

This paper describes an experimental investigation into the pore structure of cement mortar using mercury porosimeter. Ordinary Portland cement, manufactured sand, and natural sand were used. The porosity of the manufactured sand mortar is higher than that of natural sand at the same mix proportion; on the contrary, the probable pore size and threshold radius of manufactured sand mortar are finer. Besides, the probable pore size and threshold radius increased with increasing water to cement ratio and sand to cement ratio. In addition, the existing models of pore size distribution of cement-based materials have been reviewed and compared with test results in this paper. Finally, the extended Bhattacharjee model was built to examine the relationship between compressive strength and pore structure. PMID:24757414

Single-Crystalline, Nanoporous Gallium Nitride Films With Fine Tuning of Pore Size for Stem Cell Engineering.

PubMed

Han, Lin; Zhou, Jing; Sun, Yubing; Zhang, Yu; Han, Jung; Fu, Jianping; Fan, Rong

2014-11-01

Single-crystalline nanoporous gallium nitride (GaN) thin films were fabricated with the pore size readily tunable in 20-100 nm. Uniform adhesion and spreading of human mesenchymal stem cells (hMSCs) seeded on these thin films peak on the surface with pore size of 30 nm. Substantial cell elongation emerges as pore size increases to ∼80 nm. The osteogenic differentiation of hMSCs occurs preferentially on the films with 30 nm sized nanopores, which is correlated with the optimum condition for cell spreading, which suggests that adhesion, spreading, and stem cell differentiation are interlinked and might be coregulated by nanotopography.

Efficiency of Sampling and Analysis of Asbestos Fibers on Filter Media: Implications for Exposure Assessment

EPA Science Inventory

To measure airborne asbestos and other fibers, an air sample must represent the actual number and size of fibers. Typically, mixed cellulose ester (MCE, 0.45 or 0.8 µm pore size) and to a much lesser extent, capillary-pore polycarbonate (PC, 0.4 µm pore size) membrane filters are...

Effects of Pore Size on the Osteoconductivity and Mechanical Properties of Calcium Phosphate Cement in a Rabbit Model.

PubMed

Zhao, Yi-Nan; Fan, Jun-Jun; Li, Zhi-Quan; Liu, Yan-Wu; Wu, Yao-Ping; Liu, Jian

2017-02-01

Calcium phosphate cement (CPC) porous scaffold is widely used as a suitable bone substitute to repair bone defect, but the optimal pore size is unclear yet. The current study aimed to evaluate the effect of different pore sizes on the processing of bone formation in repairing segmental bone defect of rabbits using CPC porous scaffolds. Three kinds of CPC porous scaffolds with 5 mm diameters and 12 mm length were prepared with the same porosity but different pore sizes (Group A: 200-300 µm, Group B: 300-450 µm, Group C: 450-600 µm, respectively). Twelve millimeter segmental bone defects were created in the middle of the radius bone and filled with different kinds of CPC cylindrical scaffolds. After 4, 12, and 24 weeks, alkaline phosphatase (ALP), histological assessment, and mechanical properties evaluation were performed in all three groups. After 4 weeks, ALP activity increased in all groups but was highest in Group A with smallest pore size. The new bone formation within the scaffolds was not obvious in all groups. After 12 weeks, the new bone formation within the scaffolds was obvious in each group and highest in Group A. At 24 weeks, no significant difference in new bone formation was observed among different groups. Besides the osteoconductive effect, Group A with smallest pore size also had the best mechanical properties in vivo at 12 weeks. We demonstrate that pore size has a significant effect on the osteoconductivity and mechanical properties of calcium phosphate cement porous scaffold in vivo. Small pore size favors the bone formation in the early stage and may be more suitable for repairing segmental bone defect in vivo. © 2016 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Fabrication of Aluminum Foams with Small Pore Size by Melt Foaming Method

NASA Astrophysics Data System (ADS)

Cheng, Ying; Li, Yanxiang; Chen, Xiang; Shi, Tong; Liu, Zhiyong; Wang, Ningzhen

2017-04-01

This article introduces an improvement to the fabrication of aluminum foams with small pore size by melt foaming method. Before added to the melt, the foaming agent (titanium hydride) was pretreated in two steps. It firstly went through the traditional pre-oxidation treatment, which delayed the decomposition of titanium hydride and made sure the dispersion stage was controllable. Then such pre-oxidized titanium hydride powder was mixed with copper powder in a planetary ball mill. This treatment can not only increase the number of foaming agent particles and make them easier to disperse in the melt, which helps to increase the number of pores, but also reduce the amount of hydrogen released in the foaming stage. Therefore, the pore size could be decreased. Using such a ball-milled foaming agent in melt foaming method, aluminum foams with small pore size (average size of 1.6 mm) were successfully fabricated.

Mesoporous Akaganeite of Adjustable Pore Size Synthesized using Mixed Templates

NASA Astrophysics Data System (ADS)

Zhang, Y.; Ge, D. L.; Ren, H. P.; Fan, Y. J.; Wu, L. M.; Sun, Z. X.

2017-12-01

Mesoporous akaganeite with large and adjustable pore size was synthesized through a co-template method, which was achieved by the combined interaction between PEG2000 and alkyl amines with different lengths of the straight carbon chain. The characterized results indicate that the synthesized samples show comparatively narrow BJH pore size distributions and centered at 14.3 nm when PEG and HEPA was used, and it could be enlarged to 16.8 and 19.4 nm respectively through changing the alkyl amines to DDA and HDA. Meanwhile, all the synthesized akaganeite possess relativity high specific surface area ranging from 183 to 281 m2/g and high total pore volume of 0.98 to 1.5 cm3/g. A possible mechanism leading to the pore size changing was also proposed.

Removal of bacteriophages with different surface charges by diverse ceramic membrane materials in pilot spiking tests.

PubMed

Hambsch, B; Bösl, M; Eberhagen, I; Müller, U

2012-01-01

This study examines mechanisms for removal of bacteriophages (MS2 and phiX174) by ceramic membranes without application of flocculants. The ceramic membranes considered included ultra- and microfiltration membranes of different materials. Phages were spiked into the feed water in pilot scale tests in a waterworks. The membranes with pore sizes of 10 nm provided a 2.5-4.0 log removal of the phages. For pore sizes of 50 nm, the log removal dropped to 0.96-1.8. The membrane with a pore size of 200 nm did not remove phages. So, the removal of both MS2- and phiX174-phages depended on the pore size of the membranes. But apart from pore size also other factors influence the removal of phages. Removal was 0.5-0.9 log higher for MS2-phages compared with phiX174-phages. Size exclusion seems to be the major but not the only mechanism which influences the efficiency of phage removal by ceramic membranes.

Multiple Approaches to Characterizing Nano-Pore Structure of Barnett Shale

NASA Astrophysics Data System (ADS)

Hu, Q.; Gao, Z.; Ewing, R. P.; Dultz, S.; Kaufmann, J.; Hamamoto, S.; Webber, B.; Ding, M.

2013-12-01

Microscopic characteristics of porous media - pore shape, pore-size distribution, and pore connectivity - control fluid flow and mass transport. This presentation discusses various approaches to investigating nano-pore structure of Barnett shale, with its implications in gas production behavior. The innovative approaches include imbibition, tracer diffusion, edge-accessible porosity, porosimetry (mercury intrusion porosimetry, nitrogen and water vapor sorption isotherms, and nuclear magnetic resonance cyroporometry), and imaging (Wood's metal impregnation followed with laser ablation-inductively coupled plasma-mass spectrometry, focused ion beam/scanning electron microscopy, and small angle neutron scattering). Results show that the shale pores are predominantly in the nm size range, with measured median pore-throat diameters about 5 nm. But small pore size is not the major contributor to low gas recovery; rather, the low mass diffusivity appears to be caused by low pore connectivity of Barnett shale. Chemical diffusion in sparsely-connected pore spaces is not well described by classical Fickian behavior; anomalous behavior is suggested by percolation theory, and confirmed by results of imbibition and diffusion tests. Our evolving complementary approaches, with their several advantages and disadvantages, provide a rich toolbox for tackling the nano-pore structure characteristics of shales and other natural rocks.

Synthesis, characterization, and evaluation of a superficially porous particle with unique, elongated pore channels normal to the surface.

PubMed

Wei, Ta-Chen; Mack, Anne; Chen, Wu; Liu, Jia; Dittmann, Monika; Wang, Xiaoli; Barber, William E

2016-04-01

In recent years, superficially porous particles (SPPs) have drawn great interest because of their special particle characteristics and improvement in separation efficiency. Superficially porous particles are currently manufactured by adding silica nanoparticles onto solid cores using either a multistep multilayer process or one-step coacervation process. The pore size is mainly controlled by the size of the silica nanoparticles and the tortuous pore channel geometry is determined by how those nanoparticles randomly aggregate. Such tortuous pore structure is also similar to that of all totally porous particles used in HPLC today. In this article, we report on the development of a next generation superficially porous particle with a unique pore structure that includes a thinner shell thickness and ordered pore channels oriented normal to the particle surface. The method of making the new superficially porous particles is a process called pseudomorphic transformation (PMT), which is a form of micelle templating. Porosity is no longer controlled by randomly aggregated nanoparticles but rather by micelles that have an ordered liquid crystal structure. The new particle possesses many advantages such as a narrower particle size distribution, thinner porous layer with high surface area and, most importantly, highly ordered, non-tortuous pore channels oriented normal to the particle surface. This PMT process has been applied to make 1.8-5.1μm SPPs with pore size controlled around 75Å and surface area around 100m(2)/g. All particles with different sizes show the same unique pore structure with tunable pore size and shell thickness. The impact of the novel pore structure on the performance of these particles is characterized by measuring van Deemter curves and constructing kinetic plots. Reduced plate heights as low as 1.0 have been achieved on conventional LC instruments. This indicates higher efficiency of such particles compared to conventional totally porous and superficially porous particles. Copyright © 2016 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yanping Guo; Abhishek Yadav; Tanju Karanfil

Adsorption of trichloroethylene (TCE) and atrazine, two synthetic organic contaminants (SOCs) having different optimum adsorption pore regions, by four activated carbons and an activated carbon fiber (ACF) was examined. Adsorbents included two coconut-shell based granular activated carbons (GACs), two coal-based GACs (F400 and HD4000) and a phenol formaldehyde-based activated carbon fiber. The selected adsorbents had a wide range of pore size distributions but similar surface acidity and hydrophobicity. Single solute and preloading (with a dissolved organic matter (DOM)) isotherms were performed. Single solute adsorption results showed that (i) the adsorbents having higher amounts of pores with sizes about the dimensionsmore » of the adsorbate molecules exhibited higher uptakes, (ii) there were some pore structure characteristics, which were not completely captured by pore size distribution analysis, that also affected the adsorption, and (iii) the BET surface area and total pore volume were not the primary factors controlling the adsorption of SOCs. The preloading isotherm results showed that for TCE adsorbing primarily in pores <10 {angstrom}, the highly microporous ACF and GACs, acting like molecular sieves, exhibited the highest uptakes. For atrazine with an optimum adsorption pore region of 10-20 {angstrom}, which overlaps with the adsorption region of some DOM components, the GACs with a broad pore size distribution and high pore volumes in the 10-20 {angstrom} region had the least impact of DOM on the adsorption. 25 refs., 3 figs., 3 tabs.« less

Fabrication of biocompatible and efficient antimicrobial porous polymer surfaces by the Breath Figures approach.

PubMed

Vargas-Alfredo, Nelson; Martínez-Campos, Enrique; Santos-Coquillat, Ana; Dorronsoro, Ane; Cortajarena, Aitziber L; Del Campo, Adolfo; Rodríguez-Hernández, Juan

2018-03-01

We designed and fabricated highly efficient and selective antibacterial substrates, i.e. surface non-cytotoxic against mammalian cells but exhibiting strong antibacterial activity. For that purpose, microporous substrates (pore sizes in the range of 3-5 μm) were fabricated using the Breath Figures approach (BFs). These substrates have additionally a defined chemical composition in the pore cavity (herein either a poly(acrylic acid) or the antimicrobial peptide Nisin) while the composition of the rest of the surface is identical to the polymer matrix. As a result, considering the differences in size of bacteria (1-4 μm) in comparison to mammalian cells (above 10 µm) the bacteria were able to enter in contact with the inner part of the pores where the antimicrobial functionality has been placed. On the opposite, mammalian cells remain in contact with the top surface thus preventing cytotoxic effects and enhancing the biocompatibility of the substrates. The resulting antimicrobial surfaces were exposed to Staphylococcus aureus as a model bacteria and murine endothelial C166-GFP cells. Superior antibacterial performance while maintaining an excellent biocompatibility was obtained by those surfaces prepared using PAA while no evidence of significant antibacterial activity was observed at those surfaces prepared using Nisin. Copyright © 2017 Elsevier Inc. All rights reserved.

Evolution of the pore structure during the early stages of the alkali-activation reaction: An in situ small-angle neutron scattering investigation

DOE PAGES

White, Claire E.; Olds, Daniel P.; Hartl, Monika; ...

2017-02-01

The long-term durability of cement-based materials is influenced by the pore structure and associated permeability at the sub-micrometre length scale. With the emergence of new types of sustainable cements in recent decades, there is a pressing need to be able to predict the durability of these new materials, and therefore nondestructive experimental techniques capable of characterizing the evolution of the pore structure are increasingly crucial for investigating cement durability. Here, small-angle neutron scattering is used to analyze the evolution of the pore structure in alkali-activated materials over the initial 24 h of reaction in order to assess the characteristic poremore » sizes that emerge during these short time scales. By using a unified fitting approach for data modeling, information on the pore size and surface roughness is obtained for a variety of precursor chemistries and morphologies (metakaolin- and slag-based pastes). Furthermore, the impact of activator chemistry is elucidatedviathe analysis of pastes synthesized using hydroxide- and silicate-based activators. It is found that the main aspect influencing the size of pores that are accessible using small-angle neutron scattering analysis (approximately 10–500 Å in diameter) is the availability of free silica in the activating solution, which leads to a more refined pore structure with smaller average pore size. Furthermore, as the reaction progresses the gel pores visible using this scattering technique are seen to increase in size.« less

Resolving structural influences on water-retention properties of alluvial deposits

USGS Publications Warehouse

Winfield, K.A.; Nimmo, J.R.; Izbicki, J.A.; Martin, P.M.

2006-01-01

With the goal of improving property-transfer model (PTM) predictions of unsaturated hydraulic properties, we investigated the influence of sedimentary structure, defined as particle arrangement during deposition, on laboratory-measured water retention (water content vs. potential [??(??)]) of 10 undisturbed core samples from alluvial deposits in the western Mojave Desert, California. The samples were classified as having fluvial or debris-flow structure based on observed stratification and measured spread of particle-size distribution. The ??(??) data were fit with the Rossi-Nimmo junction model, representing water retention with three parameters: the maximum water content (??max), the ??-scaling parameter (??o), and the shape parameter (??). We examined trends between these hydraulic parameters and bulk physical properties, both textural - geometric mean, Mg, and geometric standard deviation, ??g, of particle diameter - and structural - bulk density, ??b, the fraction of unfilled pore space at natural saturation, Ae, and porosity-based randomness index, ??s, defined as the excess of total porosity over 0.3. Structural parameters ??s and Ae were greater for fluvial samples, indicating greater structural pore space and a possibly broader pore-size distribution associated with a more systematic arrangement of particles. Multiple linear regression analysis and Mallow's Cp statistic identified combinations of textural and structural parameters for the most useful predictive models: for ??max, including Ae, ??s, and ??g, and for both ??o and ??, including only textural parameters, although use of Ae can somewhat improve ??o predictions. Textural properties can explain most of the sample-to-sample variation in ??(??) independent of deposit type, but inclusion of the simple structural indicators Ae and ??s can improve PTM predictions, especially for the wettest part of the ??(??) curve. ?? Soil Science Society of America.

SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy

PubMed Central

Nikolaus, Joerg; Karatekin, Erdem

2016-01-01

In the ubiquitous process of membrane fusion the opening of a fusion pore establishes the first connection between two formerly separate compartments. During neurotransmitter or hormone release via exocytosis, the fusion pore can transiently open and close repeatedly, regulating cargo release kinetics. Pore dynamics also determine the mode of vesicle recycling; irreversible resealing results in transient, "kiss-and-run" fusion, whereas dilation leads to full fusion. To better understand what factors govern pore dynamics, we developed an assay to monitor membrane fusion using polarized total internal reflection fluorescence (TIRF) microscopy with single molecule sensitivity and ~15 msec time resolution in a biochemically well-defined in vitro system. Fusion of fluorescently labeled small unilamellar vesicles containing v-SNARE proteins (v-SUVs) with a planar bilayer bearing t-SNAREs, supported on a soft polymer cushion (t-SBL, t-supported bilayer), is monitored. The assay uses microfluidic flow channels that ensure minimal sample consumption while supplying a constant density of SUVs. Exploiting the rapid signal enhancement upon transfer of lipid labels from the SUV to the SBL during fusion, kinetics of lipid dye transfer is monitored. The sensitivity of TIRF microscopy allows tracking single fluorescent lipid labels, from which lipid diffusivity and SUV size can be deduced for every fusion event. Lipid dye release times can be much longer than expected for unimpeded passage through permanently open pores. Using a model that assumes retardation of lipid release is due to pore flickering, a pore "openness", the fraction of time the pore remains open during fusion, can be estimated. A soluble marker can be encapsulated in the SUVs for simultaneous monitoring of lipid and soluble cargo release. Such measurements indicate some pores may reseal after losing a fraction of the soluble cargo. PMID:27585113

Impact of pore size variability and network coupling on electrokinetic transport in porous media

NASA Astrophysics Data System (ADS)

Alizadeh, Shima; Bazant, Martin Z.; Mani, Ali

2016-11-01

We have developed and validated an efficient and robust computational model to study the coupled fluid and ion transport through electrokinetic porous media, which are exposed to external gradients of pressure, electric potential, and concentration. In our approach a porous media is modeled as a network of many pores through which the transport is described by the coupled Poisson-Nernst-Planck-Stokes equations. When the pore sizes are random, the interactions between various modes of transport may provoke complexities such as concentration polarization shocks and internal flow circulations. These phenomena impact mixing and transport in various systems including deionization and filtration systems, supercapacitors, and lab-on-a-chip devices. In this work, we present simulations of massive networks of pores and we demonstrate the impact of pore size variation, and pore-pore coupling on the overall electrokinetic transport in porous media.

Effect of Pore Size, Morphology and Orientation on the Bulk Stiffness of a Porous Ti35Nb4Sn Alloy

NASA Astrophysics Data System (ADS)

Torres-Sanchez, Carmen; McLaughlin, John; Bonallo, Ross

2018-04-01

The metal foams of a titanium alloy were designed to study porosity as well as pore size and shape independently. These were manufactured using a powder metallurgy/space-holder technique that allowed a fine control of the pore size and morphology; and then characterized and tested against well-established models to predict a relationship between porosity, pore size and shape, and bulk stiffness. Among the typically used correlations, existing power-law models were found to be the best fit for the prediction of macropore morphology against compressive elastic moduli, outperforming other models such as exponential, polynomial or binomial. Other traditional models such as linear ones required of updated coefficients to become relevant to metal porous sintered macrostructures. The new coefficients reported in this study contribute toward a design tool that allows the tailoring of mechanical properties through porosity macrostructure. The results show that, for the same porosity range, pore shape and orientation have a significant effect on mechanical performance and that they can be predicted. Conversely, pore size has only a mild impact on bulk stiffness.

Gas permeability of ice-templated, unidirectional porous ceramics

NASA Astrophysics Data System (ADS)

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J.

2016-01-01

We investigate the gas flow behavior of unidirectional porous ceramics processed by ice-templating. The pore volume ranged between 54% and 72% and pore size between 2.9 ?m and 19.1 ?m. The maximum permeability (?? m?) was measured in samples with the highest total pore volume (72%) and pore size (19.1 ?m). However, we demonstrate that it is possible to achieve a similar permeability (?? m?) at 54% pore volume by modification of the pore shape. These results were compared with those reported and measured for isotropic porous materials processed by conventional techniques. In unidirectional porous materials tortuosity (?) is mainly controlled by pore size, unlike in isotropic porous structures where ? is linked to pore volume. Furthermore, we assessed the applicability of Ergun and capillary model in the prediction of permeability and we found that the capillary model accurately describes the gas flow behavior of unidirectional porous materials. Finally, we combined the permeability data obtained here with strength data for these materials to establish links between strength and permeability of ice-templated materials.

Synthesis and characterization of mesoporous ZnS with narrow size distribution of small pores

NASA Astrophysics Data System (ADS)

Nistor, L. C.; Mateescu, C. D.; Birjega, R.; Nistor, S. V.

2008-08-01

Pure, nanocrystalline cubic ZnS forming a stable mesoporous structure was synthesized at room temperature by a non-toxic surfactant-assisted liquid liquid reaction, in the 9.5 10.5 pH range of values. The appearance of an X-ray diffraction (XRD) peak in the region of very small angles (˜ 2°) reveals the presence of a porous material with a narrow pore size distribution, but with an irregular arrangement of the pores, a so-called worm hole or sponge-like material. The analysis of the wide angle XRD diffractograms shows the building blocks to be ZnS nanocrystals with cubic structure and average diameter of 2 nm. Transmission electron microscopy (TEM) investigations confirm the XRD results; ZnS crystallites of 2.5 nm with cubic (blende) structure are the building blocks of the pore walls with pore sizes from 1.9 to 2.5 nm, and a broader size distribution for samples with smaller pores. Textural measurements (N2 adsorption desorption isotherms) confirm the presence of mesoporous ZnS with a narrow range of small pore sizes. The relatively lower surface area of around 100 m2/g is attributed to some remaining organic molecules, which are filling the smallest pores. Their presence, confirmed by IR spectroscopy, seems to be responsible for the high stability of the resulting mesoporous ZnS as well.

Episodic Tremor and Slip Explained by Fluid-Enhanced Microfracturing and Sealing

NASA Astrophysics Data System (ADS)

Bernaudin, M.; Gueydan, F.

2018-04-01

Episodic tremor and slow-slip events at the deep extension of plate boundary faults illuminate seismic to aseismic processes around the brittle-ductile transition. These events occur in volumes characterized by overpressurized fluids and by near failure shear stress conditions. We present a new modeling approach based on a ductile grain size-sensitive rheology with microfracturing and sealing, which provides a mechanical and field-based explanation of such phenomena. We also model pore fluid pressure variation as a function of changes in porosity/permeability and strain rate-dependent fluid pumping. The fluid-enhanced dynamic evolution of microstructures defines cycles of ductile strain localization and implies increase in pore fluid pressure. We propose that slow-slip events are ductile processes related to transient strain localization, while nonvolcanic tremor corresponds to fracturing of the whole rock at the peak of pore fluid pressure. Our model shows that the availability of fluids and the efficiency of fluid pumping control the occurrence and the P-T conditions of episodic tremor and slip.

Metal oxide porous ceramic membranes with small pore sizes

DOEpatents

Anderson, Marc A.; Xu, Qunyin

1992-01-01

A method is disclosed for the production of metal oxide ceramic membranes of very small pore size. The process is particularly useful in the creation of titanium and other transition metal oxide membranes. The method utilizes a sol-gel process in which the rate of particle formation is controlled by substituting a relatively large alcohol in the metal alkoxide and by limiting the available water. Stable, transparent metal oxide ceramic membranes are created having a narrow distribution of pore size, with the pore diameter being manipulable in the range of 5 to 40 Angstroms.

Metal oxide porous ceramic membranes with small pore sizes

DOEpatents

Anderson, Marc A.; Xu, Qunyin

1991-01-01

A method is disclosed for the production of metal oxide ceramic membranes of very small pore size. The process is particularly useful in the creation of titanium and other transition metal oxide membranes. The method utilizes a sol-gel process in which the rate of particle formation is controlled by substituting a relatively large alcohol in the metal alkoxide and by limiting the available water. Stable, transparent metal oxide ceramic membranes are created having a narrow distribution of pore size, with the pore diameter being manipulable in the range of 5 to 40 Angstroms.

Multi-scale Pore Imaging Techniques to Characterise Heterogeneity Effects on Flow in Carbonate Rock

NASA Astrophysics Data System (ADS)

Shah, S. M.

2017-12-01

Digital rock analysis and pore-scale studies have become an essential tool in the oil and gas industry to understand and predict the petrophysical and multiphase flow properties for the assessment and exploitation of hydrocarbon reserves. Carbonate reservoirs, accounting for majority of the world's hydrocarbon reserves, are well known for their heterogeneity and multiscale pore characteristics. The pore sizes in carbonate rock can vary over orders of magnitudes, the geometry and topology parameters of pores at different scales have a great impact on flow properties. A pore-scale study is often comprised of two key procedures: 3D pore-scale imaging and numerical modelling techniques. The fundamental problem in pore-scale imaging and modelling is how to represent and model the different range of scales encountered in porous media, from the pore-scale to macroscopic petrophysical and multiphase flow properties. However, due to the restrictions of image size vs. resolution, the desired detail is rarely captured at the relevant length scales using any single imaging technique. Similarly, direct simulations of transport properties in heterogeneous rocks with broad pore size distributions are prohibitively expensive computationally. In this study, we present the advances and review the practical limitation of different imaging techniques varying from core-scale (1mm) using Medical Computed Tomography (CT) to pore-scale (10nm - 50µm) using Micro-CT, Confocal Laser Scanning Microscopy (CLSM) and Focussed Ion Beam (FIB) to characterise the complex pore structure in Ketton carbonate rock. The effect of pore structure and connectivity on the flow properties is investigated using the obtained pore scale images of Ketton carbonate using Pore Network and Lattice-Boltzmann simulation methods in comparison with experimental data. We also shed new light on the existence and size of the Representative Element of Volume (REV) capturing the different scales of heterogeneity from the pore-scale imaging.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jomekian, A.; Faculty of Chemical Engineering, Iran University of Science and Technology; Behbahani, R.M., E-mail: behbahani@put.ac.ir

Ultra porous ZIF-8 particles synthesized using PEO/PA6 based poly(ether-block-amide) (Pebax 1657) as structure directing agent. Structural properties of ZIF-8 samples prepared under different synthesis parameters were investigated by laser particle size analysis, XRD, N{sub 2} adsorption analysis, BJH and BET tests. The overall results showed that: (1) The mean pore size of all ZIF-8 samples increased remarkably (from 0.34 nm to 1.1–2.5 nm) compared to conventionally synthesized ZIF-8 samples. (2) Exceptional BET surface area of 1869 m{sup 2}/g was obtained for a ZIF-8 sample with mean pore size of 2.5 nm. (3) Applying high concentrations of Pebax 1657 to themore » synthesis solution lead to higher surface area, larger pore size and smaller particle size for ZIF-8 samples. (4) Both, Increase in temperature and decrease in molar ratio of MeIM/Zn{sup 2+} had increasing effect on ZIF-8 particle size, pore size, pore volume, crystallinity and BET surface area of all investigated samples. - Highlights: • The pore size of ZIF-8 samples synthesized with Pebax 1657 increased remarkably. • The BET surface area of 1869 m{sup 2}/gr obtained for a ZIF-8 synthesized sample with Pebax. • Increase in temperature had increasing effect on textural properties of ZIF-8 samples. • Decrease in MeIM/Zn{sup 2+} had increasing effect on textural properties of ZIF-8 samples.« less

Fluid Absorption and Release of Nonwovens and their Response to Compression

NASA Astrophysics Data System (ADS)

Bateny, Fatemeh

Fluid handling is a key property in one of the major nonwoven applications in absorbent product such as wipes, hygiene products, and baby diapers. These products are subjected to various levels of compression in real-use. The aim of this study was to investigate the liquid absorption and release properties of nonwovens to establish the absorption structure-property relationship at various compression levels. A comprehensive methodology, considering various flow directions, was employed to establish the relationship by decoupling the effect of structural parameters and material properties in two phases of this study respectively. In the first phase, the mechanism of absorption by pore structure was investigated through considering various fiber cross-sectional size and shape, as well as heterogeneous layered structures having a pore size reduction and expansion. In the second phase, the mechanism of absorption by fiber and consequent swelling was evaluated in view of fluid diffusion into the rayon fibers in samples having different percentages of PET fiber (non-absorbent) and rayon fiber (absorbent). The analysis of absorption and release properties through the entire dissertation was based on the pore characteristics of the nonwovens by measuring the average pore sizes, pore size distribution, and solidity. The investigation revealed that the absorption and release properties of nonwovens are governed by their pore characteristics. In homogeneous non-layered nonwoven fabrics, maximum absorption is mainly governed by the available pore volume. Absorbency rate is determined according to pore size and the maximum rate of absorption is achieved at a specific range of pore sizes. This indicates that an in-depth understanding of the absorption and release properties brings about valuable information for the absorbent product engineering.

Porotic paradox: distribution of cortical bone pore sizes at nano- and micro-levels in healthy vs. fragile human bone.

PubMed

Milovanovic, Petar; Vukovic, Zorica; Antonijevic, Djordje; Djonic, Danijela; Zivkovic, Vladimir; Nikolic, Slobodan; Djuric, Marija

2017-05-01

Bone is a remarkable biological nanocomposite material showing peculiar hierarchical organization from smaller (nano, micro) to larger (macro) length scales. Increased material porosity is considered as the main feature of fragile bone at larger length-scales. However, there is a shortage of quantitative information on bone porosity at smaller length-scales, as well as on the distribution of pore sizes in healthy vs. fragile bone. Therefore, here we investigated how healthy and fragile bones differ in pore volume and pore size distribution patterns, considering a wide range of mostly neglected pore sizes from nano to micron-length scales (7.5 to 15000 nm). Cortical bone specimens from four young healthy women (age: 35 ± 6 years) and five women with bone fracture (age: 82 ± 5 years) were analyzed by mercury porosimetry. Our findings showed that, surprisingly, fragile bone demonstrated lower pore volume at the measured scales. Furtnermore, pore size distribution showed differential patterns between healthy and fragile bones, where healthy bone showed especially high proportion of pores between 200 and 15000 nm. Therefore, although fragile bones are known for increased porosity at macroscopic level and level of tens or hundreds of microns as firmly established in the literature, our study with a unique assessment range of nano-to micron-sized pores reveal that osteoporosis does not imply increased porosity at all length scales. Our thorough assessment of bone porosity reveals a specific distribution of porosities at smaller length-scales and contributes to proper understanding of bone structure which is important for designing new biomimetic bone substitute materials.

On the size of pores arising in erythrocytes under the action of detergents.

PubMed

Senkovich, O A; Chernitsky, E A

1998-01-01

The size of pores arising in human erythrocytes under the action of two detergents (Triton X-100 and sodium dodecyl sulfate) and causing the slow component of hemolysis was estimated by the method of osmotic protectors. The pore diameters were found to be about 40 A. The pores responsible for the fast component of hemolysis induced by sodium dodecyl sulfate were shown to be of greater size and even molecules of polyethylene glycol 4000 could pass through them. The unusual decrease. In the rate and percentage of this hemolytic component was caused by the side action of the protectors, i.e., by the acceleration of erythrocyte vesiculation, a process that competed with pore formation. Vesiculation protected erythrocytes against fast and slow detergent-induced hemolysis. It is shown that the method of osmotic protectors can not be used for estimation of pore size in fast hemolysis by sodium dodecyl sulfate. The application of this method for hemolysis by other amphiphilic compounds is discussed.

Pore dilatation increases the bicarbonate permeability of CFTR, ANO1 and glycine receptor anion channels

PubMed Central

Jun, Ikhyun; Cheng, Mary Hongying; Sim, Eunji; Jung, Jinsei; Suh, Bong Lim; Kim, Yonjung; Son, Hankil; Park, Kyungsoo; Kim, Chul Hoon; Yoon, Joo‐Heon; Whitcomb, David C.; Bahar, Ivet

2016-01-01

Key points Cellular stimuli can modulate the ion selectivity of some anion channels, such as CFTR, ANO1 and the glycine receptor (GlyR), by changing pore size.Ion selectivity of CFTR, ANO1 and GlyR is critically affected by the electric permittivity and diameter of the channel pore.Pore size change affects the energy barriers of ion dehydration as well as that of size‐exclusion of anion permeation.Pore dilatation increases the bicarbonate permeability (P HC O3/ Cl ) of CFTR, ANO1 and GlyR.Dynamic change in P HC O3/ Cl may mediate many physiological and pathological processes. Abstract Chloride (Cl−) and bicarbonate (HCO3 −) are two major anions and their permeation through anion channels plays essential roles in our body. However, the mechanism of ion selection by the anion channels is largely unknown. Here, we provide evidence that pore dilatation increases the bicarbonate permeability (P HC O3/ Cl ) of anion channels by reducing energy barriers of size‐exclusion and ion dehydration of HCO3 − permeation. Molecular, physiological and computational analyses of major anion channels, such as cystic fibrosis transmembrane conductance regulator (CFTR), anoctamin‐1(ANO1/TMEM16A) and the glycine receptor (GlyR), revealed that the ion selectivity of anion channels is basically determined by the electric permittivity and diameter of the pore. Importantly, cellular stimuli dynamically modulate the anion selectivity of CFTR and ANO1 by changing the pore size. In addition, pore dilatation by a mutation in the pore‐lining region alters the anion selectivity of GlyR. Changes in pore size affected not only the energy barriers of size exclusion but that of ion dehydration by altering the electric permittivity of water‐filled cavity in the pore. The dynamic increase in P HC O3/ Cl by pore dilatation may have many physiological and pathophysiological implications ranging from epithelial HCO3 − secretion to neuronal excitation. PMID:26663196

Improved capacitance characteristics of electrospun ACFs by pore size control and vanadium catalyst.

PubMed

Im, Ji Sun; Woo, Sang-Wook; Jung, Min-Jung; Lee, Young-Seak

2008-11-01

Nano-sized carbon fibers were prepared by using electrospinning, and their electrochemical properties were investigated as a possible electrode material for use as an electric double-layer capacitor (EDLC). To improve the electrode capacitance of EDLC, we implemented a three-step optimization. First, metal catalyst was introduced into the carbon fibers due to the excellent conductivity of metal. Vanadium pentoxide was used because it could be converted to vanadium for improved conductivity as the pore structure develops during the carbonization step. Vanadium catalyst was well dispersed in the carbon fibers, improving the capacitance of the electrode. Second, pore-size development was manipulated to obtain small mesopore sizes ranging from 2 to 5 nm. Through chemical activation, carbon fibers with controlled pore sizes were prepared with a high specific surface and pore volume, and their pore structure was investigated by using a BET apparatus. Finally, polyacrylonitrile was used as a carbon precursor to enrich for nitrogen content in the final product because nitrogen is known to improve electrode capacitance. Ultimately, the electrospun activated carbon fibers containing vanadium show improved functionality in charge/discharge, cyclic voltammetry, and specific capacitance compared with other samples because of an optimal combination of vanadium, nitrogen, and fixed pore structures.

Ion-Gated Gas Separation through Porous Graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Ziqi; Mahurin, Shannon M.; Dai, Sheng

Porous graphene holds great promise as an atom-thin, high-permeance membrane for gas separation, but to precisely control the pore size at three to five angstroms proves challenging. Here we propose an ion-gated graphene membrane comprising a monolayer of ionic liquid coated porous graphene to dynamically modulate the pore size to achieve selective gas separation. This approach enables the otherwise non-selective large pores on the order of 1 nm in size to be selective for gases whose diameters range from three to four angstroms. We show from molecular dynamics simulations that CO 2, N 2 and CH 4 all can permeatemore » through a 1-nm pore in graphene without any selectivity. But when a monolayer of [emim][BF 4] is deposited on the porous graphene, CO 2 has much higher permeance than the other two gases. We find that the anion dynamically modulates the pore size by hovering above the pore and provides affinity for CO 2 while the larger cation (which cannot go through the pore) holds the anion in place via electrostatic attraction. This composite membrane is especially promising for CO 2/CH 4 separation, with a CO 2/CH 4 selectivity of about 42 and CO 2 permeance ~105 GPU (gas permeation unit). We further demonstrate that selectivity and permeance can be tuned by the anion size. The present work points toward a promising direction of using the atom-thin ionic-liquid/porous-graphene hybrid membrane for high-permeance, selective gas separation that allows a greater flexibility in substrate pore size control.« less

Ion-Gated Gas Separation through Porous Graphene

DOE PAGES

Tian, Ziqi; Mahurin, Shannon M.; Dai, Sheng; ...

2017-02-10

Porous graphene holds great promise as an atom-thin, high-permeance membrane for gas separation, but to precisely control the pore size at three to five angstroms proves challenging. Here we propose an ion-gated graphene membrane comprising a monolayer of ionic liquid coated porous graphene to dynamically modulate the pore size to achieve selective gas separation. This approach enables the otherwise non-selective large pores on the order of 1 nm in size to be selective for gases whose diameters range from three to four angstroms. We show from molecular dynamics simulations that CO 2, N 2 and CH 4 all can permeatemore » through a 1-nm pore in graphene without any selectivity. But when a monolayer of [emim][BF 4] is deposited on the porous graphene, CO 2 has much higher permeance than the other two gases. We find that the anion dynamically modulates the pore size by hovering above the pore and provides affinity for CO 2 while the larger cation (which cannot go through the pore) holds the anion in place via electrostatic attraction. This composite membrane is especially promising for CO 2/CH 4 separation, with a CO 2/CH 4 selectivity of about 42 and CO 2 permeance ~105 GPU (gas permeation unit). We further demonstrate that selectivity and permeance can be tuned by the anion size. The present work points toward a promising direction of using the atom-thin ionic-liquid/porous-graphene hybrid membrane for high-permeance, selective gas separation that allows a greater flexibility in substrate pore size control.« less

Inhibition of NAADP signalling on reperfusion protects the heart by preventing lethal calcium oscillations via two-pore channel 1 and opening of the mitochondrial permeability transition pore.

PubMed

Davidson, Sean M; Foote, Kirsty; Kunuthur, Suma; Gosain, Raj; Tan, Noah; Tyser, Richard; Zhao, Yong Juan; Graeff, Richard; Ganesan, A; Duchen, Michael R; Patel, Sandip; Yellon, Derek M

2015-12-01

In the heart, a period of ischaemia followed by reperfusion evokes powerful cytosolic Ca(2+) oscillations that can cause lethal cell injury. These signals represent attractive cardioprotective targets, but the underlying mechanisms of genesis are ill-defined. Here, we investigated the role of the second messenger nicotinic acid adenine dinucleotide phosphate (NAADP), which is known in several cell types to induce Ca(2+) oscillations that initiate from acidic stores such as lysosomes, likely via two-pore channels (TPCs, TPC1 and 2). An NAADP antagonist called Ned-K was developed by rational design based on a previously existing scaffold. Ned-K suppressed Ca(2+) oscillations and dramatically protected cardiomyocytes from cell death in vitro after ischaemia and reoxygenation, preventing opening of the mitochondrial permeability transition pore. Ned-K profoundly decreased infarct size in mice in vivo. Transgenic mice lacking the endo-lysosomal TPC1 were also protected from injury. NAADP signalling plays a major role in reperfusion-induced cell death and represents a potent pathway for protection against reperfusion injury. © The Author 2015. Published by Oxford University Press on behalf of the European Society of Cardiology.

Inhibition of NAADP signalling on reperfusion protects the heart by preventing lethal calcium oscillations via two-pore channel 1 and opening of the mitochondrial permeability transition pore

PubMed Central

Davidson, Sean M.; Foote, Kirsty; Kunuthur, Suma; Gosain, Raj; Tan, Noah; Tyser, Richard; Zhao, Yong Juan; Graeff, Richard; Ganesan, A.; Duchen, Michael R.; Patel, Sandip; Yellon, Derek M.

2015-01-01

Aims In the heart, a period of ischaemia followed by reperfusion evokes powerful cytosolic Ca2+ oscillations that can cause lethal cell injury. These signals represent attractive cardioprotective targets, but the underlying mechanisms of genesis are ill-defined. Here, we investigated the role of the second messenger nicotinic acid adenine dinucleotide phosphate (NAADP), which is known in several cell types to induce Ca2+ oscillations that initiate from acidic stores such as lysosomes, likely via two-pore channels (TPCs, TPC1 and 2). Methods and results An NAADP antagonist called Ned-K was developed by rational design based on a previously existing scaffold. Ned-K suppressed Ca2+ oscillations and dramatically protected cardiomyocytes from cell death in vitro after ischaemia and reoxygenation, preventing opening of the mitochondrial permeability transition pore. Ned-K profoundly decreased infarct size in mice in vivo. Transgenic mice lacking the endo-lysosomal TPC1 were also protected from injury. Conclusion NAADP signalling plays a major role in reperfusion-induced cell death and represents a potent pathway for protection against reperfusion injury. PMID:26395965

Porous Carriers for Controlled/Modulated Drug Delivery

PubMed Central

Ahuja, G.; Pathak, K.

2009-01-01

Considerable research efforts have been directed in recent years towards the development of porous carriers as controlled drug delivery matrices because of possessing several features such as stable uniform porous structure, high surface area, tunable pore size and well-defined surface properties. Owing to wide range of useful properties porous carriers have been used in pharmaceuticals for many purposes including development of floating drug delivery systems, sustained drug delivery systems. Various types of pores like open, closed, transport and blind pores in the porous solid allow them to adsorb drugs and release them in a more reproducible and predictable manner. Pharmaceutically exploited porous adsorbents includes, silica (mesoporous), ethylene vinyl acetate (macroporous), polypropylene foam powder (microporous), titanium dioxide (nanoporous). When porous polymeric drug delivery system is placed in contact with appropriate dissolution medium, release of drug to medium must be preceded by the drug dissolution in the water filled pores or from surface and by diffusion through the water filled channels. The porous carriers are used to improve the oral bioavailability of poorly water soluble drugs, to increase the dissolution of relatively insoluble powders and conversion of crystalline state to amorphous state. PMID:20376211

Characterization of pore structure in cement-based materials using pressurization-depressurization cycling mercury intrusion porosimetry (PDC-MIP)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou Jian, E-mail: Jian.Zhou@tudelft.n; Ye Guang, E-mail: g.ye@tudelft.n; Magnel Laboratory for Concrete Research, Department of Structural Engineering, Ghent University, Technologiepark-Zwijnaarde 904 B-9052, Ghent

2010-07-15

Numerous mercury intrusion porosimetry (MIP) studies have been carried out to investigate the pore structure in cement-based materials. However, the standard MIP often results in an underestimation of large pores and an overestimation of small pores because of its intrinsic limitation. In this paper, an innovative MIP method is developed in order to provide a more accurate estimation of pore size distribution. The new MIP measurements are conducted following a unique mercury intrusion procedure, in which the applied pressure is increased from the minimum to the maximum by repeating pressurization-depressurization cycles instead of a continuous pressurization followed by a continuousmore » depressurization. Accordingly, this method is called pressurization-depressurization cycling MIP (PDC-MIP). By following the PDC-MIP testing sequence, the volumes of the throat pores and the corresponding ink-bottle pores can be determined at every pore size. These values are used to calculate pore size distribution by using the newly developed analysis method. This paper presents an application of PDC-MIP on the investigation of the pore size distribution in cement-based materials. The experimental results of PDC-MIP are compared with those measured by standard MIP. The PDC-MIP is further validated with the other experimental methods and numerical tool, including nitrogen sorption, backscanning electron (BSE) image analysis, Wood's metal intrusion porosimetry (WMIP) and the numerical simulation by the cement hydration model HYMOSTRUC3D.« less

Porosity of the Marcellus Shale: A contrast matching small-angle neutron scattering study

USGS Publications Warehouse

Bahadur, Jitendra; Ruppert, Leslie F.; Pipich, Vitaliy; Sakurovs, Richard; Melnichenko, Yuri B.

2018-01-01

Neutron scattering techniques were used to determine the effect of mineral matter on the accessibility of water and toluene to pores in the Devonian Marcellus Shale. Three Marcellus Shale samples, representing quartz-rich, clay-rich, and carbonate-rich facies, were examined using contrast matching small-angle neutron scattering (CM-SANS) at ambient pressure and temperature. Contrast matching compositions of H2O, D2O and toluene, deuterated toluene were used to probe open and closed pores of these three shale samples. Results show that although the mean pore radius was approximately the same for all three samples, the fractal dimension of the quartz-rich sample was higher than for the clay-rich and carbonate-rich samples, indicating different pore size distributions among the samples. The number density of pores was highest in the clay-rich sample and lowest in the quartz-rich sample. Contrast matching with water and toluene mixtures shows that the accessibility of pores to water and toluene also varied among the samples. In general, water accessed approximately 70–80% of the larger pores (>80 nm radius) in all three samples. At smaller pore sizes (~5–80 nm radius), the fraction of accessible pores decreases. The lowest accessibility to both fluids is at pore throat size of ~25 nm radii with the quartz-rich sample exhibiting lower accessibility than the clay- and carbonate-rich samples. The mechanism for this behaviour is unclear, but because the mineralogy of the three samples varies, it is likely that the inaccessible pores in this size range are associated with organics and not a specific mineral within the samples. At even smaller pore sizes (~<2.5 nm radius), in all samples, the fraction of accessible pores to water increases again to approximately 70–80%. Accessibility to toluene generally follows that of water; however, in the smallest pores (~<2.5 nm radius), accessibility to toluene decreases, especially in the clay-rich sample which contains about 30% more closed pores than the quartz- and carbonate-rich samples. Results from this study show that mineralogy of producing intervals within a shale reservoir can affect accessibility of pores to water and toluene and these mineralogic differences may affect hydrocarbon storage and production and hydraulic fracturing characteristics

Bioaccessible Porosity in Soil Aggregates and Implications for Biodegradation of High Molecular Weight Petroleum Compounds.

PubMed

Akbari, Ali; Ghoshal, Subhasis

2015-12-15

We evaluated the role of soil aggregate pore size on biodegradation of essentially insoluble petroleum hydrocarbons that are biodegraded primarily at the oil-water interface. The size and spatial distribution of pores in aggregates sampled from biodegradation experiments of a clayey, aggregated, hydrocarbon-contaminated soil with relatively high bioremediation end point were characterized by image analyses of X-ray micro-CT scans and N2 adsorption. To determine the bioaccessible pore sizes, we performed separate experiments to assess the ability of hydrocarbon degrading bacteria isolated from the soil to pass through membranes with specific sized pores and to access hexadecane (model insoluble hydrocarbon). Hexadecane biodegradation occurred only when pores were 5 μm or larger, and did not occur when pores were 3 μm and smaller. In clayey aggregates, ∼ 25% of the aggregate volume was attributed to pores larger than 4 μm, which was comparable to that in aggregates from a sandy, hydrocarbon-contaminated soil (~23%) scanned for comparison. The ratio of volumes of inaccessible pores (<4 μm) to bioaccessible pores (>4 μm) in the clayey aggregates was 0.32, whereas in the sandy aggregates it was approximately 10 times lower. The role of soil microstructure on attainable bioremediation end points could be qualitatively assessed in various soils by the aggregate characterization approach outlined herein.

Detection, 3-D positioning, and sizing of small pore defects using digital radiography and tracking

NASA Astrophysics Data System (ADS)

Lindgren, Erik

2014-12-01

This article presents an algorithm that handles the detection, positioning, and sizing of submillimeter-sized pores in welds using radiographic inspection and tracking. The possibility to detect, position, and size pores which have a low contrast-to-noise ratio increases the value of the nondestructive evaluation of welds by facilitating fatigue life predictions with lower uncertainty. In this article, a multiple hypothesis tracker with an extended Kalman filter is used to track an unknown number of pore indications in a sequence of radiographs as an object is rotated. Each pore is not required to be detected in all radiographs. In addition, in the tracking step, three-dimensional (3-D) positions of pore defects are calculated. To optimize, set up, and pre-evaluate the algorithm, the article explores a design of experimental approach in combination with synthetic radiographs of titanium laser welds containing pore defects. The pre-evaluation on synthetic radiographs at industrially reasonable contrast-to-noise ratios indicate less than 1% false detection rates at high detection rates and less than 0.1 mm of positioning errors for more than 90% of the pores. A comparison between experimental results of the presented algorithm and a computerized tomography reference measurement shows qualitatively good agreement in the 3-D positions of approximately 0.1-mm diameter pores in 5-mm-thick Ti-6242.

The importance of dehydration in determining ion transport in narrow pores.

PubMed

Richards, Laura A; Schäfer, Andrea I; Richards, Bryce S; Corry, Ben

2012-06-11

The transport of hydrated ions through narrow pores is important for a number of processes such as the desalination and filtration of water and the conductance of ions through biological channels. Here, molecular dynamics simulations are used to systematically examine the transport of anionic drinking water contaminants (fluoride, chloride, nitrate, and nitrite) through pores ranging in effective radius from 2.8 to 6.5 Å to elucidate the role of hydration in excluding these species during nanofiltration. Bulk hydration properties (hydrated size and coordination number) are determined for comparison with the situations inside the pores. Free energy profiles for ion transport through the pores show energy barriers depend on pore size, ion type, and membrane surface charge and that the selectivity sequence can change depending on the pore size. Ion coordination numbers along the trajectory showed that partial dehydration of the transported ion is the main contribution to the energy barriers. Ion transport is greatly hindered when the effective pore radius is smaller than the hydrated radius, as the ion has to lose some associated water molecules to enter the pore. Small energy barriers are still observed when pore sizes are larger than the hydrated radius due to re-orientation of the hydration shell or the loss of more distant water. These results demonstrate the importance of ion dehydration in transport through narrow pores, which increases the current level of mechanistic understanding of membrane-based desalination and transport in biological channels. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characteristics of nuclepore filters with large pore size—I. Physical properties

NASA Astrophysics Data System (ADS)

John, W.; Hering, S.; Reischl, G.; Sasaki, G.; Goren, S.

Measurements of pore diameter, pore density and filter thickness have been made on Nuclepore filters of 5, 8 and 12 μm pore size. The areal distribution of the pores is random, as verified by total hole counts and by counts of overlapping holes. Filter thicknesses decrease with increasing pore diameter. The Hagen-Poiseuille formula accounts for less than half of the measured pressure drop across 12 μm pore size filters. A new calculation, including a term for the pressure drop external to the filter, accounts quantitatively for the observations. There are sufficient variations among filter batches to require knowledge of the filter parameters for each batch to ensure accurate measurements using these filters.

Polystyrene-block-poly(ethylene oxide) copolymers as templates for stacked, spherical large-mesopore silica coatings: dependence of silica pore size on the PS/PEO ratio

PubMed Central

Magnacca, Giuliana; Jadhav, Sushilkumar A; Scalarone, Dominique

2016-01-01

Summary Large-mesopore silica films with a narrow pore size distribution and high porosity have been obtained by a sol–gel reaction of a silicon oxide precursor (TEOS) and using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers as templates in an acidic environment. PS-b-PEO copolymers with different molecular weight and composition have been studied in order to assess the effects of the block length on the pore size of the templated silica films. The changes in the morphology of the porous systems have been investigated by transmission electron microscopy and a systematic analysis has been carried out, evidencing the dependence between the hydrophilic/hydrophobic ratio of the two polymer blocks and the size of the final silica pores. The obtained results prove that by tuning the PS/PEO ratio, the pore size of the templated silica films can be easily and finely predicted. PMID:27826520

Possible pore size effects on the state of tris(8-quinolinato)aluminum(III) (Alq3) adsorbed in mesoporous silicas and their temperature dependence.

PubMed

Tagaya, Motohiro; Ogawa, Makoto

2008-12-07

The states of tris(8-quinolinato)aluminum(III) (Alq3) adsorbed in mesoporous silicas with different pore sizes (2.5, 3.1 and 5.0 nm) were investigated. Alq3 was successfully occluded into the mesoporous silicas from solution and the adsorbed amount of Alq3 per BET surface area was effectively controlled by changing the added amount Alq3 to the solution. The state of Alq3 in the mesopore varied depending on the pore size as well as the adsorbed amount of Alq3 as revealed by variation of the photoluminescence spectra. The luminescence of the adsorbed Alq3 was found to be temperature-dependent, indicating the mobility of the adsorbed Alq3 to temperature variations. The temperature-dependence also depended on the pore size. The guest-guest interactions between Alq3 molecules as well as the host-guest interactions between Alq3 and the mesopore were controlled by the pore size.

Facile fabrication of BiVO4 nanofilms with controlled pore size and their photoelectrochemical performances

NASA Astrophysics Data System (ADS)

Feng, Chenchen; Jiao, Zhengbo; Li, Shaopeng; Zhang, Yan; Bi, Yingpu

2015-12-01

We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures.We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06584d

Effect of Cavity Size of Mesoporous Silica on Short DNA Duplex Stability.

PubMed

Masuda, Tsubasa; Shibuya, Yuuta; Arai, Shota; Kobayashi, Sayaka; Suzuki, Sotaro; Kijima, Jun; Itoh, Tetsuji; Sato, Yusuke; Nishizawa, Seiichi; Yamaguchi, Akira

2018-05-15

We studied the stabilities of short (4- and 3-bp) DNA duplexes within silica mesopores modified with a positively charged trimethyl aminopropyl (TMAP) monolayer (BJH pore diameter 1.6-7.4 nm). The DNA fragments with fluorescent dye were introduced into the pores, and their fluorescence resonance energy transfer (FRET) response was measured to estimate the structuring energies of the short DNA duplexes under cryogenic conditions (temperature 233-323 K). The results confirmed the enthalpic stability gain of the duplex within size-matched pores (1.6 and 2.3 nm). The hybridization equilibrium constants found for the size-matched pores were 2 orders of magnitude larger than those for large pores (≥3.5 nm), and this size-matching effect for the enhanced duplex stability was explained by a tight electrostatic interaction between the duplex and the surface TMAP groups. These results indicate the requirement of the precise regulation of mesopore size to ensure the stabilization of hydrogen-bonded supramolecular assemblies.

Performance and fouling characteristics of different pore-sized submerged ceramic membrane bioreactors (SCMBR).

PubMed

Jin, Le; Ng, How Yong; Ong, Say Leong

2009-01-01

The membrane bioreactor (MBR), a combination of activated sludge process and the membrane separation system, has been widely used in wastewater treatment. However, 90% of MBR reported were employing polymeric membranes. The usage of ceramic membranes in MBR is quite rare. Four submerged ceramic membrane bioreactors (SCMBRs) with different membrane pore size were used in this study to treat sewage. The results showed that the desirable carbonaceous removal of 95% and ammonia nitrogen removal of 98% were obtained for all the SCMBRs. It was also showed that the ceramic membranes were able to reject some portions of the protein and carbohydrate, whereby the carbohydrate rejection rate was much higher than that of protein. Membrane pore size did not significantly affect the COD and TOC removal efficiencies, the composition of EPS and SMP or the membrane rejection rate, although slight differences were observed. The SCMBR with the biggest membrane pore size fouled fastest, and membrane pore size was a main contributor for the different fouling potential observed.

Synthesis of single-crystal-like nanoporous carbon membranes and their application in overall water splitting

PubMed Central

Wang, Hong; Min, Shixiong; Ma, Chun; Liu, Zhixiong; Zhang, Weiyi; Wang, Qiang; Li, Debao; Li, Yangyang; Turner, Stuart; Han, Yu; Zhu, Haibo; Abou-hamad, Edy; Hedhili, Mohamed Nejib; Pan, Jun; Yu, Weili; Huang, Kuo-Wei; Li, Lain-Jong; Yuan, Jiayin; Antonietti, Markus; Wu, Tom

2017-01-01

Nanoporous graphitic carbon membranes with defined chemical composition and pore architecture are novel nanomaterials that are actively pursued. Compared with easy-to-make porous carbon powders that dominate the porous carbon research and applications in energy generation/conversion and environmental remediation, porous carbon membranes are synthetically more challenging though rather appealing from an application perspective due to their structural integrity, interconnectivity and purity. Here we report a simple bottom–up approach to fabricate large-size, freestanding and porous carbon membranes that feature an unusual single-crystal-like graphitic order and hierarchical pore architecture plus favourable nitrogen doping. When loaded with cobalt nanoparticles, such carbon membranes serve as high-performance carbon-based non-noble metal electrocatalyst for overall water splitting. PMID:28051082

Controlling the Pore Size of Mesoporous Carbon Thin Films through Thermal and Solvent Annealing.

PubMed

Zhou, Zhengping; Liu, Guoliang

2017-04-01

Herein an approach to controlling the pore size of mesoporous carbon thin films from metal-free polyacrylonitrile-containing block copolymers is described. A high-molecular-weight poly(acrylonitrile-block-methyl methacrylate) (PAN-b-PMMA) is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The authors systematically investigate the self-assembly behavior of PAN-b-PMMA thin films during thermal and solvent annealing, as well as the pore size of mesoporous carbon thin films after pyrolysis. The as-spin-coated PAN-b-PMMA is microphase-separated into uniformly spaced globular nanostructures, and these globular nanostructures evolve into various morphologies after thermal or solvent annealing. Surprisingly, through thermal annealing and subsequent pyrolysis of PAN-b-PMMA into mesoporous carbon thin films, the pore size and center-to-center spacing increase significantly with thermal annealing temperature, different from most block copolymers. In addition, the choice of solvent in solvent annealing strongly influences the block copolymer nanostructure and the pore size of mesoporous carbon thin films. The discoveries herein provide a simple strategy to control the pore size of mesoporous carbon thin films by tuning thermal or solvent annealing conditions, instead of synthesizing a series of block copolymers of various molecular weights and compositions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Method of making metal oxide ceramic membranes with small pore sizes

DOEpatents

Anderson, Marc A.; Xu, Qunyin

1992-01-01

A method for the production of metal oxide ceramic membranes is composed of very small pore size. The process is particularly useful in the creation of titanium and other transition metal oxide membranes. The method utilizes a sol-gel process in which the rate of particle formation is controlled by substituting a relatively large alcohol in the metal alkoxide and by limiting the available water. Stable, transparent metal oxide ceramic membranes are created having a narrow distribution of pore size, with the pore diameter being manipulable in the range of 5 to 40 Angstroms.

Drying regimes in homogeneous porous media from macro- to nanoscale

NASA Astrophysics Data System (ADS)

Thiery, J.; Rodts, S.; Weitz, D. A.; Coussot, P.

2017-07-01

Magnetic resonance imaging visualization down to nanometric liquid films in model porous media with pore sizes from micro- to nanometers enables one to fully characterize the physical mechanisms of drying. For pore size larger than a few tens of nanometers, we identify an initial constant drying rate period, probing homogeneous desaturation, followed by a falling drying rate period. This second period is associated with the development of a gradient in saturation underneath the sample free surface that initiates the inward recession of the contact line. During this latter stage, the drying rate varies in accordance with vapor diffusion through the dry porous region, possibly affected by the Knudsen effect for small pore size. However, we show that for sufficiently small pore size and/or saturation the drying rate is increasingly reduced by the Kelvin effect. Subsequently, we demonstrate that this effect governs the kinetics of evaporation in nanopores as a homogeneous desaturation occurs. Eventually, under our experimental conditions, we show that the saturation unceasingly decreases in a homogeneous manner throughout the wet regions of the medium regardless of pore size or drying regime considered. This finding suggests the existence of continuous liquid flow towards the interface of higher evaporation, down to very low saturation or very small pore size. Paradoxically, even if this net flow is unidirectional and capillary driven, it corresponds to a series of diffused local capillary equilibrations over the full height of the sample, which might explain that a simple Darcy's law model does not predict the effect of scaling of the net flow rate on the pore size observed in our tests.

Pore size assessment during corneal endothelial cells permeabilization by femtosecond laser activated carbon nanoparticles

NASA Astrophysics Data System (ADS)

Jumelle, C.; Mauclair, C.; Houzet, J.; Bernard, A.; He, Z.; Piselli, S.; Perrache, C.; Egaud, G.; Baubeau, E.; Gain, P.; Thuret, G.

2015-07-01

Corneal therapeutic molecules delivery represents a promising solution to maintain human corneal endothelial cells (HCECs) viability, but the difficulty is transport across cell membrane. A new delivery method published recently consists in ephemerally permeabilizing cell membranes using a photo-acoustic reaction produced by carbon nanoparticles (CNPs) and femtosecond laser (FsL). The aim of this work is to investigate the size of pores formed at cell membrane by this technique. To induce cell permeabilization, HCECs were put in contact with CNPs and irradiated with a 500 μm diameter Ti:Sa FsL focalized spot. Four sizes of marker molecules were delivered into HCECs to investigate pore sizes: calcein (1.2 nm), FITC-Dextran 4kDa (2.8 nm) and FITC-Dextran 70kDa (12 nm) and FITC-Dextran 2MDa (50 nm). Delivery of each molecule was assessed by flow cytometry, a technique able to measure their presence into cells. We showed that the delivery rate was dependent of their size. Calcein was delivered in 56.1±8.2% of HCECs, FITC-Dextran 4kDa in 42.2±3.5%, FITC-Dextran 70 kDa in 21.5±2.7% and finally FITC-Dextran 2MDa in 12.9±2.0%. It means that a large number of pores in the size ranging from 1.2 to 2.8 nm were formed. However, 12 nm and larger pores were almost half more infrequent. Pore sizes formed at cell membrane by the technique of cell permeabilization by FsL activated CNPs was investigated. The results indicated that the pore sizes are large enough for the efficient delivery of small, medium and big therapeutics molecules on HCECs by this technique.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majid, Z.A.; Mahmud, H.; Shaaban, M.G.

Stabilization/solidification of hazardous wastes is used to convert hazardous metal hydroxide waste sludge into a solid mass with better handling properties. This study investigated the pore size development of ordinary portland cement pastes containing metal hydroxide waste sludge and rice husk ash using mercury intrusion porosimetry. The effects of acre and the addition of rice husk ash on pore size development and strength were studied. It was found that the pore structures of mixes changed significantly with curing acre. The pore size shifted from 1,204 to 324 {angstrom} for 3-day old cement paste, and from 956 to 263 {angstrom} formore » a 7-day old sample. A reduction in pore size distribution for different curing ages was also observed in the other mixtures. From this limited study, no conclusion could be made as to any correlation between strength development and porosity. 10 refs., 6 figs., 3 tabs.« less

The effect of pore size and porosity on mechanical properties and biological response of porous titanium scaffolds.

PubMed

Torres-Sanchez, C; Al Mushref, F R A; Norrito, M; Yendall, K; Liu, Y; Conway, P P

2017-08-01

The effect of pore size and porosity on elastic modulus, strength, cell attachment and cell proliferation was studied for Ti porous scaffolds manufactured via powder metallurgy and sintering. Porous scaffolds were prepared in two ranges of porosities so that their mechanical properties could mimic those of cortical and trabecular bone respectively. Space-holder engineered pore size distributions were carefully determined to study the impact that small changes in pore size may have on mechanical and biological behaviour. The Young's moduli and compressive strengths were correlated with the relative porosity. Linear, power and exponential regressions were studied to confirm the predictability in the characterisation of the manufactured scaffolds and therefore establish them as a design tool for customisation of devices to suit patients' needs. The correlations were stronger for the linear and the power law regressions and poor for the exponential regressions. The optimal pore microarchitecture (i.e. pore size and porosity) for scaffolds to be used in bone grafting for cortical bone was set to <212μm with volumetric porosity values of 27-37%, and for trabecular tissues to 300-500μm with volumetric porosity values of 54-58%. The pore size range 212-300μm with volumetric porosity values of 38-56% was reported as the least favourable to cell proliferation in the longitudinal study of 12days of incubation. Copyright © 2017 Elsevier B.V. All rights reserved.

Influence of Rubber Size on Properties of Crumb Rubber Mortars

PubMed Central

Yu, Yong; Zhu, Han

2016-01-01

Studies on the properties and applications of rubber cement-based materials are well documented. The sizes of rubbers used in these materials varied. However, information about the effects of rubber size on the properties of rubber cement-based materials, especially pore structure, mechanical strengths, and drying shrinkage properties, remains limited. Three groups of rubber with major particle sizes of 2–4 mm, 1–3 mm, and 0–2 mm were selected in this study. This paper presents experimental studies on the effects of rubber size on the consistency, fresh density, pore structure, mechanical properties, and drying shrinkage properties of crumb rubber mortars (CRMs). Results demonstrated that the consistency and fresh density of CRMs decreased with the rubber size. As to the pore structure, the total pore volume increased with the decrease of the rubber size. By contrast, the influence of the rubber size on the mesopore (<50 nm) volume is not as significant as that of the rubber content. The mechanical properties of CRMs decreased with the rubber size. Low rubber stiffness and large pore volumes, especially those of small sized rubbers, contribute to the reduction of CRMs strength. The drying shrinkage of CRM increases as the rubber size decreases. The influences of rubber size on capillary tension are not significant. Thus, the shrinkage increases with the decrease of rubber size mainly because of its function in the deformation modulus reduction of CRMs. PMID:28773649

Macromolecular shape and interactions in layer-by-layer assemblies within cylindrical nanopores.

PubMed

Lazzara, Thomas D; Lau, K H Aaron; Knoll, Wolfgang; Janshoff, Andreas; Steinem, Claudia

2012-01-01

Layer-by-layer (LbL) deposition of polyelectrolytes and proteins within the cylindrical nanopores of anodic aluminum oxide (AAO) membranes was studied by optical waveguide spectroscopy (OWS). AAO has aligned cylindrical, nonintersecting pores with a defined pore diameter d(0) and functions as a planar optical waveguide so as to monitor, in situ, the LbL process by OWS. The LbL deposition of globular proteins, i.e., avidin and biotinylated bovine serum albumin was compared with that of linear polyelectrolytes (linear-PEs), both species being of similar molecular weight. LbL deposition within the cylindrical AAO geometry for different pore diameters (d(0) = 25-80 nm) for the various macromolecular species, showed that the multilayer film growth was inhibited at different maximum numbers of LbL steps (n(max)). The value of n(max) was greatest for linear-PEs, while proteins had a lower value. The cylindrical pore geometry imposes a physical limit to LbL growth such that n(max) is strongly dependent on the overall internal structure of the LbL film. For all macromolecular species, deposition was inhibited in native AAO, having pores of d(0) = 25-30 nm. Both, OWS and scanning electron microscopy showed that LbL growth in larger AAO pores (d(0) > 25-30 nm) became inhibited when approaching a pore diameter of d(eff,n_max) = 25-35 nm, a similar size to that of native AAO pores, with d(0) = 25-30 nm. For a reasonable estimation of d(eff,n_max), the actual volume occupied by a macromolecular assembly must be taken into consideration. The results clearly show that electrostatic LbL allowed for compact macromolecular layers, whereas proteins formed loosely packed multilayers.

Porosity control in nanoporous carbide-derived carbon by oxidation in air and carbon dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osswald, S.; Portet, C.; Gogotsi, Y., E-mail: gogotsi@drexel.ed

2009-07-15

Carbide-derived carbons (CDC) allow a precise control over the pore size through the selection of the carbide precursor and varying of the synthesis conditions. However, their pore volume is limited by the carbide stoichiometry. While activation of carbons derived from various organic precursors has been widely studied, this process may similarly be able to increase the pore volume and specific surface area of CDC. Oxidation of carbide-derived carbon in air and CO{sub 2} at different temperatures and times allows for significant increase in pore volume and specific surface area as well as control over average pore size with subnanometer accuracy.more » The effect of activation and associated changes in the pore volume and surface area on the hydrogen uptake are also discussed. - Graphical abstract: Carbide-derived carbons (CDC) provide great potential for sorption of toxicants and gas storage applications. Activation of CDC in air and CO{sub 2} at different temperatures and times is applied in order to maximize pore volume and specific surface area, and control the average pore size with subnanometer accuracy.« less

Visual and functional demonstration of growing Bax-induced pores in mitochondrial outer membranes

PubMed Central

Gillies, Laura A; Du, Han; Peters, Bjoern; Knudson, C. Michael; Newmeyer, Donald D.; Kuwana, Tomomi

2015-01-01

Bax induces mitochondrial outer membrane permeabilization (MOMP), a critical step in apoptosis in which proteins are released into the cytoplasm. To resolve aspects of the mechanism, we used cryo-electron microscopy (cryo-EM) to visualize Bax-induced pores in purified mitochondrial outer membranes (MOMs). We observed solitary pores that exhibited negative curvature at their edges. Over time, the pores grew to ∼100–160 nm in diameter after 60–90 min, with some pores measuring more than 300 nm. We confirmed these results using flow cytometry, which we used to monitor the release of fluorescent dextrans from isolated MOM vesicles. The dextran molecules were released gradually, in a manner constrained by pore size. However, the release rates were consistent over a range of dextran sizes (10–500 kDa). We concluded that the pores were not static but widened dramatically to release molecules of different sizes. Taken together, the data from cryo-EM and flow cytometry argue that Bax promotes MOMP by inducing the formation of large, growing pores through a mechanism involving membrane-curvature stress. PMID:25411335

Electrochemically-Driven Insertion of Biological Nanodiscs into Solid State Membrane Pores as a Basis for “Pore-In-Pore” Membranes

PubMed Central

Farajollahi, Farid; Seidenstücker, Axel; Altintoprak, Klara; Walther, Paul; Ziemann, Paul; Plettl, Alfred; Wege, Christina; Gliemann, Hartmut

2018-01-01

Nanoporous membranes are of increasing interest for many applications, such as molecular filters, biosensors, nanofluidic logic and energy conversion devices. To meet high-quality standards, e.g., in molecular separation processes, membranes with well-defined pores in terms of pore diameter and chemical properties are required. However, the preparation of membranes with narrow pore diameter distributions is still challenging. In the work presented here, we demonstrate a strategy, a “pore-in-pore” approach, where the conical pores of a solid state membrane produced by a multi-step top-down lithography procedure are used as a template to insert precisely-formed biomolecular nanodiscs with exactly defined inner and outer diameters. These nanodiscs, which are the building blocks of tobacco mosaic virus-deduced particles, consist of coat proteins, which self-assemble under defined experimental conditions with a stabilizing short RNA. We demonstrate that the insertion of the nanodiscs can be driven either by diffusion due to a concentration gradient or by applying an electric field along the cross-section of the solid state membrane. It is found that the electrophoresis-driven insertion is significantly more effective than the insertion via the concentration gradient. PMID:29652841

Effect of Pore Size and Pore Connectivity on Unidirectional Capillary Penetration Kinetics in 3-D Porous Media using Direct Numerical Simulation

NASA Astrophysics Data System (ADS)

Fu, An; Palakurthi, Nikhil; Konangi, Santosh; Comer, Ken; Jog, Milind

2017-11-01

The physics of capillary flow is used widely in multiple fields. Lucas-Washburn equation is developed by using a single pore-sized capillary tube with continuous pore connection. Although this equation has been extended to describe the penetration kinetics into porous medium, multiple studies have indicated L-W does not accurately predict flow patterns in real porous media. In this study, the penetration kinetics including the effect of pore size and pore connectivity will be closely examined since they are expected to be the key factors effecting the penetration process. The Liquid wicking process is studied from a converging and diverging capillary tube to the complex virtual 3-D porous structures with Direct Numerical Simulation (DNS) using the Volume-Of-Fluid (VOF) method within the OpenFOAM CFD Solver. Additionally Porous Medium properties such as Permeability (k) , Tortuosity (τ) will be also analyzed.

Linking Intra-Aggregate Pore Size Distribution with Organic Matter Decomposition Status, Evidence from FTIR and X-Ray Tomography

NASA Astrophysics Data System (ADS)

Toosi, E. R.; Quigley, M.; Kravchenko, A. N.

2014-12-01

It has been reported that conversion of intensively cultivated lands to less disturbed systems enhances soil OM storage capacity, primarily through OM stabilization in macroaggregates. We hypothesized that the potential for OM stabilization inside macro-aggregates is influenced by presence and abundance of intra-aggregate pores. Pores determine microbial access to OM and regulate diffusion of solution/gases within aggregates which drives microbial functioning. We investigated the influence of longterm disturbance intensity on soil OM composition and its relation to pore size distribution within macroaggregates. We used quantitative FTIR to determine OM decomposition status and X-ray micro-tomography to assess pore size distribution in macroaggregates as affected by management and landuse. Macroaggregates 4-6 mm in size where selected from topsoil under long term conventional tillage (CT), cover-crop (CC), and native succession vegetation (NS) treatments at Kellogg Biological Station, Michigan. Comparison of main soil OM functional groups suggested that with increasing disturbance intensity, the proportion of aromatic and carboxylic/carbohydrates associated compounds increased and it was concomitant with a decrease in the proportion of aliphatic associated compounds and lignin derivatives. Further, FTIR-based decomposition indices revealed that overall decomposition status of macroaggregates followed the pattern of CT > CC ≈ NS. X-ray micro-tomography findings suggested that greater OM decomposition within the macroaggregates was associated with i) greater percent of pores >13 micron in size within the aggregates, as well as ii) greater proportion of small to medium pores (13-110 micron). The results develop previous findings, suggesting that shift in landuse or management indirectly affects soil OM stabilization through alteration of pore size distribution within macroaggregates that itself, is coupled with OM decomposition status.

In vitro proliferation and osteogenic differentiation of mesenchymal stem cells on nanoporous alumina

PubMed Central

Song, Yuanhui; Ju, Yang; Song, Guanbin; Morita, Yasuyuki

2013-01-01

Cell adhesion, migration, and proliferation are significantly affected by the surface topography of the substrates on which the cells are cultured. Alumina is one of the most popular implant materials used in orthopedics, but few data are available concerning the cellular responses of mesenchymal stem cells (MSCs) grown on nanoporous structures. MSCs were cultured on smooth alumina substrates and nanoporous alumina substrates to investigate the interaction between surface topographies of nanoporous alumina and cellular behavior. Nanoporous alumina substrates with pore sizes of 20 nm and 100 nm were used to evaluate the effect of pore size on MSCs as measured by proliferation, morphology, expression of integrin β1, and osteogenic differentiation. An MTT assay was used to measure cell viability of MSCs on different substrates, and determined that cell viability decreased with increasing pore size. Scanning electron microscopy was used to investigate the effect of pore size on cell morphology. Extremely elongated cells and prominent cell membrane protrusions were observed in cells cultured on alumina with the larger pore size. The expression of integrin β1 was enhanced in MSCs cultured on porous alumina, revealing that porous alumina substrates were more favorable for cell growth than smooth alumina substrates. Higher levels of osteoblastic differentiation markers such as alkaline phosphatase, osteocalcin, and mineralization were detected in cells cultured on alumina with 100 nm pores compared with cells cultured on alumina with either 20 nm pores or smooth alumina. This work demonstrates that cellular behavior is affected by variation in pore size, providing new insight into the potential application of this novel biocompatible material for the developing field of tissue engineering. PMID:23935364

Nonlinear primary resonance of micro/nano-beams made of nanoporous biomaterials incorporating nonlocality and strain gradient size dependency

NASA Astrophysics Data System (ADS)

Sahmani, S.; Aghdam, M. M.

2018-03-01

A wide range of biological applications such as drug delivery, biosensors and hemodialysis can be provided by nanoporous biomaterials due to their uniform pore size as well as considerable pore density. In the current study, the size dependency in the nonlinear primary resonance of micro/nano-beams made of nanoporous biomaterials is anticipated. To accomplish this end, a refined truncated cube is introduced to model the lattice structure of nanoporous biomaterial. Accordingly, analytical expressions for the mechanical properties of material are derived as functions of pore size. After that, based upon a nonlocal strain gradient beam model, the size-dependent nonlinear Duffing type equation of motion is constructed. The Galerkin technique together with the multiple time-scales method is employed to obtain the nonlocal strain gradient frequency-response and amplitude-response related to the nonlinear primary resonance of a micro/nano-beam made of the nanoporous biomaterial with different pore sizes. It is indicated that the nonlocality causes to decrease the response amplitudes associated with the both bifurcation points of the jump phenomenon, while the strain gradient size dependency causes to increase them. Also, it is found that increasing the pore size leads to enhance the nonlinearity, so the maximum deflection of response occurs at higher excitation frequency.

Pore size distribution calculation from 1H NMR signal and N2 adsorption-desorption techniques

NASA Astrophysics Data System (ADS)

Hassan, Jamal

2012-09-01

The pore size distribution (PSD) of nano-material MCM-41 is determined using two different approaches: N2 adsorption-desorption and 1H NMR signal of water confined in silica nano-pores of MCM-41. The first approach is based on the recently modified Kelvin equation [J.V. Rocha, D. Barrera, K. Sapag, Top. Catal. 54(2011) 121-134] which deals with the known underestimation in pore size distribution for the mesoporous materials such as MCM-41 by introducing a correction factor to the classical Kelvin equation. The second method employs the Gibbs-Thompson equation, using NMR, for melting point depression of liquid in confined geometries. The result shows that both approaches give similar pore size distribution to some extent, and also the NMR technique can be considered as an alternative direct method to obtain quantitative results especially for mesoporous materials. The pore diameter estimated for the nano-material used in this study was about 35 and 38 Å for the modified Kelvin and NMR methods respectively. A comparison between these methods and the classical Kelvin equation is also presented.

Percolation Pore Network Study on the Residue Gas Saturation of Dry Reservoir Rocks

NASA Astrophysics Data System (ADS)

Cheng, T.; Tang, Y. B.; Zou, G. Y.; Jiang, K.; Li, M.

2014-12-01

We tried to model the effect of pore size heterogeneity and pore connectivity on the residue gas saturation for dry gas reservoir rocks. If we consider that snap-off does not exist and only piston displacement takes place in all pores with the same size during imbibition process, in the extreme case, the residue gas saturation will be equal to zero. Thus we can suppose that the residue gas saturation of dry rocks is mainly controlled by the pore size distribution. To verify the assumption, percolation pore networks (i.e., three-dimensional simple cubic (SC) and body-center cubic (BCC)) were used in the study. The connectivity and the pore size distribution in percolation pore network could be changed randomly. The concept of water phase connectivity zw(i.e., water coordination number) and gas phase connectivity zg (i.e., gas coordination number) was introduced here. zw and zg will change during simulation and can be estimated numerically from the results of simulations through gradually saturated networks by water. The Simulation results show that when zg less than or equal to 1.5 during water quasi - static imbibition, the gas will be trapped in rock pores. Network simulation results also shows that the residue gas saturation Srg follows a power law relationship (i.e.,Srg∝σrα, where σr is normalized standard deviation of the pore radius distribution, and exponent α is a function of coordination number). This indicates that the residue gas saturation has no explicit relationship with porosity and permeability as it should have in light of previous study, pore radius distribution is the principal factor in determining the residue gas saturation of dry reservoir rocks.

The effect of particle shape and size distribution on the acoustical properties of mixtures of hemp particles.

PubMed

Glé, Philippe; Gourdon, Emmanuel; Arnaud, Laurent; Horoshenkov, Kirill-V; Khan, Amir

2013-12-01

Hemp concrete is an attractive alternative to traditional materials used in building construction. It has a very low environmental impact, and it is characterized by high thermal insulation. Hemp aggregate particles are parallelepiped in shape and can be organized in a plurality of ways to create a considerable proportion of open pores with a complex connectivity pattern, the acoustical properties of which have never been examined systematically. Therefore this paper is focused on the fundamental understanding of the relations between the particle shape and size distribution, pore size distribution, and the acoustical properties of the resultant porous material mixture. The sound absorption and the transmission loss of various hemp aggregates is characterized using laboratory experiments and three theoretical models. These models are used to relate the particle size distribution to the pore size distribution. It is shown that the shape of particles and particle size control the pore size distribution and tortuosity in shiv. These properties in turn relate directly to the observed acoustical behavior.

Physical parameters of Fluvisols on flooded and non-flooded terraces

NASA Astrophysics Data System (ADS)

Kercheva, Milena; Sokołowska, Zofia; Hajnos, Mieczysław; Skic, Kamil; Shishkov, Toma

2017-01-01

The heterogeneity of soil physical properties of Fluvisols, lack of large pristine areas, and different moisture regimes on non-flooded and flooded terraces impede the possibility to find a soil profile which can serve as a baseline for estimating the impact of natural or anthropogenic factors on soil evolution. The aim of this study is to compare the pore size distribution of pristine Fluvisols on flooded and non-flooded terraces using the method of the soil water retention curve, mercury intrusion porosimetry, nitrogen adsorption isotherms, and water vapour sorption. The pore size distribution of humic horizons of pristine Fluvisols on the non-flooded terrace differs from pore size distribution of Fluvisols on the flooded terrace. The peaks of textural and structural pores are higher in the humic horizons under more humid conditions. The structural characteristics of subsoil horizons depend on soil texture and evolution stage. The peaks of textural pores at about 1 mm diminish with lowering of the soil organic content. Structureless horizons are characterized by uni-modal pore size distribution. Although the content of structural pores of the subsoil horizons of Fluvisols on the non-flooded terrace is low, these pores are represented by biopores, as the coefficient of filtration is moderately high. The difference between non-flooded and flooded profiles is well expressed by the available water storage, volume and mean radius of pores, obtained by mercury intrusion porosimetry and water desorption, which are higher in the surface horizons of frequently flooded Fluvisols.

Cuticular gas exchange by Antarctic sea spiders.

PubMed

Lane, Steven J; Moran, Amy L; Shishido, Caitlin M; Tobalske, Bret W; Woods, H Arthur

2018-04-25

Many marine organisms and life stages lack specialized respiratory structures, like gills, and rely instead on cutaneous respiration, which they facilitate by having thin integuments. This respiratory mode may limit body size, especially if the integument also functions in support or locomotion. Pycnogonids, or sea spiders, are marine arthropods that lack gills and rely on cutaneous respiration but still grow to large sizes. Their cuticle contains pores, which may play a role in gas exchange. Here, we examined alternative paths of gas exchange in sea spiders: (1) oxygen diffuses across pores in the cuticle, a common mechanism in terrestrial eggshells, (2) oxygen diffuses directly across the cuticle, a common mechanism in small aquatic insects, or (3) oxygen diffuses across both pores and cuticle. We examined these possibilities by modeling diffusive oxygen fluxes across all pores in the body of sea spiders and asking whether those fluxes differed from measured metabolic rates. We estimated fluxes across pores using Fick's law parameterized with measurements of pore morphology and oxygen gradients. Modeled oxygen fluxes through pores closely matched oxygen consumption across a range of body sizes, which means the pores facilitate oxygen diffusion. Furthermore, pore volume scaled hypermetrically with body size, which helps larger species facilitate greater diffusive oxygen fluxes across their cuticle. This likely presents a functional trade-off between gas exchange and structural support, in which the cuticle must be thick enough to prevent buckling due to external forces but porous enough to allow sufficient gas exchange. © 2018. Published by The Company of Biologists Ltd.

Growth of 2D Mesoporous Polyaniline with Controlled Pore Structures on Ultrathin MoS2 Nanosheets by Block Copolymer Self-Assembly in Solution.

PubMed

Tian, Hao; Zhu, Shuyan; Xu, Fugui; Mao, Wenting; Wei, Hao; Mai, Yiyong; Feng, Xinliang

2017-12-20

The development of versatile strategies toward two-dimensional (2D) porous nanocomposites with tunable pore structures draws immense scientific attention in view of their attractive physiochemical properties and a wide range of promising applications. This paper describes a self-assembly approach for the directed growth of mesoporous polyaniline (PANi) with tunable pore structures and sizes on ultrathin freestanding MoS 2 nanosheets in solution, which produces 2D mesoporous PANi/MoS 2 nanocomposites. The strategy employs spherical and cylindrical micelles, which are formed by the controlled solution self-assembly of block copolymers, as the soft templates for the construction of well-defined spherical and cylindrical mesopores in the 2D PANi/MoS 2 nanocomposites, respectively. With potential applications as supercapacitor electrode materials, the resultant 2D composites show excellent capacitive performance with a maximum capacitance of 500 F g -1 at a current density of 0.5 A g -1 , good rate performance, as well as outstanding stability for charge-discharge cycling. Moreover, the 2D mesoporous nanocomposites offer an opportunity for the study on the influence of different pore structures on their capacitive performance, which helps to understand the pore structure-property relationship of 2D porous electrode materials and to achieve their electrochemical performance control.

A facile method for the preparation of monodisperse beads with uniform pore sizes for cell culture.

PubMed

Moon, Seung-Kwan; Oh, Myeong-Jin; Paik, Dong-Hyun; Ryu, Tae-Kyung; Park, Kyeongsoon; Kim, Sung-Eun; Park, Jong-Hoon; Kim, Jung-Hyun; Choi, Sung-Wook

2013-03-12

This paper describes a facile method for the preparation of porous gelatin beads with uniform pore sizes using a simple fluidic device and their application as supporting materials for cell culture. An aqueous gelatin droplet containing many uniform toluene droplets, produced in the fluidic device, is dropped into liquid nitrogen for instant freezing and the small toluene droplets evolve into pores in the gelatin beads after removal of toluene and then freeze-drying. The porous gelatin beads exhibit a uniform pore size and monodisperse diameter as well as large open pores at the surface. Fluorescence microscopy images of fibroblast-loaded gelatin beads confirm the attachment and proliferation of the cells throughout the porous gelatin beads. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal-organic frameworks for Xe/Kr separation

DOEpatents

Ryan, Patrick J.; Farha, Omar K.; Broadbelt, Linda J.; Snurr, Randall Q.; Bae, Youn-Sang

2014-07-22

Metal-organic framework (MOF) materials are provided and are selectively adsorbent to xenon (Xe) over another noble gas such as krypton (Kr) and/or argon (Ar) as a result of having framework voids (pores) sized to this end. MOF materials having pores that are capable of accommodating a Xe atom but have a small enough pore size to receive no more than one Xe atom are desired to preferentially adsorb Xe over Kr in a multi-component (Xe--Kr mixture) adsorption method. The MOF material has 20% or more, preferably 40% or more, of the total pore volume in a pore size range of 0.45-0.75 nm which can selectively adsorb Xe over Kr in a multi-component Xe--Kr mixture over a pressure range of 0.01 to 1.0 MPa.

Metal-organic frameworks for Xe/Kr separation

DOEpatents

Ryan, Patrick J.; Farha, Omar K.; Broadbelt, Linda J.; Snurr, Randall Q.; Bae, Youn-Sang

2013-08-27

Metal-organic framework (MOF) materials are provided and are selectively adsorbent to xenon (Xe) over another noble gas such as krypton (Kr) and/or argon (Ar) as a result of having framework voids (pores) sized to this end. MOF materials having pores that are capable of accommodating a Xe atom but have a small enough pore size to receive no more than one Xe atom are desired to preferentially adsorb Xe over Kr in a multi-component (Xe--Kr mixture) adsorption method. The MOF material has 20% or more, preferably 40% or more, of the total pore volume in a pore size range of 0.45-0.75 nm which can selectively adsorb Xe over Kr in a multi-component Xe--Kr mixture over a pressure range of 0.01 to 1.0 MPa.

Investigation on size tolerance of pore defect of girth weld pipe.

PubMed

Li, Yan; Shuai, Jian; Xu, Kui

2018-01-01

Welding quality control is an important parameter for safe operation of oil and gas pipes, especially for high-strength steel pipes. Size control of welding defect is a bottleneck problem for current pipe construction. As a key part of construction procedure for butt-welding of pipes, pore defects in girth weld is difficult to ignore. A three-dimensional non-linear finite element numerical model is established to study applicability of size control indices based on groove shape and softening phenomenon of material in heat-affected zone of practical pipe girth weld. Taking design criteria of pipe as the basis, basic tensile, extremely tensile and extremely compressive loading conditions are determined for pipe stress analysis, and failure criteria based on flow stress is employed to perform stress analysis for pipe girth weld with pore defect. Results show that pipe girth welding stresses of pores at various radial locations are similar. Whereas, stress for pores of different sharpness varied significantly. Besides, tolerance capability of API 5L X90 grade pipe to pore defect of girth weld is lower than that of API 5L X80 grade pipe, and size control index of 3 mm related to pore defect in current standards is applicable to API 5L X80 and X90 grade girth welded pipes with radially non-sharp pore defects.

Investigation on size tolerance of pore defect of girth weld pipe

PubMed Central

Shuai, Jian; Xu, Kui

2018-01-01

Welding quality control is an important parameter for safe operation of oil and gas pipes, especially for high-strength steel pipes. Size control of welding defect is a bottleneck problem for current pipe construction. As a key part of construction procedure for butt-welding of pipes, pore defects in girth weld is difficult to ignore. A three-dimensional non-linear finite element numerical model is established to study applicability of size control indices based on groove shape and softening phenomenon of material in heat-affected zone of practical pipe girth weld. Taking design criteria of pipe as the basis, basic tensile, extremely tensile and extremely compressive loading conditions are determined for pipe stress analysis, and failure criteria based on flow stress is employed to perform stress analysis for pipe girth weld with pore defect. Results show that pipe girth welding stresses of pores at various radial locations are similar. Whereas, stress for pores of different sharpness varied significantly. Besides, tolerance capability of API 5L X90 grade pipe to pore defect of girth weld is lower than that of API 5L X80 grade pipe, and size control index of 3 mm related to pore defect in current standards is applicable to API 5L X80 and X90 grade girth welded pipes with radially non-sharp pore defects. PMID:29364986

Facile fabrication of BiVO4 nanofilms with controlled pore size and their photoelectrochemical performances.

PubMed

Feng, Chenchen; Jiao, Zhengbo; Li, Shaopeng; Zhang, Yan; Bi, Yingpu

2015-12-28

We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO(4) photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures.

Heterogeneous porous structures for the fastest liquid absorption

NASA Astrophysics Data System (ADS)

Shou, Dahua; Ye, Lin; Fan, Jintu

2013-08-01

Engineered porous materials, which have fast absorption of liquids under global constraints (e.g. volume, surface area, or cost of the materials), are useful in many applications including moisture management fabrics, medical wound dressings, paper-based analytical devices, liquid molding composites, etc.. The absorption in capillary tubes and porous media is driven by the surface tension of liquid, which is inversely proportional to the pore size. On the contrary, the ability of conduction (or permeability) of liquid in porous materials is linear with the square of pore size. Both mechanisms superimpose with each other leading to a possibility of the fastest absorption for a porous structure. In this work, we explore the flow behaviors for the fastest absorption using heterogeneous porous architectures, from two-portion tubes to two-layer porous media. The absorption time for filling up the voids in these porous materials is expressed in terms of pore size, height and porosity. It is shown that under the given height and void volume, these two-component porous structures with a negative gradient of pore size/porosity against the imbibition direction, have a faster absorption rate than controlled samples with uniform pore size/porosity. Particularly, optimal structural parameters including pore size, height and porosity are found for the minimum absorption time. The obtained results will be used as a priori for the design of porous structures with excellent water absorption and moisture management property in various fields.

Adsorption of binary gas mixtures in heterogeneous carbon predicted by density functional theory: on the formation of adsorption azeotropes.

PubMed

Ritter, James A; Pan, Huanhua; Balbuena, Perla B

2010-09-07

Classical density functional theory (DFT) was used to predict the adsorption of nine different binary gas mixtures in a heterogeneous BPL activated carbon with a known pore size distribution (PSD) and in single, homogeneous, slit-shaped carbon pores of different sizes. By comparing the heterogeneous results with those obtained from the ideal adsorbed solution theory and with those obtained in the homogeneous carbon, it was determined that adsorption nonideality and adsorption azeotropes are caused by the coupled effects of differences in the molecular size of the components in a gas mixture and only slight differences in the pore sizes of a heterogeneous adsorbent. For many binary gas mixtures, selectivity was found to be a strong function of pore size. As the width of a homogeneous pore increases slightly, the selectivity for two different sized adsorbates may change from being greater than unity to less than unity. This change in selectivity can be accompanied by the formation of an adsorption azeotrope when this same binary mixture is adsorbed in a heterogeneous adsorbent with a PSD, like in BPL activated carbon. These results also showed that the selectivity exhibited by a heterogeneous adsorbent can be dominated by a small number of pores that are very selective toward one of the components in the gas mixture, leading to adsorption azeotrope formation in extreme cases.

Unsaturated hydraulic properties of porous sedimentary rocks explained by mercury porosimetry

NASA Astrophysics Data System (ADS)

Clementina Caputo, Maria; Turturro, Celeste; Gerke, Horst H.

2016-04-01

The understanding of hydraulic properties is essential in the modeling of flow and solute transport including contaminants through the vadose zone, which consists of the soil as well as of the underlying porous sediments or rocks. The aim of this work is to study the relationships between unsaturated hydraulic properties of porous rocks and their pore size distribution. For this purpose, two different lithotypes belonging to Calcarenite di Gravina Formation, a Plio-Pleistocene sedimentary rock of marine origin, were investigated. The two lithotypes differ mainly in texture and came from two distinct quarry districts, Canosa di Puglia (C) and Massafra (M) in southern Italy, respectively. This relatively porous rock formation (porosities range between 43% for C and 41% for M) often constitutes a thick layer of vadose zone in several places of Mediterranean basin. The water retention curves (WRCs) and the unsaturated hydraulic conductivity functions were determined using four different experimental methods that cover the full range from low to high water contents: the WP4 psychrometer test, the Wind's evaporation method, the Stackman's method and the Quasi-steady centrifuge method. Pore size estimation by means of mercury intrusion porosimetry (MIP) was performed. WRCs were compared with the pore size distributions to understand the influence of fabric, in terms of texture and porosity, features of pores and pore size distribution on the hydraulic behavior of rocks. The preliminary results show that the pore size distributions obtained by MIP do not cover the entire pore size range of the investigated Calcarenite. In fact, some pores in the rock samples of both lithotypes were larger than the maximum size that could be investigated by MIP. This implies that for explaining the unsaturated hydraulic properties over the full moisture range MIP results need to be combined with results obtained by other methods such as image analysis and SEM.

Supercritical CO2 foaming of thermoplastic materials derived from maize: proof-of-concept use in mammalian cell culture applications.

PubMed

Trujillo-de Santiago, Grissel; Portales-Cabrera, Cynthia Guadalupe; Portillo-Lara, Roberto; Araiz-Hernández, Diana; Del Barone, Maria Cristina; García-López, Erika; Rojas-de Gante, Cecilia; de Los Angeles De Santiago-Miramontes, María; Segoviano-Ramírez, Juan Carlos; García-Lara, Silverio; Rodríguez-González, Ciro Ángel; Alvarez, Mario Moisés; Di Maio, Ernesto; Iannace, Salvatore

2015-01-01

Foams are high porosity and low density materials. In nature, they are a common architecture. Some of their relevant technological applications include heat and sound insulation, lightweight materials, and tissue engineering scaffolds. Foams derived from natural polymers are particularly attractive for tissue culture due to their biodegradability and bio-compatibility. Here, the foaming potential of an extensive list of materials was assayed, including slabs elaborated from whole flour, the starch component only, or the protein fraction only of maize seeds. We used supercritical CO2 to produce foams from thermoplasticized maize derived materials. Polyethylene-glycol, sorbitol/glycerol, or urea/formamide were used as plasticizers. We report expansion ratios, porosities, average pore sizes, pore morphologies, and pore size distributions for these materials. High porosity foams were obtained from zein thermoplasticized with polyethylene glycol, and from starch thermoplasticized with urea/formamide. Zein foams had a higher porosity than starch foams (88% and 85%, respectively) and a narrower and more evenly distributed pore size. Starch foams exhibited a wider span of pore sizes and a larger average pore size than zein (208.84 vs. 55.43 μm2, respectively). Proof-of-concept cell culture experiments confirmed that mouse fibroblasts (NIH 3T3) and two different prostate cancer cell lines (22RV1, DU145) attached to and proliferated on zein foams. We conducted screening and proof-of-concept experiments on the fabrication of foams from cereal-based bioplastics. We propose that a key indicator of foamability is the strain at break of the materials to be foamed (as calculated from stress vs. strain rate curves). Zein foams exhibit attractive properties (average pore size, pore size distribution, and porosity) for cell culture applications; we were able to establish and sustain mammalian cell cultures on zein foams for extended time periods.

Supercritical CO2 Foaming of Thermoplastic Materials Derived from Maize: Proof-of-Concept Use in Mammalian Cell Culture Applications

PubMed Central

Trujillo-de Santiago, Grissel; Portales-Cabrera, Cynthia Guadalupe; Portillo-Lara, Roberto; Araiz-Hernández, Diana; Del Barone, Maria Cristina; García-López, Erika; Rojas-de Gante, Cecilia; de los Angeles De Santiago-Miramontes, María; Segoviano-Ramírez, Juan Carlos; García-Lara, Silverio; Rodríguez-González, Ciro Ángel; Alvarez, Mario Moisés; Di Maio, Ernesto; Iannace, Salvatore

2015-01-01

Background Foams are high porosity and low density materials. In nature, they are a common architecture. Some of their relevant technological applications include heat and sound insulation, lightweight materials, and tissue engineering scaffolds. Foams derived from natural polymers are particularly attractive for tissue culture due to their biodegradability and bio-compatibility. Here, the foaming potential of an extensive list of materials was assayed, including slabs elaborated from whole flour, the starch component only, or the protein fraction only of maize seeds. Methodology/Principal Findings We used supercritical CO2 to produce foams from thermoplasticized maize derived materials. Polyethylene-glycol, sorbitol/glycerol, or urea/formamide were used as plasticizers. We report expansion ratios, porosities, average pore sizes, pore morphologies, and pore size distributions for these materials. High porosity foams were obtained from zein thermoplasticized with polyethylene glycol, and from starch thermoplasticized with urea/formamide. Zein foams had a higher porosity than starch foams (88% and 85%, respectively) and a narrower and more evenly distributed pore size. Starch foams exhibited a wider span of pore sizes and a larger average pore size than zein (208.84 vs. 55.43 μm2, respectively). Proof-of-concept cell culture experiments confirmed that mouse fibroblasts (NIH 3T3) and two different prostate cancer cell lines (22RV1, DU145) attached to and proliferated on zein foams. Conclusions/Significance We conducted screening and proof-of-concept experiments on the fabrication of foams from cereal-based bioplastics. We propose that a key indicator of foamability is the strain at break of the materials to be foamed (as calculated from stress vs. strain rate curves). Zein foams exhibit attractive properties (average pore size, pore size distribution, and porosity) for cell culture applications; we were able to establish and sustain mammalian cell cultures on zein foams for extended time periods. PMID:25859853

Achieving high permeability and enhanced selectivity for Angstrom-scale separations using artificial water channel membranes.

PubMed

Shen, Yue-Xiao; Song, Woochul C; Barden, D Ryan; Ren, Tingwei; Lang, Chao; Feroz, Hasin; Henderson, Codey B; Saboe, Patrick O; Tsai, Daniel; Yan, Hengjing; Butler, Peter J; Bazan, Guillermo C; Phillip, William A; Hickey, Robert J; Cremer, Paul S; Vashisth, Harish; Kumar, Manish

2018-06-12

Synthetic polymer membranes, critical to diverse energy-efficient separations, are subject to permeability-selectivity trade-offs that decrease their overall efficacy. These trade-offs are due to structural variations (e.g., broad pore size distributions) in both nonporous membranes used for Angstrom-scale separations and porous membranes used for nano to micron-scale separations. Biological membranes utilize well-defined Angstrom-scale pores to provide exceptional transport properties and can be used as inspiration to overcome this trade-off. Here, we present a comprehensive demonstration of such a bioinspired approach based on pillar[5]arene artificial water channels, resulting in artificial water channel-based block copolymer membranes. These membranes have a sharp selectivity profile with a molecular weight cutoff of ~ 500 Da, a size range challenging to achieve with current membranes, while achieving a large improvement in permeability (~65 L m -2  h -1  bar -1  compared with 4-7 L m -2  h -1  bar -1 ) over similarly rated commercial membranes.

Processing of large grain Y-123 superconductors with pre-defined porous structures

NASA Astrophysics Data System (ADS)

Sudhakar Reddy, E.; Babu, N. Hari; Shi, Y.; Cardwell, D. A.; Schmitz, G. J.

2005-02-01

Porous superconductors have inherent cooling advantages over their bulk counterparts and, as a result, are emerging as an important class of materials for practical applications. Single-domain Y-Ba-Cu-O (YBCO) foams processed with a pre-defined, open porous structure, for example, have significant potential for use as elements in resistive superconducting fault current limiters. In this case, the interconnected porosity is ideal for producing reinforced composites with improved mechanical and heat conducting properties. In this paper we describe a few simple methods for fabricating large grain YBCO superconductors with various predefined porous structures via an infiltration process from tailored, porous Y2BaCuO5 (Y-211) pre-forms manufactured by a variety of techniques, including slurry-coating of standard polyurethane foams to replicate their structure. Foams produced by this method typically have a strut thickness of a few hundred µm and pore sizes ranging from 10 to 100 pores per inch (PPI). Foams with increased strut thickness of up to millimetre dimensions can be produced by embedding organic ball spacers within the Y-211 pre-form followed by a burn-out and sintering process. Single-domain YBCO bulk materials with cellular and pre-defined 3D interconnected porosity may be produced by a similar process using tailored wax structures in Y-211 castings.

Mesoporous Silica Gel-Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler.

PubMed

Lee, Jian-Yuan; Wang, Yining; Tang, Chuyang Y; Huo, Fengwei

2015-11-23

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4-30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores.

Importance of filter’s microstructure in dynamic filtration modeling of gasoline particulate filters (GPFs): Inhomogeneous porosity and pore size distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jian; Stewart, Mark L.; Zelenyuk, Alla

The state-of-the-art multiscale modeling of GPFs including channel scale, wall scale, and pore scale is described. The microstructures of two GPFs were experimentally characterized. The pore size distributions of the GPFs were determined by mercury porosimetry. The porosity was measured by X-ray computed tomography (CT) and found to be inhomogeneous across the substrate wall. The significance of pore size distribution with respect to filtration performance was analyzed. The predictions of filtration efficiency were improved by including the pore size distribution in the filtration model. A dynamic heterogeneous multiscale filtration (HMF) model was utilized to simulate particulate filtration on a singlemore » channel particulate filter with realistic particulate emissions from a spark-ignition direct-injection (SIDI) gasoline engine. The dynamic evolution of filter’s microstructure and macroscopic filtration characteristics including mass- and number-based filtration efficiencies and pressure drop were predicted and discussed. The microstructure of the GPF substrate including inhomogeneous porosity and pore size distribution is found to significantly influence local particulate deposition inside the substrate and macroscopic filtration performance and is recommended to be resolved in the filtration model to simulate and evaluate the filtration performance of GPFs.« less

Importance of filter’s microstructure in dynamic filtration modeling of gasoline particulate filters (GPFs): Inhomogeneous porosity and pore size distribution

DOE PAGES

Gong, Jian; Stewart, Mark L.; Zelenyuk, Alla; ...

2018-01-03

The state-of-the-art multiscale modeling of gasoline particulate filter (GPF) including channel scale, wall scale, and pore scale is described. The microstructures of two GPFs were experimentally characterized. The pore size distributions of the GPFs were determined by mercury porosimetry. The porosity was measured by X-ray computed tomography (CT) and found to be inhomogeneous across the substrate wall. The significance of pore size distribution with respect to filtration performance was analyzed. The predictions of filtration efficiency were improved by including the pore size distribution in the filtration model. A dynamic heterogeneous multiscale filtration (HMF) model was utilized to simulate particulate filtrationmore » on a single channel particulate filter with realistic particulate emissions from a spark-ignition direct-injection (SIDI) gasoline engine. The dynamic evolution of filter’s microstructure and macroscopic filtration characteristics including mass- and number-based filtration efficiencies and pressure drop were predicted and discussed. In conclusion, the microstructure of the GPF substrate including inhomogeneous porosity and pore size distribution is found to significantly influence local particulate deposition inside the substrate and macroscopic filtration performance and is recommended to be resolved in the filtration model to simulate and evaluate the filtration performance of GPFs.« less

Mesoporous Silica Gel–Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler

PubMed Central

Lee, Jian-Yuan; Wang, Yining; Tang, Chuyang Y.; Huo, Fengwei

2015-01-01

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4–30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores. PMID:26592565

Importance of filter’s microstructure in dynamic filtration modeling of gasoline particulate filters (GPFs): Inhomogeneous porosity and pore size distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jian; Stewart, Mark L.; Zelenyuk, Alla

The state-of-the-art multiscale modeling of gasoline particulate filter (GPF) including channel scale, wall scale, and pore scale is described. The microstructures of two GPFs were experimentally characterized. The pore size distributions of the GPFs were determined by mercury porosimetry. The porosity was measured by X-ray computed tomography (CT) and found to be inhomogeneous across the substrate wall. The significance of pore size distribution with respect to filtration performance was analyzed. The predictions of filtration efficiency were improved by including the pore size distribution in the filtration model. A dynamic heterogeneous multiscale filtration (HMF) model was utilized to simulate particulate filtrationmore » on a single channel particulate filter with realistic particulate emissions from a spark-ignition direct-injection (SIDI) gasoline engine. The dynamic evolution of filter’s microstructure and macroscopic filtration characteristics including mass- and number-based filtration efficiencies and pressure drop were predicted and discussed. In conclusion, the microstructure of the GPF substrate including inhomogeneous porosity and pore size distribution is found to significantly influence local particulate deposition inside the substrate and macroscopic filtration performance and is recommended to be resolved in the filtration model to simulate and evaluate the filtration performance of GPFs.« less

Easy-to-Fabricate and High-Sensitivity LSPR Type Specific Protein Detection Sensor Using AAO Nano-Pore Size Control

PubMed Central

Kim, Sae-Wan; Lee, Jae-Sung; Lee, Sang-Won; Kang, Byoung-Ho; Kwon, Jin-Beom; Kim, Ok-Sik; Kim, Ju-Seong; Kim, Eung-Soo; Kwon, Dae-Hyuk; Kang, Shin-Won

2017-01-01

In this study, we developed a pore size/pore area-controlled optical biosensor-based anodic aluminum oxide (AAO) nanostructure. As the pore size of AAO increases, the unit cell of AAO increases, which also increases the non-pore area to which the antibody binds. The increase in the number of antibodies immobilized on the surface of the AAO enables effective detection of trace amounts of antigen, because increased antigen-antibody bonding results in a larger surface refractive index change. High sensitivity was thus achieved through amplification of the interference wave of two vertically-incident reflected waves through the localized surface plasmon resonance phenomenon. The sensitivity of the fabricated sensor was evaluated by measuring the change in wavelength with the change in the refractive index of the device surface, and sensitivity was increased with increasing pore-size and non-pore area. The sensitivity of the fabricated sensor was improved and up to 11.8 ag/mL serum amyloid A1 antigen was detected. In addition, the selectivity of the fabricated sensor was confirmed through a reaction with a heterogeneous substance, C-reactive protein antigen. By using hard anodization during fabrication of the AAO, the fabrication time of the device was reduced and the AAO chip was fabricated quickly and easily. PMID:28406469

Investigating the effect of sputtering conditions on the physical properties of aluminum thin film and the resulting alumina template

NASA Astrophysics Data System (ADS)

Taheriniya, Shabnam; Parhizgar, Sara Sadat; Sari, Amir Hossein

2018-06-01

To study the alumina template pore size distribution as a function of Al thin film grain size distribution, porous alumina templates were prepared by anodizing sputtered aluminum thin films. To control the grain size the aluminum samples were sputtered with the rate of 0.5, 1 and 2 Å/s and the substrate temperature was either 25, 75 or 125 °C. All samples were anodized for 120 s in 1 M sulfuric acid solution kept at 1 °C while a 15 V potential was being applied. The standard deviation value for samples deposited at room temperature but with different rates is roughly 2 nm in both thin film and porous template form but it rises to approximately 4 nm with substrate temperature. Samples with the average grain size of 13, 14, 18.5 and 21 nm respectively produce alumina templates with an average pore size of 8.5, 10, 15 and 16 nm in that order which shows the average grain size limits the average pore diameter in the resulting template. Lateral correlation length and grain boundary effect are other factors that affect the pore formation process and pore size distribution by limiting the initial current density.

Revealing the influence of water-cement ratio on the pore size distribution in hydrated cement paste by using cyclohexane

NASA Astrophysics Data System (ADS)

Bede, Andrea; Ardelean, Ioan

2017-12-01

Varying the amount of water in a concrete mix will influence its final properties considerably due to the changes in the capillary porosity. That is why a non-destructive technique is necessary for revealing the capillary pore distribution inside hydrated cement based materials and linking the capillary porosity with the macroscopic properties of these materials. In the present work, we demonstrate a simple approach for revealing the differences in capillary pore size distributions introduced by the preparation of cement paste with different water-to-cement ratios. The approach relies on monitoring the nuclear magnetic resonance transverse relaxation distribution of cyclohexane molecules confined inside the cement paste pores. The technique reveals the whole spectrum of pores inside the hydrated cement pastes, allowing a qualitative and quantitative analysis of different pore sizes. The cement pastes with higher water-to-cement ratios show an increase in capillary porosity, while for all the samples the intra-C-S-H and inter-C-S-H pores (also known as gel pores) remain unchanged. The technique can be applied to various porous materials with internal mineral surfaces.

Gas permeability of ice-templated, unidirectional porous ceramics.

PubMed

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J

2016-01-01

We investigate the gas flow behavior of unidirectional porous ceramics processed by ice-templating. The pore volume ranged between 54% and 72% and pore size between 2.9 [Formula: see text]m and 19.1 [Formula: see text]m. The maximum permeability ([Formula: see text] [Formula: see text] m[Formula: see text]) was measured in samples with the highest total pore volume (72%) and pore size (19.1 [Formula: see text]m). However, we demonstrate that it is possible to achieve a similar permeability ([Formula: see text] [Formula: see text] m[Formula: see text]) at 54% pore volume by modification of the pore shape. These results were compared with those reported and measured for isotropic porous materials processed by conventional techniques. In unidirectional porous materials tortuosity ([Formula: see text]) is mainly controlled by pore size, unlike in isotropic porous structures where [Formula: see text] is linked to pore volume. Furthermore, we assessed the applicability of Ergun and capillary model in the prediction of permeability and we found that the capillary model accurately describes the gas flow behavior of unidirectional porous materials. Finally, we combined the permeability data obtained here with strength data for these materials to establish links between strength and permeability of ice-templated materials.

Partitioning of habitable pore space in earthworm burrows.

PubMed

Gorres, Josef H; Amador, Jose A

2010-03-01

Earthworms affect macro-pore structure of soils. However, some studies suggest that earthworm burrow walls and casts themselves differ greatly in structure from surrounding soils, potentially creating habitat for microbivorours nematodes which accelerate the decomposition and C and N mineralization. In this study aggregates were sampled from the burrow walls of the anecic earthworm Lumbricus terrestris and bulk soil (not altered by earthworms) from mesocosm incubated in the lab for 0, 1, 3, 5 and 16 weeks. Pore volumes and pore sizes were measured in triplicate with Mercury Intrusion Porosimetry (MIP). This method is well suited to establish pore size structure in the context of habitat, because it measures the stepwise intrusion of mercury from the outside of the aggregate into ever smaller pores. The progress of mercury into the aggregate interior thus resembles potential paths of a nematode into accessible habitable pore spaces residing in an aggregate. Total specific pore volume, V(s), varied between 0.13 and 0.18 mL/g and increased from 3 to 16 weeks in both burrow and bulk soil. Differences between total V(s) of bulk and burrow samples were not significant on any sampling date. However, differences were significant for pore size fractions at the scale of nematode body diameter.

Partitioning of habitable pore space in earthworm burrows

PubMed Central

Amador, Jose A.

2010-01-01

Earthworms affect macro-pore structure of soils. However, some studies suggest that earthworm burrow walls and casts themselves differ greatly in structure from surrounding soils, potentially creating habitat for microbivorours nematodes which accelerate the decomposition and C and N mineralization. In this study aggregates were sampled from the burrow walls of the anecic earthworm Lumbricus terrestris and bulk soil (not altered by earthworms) from mesocosm incubated in the lab for 0, 1, 3, 5 and 16 weeks. Pore volumes and pore sizes were measured in triplicate with Mercury Intrusion Porosimetry (MIP). This method is well suited to establish pore size structure in the context of habitat, because it measures the stepwise intrusion of mercury from the outside of the aggregate into ever smaller pores. The progress of mercury into the aggregate interior thus resembles potential paths of a nematode into accessible habitable pore spaces residing in an aggregate. Total specific pore volume, Vs, varied between 0.13 and 0.18 mL/g and increased from 3 to 16 weeks in both burrow and bulk soil. Differences between total Vs of bulk and burrow samples were not significant on any sampling date. However, differences were significant for pore size fractions at the scale of nematode body diameter. PMID:22736839

Tailoring Pore Size and Chemical Interior of near 1 nm Sized Pores in a Nanoporous Polymer Based on a Discotic Liquid Crystal

PubMed Central

2017-01-01

A triazine based disc shaped molecule with two hydrolyzable units, imine and ester groups, was polymerized via acyclic diene metathesis in the columnar hexagonal (Colhex) LC phase. Fabrication of a cationic nanoporous polymer (pore diameter ∼1.3 nm) lined with ammonium groups at the pore surface was achieved by hydrolysis of the imine linkage. Size selective aldehyde uptake by the cationic porous polymer was demonstrated. The anilinium groups in the pores were converted to azide as well as phenyl groups by further chemical treatment, leading to porous polymers with neutral functional groups in the pores. The pores were enlarged by further hydrolysis of the ester groups to create ∼2.6 nm pores lined with −COONa surface groups. The same pores could be obtained in a single step without first hydrolyzing the imine linkage. XRD studies demonstrated that the Colhex order of the monomer was preserved after polymerization as well as in both the nanoporous polymers. The porous anionic polymer lined with −COOH groups was further converted to the −COOLi, −COONa, −COOK, −COOCs, and −COONH4 salts. The porous polymer lined with −COONa groups selectively adsorbs a cationic dye, methylene blue, over an anionic dye. PMID:28416888

The use of magnetic resonance sounding for quantifying specific yield and transmissivity in hard rock aquifers: The example of Benin

NASA Astrophysics Data System (ADS)

Vouillamoz, J. M.; Lawson, F. M. A.; Yalo, N.; Descloitres, M.

2014-08-01

Hundreds of thousands of boreholes have been drilled in hard rocks of Africa and Asia for supplying human communities with drinking water. Despite the common use of geophysics for improving the siting of boreholes, a significant number of drilled holes does not deliver enough water to be equipped (e.g. 40% on average in Benin). As compared to other non-invasive geophysical methods, magnetic resonance sounding (MRS) is selective to groundwater. However, this distinctive feature has not been fully used in previous published studies for quantifying the drainable groundwater in hard rocks (i.e. the specific yield) and the short-term productivity of aquifer (i.e. the transmissivity). We present in this paper a comparison of MRS results (i.e. the water content and pore-size parameter) with both specific yield and transmissivity calculated from long duration pumping tests. We conducted our experiments in six sites located in different hard rock groups in Benin, thus providing a unique data set to assess the usefulness of MRS in hard rock aquifers. We found that the MRS water content is about twice the specific yield. We also found that the MRS pore-size parameter is well correlated with the specific yield. Thus we proposed two linear equations for calculating the specific yield from the MRS water content (with an uncertainty of about 10%) and from the pore-size parameter (with an uncertainty of about 20%). The later has the advantage of defining a so-named MRS cutoff time value for indentifying non-drainable MRS water content and thus low groundwater reserve. We eventually propose a nonlinear equation for calculating the specific yield using jointly the MRS water content and the pore-size parameters, but this approach has to be confirmed with further investigations. This study also confirmed that aquifer transmissivity can be estimated from MRS results with an uncertainty of about 70%. We conclude that MRS can be usefully applied for estimating aquifer specific yield and transmissivity in weathered hard rock aquifers. Our result will contribute to the improvement of well siting and groundwater management in hard rocks.

Linear-sweep voltammetry of a soluble redox couple in a cylindrical electrode

NASA Technical Reports Server (NTRS)

Weidner, John W.

1991-01-01

An approach is described for using the linear sweep voltammetry (LSV) technique to study the kinetics of flooded porous electrodes by assuming a porous electrode as a collection of identical noninterconnected cylindrical pores that are filled with electrolyte. This assumption makes possible to study the behavior of this ideal electrode as that of a single pore. Alternatively, for an electrode of a given pore-size distribution, it is possible to predict the performance of different pore sizes and then combine the performance values.

Freeze-cast alumina pore networks: Effects of freezing conditions and dispersion medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, S. M.; Xiao, X.; Faber, K. T.

Alumina ceramics were freeze-cast from water- and camphene-based slurries under varying freezing conditions and examined using X-ray computed tomography (XCT). Pore network characteristics, i.e., porosity, pore size, geometric surface area, and tortuosity, were measured from XCT reconstructions and the data were used to develop a model to predict feature size from processing conditions. Classical solidification theory was used to examine relationships between pore size, temperature gradients, and freezing front velocity. Freezing front velocity was subsequently predicted from casting conditions via the two-phase Stefan problem. Resulting models for water-based samples agreed with solidification-based theories predicting lamellar spacing of binary eutectic alloys,more » and models for camphene-based samples concurred with those for dendritic growth. Relationships between freezing conditions and geometric surface area were also modeled by considering the inverse relationship between pore size and surface area. Tortuosity was determined to be dependent primarily on the type of dispersion medium. (C) 2015 Elsevier Ltd. All rights reserved.« less

A solid with a hierarchical tetramodal micro-meso-macro pore size distribution

PubMed Central

Ren, Yu; Ma, Zhen; Morris, Russell E.; Liu, Zheng; Jiao, Feng; Dai, Sheng; Bruce, Peter G.

2013-01-01

Porous solids have an important role in addressing some of the major energy-related problems facing society. Here we describe a porous solid, α-MnO2, with a hierarchical tetramodal pore size distribution spanning the micro-, meso- and macro pore range, centred at 0.48, 4.0, 18 and 70 nm. The hierarchical tetramodal structure is generated by the presence of potassium ions in the precursor solution within the channels of the porous silica template; the size of the potassium ion templates the microporosity of α-MnO2, whereas their reactivity with silica leads to larger mesopores and macroporosity, without destroying the mesostructure of the template. The hierarchical tetramodal pore size distribution influences the properties of α-MnO2 as a cathode in lithium batteries and as a catalyst, changing the behaviour, compared with its counterparts with only micropores or bimodal micro/mesopores. The approach has been extended to the preparation of LiMn2O4 with a hierarchical pore structure. PMID:23764887

Structural characterization of porous low-k thin films prepared by different techniques using x-ray porosimetry

NASA Astrophysics Data System (ADS)

Lee, Hae-Jeong; Soles, Christopher L.; Liu, Da-Wei; Bauer, Barry J.; Lin, Eric K.; Wu, Wen-li; Grill, Alfred

2004-03-01

Three different types of porous low-k dielectric films, with similar dielectric constants, are characterized using x-ray porosimetry (XRP). XRP is used to extract critical structural information, such as the average density, wall density, porosity, and pore size distribution. The materials include a plasma-enhanced-chemical-vapor-deposited carbon-doped oxide film composed of Si, C, O, and H (SiCOH) and two spin cast silsesquioxane type films—methylsilsesquioxane with a polymeric porogen (porous MSQ) and hydrogensilsesquioxane with a high boiling point solvent (porous HSQ). The porous SiCOH film displays the smallest pore sizes, while porous HSQ film has both the highest density wall material and porosity. The porous MSQ film exhibits a broad range of pores with the largest average pore size. We demonstrate that the average pore size obtained by the well-established method of neutron scattering and x-ray reflectivity is in good agreement with the XRP results.

Influence of lyophilization factors and gelatin concentration on pore structures of atelocollagen/gelatin sponge biomaterial.

PubMed

Yang, Longqiang; Tanabe, Koji; Miura, Tadashi; Yoshinari, Masao; Takemoto, Shinji; Shintani, Seikou; Kasahara, Masataka

2017-07-26

This study aimed to investigate influences of lyophilization factors and gelatin concentration on pore structures of ACG sponge. ACG sponges of different freezing temperatures (-30, -80 and -196 o C), freezing times (1, 2 and 24 h), gelatin concentrations (0.6%AC+0.15%G, 0.6%AC+0.6%G and 0.6%AC+2.4%G), and with 500 μM fluvastatin were fabricated. Pore structures including porosity and pore size were analyzed by scanning electron microscopy and ImageJ. The cytotoxic effects of ACG sponges were evaluated in vitro. Freezing temperature did not affect porosity while high freezing temperature (-30 o C) increased pore size. The high gelatin concentration group (0.6%AC+2.4%G) had decreased porosity and pore size. Freezing time and 500 μM fluvastatin did not affect pore structures. The cytotoxicity and cell proliferation assays revealed that ACG sponges had no cytotoxic effects on human mesenchymal stromal cell growth and proliferation. These results indicate that ACG sponge may be a good biomaterial scaffold for bone regeneration.

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix

PubMed Central

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N.

2017-01-01

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix. PMID:28772465

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix.

PubMed

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N

2017-01-25

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix.

Synthesis and chromatographic characterization of dextran-coated zirconia high-performance liquid chromatographic stationary phases.

PubMed

Dunlap, C J; Carr, P W

1996-10-11

Porous zirconia particles made by the oil emulsion (OE) method and the polymerization-induced colloid aggregation (PICA) method have been coated with a small, carboxymethylated (approximately 5%) dextran polymer and crosslinked in place. The parameters of the coating process (dextran concentration, adsorption time and crosslinker concentration) have all been examined and an optimum value for each determined. The coated and uncoated materials were characterized by nitrogen sorptometry and size-exclusion chromatography (SEC) using solutes (polystyrenes and dextrans) of well-defined molecular masses. Nitrogen sorptometry results show that the PICA material has a much lower pore volume and smaller pore diameter than do the OE materials. Despite this, the elution volumes of the SEC probes change very little upon polymer coating the PICA material while the OE material shows a very large change upon coating.

Fibril growth kinetics link buffer conditions and topology of 3D collagen I networks.

PubMed

Kalbitzer, Liv; Pompe, Tilo

2018-02-01

Three-dimensional fibrillar networks reconstituted from collagen I are widely used as biomimetic scaffolds for in vitro and in vivo cell studies. Various physicochemical parameters of buffer conditions for in vitro fibril formation are well known, including pH-value, ion concentrations and temperature. However, there is a lack of a detailed understanding of reconstituting well-defined 3D network topologies, which is required to mimic specific properties of the native extracellular matrix. We screened a wide range of relevant physicochemical buffer conditions and characterized the topology of the reconstituted 3D networks in terms of mean pore size and fibril diameter. A congruent analysis of fibril formation kinetics by turbidimetry revealed the adjustment of the lateral growth phase of fibrils by buffer conditions to be key in the determination of pore size and fibril diameter of the networks. Although the kinetics of nucleation and linear growth phase were affected by buffer conditions as well, network topology was independent of those two growth phases. Overall, the results of our study provide necessary insights into how to engineer 3D collagen matrices with an independent control over topology parameters, in order to mimic in vivo tissues in in vitro experiments and tissue engineering applications. The study reports a comprehensive analysis of physicochemical conditions of buffer solutions to reconstitute defined 3D collagen I matrices. By a combined analysis of network topology, i.e., pore size and fibril diameter, and the kinetics of fibril formation we can reveal the dependence of 3D network topology on buffer conditions, such as pH-value, phosphate concentration and sodium chloride content. With those results we are now able to provide engineering strategies to independently tune the topology parameters of widely used 3D collagen scaffolds based on the buffer conditions. By that, we enable the straightforward mimicking of extracellular matrices of in vivo tissues for in vitro cell culture experiments and tissue engineering applications. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Performance of Small Pore Microchannel Plates

NASA Technical Reports Server (NTRS)

Siegmund, O. H. W.; Gummin, M. A.; Ravinett, T.; Jelinsky, S. R.; Edgar, M.

1995-01-01

Small pore size microchannel plates (MCP's) are needed to satisfy the requirements for future high resolution small and large format detectors for astronomy. MCP's with pore sizes in the range 5 micron to 8 micron are now being manufactured, but they are of limited availability and are of small size. We have obtained sets of Galileo 8 micron and 6.5 micron MCP's, and Philips 6 micron and 7 micron pore MCP's, and compared them to our larger pore MCP Z stacks. We have tested back to back MCP stacks of four of these MCP's and achieved gains greater than 2 x 1O(exp 7) with pulse height distributions of less than 40% FWHM, and background rates of less than 0.3 events sec(exp -1) cm(exp -2). Local counting rates up to approx. 100 events/pore/sec have been attained with little drop of the MCP gain. The bare MCP quantum efficiencies are somewhat lower than those expected, however. Flat field images are characterized by an absence of MCP fixed pattern noise.

Hydroxyapatite scaffolds processed using a TBA-based freeze-gel casting/polymer sponge technique.

PubMed

Yang, Tae Young; Lee, Jung Min; Yoon, Seog Young; Park, Hong Chae

2010-05-01

A novel freeze-gel casting/polymer sponge technique has been introduced to fabricate porous hydroxyapatite scaffolds with controlled "designer" pore structures and improved compressive strength for bone tissue engineering applications. Tertiary-butyl alcohol (TBA) was used as a solvent in this work. The merits of each production process, freeze casting, gel casting, and polymer sponge route were characterized by the sintered microstructure and mechanical strength. A reticulated structure with large pore size of 180-360 microm, which formed on burn-out of polyurethane foam, consisted of the strut with highly interconnected, unidirectional, long pore channels (approximately 4.5 microm in dia.) by evaporation of frozen TBA produced in freeze casting together with the dense inner walls with a few, isolated fine pores (<2 microm) by gel casting. The sintered porosity and pore size generally behaved in an opposite manner to the solid loading, i.e., a high solid loading gave low porosity and small pore size, and a thickening of the strut cross section, thus leading to higher compressive strengths.

Size Control of Porous Silicon-Based Nanoparticles via Pore-Wall Thinning.

PubMed

Secret, Emilie; Leonard, Camille; Kelly, Stefan J; Uhl, Amanda; Cozzan, Clayton; Andrew, Jennifer S

2016-02-02

Photoluminescent silicon nanocrystals are very attractive for biomedical and electronic applications. Here a new process is presented to synthesize photoluminescent silicon nanocrystals with diameters smaller than 6 nm from a porous silicon template. These nanoparticles are formed using a pore-wall thinning approach, where the as-etched porous silicon layer is partially oxidized to silica, which is dissolved by a hydrofluoric acid solution, decreasing the pore-wall thickness. This decrease in pore-wall thickness leads to a corresponding decrease in the size of the nanocrystals that make up the pore walls, resulting in the formation of smaller nanoparticles during sonication of the porous silicon. Particle diameters were measured using dynamic light scattering, and these values were compared with the nanocrystallite size within the pore wall as determined from X-ray diffraction. Additionally, an increase in the quantum confinement effect is observed for these particles through an increase in the photoluminescence intensity of the nanoparticles compared with the as-etched nanoparticles, without the need for a further activation step by oxidation after synthesis.

Structural control in the synthesis of inorganic porous materials

NASA Astrophysics Data System (ADS)

Holland, Brian Thomas

Mesoporous (2.0--50.0 nm pore diameter) and macroporous (50.0 nm on up) materials have been the basis of my studies. These materials, for many years, possessed large pore size distributions. Recently, however, it has been possible to synthesize both mesoporous and macroporous materials that possess highly ordered uniform pores throughout the material. Workers at Mobil Corporation in 1992 discovered a hexagonally arrayed mesoporous material, designated MCM-41, which exhibited uniform pores ranging from 2.0--10.0 nm in diameter. In my work MCM-41 was used as a host for the incorporation of meso-tetrakis(5-trimethylammoniumpentyl)porphyrin (TMAP-Cl) and as a model for the synthesis of mesoporous alumino- and galloaluminophosphates which were created using cluster precursors of the type MO4Al 12(OH)24(H2O)12 7+, M = Al or Ga. Macroporous materials with uniform pore sizes have been synthesized by our group with frameworks consisting of a variety of metal oxides, metals, organosilanes, aluminophosphates and bimodal pores. These materials are synthesized from the addition of metal precursors to preordered polystyrene spheres. Removal of the spheres results in the formation of macropores with highly uniform pores extending microns in length. Porous materials with uniform and adjustable pore sizes in the mesoporous and macroporous size regimes offer distinct advantages over non-ordered materials for numerous reasons. First, catalysis reactions that are based on the ability of the porous materials to impose size and shape restrictions on the substrate are of considerable interest in the petroleum and petrochemical industries. As pore diameters increase larger molecules can be incorporated into the pores, i.e., biological molecules, dyes, etc. For the macroporous materials synthesized by our group it has been envisioned that these structures may not only be used for catalysis because of increased efficiencies of flow but for more advanced applications, e.g., photonic crystals, porous electrodes, electrochemical capacitors, etc. One of the more interesting macroporous materials takes advantage of having silicalite as the framework. This bimodal pore material may find use as an acid catalyst as aluminum is doped into the framework.

Multiscale modeling of porous ceramics using movable cellular automaton method

NASA Astrophysics Data System (ADS)

Smolin, Alexey Yu.; Smolin, Igor Yu.; Smolina, Irina Yu.

2017-10-01

The paper presents a multiscale model for porous ceramics based on movable cellular automaton method, which is a particle method in novel computational mechanics of solid. The initial scale of the proposed approach corresponds to the characteristic size of the smallest pores in the ceramics. At this scale, we model uniaxial compression of several representative samples with an explicit account of pores of the same size but with the unique position in space. As a result, we get the average values of Young's modulus and strength, as well as the parameters of the Weibull distribution of these properties at the current scale level. These data allow us to describe the material behavior at the next scale level were only the larger pores are considered explicitly, while the influence of small pores is included via effective properties determined earliar. If the pore size distribution function of the material has N maxima we need to perform computations for N-1 levels in order to get the properties step by step from the lowest scale up to the macroscale. The proposed approach was applied to modeling zirconia ceramics with bimodal pore size distribution. The obtained results show correct behavior of the model sample at the macroscale.

Modeling of submicrometer aerosol penetration through sintered granular membrane filters.

PubMed

Marre, Sonia; Palmeri, John; Larbot, André; Bertrand, Marielle

2004-06-01

We present a deep-bed aerosol filtration model that can be used to estimate the efficiency of sintered granular membrane filters in the region of the most penetrating particle size. In this region the capture of submicrometer aerosols, much smaller than the filter pore size, takes place mainly via Brownian diffusion and direct interception acting in synergy. By modeling the disordered sintered grain packing of such filters as a simple cubic lattice, and mapping the corresponding 3D connected pore volume onto a discrete cylindrical pore network, the efficiency of a granular filter can be estimated, using new analytical results for the efficiency of cylindrical pores. This model for aerosol penetration in sintered granular filters includes flow slip and the kinetics of particle capture by the pore surface. With a unique choice for two parameters, namely the structural tortuosity and effective kinetic coefficient of particle adsorption, this semiempirical model can account for the experimental efficiency of a new class of "high-efficiency particulate air" ceramic membrane filters as a function of particle size over a wide range of filter thickness and texture (pore size and porosity) and operating conditions (face velocity).

Non-scaling behavior of electroosmotic flow in voltage-gated nanopores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lian, Cheng; Gallegos, Alejandro; Liu, Honglai

2017-01-01

Ionic size effects and electrostatic correlations result in the non-monotonic dependence of the electrical conductivity on the pore size. For ion transport at a high gating voltage, the conductivity oscillates with the pore size due to a significant overlap of the electric double layers.

Pore size regulates cell and tissue interactions with PLGA-CaP scaffolds used for bone engineering.

PubMed

Sicchieri, Luciana Gonçalves; Crippa, Grasiele Edilaine; de Oliveira, Paulo Tambasco; Beloti, Marcio Mateus; Rosa, Adalberto Luiz

2012-02-01

A common subject in bone tissue engineering is the need for porous scaffolds to support cell and tissue interactions aiming at repairing bone tissue. As poly(lactide-co-glycolide)-calcium phosphate (PLGA-CaP) scaffolds can be manufactured with different pore sizes, the aim of this study was to evaluate the effect of pore diameter on osteoblastic cell responses and bone tissue formation. Scaffolds were prepared with 85% porosity, with pore diameters in the ranges 470-590, 590-850 and 850-1200 µm. Rat bone marrow stem cells differentiated into osteoblasts were cultured on the scaffolds for up to 10 days to evaluate cell growth, alkaline phosphatase (ALP) activity and the gene expression of the osteoblast markers RUNX2, OSX, COL, MSX2, ALP, OC and BSP by real-time PCR. Scaffolds were implanted in critical size rat calvarial defects for 2, 4, and 8 weeks for histomorphometric analysis. Cell growth and ALP activity were not affected by the pore size; however, there was an increase in the gene expression of osteoblastic markers with the increase in the pore sizes. At 2 weeks all scaffolds displayed a similar amount of bone and blood vessels formation. At 4 and 8 weeks much more bone formation and an increased number of blood vessels were observed in scaffolds with pores of 470-590 µm. These results show that PLGA-CaP is a promising biomaterial for bone engineering. However, ideally, combinations of larger (-1000 µm) and smaller (-500 µm) pores in a single scaffold would optimize cellular and tissue responses during bone healing. Copyright © 2011 John Wiley & Sons, Ltd.

Structural evolution of nanoporous silica thin films studied by positron annihilation spectroscopy and Fourier transform infrared spectroscopy

NASA Astrophysics Data System (ADS)

Patel, N.; Mariazzi, S.; Toniutti, L.; Checchetto, R.; Miotello, A.; Dirè, S.; Brusa, R. S.

2007-09-01

Three series of silica thin films with thicknesses in the 300 nm range were deposited by spin coating on Si substrates using different compositions of the sol precursors. Film samples were thermally treated in static air at temperatures ranging from 300 to 900 °C. The effect of sol precursors and thermal treatment temperature on the film porosity was analysed by Fourier transform infrared (FTIR) spectroscopy, depth profiling with positron annihilation spectroscopy (DP-PAS) and the analysis of the capacitance-voltage (C-V) characteristic. The maximum of the total porosity was found to occur at a temperature of 600 °C when removal of porogen and OH groups was completed. Film densification due to the collapsing of the pores was observed after drying at 900 °C. DP-PAS provides evidence that the increase in the total porosity is related to a progressive increase in the pore size. The increase in the pore size never gives rise to the onset of connected porosity. In the silica film samples prepared using a low acidity sol precursor, the pore size is always lower than 1 nm. By increasing the acid catalyst ratio in the sol, larger pores are formed. Pores with size larger than 2.3 nm can be obtained by adding porogen to the sol. In each series of silica film samples the shift of the antisymmetric Si-O-Si transversal optical (TO3) mode upon thermal treatment correlates with a change of the pore size as evidenced by DP-PAS analysis. The pore microstructure of the three series of silica films is different at all the examined treatment temperatures and depends on the composition of the precursor sol.

Fabrication of channeled scaffolds with ordered array of micro-pores through microsphere leaching and indirect Rapid Prototyping technique.

PubMed

Tan, J Y; Chua, C K; Leong, K F

2013-02-01

Advanced scaffold fabrication techniques such as Rapid Prototyping (RP) are generally recognized to be advantageous over conventional fabrication methods in terms architectural control and reproducibility. Yet, most RP techniques tend to suffer from resolution limitations which result in scaffolds with uncontrollable, random-size pores and low porosity, albeit having interconnected channels which is characteristically present in most RP scaffolds. With the increasing number of studies demonstrating the profound influences of scaffold pore architecture on cell behavior and overall tissue growth, a scaffold fabrication method with sufficient architectural control becomes imperative. The present study demonstrates the use of RP fabrication techniques to create scaffolds having interconnected channels as well as controllable micro-size pores. Adopted from the concepts of porogen leaching and indirect RP techniques, the proposed fabrication method uses monodisperse microspheres to create an ordered, hexagonal closed packed (HCP) array of micro-pores that surrounds the existing channels of the RP scaffold. The pore structure of the scaffold is shaped using a single sacrificial construct which comprises the microspheres and a dissolvable RP mold that were sintered together. As such, the size of pores as well as the channel configuration of the scaffold can be tailored based on the design of the RP mold and the size of microspheres used. The fabrication method developed in this work can be a promising alternative way of preparing scaffolds with customized pore structures that may be required for specific studies concerning cell-scaffold interactions.

3D Printing of Hierarchical Silk Fibroin Structures.

PubMed

Sommer, Marianne R; Schaffner, Manuel; Carnelli, Davide; Studart, André R

2016-12-21

Like many other natural materials, silk is hierarchically structured from the amino acid level up to the cocoon or spider web macroscopic structures. Despite being used industrially in a number of applications, hierarchically structured silk fibroin objects with a similar degree of architectural control as in natural structures have not been produced yet due to limitations in fabrication processes. In a combined top-down and bottom-up approach, we exploit the freedom in macroscopic design offered by 3D printing and the template-guided assembly of ink building blocks at the meso- and nanolevel to fabricate hierarchical silk porous materials with unprecedented structural control. Pores with tunable sizes in the range 40-350 μm are generated by adding sacrificial organic microparticles as templates to a silk fibroin-based ink. Commercially available wax particles or monodisperse polycaprolactone made by microfluidics can be used as microparticle templates. Since closed pores are generated after template removal, an ultrasonication treatment can optionally be used to achieve open porosity. Such pore templating particles can be further modified with nanoparticles to create a hierarchical template that results in porous structures with a defined nanotopography on the pore walls. The hierarchically porous silk structures obtained with this processing technique can potentially be utilized in various application fields from structural materials to thermal insulation to tissue engineering scaffolds.

Predicting permeability with NMR imaging in the Edwards Limestone/Stuart City Trend

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dewitt, H.; Globe, M.; Sorenson, R.

1996-09-01

Determining pore size and pore geometry relationships in carbonate rocks and relating both to permeability is difficult using traditional logging methods. This problem is further complicated by the presence of abundant microporosity (pore size less than 62 microns) in the Edwards Limestone. The use of Nuclear Magnetic Resonance Imaging (NMR) allows for an alternative approach to evaluating the pore types present by examining the response of hydrogen nuclei contained within the free fluid pore space. By testing the hypothesis that larger pore types exhibit an NMR signal decay much slower than smaller pore types, an estimate of the pore typemore » present, (i.e.) vuggy, interparticle, or micropores, can be inferred. Calibration of the NMR decay curve to known samples with measured petrophysical properties allows for improved predictability of pore types and permeability. The next stage of the analysis involves the application of the calibration technique to the borehole environment using an NMR logging tool to more accurately predict production performance.« less

Ribbed electrode substrates

DOEpatents

Breault, Richard D.; Goller, Glen J.

1983-01-01

A ribbed substrate for an electrochemical cell electrode is made from a mixture of carbon fibers and carbonizable resin and has a mean pore size in the ribs which is 60-75% of the mean pore size of the web portions of the substrate which interconnect the ribs. Preferably the mean pore size of the web portion is 25-45 microns; and, if the substrate includes edge seals parallel to the ribs, the edge seals preferably have a mean pore size no greater than about ten microns. Most preferably the substrate has the same ratio of carbon fibers to polymeric carbon in all areas, including the ribs, webs, and edge seals. A substrate according to the present invention will have better overall performance than prior art substrates and minimizes the substrate thickness required for the substrate to perform all its functions well.

Application of SAXS and SANS in evaluation of porosity, pore size distribution and surface area of coal

USGS Publications Warehouse

Radlinski, A.P.; Mastalerz, Maria; Hinde, A.L.; Hainbuchner, M.; Rauch, H.; Baron, M.; Lin, J.S.; Fan, L.; Thiyagarajan, P.

2004-01-01

This paper discusses the applicability of small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) techniques for determining the porosity, pore size distribution and internal specific surface area in coals. The method is noninvasive, fast, inexpensive and does not require complex sample preparation. It uses coal grains of about 0.8 mm size mounted in standard pellets as used for petrographic studies. Assuming spherical pore geometry, the scattering data are converted into the pore size distribution in the size range 1 nm (10 A??) to 20 ??m (200,000 A??) in diameter, accounting for both open and closed pores. FTIR as well as SAXS and SANS data for seven samples of oriented whole coals and corresponding pellets with vitrinite reflectance (Ro) values in the range 0.55% to 5.15% are presented and analyzed. Our results demonstrate that pellets adequately represent the average microstructure of coal samples. The scattering data have been used to calculate the maximum surface area available for methane adsorption. Total porosity as percentage of sample volume is calculated and compared with worldwide trends. By demonstrating the applicability of SAXS and SANS techniques to determine the porosity, pore size distribution and surface area in coals, we provide a new and efficient tool, which can be used for any type of coal sample, from a thin slice to a representative sample of a thick seam. ?? 2004 Elsevier B.V. All rights reserved.

Pore structure modification of diatomite as sulfuric acid catalyst support by high energy electron beam irradiation and hydrothermal treatment

NASA Astrophysics Data System (ADS)

Li, Chong; Zhang, Guilong; Wang, Min; Chen, Jianfeng; Cai, Dongqing; Wu, Zhengyan

2014-08-01

High energy electron beam (HEEB) irradiation and hydrothermal treatment (HT), were applied in order to remove the impurities and enlarge the pore size of diatomite, making diatomite more suitable to be a catalyst support. The results demonstrated that, through thermal, charge, impact and etching effects, HEEB irradiation could make the impurities in the pores of diatomite loose and remove some of them. Then HT could remove rest of them from the pores and contribute significantly to the modification of the pore size distribution of diatomite due to thermal expansion, water swelling and thermolysis effects. Moreover, the pore structure modification improved the properties (BET (Brunauer-Emmett-Teller) specific surface area, bulk density and pore volume) of diatomite and the catalytic efficiency of the catalyst prepared from the treated diatomite.

A multifunctional role of trialkylbenzenes for the preparation of aqueous colloidal mesostructured/mesoporous silica nanoparticles with controlled pore size, particle diameter, and morphology

NASA Astrophysics Data System (ADS)

Yamada, Hironori; Ujiie, Hiroto; Urata, Chihiro; Yamamoto, Eisuke; Yamauchi, Yusuke; Kuroda, Kazuyuki

2015-11-01

Both the pore size and particle diameter of aqueous colloidal mesostructured/mesoporous silica nanoparticles (CMSS/CMPS) derived from tetrapropoxysilane were effectively and easily controlled by the addition of trialkylbenzenes (TAB). Aqueous highly dispersed CMPS with large pores were successfully obtained through removal of surfactants and TAB by a dialysis process. The pore size (from 4 nm to 8 nm) and particle diameter (from 50 nm to 380 nm) were more effectively enlarged by the addition of 1,3,5-triisopropylbenzene (TIPB) than 1,3,5-trimethylbenzene (TMB), and the enlargement did not cause the variation of the mesostructure and particle morphology. The larger molecular size and higher hydrophobicity of TIPB than TMB induce the incorporation of TIPB into micelles without the structural change. When TMB was used as TAB, the pore size of CMSS was also enlarged while the mesostructure and particle morphology were varied. Interestingly, when tetramethoxysilane and TIPB were used, CMSS with a very small particle diameter (20 nm) with concave surfaces and large mesopores were obtained, which may strongly be related to the initial nucleation of CMSS. A judicious choice of TAB and Si sources is quite important to control the mesostructure, size of mesopores, particle diameter, and morphology.Both the pore size and particle diameter of aqueous colloidal mesostructured/mesoporous silica nanoparticles (CMSS/CMPS) derived from tetrapropoxysilane were effectively and easily controlled by the addition of trialkylbenzenes (TAB). Aqueous highly dispersed CMPS with large pores were successfully obtained through removal of surfactants and TAB by a dialysis process. The pore size (from 4 nm to 8 nm) and particle diameter (from 50 nm to 380 nm) were more effectively enlarged by the addition of 1,3,5-triisopropylbenzene (TIPB) than 1,3,5-trimethylbenzene (TMB), and the enlargement did not cause the variation of the mesostructure and particle morphology. The larger molecular size and higher hydrophobicity of TIPB than TMB induce the incorporation of TIPB into micelles without the structural change. When TMB was used as TAB, the pore size of CMSS was also enlarged while the mesostructure and particle morphology were varied. Interestingly, when tetramethoxysilane and TIPB were used, CMSS with a very small particle diameter (20 nm) with concave surfaces and large mesopores were obtained, which may strongly be related to the initial nucleation of CMSS. A judicious choice of TAB and Si sources is quite important to control the mesostructure, size of mesopores, particle diameter, and morphology. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04465k

Pore network extraction from pore space images of various porous media systems

NASA Astrophysics Data System (ADS)

Yi, Zhixing; Lin, Mian; Jiang, Wenbin; Zhang, Zhaobin; Li, Haishan; Gao, Jian

2017-04-01

Pore network extraction, which is defined as the transformation from irregular pore space to a simplified network in the form of pores connected by throats, is significant to microstructure analysis and network modeling. A physically realistic pore network is not only a representation of the pore space in the sense of topology and morphology, but also a good tool for predicting transport properties accurately. We present a method to extract pore network by employing the centrally located medial axis to guide the construction of maximal-balls-like skeleton where the pores and throats are defined and parameterized. To validate our method, various rock samples including sand pack, sandstones, and carbonates were used to extract pore networks. The pore structures were compared quantitatively with the structures extracted by medial axis method or maximal ball method. The predicted absolute permeability and formation factor were verified against the theoretical solutions obtained by lattice Boltzmann method and finite volume method, respectively. The two-phase flow was simulated through the networks extracted from homogeneous sandstones, and the generated relative permeability curves were compared with the data obtained from experimental method and other numerical models. The results show that the accuracy of our network is higher than that of other networks for predicting transport properties, so the presented method is more reliable for extracting physically realistic pore network.

Fabrication and electrochemical properties of carbon nanotube/polypyrrole composite film electrodes with controlled pore size

NASA Astrophysics Data System (ADS)

Kim, Ji-Young; Kim, Kwang Heon; Kim, Kwang Bum

Carbon nanotube (CNT)/polypyrrole (PPy) composites with controlled pore size in a three-dimensional entangled structure of a CNT film are prepared as electrode materials for a pseudocapacitor. A CNT film electrode containing nanosize silica between the CNTs is first fabricated using an electrostatic spray deposition of a mixed suspension of CNTs and nanosize silica on to a platinium-coated silicon wafer. Later, nanosize silica is removed leaving a three-dimensional entangled structure of a CNT film. Before removal of the silica from the CNT/silica film electrode, PPy is electrochemically deposited on to the CNTs to anchor them in their entangled structure. Control of the pore size of the final CNT/PPy composite film can be achieved by changing the amount of silica in the mixed suspension of CNTs and nanosize silica. Nanosize silica acts as a sacrificial filler to change the pore size of the entangled CNT film. Scanning electron microscopy of the electrochemically prepared PPy on the CNT film substrate shows that the PPy nucleated heterogeneously and deposited on the surface of the CNTs. The specific capacitance and rate capability of the CNT/PPy composite electrode with a heavy loading of PPy of around 80 wt.% can be improved when it is made to have a three-dimensional network of entangled CNTs with interconnected pores through pore size control.

Effects of pore size and dissolved organic matters on diffusion of arsenate in aqueous solution.

PubMed

Wang, Yulong; Wang, Shaofeng; Wang, Xin; Jia, Yongfeng

2017-02-01

Presented here is the influence of membrane pore size and dissolved organic matters on the diffusion coefficient (D) of aqueous arsenate, investigated by the diffusion cell method for the first time. The pH-dependent diffusion coefficient of arsenate was determined and compared with values from previous studies; the coefficient was found to decrease with increasing pH, showing the validity of our novel diffusion cell method. The D value increased dramatically as a function of membrane pore size at small pore sizes, and then increased slowly at pore sizes larger than 2.0μm. Using the ExpAssoc model, the maximum D value was determined to be 11.2565×10 -6 cm 2 /sec. The presence of dissolved organic matters led to a dramatic increase of the D of arsenate, which could be attributed to electrostatic effects and ionic effects of salts. These results improve the understanding of the diffusion behavior of arsenate, especially the important role of various environmental parameters in the study and prediction of the migration of arsenate in aquatic water systems. Copyright © 2016. Published by Elsevier B.V.

Construction of hierarchically porous metal–organic frameworks through linker labilization

DOE PAGES

Yuan, Shuai; Zou, Lanfang; Qin, Jun-Sheng; ...

2017-05-25

One major goal of metal–organic framework (MOF) research is the expansion of pore size and volume. Although many approaches have been attempted to increase the pore size of MOF materials, it is still a challenge to construct MOFs with precisely customized pore apertures for specific applications. W present a new method, namely linker labilization, to increase the MOF porosity and pore size, giving rise to hierarchical-pore architectures. Microporous MOFs with robust metal nodes and pro-labile linkers were initially synthesized. The mesopores were subsequently created as crystal defects through the splitting of a pro-labile-linker and the removal of the linker fragmentsmore » by acid treatment. We also demonstrate that linker labilization method can create controllable hierarchical porous structures in stable MOFs, which facilitates the diffusion and adsorption process of guest molecules to improve the performances of MOFs in adsorption and catalysis.« less

Advances in Porous Biomaterials for Dental and Orthopaedic Applications

PubMed Central

Mour, Meenakshi; Das, Debarun; Winkler, Thomas; Hoenig, Elisa; Mielke, Gabriela; Morlock, Michael M.; Schilling, Arndt F.

2010-01-01

The connective hard tissues bone and teeth are highly porous on a micrometer scale, but show high values of compression strength at a relatively low weight. The fabrication of porous materials has been actively researched and different processes have been developed that vary in preparation complexity and also in the type of porous material that they produce. Methodologies are available for determination of pore properties. The purpose of the paper is to give an overview of these methods, the role of porosity in natural porous materials and the effect of pore properties on the living tissues. The minimum pore size required to allow the ingrowth of mineralized tissue seems to be in the order of 50 µm: larger pore sizes seem to improve speed and depth of penetration of mineralized tissues into the biomaterial, but on the other hand impair the mechanical properties. The optimal pore size is therefore dependent on the application and the used material.

Construction of hierarchically porous metal-organic frameworks through linker labilization

NASA Astrophysics Data System (ADS)

Yuan, Shuai; Zou, Lanfang; Qin, Jun-Sheng; Li, Jialuo; Huang, Lan; Feng, Liang; Wang, Xuan; Bosch, Mathieu; Alsalme, Ali; Cagin, Tahir; Zhou, Hong-Cai

2017-05-01

A major goal of metal-organic framework (MOF) research is the expansion of pore size and volume. Although many approaches have been attempted to increase the pore size of MOF materials, it is still a challenge to construct MOFs with precisely customized pore apertures for specific applications. Herein, we present a new method, namely linker labilization, to increase the MOF porosity and pore size, giving rise to hierarchical-pore architectures. Microporous MOFs with robust metal nodes and pro-labile linkers were initially synthesized. The mesopores were subsequently created as crystal defects through the splitting of a pro-labile-linker and the removal of the linker fragments by acid treatment. We demonstrate that linker labilization method can create controllable hierarchical porous structures in stable MOFs, which facilitates the diffusion and adsorption process of guest molecules to improve the performances of MOFs in adsorption and catalysis.

Construction of hierarchically porous metal–organic frameworks through linker labilization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Shuai; Zou, Lanfang; Qin, Jun-Sheng

One major goal of metal–organic framework (MOF) research is the expansion of pore size and volume. Although many approaches have been attempted to increase the pore size of MOF materials, it is still a challenge to construct MOFs with precisely customized pore apertures for specific applications. W present a new method, namely linker labilization, to increase the MOF porosity and pore size, giving rise to hierarchical-pore architectures. Microporous MOFs with robust metal nodes and pro-labile linkers were initially synthesized. The mesopores were subsequently created as crystal defects through the splitting of a pro-labile-linker and the removal of the linker fragmentsmore » by acid treatment. We also demonstrate that linker labilization method can create controllable hierarchical porous structures in stable MOFs, which facilitates the diffusion and adsorption process of guest molecules to improve the performances of MOFs in adsorption and catalysis.« less

Visualization of Membrane Pore in Live Cells Reveals a Dynamic-Pore Theory Governing Fusion and Endocytosis.

PubMed

Shin, Wonchul; Ge, Lihao; Arpino, Gianvito; Villarreal, Seth A; Hamid, Edaeni; Liu, Huisheng; Zhao, Wei-Dong; Wen, Peter J; Chiang, Hsueh-Cheng; Wu, Ling-Gang

2018-05-03

Fusion is thought to open a pore to release vesicular cargoes vital for many biological processes, including exocytosis, intracellular trafficking, fertilization, and viral entry. However, fusion pores have not been observed and thus proved in live cells. Its regulatory mechanisms and functions remain poorly understood. With super-resolution STED microscopy, we observed dynamic fusion pore behaviors in live (neuroendocrine) cells, including opening, expansion, constriction, and closure, where pore size may vary between 0 and 490 nm within 26 milliseconds to seconds (vesicle size: 180-720 nm). These pore dynamics crucially determine the efficiency of vesicular cargo release and vesicle retrieval. They are generated by competition between pore expansion and constriction. Pharmacology and mutation experiments suggest that expansion and constriction are mediated by F-actin-dependent membrane tension and calcium/dynamin, respectively. These findings provide the missing live-cell evidence, proving the fusion-pore hypothesis, and establish a live-cell dynamic-pore theory accounting for fusion, fission, and their regulation. Published by Elsevier Inc.

Characterization of nanoporous shales with gas sorption

NASA Astrophysics Data System (ADS)

Joewondo, N.; Prasad, M.

2017-12-01

The understanding of the fluid flow in porous media requires the knowledge of the pore system involved. Fluid flow in fine grained shales falls under different regime than transport regime in conventional reservoir due to the different average pore sizes in the two materials; the average pore diameter of conventional sandstones is on the micrometer scale, while of shales can be as small as several nanometers. Mercury intrusion porosimetry is normally used to characterize the pores of conventional reservoir, however with increasingly small pores, the injection pressure required to imbibe the pores becomes infinitely large due to surface tension. Characterization of pores can be expressed by a pore size distribution (PSD) plot, which reflects distribution of pore volume or surface area with respect to pore size. For the case of nanoporous materials, the surface area, which serves as the interface between the rock matrix and fluid, becomes increasingly large and important. Physisorption of gas has been extensively studied as a method of nanoporous solid characterization (particularly for the application of catalysis, metal organic frameworks, etc). The PSD is obtained by matching the experimental result to the calculated theoretical result (using Density Functional Theory (DFT), a quantum mechanics based modelling method for molecular scale interactions). We present the challenges and experimental result of Nitrogen and CO2 gas sorption on shales with various mineralogy and the interpreted PSD obtained by DFT method. Our result shows significant surface area contributed by the nanopores of shales, hence the importance of surface area measurements for the characterization of shales.

Investigation of the stability of Platinum nanoparticles incorporated in mesoporous silica with different pore sizes.

PubMed

Yano, Kazuhisa; Zhang, Shuyi; Pan, Xiaoqing; Tatsuda, Narihito

2014-05-01

The effect of the pore size of mesoporous silica on the stability of Pt nanoparticles (NPs) has been investigated. TEM observation and XRD measurement were conducted in situ for Pt loaded mesoporous silica with different mesopore sizes. It turns out that smaller pores are more effective to stabilize Pt NPs below 600 °C. However, aggregation of Pt NPs on the surface of particles is not fully suppressed more than 1000 °C in ambient atmosphere even though smaller mesopore size is applied. The type of precursor does not affect the stability of Pt NPs. Copyright © 2014. Published by Elsevier Inc.

Multiscale modeling of fluid flow and mass transport

NASA Astrophysics Data System (ADS)

Masuoka, K.; Yamamoto, H.; Bijeljic, B.; Lin, Q.; Blunt, M. J.

2017-12-01

In recent years, there are some reports on a simulation of fluid flow in pore spaces of rocks using Navier-Stokes equations. These studies mostly adopt a X-ray CT to create 3-D numerical grids of the pores in micro-scale. However, results may be of low accuracy when the rock has a large pore size distribution, because pores, whose size is smaller than resolution of the X-ray CT may be neglected. We recently found out by tracer tests in a laboratory using a brine saturated Ryukyu limestone and inject fresh water that a decrease of chloride concentration took longer time. This phenomenon can be explained due to weak connectivity of the porous networks. Therefore, it is important to simulate entire pore spaces even those of very small sizes in which diffusion is dominant. We have developed a new methodology for multi-level modeling for pore scale fluid flow in porous media. The approach is to combine pore-scale analysis with Darcy-flow analysis using two types of X-ray CT images in different resolutions. Results of the numerical simulations showed a close match with the experimental results. The proposed methodology is an enhancement for analyzing mass transport and flow phenomena in rocks with complicated pore structure.

Characterization and investigation of the deformation behavior of porous magnesium scaffolds with entangled architectured pore channels.

PubMed

Jiang, Guofeng; Li, Qiuyan; Wang, Cunlong; Dong, Jie; He, Guo

2016-12-01

We report a kind of porous magnesium with entangled architectured pore structure for potential applications in biomedical implant. The pore size, spatial structure and Young׳s modulus of the as-prepared porous Mg are suitable for bone tissue engineering applications. Particularly, with regard to the load-bearing conditions, a new analytical model is employed to investigate its structure and mechanical response under compressive stress based on Gibson-Ashby model. It is found that there are three types of stress-strain behaviors in the large range of porosity from 20% to 80%. When the porosity is larger than an upper critical value, the porous magnesium exhibits densifying behavior with buckling deformation mechanism. When the porosity is smaller than a lower critical value, the porous magnesium exhibits shearing behavior with cracking along the maximum shear stress. Between the two critical porosities, both the buckling deformation and shearing behavior coexist. The upper critical porosity is experimentally determined to be 60% for 270μm pore size and 62% for 400μm pore size, while the lower critical porosity is 40% for 270μm pore size and 42% for 400μm pore size. A new analytical model could be used to accurately predict the mechanical response of the porous magnesium. No matter the calculated critical porosity or yielding stress in a large range of porosity by using the new model are well consistent with the experimental values. All these results could help to provide valuable data for developing the present porous magnesium for potential bio applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Factors affecting plant growth in membrane nutrient delivery

NASA Technical Reports Server (NTRS)

Dreschel, T. W.; Wheeler, R. M.; Sager, J. C.; Knott, W. M.

1990-01-01

The development of the tubular membrane plant growth unit for the delivery of water and nutrients to roots in microgravity has recently focused on measuring the effects of changes in physical variables controlling solution availability to the plants. Significant effects of membrane pore size and the negative pressure used to contain the solution were demonstrated. Generally, wheat grew better in units with a larger pore size but equal negative pressure and in units with the same pore size but less negative pressure. Lettuce also exhibited better plant growth at less negative pressure.

In-situ polymerized PLOT columns III: divinylbenzene copolymers and dimethacrylate homopolymers

NASA Technical Reports Server (NTRS)

Shen, T. C.; Fong, M. M.

1994-01-01

Studies of divinylbenzene copolymers and dimethacrylate homopolymers indicate that the polymer pore size controls the separation of water and ammonia on porous-layer-open-tubular (PLOT) columns. To a lesser degree, the polarity of the polymers also affects the separation of a water-ammonia gas mixture. Our results demonstrate that the pore size can be regulated by controlling the cross-linking density or the chain length between the cross-linking functional groups. An optimum pore size will provide the best separation of water and ammonia.

Study of shale reservoir nanometer-sized pores in Member 1 of Shahejie Formation in JX area, Liaozhong sag

NASA Astrophysics Data System (ADS)

Cheng, Yong; Zhang, Yu; Wen, Yiming

2018-02-01

The microscopic pore structure is the key of the shale reservoir study; however, traditional Scanning Electron Microscopy (SEM) methods cannot identify the irregular morphology caused by mechanical polishing. In this work, Scanning Electron Microscopy combined argon ion polishing technology was taken to study the characteristics of shale reservoir pores of Member 1 of Shahejie Formation (E3s1) located in JX1-1 area of Liaozhong Sag. The results show that pores between clay platelets, intraplatelet pores within clay aggregates and organic-matter pores are very rich in the area and with good pore connectivity, so these types of pores are of great significance for oil-gas exporation. Pores between clay platelets are formed by directional or semi-directional contact between edge and surface, edge and edge or surface and surface of laminated clay minerals, whose shapes are linear, mesh, and irregular with the size of 500 nm to 5 μm. The intraplatelet pores within clay aggregates are formed in the process of the transformation and compaction of clay minerals, whose shapes are usually linear with the width of 30 to 500 nm and the length of 2 to 50 μm. The organic-matter pores are from the process of the conversion from organic matters to the hydrocarbon under thermal evolution, whose shapes are gneissic, irregular, pitted and elliptical with the size of 100 nm to 2 μm. This study is of certain guiding significance to selecting target zones, evaluating resource potential and exploring & developing of shale gas in this region.

Numerical Simulation of Multiphase Flow in Nanoporous Organic Matter With Application to Coal and Gas Shale Systems

NASA Astrophysics Data System (ADS)

Song, Wenhui; Yao, Jun; Ma, Jingsheng; Sun, Hai; Li, Yang; Yang, Yongfei; Zhang, Lei

2018-02-01

Fluid flow in nanoscale organic pores is known to be affected by fluid transport mechanisms and properties within confined pore space. The flow of gas and water shows notably different characteristics compared with conventional continuum modeling approach. A pore network flow model is developed and implemented in this work. A 3-D organic pore network model is constructed from 3-D image that is reconstructed from 2-D shale SEM image of organic-rich sample. The 3-D pore network model is assumed to be gas-wet and to contain initially gas-filled pores only, and the flow model is concerned with drainage process. Gas flow considers a full range of gas transport mechanisms, including viscous flow, Knudsen diffusion, surface diffusion, ad/desorption, and gas PVT and viscosity using a modified van der Waals' EoS and a correlation for natural gas, respectively. The influences of slip length, contact angle, and gas adsorption layer on water flow are considered. Surface tension considers the pore size and temperature effects. Invasion percolation is applied to calculate gas-water relative permeability. The results indicate that the influences of pore pressure and temperature on water phase relative permeabilities are negligible while gas phase relative permeabilities are relatively larger in higher temperatures and lower pore pressures. Gas phase relative permeability increases while water phase relative permeability decreases with the shrinkage of pore size. This can be attributed to the fact that gas adsorption layer decreases the effective flow area of the water phase and surface diffusion capacity for adsorbed gas is enhanced in small pore size.

Exploring molecular sieve capabilities of activated carbon fibers to reduce the impact of NOM preloading on trichloroethylene adsorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanju Karanfil; Seyed A. Dastgheib; Dina Mauldin

2006-02-15

Adsorption of trichloroethylene (TCE) by two activated carbon fibers ACF10 and ACF20H and two granular activated carbons, coal-based F400 and Macro preloaded with hydrophobic and transphilic fractions of natural organic matter (NOM) was examined. ACF10, the most microporous activated carbon used in this study, had over 90% of its pore volume in pores smaller than 10 {angstrom}. It also had the highest volume in pores 5-8 {angstrom}, which is the optimum pore size region for TCE adsorption, among the four activated carbons. Adsorption of NOM fractions by ACF10 was, in general, negligible. Therefore, ACF10, functioning as a molecular sieve duringmore » preloading, exhibited the least NOM uptake for each fraction, and subsequently the highest TCE adsorption. The other three sorbents had wider pore size distributions, including high volumes in pores larger than 10 {angstrom}, where NOM molecules can adsorb. As a result, they showed a higher degree of uptake for all NOM fractions, and subsequently lower adsorption capacities for TCE, as compared to ACF10. The results obtained in this study showed that understanding the interplay between the optimum pore size region for the adsorption of target synthetic organic contaminant (SOC) and the pore size region for the adsorption of NOM molecules is important for controlling NOM-SOC competitions. Experiments with different NOM fractions indicated that the degree of NOM loading is important in terms of preloading effects; however the way that the carbon pores are filled and loaded by different NOM fractions can be different and may create an additional negative impact on TCE adsorption. 40 refs., 3 figs., 2 tabs.« less

Individual pore and interconnection size analysis of macroporous ceramic scaffolds using high-resolution X-ray tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jerban, Saeed, E-mail: saeed.jerban@usherbrooke.ca

2016-08-15

The pore interconnection size of β-tricalcium phosphate scaffolds plays an essential role in the bone repair process. Although, the μCT technique is widely used in the biomaterial community, it is rarely used to measure the interconnection size because of the lack of algorithms. In addition, discrete nature of the μCT introduces large systematic errors due to the convex geometry of interconnections. We proposed, verified and validated a novel pore-level algorithm to accurately characterize the individual pores and interconnections. Specifically, pores and interconnections were isolated, labeled, and individually analyzed with high accuracy. The technique was verified thoroughly by visually inspecting andmore » verifying over 3474 properties of randomly selected pores. This extensive verification process has passed a one-percent accuracy criterion. Scanning errors inherent in the discretization, which lead to both dummy and significantly overestimated interconnections, have been examined using computer-based simulations and additional high-resolution scanning. Then accurate correction charts were developed and used to reduce the scanning errors. Only after the corrections, both the μCT and SEM-based results converged, and the novel algorithm was validated. Material scientists with access to all geometrical properties of individual pores and interconnections, using the novel algorithm, will have a more-detailed and accurate description of the substitute architecture and a potentially deeper understanding of the link between the geometric and biological interaction. - Highlights: •An algorithm is developed to analyze individually all pores and interconnections. •After pore isolating, the discretization errors in interconnections were corrected. •Dummy interconnections and overestimated sizes were due to thin material walls. •The isolating algorithm was verified through visual inspection (99% accurate). •After correcting for the systematic errors, algorithm was validated successfully.« less

Effect of the three-dimensional microstructure on the sound absorption of foams: A parametric study.

PubMed

Chevillotte, Fabien; Perrot, Camille

2017-08-01

The purpose of this work is to systematically study the effect of the throat and the pore sizes on the sound absorbing properties of open-cell foams. The three-dimensional idealized unit cell used in this work enables to mimic the acoustical macro-behavior of a large class of cellular solid foams. This study is carried out for a normal incidence and also for a diffuse field excitation, with a relatively large range of sample thicknesses. The transport and sound absorbing properties are numerically studied as a function of the throat size, the pore size, and the sample thickness. The resulting diagrams show the ranges of the specific throat sizes and pore sizes where the sound absorption grading is maximized due to the pore morphology as a function of the sample thickness, and how it correlates with the corresponding transport parameters. These charts demonstrate, together with typical examples, how the morphological characteristics of foam could be modified in order to increase the visco-thermal dissipation effects.

Effects of Coke Calcination Level on Pore Structure in Carbon Anodes

NASA Astrophysics Data System (ADS)

Fang, Ning; Xue, Jilai; Lang, Guanghui; Bao, Chongai; Gao, Shoulei

2016-02-01

Effects of coke calcination levels on pore structure of carbon anodes have been investigated. Bench anodes were prepared by 3 types of cokes with 4 calcination temperatures (800°C, 900°C, 1000°C and 1100°C). The cokes and anodes were characterized using hydrostatic method, air permeability determination, mercury porosimetry, image analysis and confocal microscopy (CSLM). The cokes with different calcination levels are almost the same in LC values (19-20 Å) and real density (1.967-1.985 g/cm3), while the anode containing coke calcined at 900°C has the lowest open porosity and air permeability. Pore size distribution (represented by Anode H sample) can be roughly divided into two ranges: small and medium pores in diameter of 10-400 μm and large pores of 400-580 μm. For the anode containing coke calcined at 800°C, a number of long, narrow pores in the pore size range of 400-580 μm are presented among cokes particles. Formation of these elongated pores may be attributed to coke shrinkages during the anode baking process, which may develop cracking in the anode under cell operations. More small or medium rounded pores with pore size range of 10-400 μm emerge in the anodes with coke calcination temperatures of 900°C, 1000°C and 1100°C, which may be generated due to release of volatiles from the carbon anode during baking. For the anode containing coke calcined at 1100°C, it is found that many rounded pores often closely surround large coke particles, which have potential to form elongated, narrow pores.

Visualizing and Quantifying Bioaccessible Pores in Field-Aged Petroleum Hydrocarbon-Contaminated Clay Soils Using Synchrotron-based X-ray Computed Tomography

NASA Astrophysics Data System (ADS)

Chang, W.; Kim, J.; Zhu, N.; McBeth, J. M.

2015-12-01

Microbial hydrocarbon degradation is environmentally significant and applicable to contaminated site remediation practices only when hydrocarbons (substrates) are physically bioaccessible to bacteria in soil matrices. Powerful X-rays are produced by synchrotron radiation, allowing for bioaccessible pores in soil (larger than 4 microns), where bacteria can be accommodated, colonize and remain active, can be visualized at a much higher resolution. This study visualized and quantified such bioaccessible pores in intact field-aged, oil-contaminated unsaturated soil fractions, and examined the relationship between the abundance of bioaccessible pores and hydrocarbon biodegradation. Using synchrotron-based X-ray Computed Tomography (CT) at the Canadian Light Source, a large dataset of soil particle characteristics, such as pore volumes, surface areas, number of pores and pore size distribution, was generated. Duplicate samples of five different soil fractions with different soil aggregate sizes and water contents (13, 18 and 25%) were examined. The method for calculating the number and distribution of bioaccessible pores using CT images was validated using the known porosity of Ottawa sand. This study indicated that the distribution of bioaccessible pore sizes in soil fractions are very closely related to microbial enhancement. A follow-up aerobic biodegradation experiment for the soils at 17 °C (average site temperature) over 90 days confirmed that a notable decrease in hydrocarbon concentrations occurred in soils fractions with abundant bioaccessible pores and with a larger number of pores between 10 and 100 μm. The hydrocarbon degradation in bioactive soil fractions was extended to relatively high-molecular-weight hydrocarbons (C16-C34). This study provides quantitative information about how internal soil pore characteristics can influence bioremediation performance.

Accounting for microbial habitats in modeling soil organic matter dynamics

NASA Astrophysics Data System (ADS)

Chenu, Claire; Garnier, Patricia; Nunan, Naoise; Pot, Valérie; Raynaud, Xavier; Vieublé, Laure; Otten, Wilfred; Falconer, Ruth; Monga, Olivier

2017-04-01

The extreme heterogeneity of soils constituents, architecture and inhabitants at the microscopic scale is increasingly recognized. Microbial communities exist and are active in a complex 3-D physical framework of mineral and organic particles defining pores of various sizes, more or less inter-connected. This results in a frequent spatial disconnection between soil carbon, energy sources and the decomposer organisms and a variety of microhabitats that are more or less suitable for microbial growth and activity. However, current biogeochemical models account for C dynamics at the macroscale (cm, m) and consider time- and spatially averaged relationships between microbial activity and soil characteristics. Different modelling approaches have intended to account for this microscale heterogeneity, based either on considering aggregates as surrogates for microbial habitats, or pores. Innovative modelling approaches are based on an explicit representation of soil structure at the fine scale, i.e. at µm to mm scales: pore architecture and their saturation with water, localization of organic resources and of microorganisms. Three recent models are presented here, that describe the heterotrophic activity of either bacteria or fungi and are based upon different strategies to represent the complex soil pore system (Mosaic, LBios and µFun). These models allow to hierarchize factors of microbial activity in soil's heterogeneous architecture. Present limits of these approaches and challenges are presented, regarding the extensive information required on soils at the microscale and to up-scale microbial functioning from the pore to the core scale.

Fabrication of Subnanometer-Precision Nanopores in Hexagonal Boron Nitride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilbert, S. Matt; Dunn, Gabriel; Azizi, Amin

Here, we demonstrate the fabrication of individual nanopores in hexagonal boron nitride (h-BN) with atomically precise control of the pore shape and size. Previous methods of pore production in other 2D materials typically create pores with irregular geometry and imprecise diameters. In contrast, other studies have shown that with careful control of electron irradiation, defects in h-BN grow with pristine zig-zag edges at quantized triangular sizes, but they have failed to demonstrate production and control of isolated defects. In this work, we combine these techniques to yield a method in which we can create individual size-quantized triangular nanopores through anmore » h-BN sheet. The pores are created using the electron beam of a conventional transmission electron microscope; which can strip away multiple layers of h-BN exposing single-layer regions, introduce single vacancies, and preferentially grow vacancies only in the single-layer region. We further demonstrate how the geometry of these pores can be altered beyond triangular by changing beam conditions. Precisely size- and geometry-tuned nanopores could find application in molecular sensing, DNA sequencing, water desalination, and molecular separation.« less

Fabrication of Subnanometer-Precision Nanopores in Hexagonal Boron Nitride

DOE PAGES

Gilbert, S. Matt; Dunn, Gabriel; Azizi, Amin; ...

2017-11-08

Here, we demonstrate the fabrication of individual nanopores in hexagonal boron nitride (h-BN) with atomically precise control of the pore shape and size. Previous methods of pore production in other 2D materials typically create pores with irregular geometry and imprecise diameters. In contrast, other studies have shown that with careful control of electron irradiation, defects in h-BN grow with pristine zig-zag edges at quantized triangular sizes, but they have failed to demonstrate production and control of isolated defects. In this work, we combine these techniques to yield a method in which we can create individual size-quantized triangular nanopores through anmore » h-BN sheet. The pores are created using the electron beam of a conventional transmission electron microscope; which can strip away multiple layers of h-BN exposing single-layer regions, introduce single vacancies, and preferentially grow vacancies only in the single-layer region. We further demonstrate how the geometry of these pores can be altered beyond triangular by changing beam conditions. Precisely size- and geometry-tuned nanopores could find application in molecular sensing, DNA sequencing, water desalination, and molecular separation.« less

The pressure-dependence of the size of extruded vesicles.

PubMed

Patty, Philipus J; Frisken, Barbara J

2003-08-01

Variations in the size of vesicles formed by extrusion through small pores are discussed in terms of a simple model. Our model predicts that the radius should decrease as the square root of the applied pressure, consistent with data for vesicles extruded under various conditions. The model also predicts dependencies on the pore size used and on the lysis tension of the vesicles being extruded that are consistent with our data. The pore size was varied by using track-etched polycarbonate membranes with average pore diameters ranging from 50 to 200 nm. To vary the lysis tension, vesicles made from POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine), mixtures of POPC and cholesterol, and mixtures of POPC and C(16)-ceramide were studied. The lysis tension, as measured by an extrusion-based technique, of POPC:cholesterol vesicles is higher than that of pure POPC vesicles whereas POPC:ceramide vesicles have lower lysis tensions than POPC vesicles.

Strategies for Tailoring the Pore-Size Distribution of Virus Retention Filter Papers.

PubMed

Gustafsson, Simon; Mihranyan, Albert

2016-06-08

The goal of this work is to demonstrate how the pore-size distribution of the nanocellulose-based virus-retentive filter can be tailored. The filter paper was produced using cellulose nanofibers derived from Cladophora sp. green algae using the hot-press drying at varying drying temperatures. The produced filters were characterized using scanning electron microscopy, atomic force microscopy, and N2 gas sorption analysis. Further, hydraulic permeability and retention efficiency toward surrogate 20 nm model particles (fluorescent carboxylate-modified polystyrene spheres) were assessed. It was shown that by controlling the rate of water evaporation during hot-press drying the pore-size distribution can be precisely tailored in the region between 10 and 25 nm. The mechanism of pore formation and critical parameters are discussed in detail. The results are highly valuable for development of advanced separation media, especially for virus-retentive size-exclusion filtration.

Effective Thermal Conductivity of an Aluminum Foam + Water Two Phase System

NASA Technical Reports Server (NTRS)

Moskito, John

1996-01-01

This study examined the effect of volume fraction and pore size on the effective thermal conductivity of an aluminum foam and water system. Nine specimens of aluminum foam representing a matrix of three volume fractions (4-8% by vol.) and three pore sizes (2-4 mm) were tested with water to determine relationships to the effective thermal conductivity. It was determined that increases in volume fraction of the aluminum phase were correlated to increases in the effective thermal conductivity. It was not statistically possible to prove that changes in pore size of the aluminum foam correlated to changes in the effective thermal conductivity. However, interaction effects between the volume fraction and pore size of the foam were statistically significant. Ten theoretical models were selected from the published literature to compare against the experimental data. Models by Asaad, Hadley, and de Vries provided effective thermal conductivity predictions within a 95% confidence interval.

1.9 μm superficially porous packing material with radially oriented pores and tailored pore size for ultra-fast separation of small molecules and biomolecules.

PubMed

Min, Yi; Jiang, Bo; Wu, Ci; Xia, Simin; Zhang, Xiaodan; Liang, Zhen; Zhang, Lihua; Zhang, Yukui

2014-08-22

In this work, 1.9 μm reversed-phase packing materials with superficially porous structure were prepared to achieve the rapid and high efficient separation of peptides and proteins. The silica particles were synthesized via three steps, nonporous silica particle preparation by a modified seeded growth method, mesoporous shell formation by a one pot templated dissolution and redeposition strategy, and pore size expansion via acid-refluxing. By such a method, 1.9 μm superficially porous materials with 0.18 μm shell thickness and tailored pore diameter (10 nm, 15 nm) were obtained. After pore enlargement, the formerly dense arrays of mesoporous structure changed, the radially oriented pores dominated the superficially porous structure. The chromatographic performance of such particles was investigated after C18 derivatization. For packing materials with 1.9 μm diameter and 10 nm pore size, the column efficiency could reach 211,300 plates per m for naphthalene. To achieve the high resolution separation of peptides and proteins, particles with pore diameter of 15 nm were tailored, by which the baseline separation of 5 peptides and 5 intact proteins could be respectively achieved within 1 min, demonstrating the superiority in the high efficiency and high throughput analysis of biomolecules. Furthermore, BSA digests were well separated with peak capacity of 120 in 30 min on a 15 cm-long column. Finally, we compared our columns with a 1.7 μm Kinetex C18 column under the same conditions, our particles with 10nm pore size demonstrated similar performance for separation of the large intact proteins. Moreover, the particles with 15 nm pore size showed more symmetrical peaks for the separation of large proteins (BSA, OVA and IgG) and provided rapid separation of protein extracts from Escherichia coli in 5 min. All these results indicated that the synthesized 1.9 μm superficially porous silica packing materials would be promising in the ultra-fast and high-resolution separation of biomolecules. Copyright © 2014 Elsevier B.V. All rights reserved.

Pore scale investigation of salt precipitation inside drying porous media resolved by 4D X-ray Microscopy Imaging

NASA Astrophysics Data System (ADS)

Norouzi Rad, M.

2016-12-01

Precipitation and deposition of salts in porous media is important in many natural processes as well as industrial and environmental applications since it can modify the structure and transport properties of porous media. In the presence of soluble salt in water during evaporation from porous media, salt is transported by convection induced by capillary liquid flow toward the evaporating surface where it accumulates, whereas diffusion tends to spread the salt and homogenize concentrations in space. Therefore, the competition between the convection and diffusion (characterized by Peclet number) affects the dynamics of salt distribution in porous media. As shown in previous studies (1-3) salt crust thickness and its coverage on the surface are highly influenced by the pore size distribution on the surface and active evaporation spots. In the current study, we focus on the precipitation dynamics and pattern during diffusion-driven evaporation period (the so-called stage-2 of evaporation) when the surface is dried and vaporization plane moves below the surface. Therefore, precipitation occurs inside the porous media during this period. To investigate the details of this process, 4D X-ray Microscopy was utilized. To do so, a packed bed of silica sand was saturated with 4 Molal NaCl solution and X-ray Microscopy was used to image the sample at well-defined time intervals during the evaporation process to provide pore scale information on evaporation and precipitation dynamics. The resulted 3-D pore-scale images were segmented to quantify the evaporative water losses and the dynamics and patterns of salt precipitation inside porous media with particular focus on the characterization of the processes occurring during stage-2 evaporation affecting the precipitation dynamics. [1] Norouzi Rad, M., N. Shokri, A. Keshmiri, P. Withers (2015), Effects of grain and pore size on salt precipitation during evaporation from porous media: A pore-scale investigation, Trans. Porous. Med., 110(2), 281-294. [2] Norouzi Rad, M., N. Shokri (2014), Effects of grain angularity on NaCl precipitation in porous media during evaporation, Water Resour. Res., 50, 9020-9030. [3] Norouzi Rad, M., N. Shokri, M. Sahimi (2013), Pore-Scale Dynamics of Salt Precipitation in Drying Porous Media, Phys. Rev. E, 88, 032404.

Computational study of 3-D hot-spot initiation in shocked insensitive high-explosive

NASA Astrophysics Data System (ADS)

Najjar, F. M.; Howard, W. M.; Fried, L. E.; Manaa, M. R.; Nichols, A., III; Levesque, G.

2012-03-01

High-explosive (HE) material consists of large-sized grains with micron-sized embedded impurities and pores. Under various mechanical/thermal insults, these pores collapse generating hightemperature regions leading to ignition. A hydrodynamic study has been performed to investigate the mechanisms of pore collapse and hot spot initiation in TATB crystals, employing a multiphysics code, ALE3D, coupled to the chemistry module, Cheetah. This computational study includes reactive dynamics. Two-dimensional high-resolution large-scale meso-scale simulations have been performed. The parameter space is systematically studied by considering various shock strengths, pore diameters and multiple pore configurations. Preliminary 3-D simulations are undertaken to quantify the 3-D dynamics.

Multiscale Simulation of Porous Ceramics Based on Movable Cellular Automaton Method

NASA Astrophysics Data System (ADS)

Smolin, A.; Smolin, I.; Eremina, G.; Smolina, I.

2017-10-01

The paper presents a model for simulating mechanical behaviour of multiscale porous ceramics based on movable cellular automaton method, which is a novel particle method in computational mechanics of solid. The initial scale of the proposed approach corresponds to the characteristic size of the smallest pores in the ceramics. At this scale, we model uniaxial compression of several representative samples with an explicit account of pores of the same size but with the random unique position in space. As a result, we get the average values of Young’s modulus and strength, as well as the parameters of the Weibull distribution of these properties at the current scale level. These data allow us to describe the material behaviour at the next scale level were only the larger pores are considered explicitly, while the influence of small pores is included via the effective properties determined at the previous scale level. If the pore size distribution function of the material has N maxima we need to perform computations for N - 1 levels in order to get the properties from the lowest scale up to the macroscale step by step. The proposed approach was applied to modelling zirconia ceramics with bimodal pore size distribution. The obtained results show correct behaviour of the model sample at the macroscale.

Molecular simulation and experimental validation of resorcinol adsorption on Ordered Mesoporous Carbon (OMC).

PubMed

Ahmad, Zaki Uddin; Chao, Bing; Konggidinata, Mas Iwan; Lian, Qiyu; Zappi, Mark E; Gang, Daniel Dianchen

2018-04-27

Numerous research works have been devoted in the adsorption area using experimental approaches. All these approaches are based on trial and error process and extremely time consuming. Molecular simulation technique is a new tool that can be used to design and predict the performance of an adsorbent. This research proposed a simulation technique that can greatly reduce the time in designing the adsorbent. In this study, a new Rhombic ordered mesoporous carbon (OMC) model is proposed and constructed with various pore sizes and oxygen contents using Materials Visualizer Module to optimize the structure of OMC for resorcinol adsorption. The specific surface area, pore volume, small angle X-ray diffraction pattern, and resorcinol adsorption capacity were calculated by Forcite and Sorption module in Materials Studio Package. The simulation results were validated experimentally through synthesizing OMC with different pore sizes and oxygen contents prepared via hard template method employing SBA-15 silica scaffold. Boric acid was used as the pore expanding reagent to synthesize OMC with different pore sizes (from 4.6 to 11.3 nm) and varying oxygen contents (from 11.9% to 17.8%). Based on the simulation and experimental validation, the optimal pore size was found to be 6 nm for maximum adsorption of resorcinol. Copyright © 2018 Elsevier B.V. All rights reserved.

Pore-size dependence and characteristics of water diffusion in slitlike micropores

DOE PAGES

Diallo, S. O.

2015-07-16

The temperature dependence of the dynamics of water inside microporous activated carbon fibers (ACF) is investigated by means of incoherent elastic and quasielastic neutron-scattering techniques. The aim is to evaluate the effect of increasing pore size on the water dynamics in these primarily hydrophobic slit-shaped channels. Using two different micropore sizes (similar to 12 and 18 angstrom, denoted, respectively, ACF-10 and ACF-20), a clear suppression of the mobility of the water molecules is observed as the pore gap or temperature decreases. Suppression, we found, is accompanied by a systematic dependence of the average translational diffusion coefficient D-r and relaxation timemore » [tau(0)] of the restricted water on pore size and temperature. We observed D-r values and tested against a proposed scaling law, in which the translational diffusion coefficient D-r of water within a porous matrix was found to depend solely on two single parameters, a temperature-independent translational diffusion coefficient D-c associated with the water bound to the pore walls and the ratio theta of this strictly confined water to the total water inside the pore, yielding unique characteristic parameters for water transport in these carbon channels across the investigated temperature range.« less

Research of CO2 and N2 Adsorption Behavior in K-Illite Slit Pores by GCMC Method

PubMed Central

Chen, Guohui; Lu, Shuangfang; Zhang, Junfang; Xue, Qingzhong; Han, Tongcheng; Xue, Haitao; Tian, Shansi; Li, Jinbu; Xu, Chenxi; Pervukhina, Marina; Clennell, Ben

2016-01-01

Understanding the adsorption mechanisms of CO2 and N2 in illite, one of the main components of clay in shale, is important to improve the precision of the shale gas exploration and development. We investigated the adsorption mechanisms of CO2 and N2 in K-illite with varying pore sizes at the temperature of 333, 363 and 393 K over a broad range of pressures up to 30 MPa using the grand canonical Monte Carlo (GCMC) simulation method. The simulation system is proved to be reasonable and suitable through the discussion of the impact of cation dynamics and pore wall thickness. The simulation results of the excess adsorption amount, expressed per unit surface area of illite, is in general consistency with published experimental results. It is found that the sorption potential overlaps in micropores, leading to a decreasing excess adsorption amount with the increase of pore size at low pressure, and a reverse trend at high pressure. The excess adsorption amount increases with increasing pressure to a maximum and then decreases with further increase in the pressure, and the decreasing amount is found to increase with the increasing pore size. For pores with size greater larger than 2 nm, the overlap effect disappears. PMID:27897232

Recent studies on activated carbons and fly ashes from Turkish resources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayhan Demirbas; Gulsin Arslan; Erol Pehlivan

2006-05-15

This article deals with adsorptive properties of activated carbons (ACs) and fly ashes from Turkish coal and biomass resources. ACs because of their high surface area, microporous character and the chemical nature of their surface have been considered potential adsorbents for the removal of heavy metals from industrial wastewater. Pyrolysis is an established process method for preparation of activated carbon from biomass. The bio-char is can be used as AC. The adsorption properties of ACs were strictly defined by the physicochemical nature of their surface and their texture, i.e., pore volume, pore size distribution, surface area. It is well knownmore » that the pH of the solution-adsorbant mixture is an important variable in the adsorption process. Fly ash has the highest adsorption capacity (198.2 mg/g for Cd(II)). Almond shell AC has the lowest adsorption capacity (2.7 mg/g).« less

Influence of Electrostatics on Small Molecule Flux through a Protein Nanoreactor.

PubMed

Glasgow, Jeff E; Asensio, Michael A; Jakobson, Christopher M; Francis, Matthew B; Tullman-Ercek, Danielle

2015-09-18

Nature uses protein compartmentalization to great effect for control over enzymatic pathways, and the strategy has great promise for synthetic biology. In particular, encapsulation in nanometer-sized containers to create nanoreactors has the potential to elicit interesting, unexplored effects resulting from deviations from well-understood bulk processes. Self-assembled protein shells for encapsulation are especially desirable for their uniform structures and ease of perturbation through genetic mutation. Here, we use the MS2 capsid, a well-defined porous 27 nm protein shell, as an enzymatic nanoreactor to explore pore-structure effects on substrate and product flux during the catalyzed reaction. Our results suggest that the shell can influence the enzymatic reaction based on charge repulsion between small molecules and point mutations around the pore structure. These findings also lend support to the hypothesis that protein compartments modulate the transport of small molecules and thus influence metabolic reactions and catalysis in vitro.

Nanospace-Mediated Self-Organization of Nanoparticles in Flexible Porous Polymer Templates.

PubMed

Kuroda, Yoshiyuki; Muto, Itaru; Shimojima, Atsushi; Wada, Hiroaki; Kuroda, Kazuyuki

2017-09-12

Self-organization is a fundamental process for the construction of complex hierarchically ordered nanostructures, which are widespread in biological systems. However, precise control of size, shape, and surface properties is required for self-organization of nanoparticles. Here, we demonstrate a novel self-organization phenomenon mediated by flexible nanospaces in templates. Inorganic nanoparticles (e.g., silica, zirconia, and titania) are deposited in porous polymer thin films with randomly distributed pores on the surface, leaving a partially filled nanospace in each pore. Heating at temperatures beyond the glass transition temperature of the template leads to self-organization of the inorganic nanoparticles into one-dimensional chainlike networks. The self-organization is mediated by the deformation and fusion of the residual nanospaces, and it can be rationally controlled by sequential heat treatments. These results show that a nanospace, defined by the nonexistence of matter, interacts indirectly with matter and can be used as a component of self-organization systems.

Kinetic models of controllable pore growth of anodic aluminum oxide membrane

NASA Astrophysics Data System (ADS)

Huang, Yan; Zeng, Hong-yan; Zhao, Ce; Qu, Ye-qing; Zhang, Pin

2012-06-01

An anodized Al2O3 (AAO) membrane with apertures about 72 nm in diameter was prepared by two-step anodic oxidation. The appearance and pore arrangement of the AAO membrane were characterized by energy dispersive x-ray spectroscopy and scanning electron microscopy. It was confirmed that the pores with high pore aspect ratio were parallel, well-ordered, and uniform. The kinetics of pores growth in the AAO membrane was derived, and the kinetic models showed that pores stopped developing when the pressure ( σ) trended to equal the surface tension at the end of anodic oxidation. During pore expansion, the effects of the oxalic acid concentration and expansion time on the pore size were investigated, and the kinetic behaviors were explained with two kinetic models derived in this study. They showed that the pore size increased with extended time ( r= G· t+ G'), but decreased with increased concentration ( r = - K·ln c- K') through the derived mathematic formula. Also, the values of G, G', K, and K' were derived from our experimental data.

A Universal Isotherm Model to Capture Adsorption Uptake and Energy Distribution of Porous Heterogeneous Surface.

PubMed

Ng, Kim Choon; Burhan, Muhammad; Shahzad, Muhammad Wakil; Ismail, Azahar Bin

2017-09-06

The adsorbate-adsorbent thermodynamics are complex as it is influenced by the pore size distributions, surface heterogeneity and site energy distribution, as well as the adsorbate properties. Together, these parameters defined the adsorbate uptake forming the state diagrams, known as the adsorption isotherms, when the sorption site energy on the pore surfaces are favorable. The available adsorption models for describing the vapor uptake or isotherms, hitherto, are individually defined to correlate to a certain type of isotherm patterns. There is yet a universal approach in developing these isotherm models. In this paper, we demonstrate that the characteristics of all sorption isotherm types can be succinctly unified by a revised Langmuir model when merged with the concepts of Homotattic Patch Approximation (HPA) and the availability of multiple sets of site energy accompanied by their respective fractional probability factors. The total uptake (q/q*) at assorted pressure ratios (P/P s ) are inextricably traced to the manner the site energies are spread, either naturally or engineered by scientists, over and across the heterogeneous surfaces. An insight to the porous heterogeneous surface characteristics, in terms of adsorption site availability has been presented, describing the unique behavior of each isotherm type.

Ceramic membrane by tape casting and sol-gel coating for microfiltration and ultrafiltration application

NASA Astrophysics Data System (ADS)

Das, Nandini; Maiti, H. S.

2009-11-01

Alumina membrane filters in the form of thin (0.3-0.8 mm) discs of 25-30 mm diameter suitable for microfiltration application have been fabricated by tape-casting technique. Further using this microfiltration membrane as substrate, boehmite sol coating was applied on it and ultrafiltration membrane with very small thickness was formed. The pore size of the microfiltration membrane could be varied in the range of 0.1-0.7 μm through optimisation of experimental parameter. In addition, each membrane shows a very narrow pore size distribution. The most important factor, which determines the pore size of the membrane, is the initial particle size and its distribution of the ceramic powder. The top thin ultrafiltration, boehmite layer was prepared by sol-gel method, with a thickness of 0.5 μm. Particle size of the sol was approximately 30-40 nm. The structure and formation of the layer was analysed through TEM. At 550 °C formation of the top layer was completed. The pore size of the ultrafiltration membrane measured from TEM micrograph was almost 10 nm. Results of microbial (Escherichia coli—smallest-sized water-borne bacteria) test confirm the possibility of separation through this membrane

Unlocking the Physiochemical Controls on Organic Carbon Dynamics from the Soil Pore- to Core-Scale

NASA Astrophysics Data System (ADS)

Smith, A. P.; Tfaily, M. M.; Bond-Lamberty, B. P.; Todd-Brown, K. E.; Bailey, V. L.

2015-12-01

The physical organization of soil includes pore networks of varying size and connectivity. These networks control microbial access to soil organic carbon (C) by spatially separating microorganisms and C by both distance and size exclusion. The extent to which this spatially isolated C is vulnerable to microbial transformation under hydrologically dynamic conditions is unknown, and limits our ability to predict the source and sink capacity of soils. We investigated the effects of shifting hydrologic connectivity and soil structure on greenhouse gas C emissions from surface soils collected from the Disney Wilderness Preserve (Florida, USA). We subjected intact soil cores and re-packed homogenized soil cores to simulated groundwater rise or precipitation, monitoring their CO2 and CH4 emissions over 24 hours. Soil pore water was then extracted from each core using different suctions to sample water retained by pore throats of different sizes and then characterized by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Greater respiration rates were observed from homogenized cores compared to intact cores, and from soils wet from below, in which the wetting front is driven by capillary forces, filling fine pores first. This suggests that C located in fine pores may turn over via diffusion processes that lead to the colocation of this C with other resources and microorganisms. Both the complexity and concentration of soluble-C increased with decreasing pore size domains. Pore water extracted from homogenized cores had greater C concentrations than from intact cores, with the greatest concentrations in pore waters sampled from very fine pores, highlighting the importance of soil structure in physically protecting C. These results suggest that the spatial separation of decomposers from C is a key mechanism stabilizing C in these soils. Further research is ongoing to accurately represent this protection mechanism, and the conditions under which it breaks down, in new and improved Earth system models.

Substrats poreux biodegradables prepares a partir de phases co-continues dans les melanges de polymeres immiscibles

NASA Astrophysics Data System (ADS)

Sarazin, Pierre

2003-06-01

In this thesis a novel approach to preparing biodegradable materials with highly structured and interconnected porosity is proposed. The method involves the controlled preparation of immiscible co-continuous polymer blends using melt-processing technology followed by a bulk solvent extraction step of one of the phases (the porogen phase). A co-continuous structure is defined as the state when each phase of the blend is fully interconnected through a continuous pathway. This method allows for the preparation of porous materials with highly controlled pore size, pore volume and pore shape which can then be transformed and shaped in various forms useful for biomedical applications. Various properties of the skin of the polymeric articles (closed-cell, open-cell, modification of the pore size) can be controlled. Initially, the study on the immiscible binary and compatibilized poly(L-lactide)/polystyrene blends (PLLA/PS) after extraction of the PS phase demonstrated that highly percolated blends exist from 40--75%PS and 40--60%PS for the binary and compatibilized blends, respectively. It is demonstrated that both the pore size and extent of co-continuity can be controlled through composition and interfacial modification. The subsequent part of our work treats of the preparation of porous PLLA from a blend of two biodegradable polymers and the performance of such porous materials. This portion of the work uses only polymer materials which have been medically approved for internal use. In this case, small amounts of the porogen phase can be tolerated in the final porous substrate. Co-continuous blends comprised of poly(L-lactide)/Poly(epsilon-caprolactone) PLLA/PCL, were prepared via melt processing. A wide range of phase sizes for the co-continuous blend is generated through a combination of concentration control and quiescent annealing. As the PLLA phase can not be dissolved selectively in PLLA/PS blends, the co-continuity range was evaluated indirectly. To precisely assess the formation of the co-continuous morphology, the polylactide was replaced by a poly(epsilon-caprolactone) (PCL) in the following work. PCL possesses a similar biocompatibility, although it exhibits a much slower degradation rate. These results practically allow for a separation of the effects of deformation/disintegration processes and coalescence on continuous and co-continuous morphology development. Coalescence phenomena for systems such as the PS in PCL case is clearly the dominant parameter controlling phase size at higher compositions. These results underline the requirement of co-continuity models to include parameters related to coalescence effects. The data indicate the significant potential of mixing temperature as a tool for the morphology control of co-continuous polymer blends. (Abstract shortened by UMI.)

SEM-induced shrinkage and site-selective modification of single-crystal silicon nanopores

NASA Astrophysics Data System (ADS)

Chen, Qi; Wang, Yifan; Deng, Tao; Liu, Zewen

2017-07-01

Solid-state nanopores with feature sizes around 5 nm play a critical role in bio-sensing fields, especially in single molecule detection and sequencing of DNA, RNA and proteins. In this paper we present a systematic study on shrinkage and site-selective modification of single-crystal silicon nanopores with a conventional scanning electron microscope (SEM). Square nanopores with measurable sizes as small as 8 nm × 8 nm and rectangle nanopores with feature sizes (the smaller one between length and width) down to 5 nm have been obtained, using the SEM-induced shrinkage technique. The analysis of energy dispersive x-ray spectroscopy and the recovery of the pore size and morphology reveal that the grown material along with the edge of the nanopore is the result of deposition of hydrocarbon compounds, without structural damage during the shrinking process. A simplified model for pore shrinkage has been developed based on observation of the cross-sectional morphology of the shrunk nanopore. The main factors impacting on the task of controllably shrinking the nanopores, such as the accelerating voltage, spot size, scanned area of e-beam, and the initial pore size have been discussed. It is found that single-crystal silicon nanopores shrink linearly with time under localized irradiation by SEM e-beam in all cases, and the pore shrinkage rate is inversely proportional to the initial equivalent diameter of the pore under the same e-beam conditions.

Time evolution of pore system in lime - Pozzolana composites

NASA Astrophysics Data System (ADS)

Doleželová, Magdaléna; Čáchová, Monika; Scheinherrová, Lenka; Keppert, Martin

2017-11-01

The lime - pozzolana mortars and plasters are used in restoration works on building cultural heritage but these materials are also following the trend of energy - efficient solutions in civil engineering. Porosity and pore size distribution is one of crucial parameters influencing engineering properties of porous materials. The pore size distribution of lime based system is changing in time due to chemical processes occurring in the material. The present paper describes time evolution of pore system in lime - pozzolana composites; the obtained results are useful in prediction of performance of lime - pozzolana systems in building structures.

Guest–host interactions of a rigid organic molecule in porous silica frameworks

PubMed Central

Wu, Di; Hwang, Son-Jong; Zones, Stacey I.; Navrotsky, Alexandra

2014-01-01

Molecular-level interactions at organic–inorganic interfaces play crucial roles in many fields including catalysis, drug delivery, and geological mineral precipitation in the presence of organic matter. To seek insights into organic–inorganic interactions in porous framework materials, we investigated the phase evolution and energetics of confinement of a rigid organic guest, N,N,N-trimethyl-1-adamantammonium iodide (TMAAI), in inorganic porous silica frameworks (SSZ-24, MCM-41, and SBA-15) as a function of pore size (0.8 nm to 20.0 nm). We used hydrofluoric acid solution calorimetry to obtain the enthalpies of interaction between silica framework materials and TMAAI, and the values range from −56 to −177 kJ per mole of TMAAI. The phase evolution as a function of pore size was investigated by X-ray diffraction, IR, thermogravimetric differential scanning calorimetry, and solid-state NMR. The results suggest the existence of three types of inclusion depending on the pore size of the framework: single-molecule confinement in a small pore, multiple-molecule confinement/adsorption of an amorphous and possibly mobile assemblage of molecules near the pore walls, and nanocrystal confinement in the pore interior. These changes in structure probably represent equilibrium and minimize the free energy of the system for each pore size, as indicated by trends in the enthalpy of interaction and differential scanning calorimetry profiles, as well as the reversible changes in structure and mobility seen by variable temperature NMR. PMID:24449886

Development of hierarchical, tunable pore size polymer foams for ICF targets

DOE PAGES

Hamilton, Christopher E.; Lee, Matthew Nicholson; Parra-Vasquez, A. Nicholas Gerardo

2016-08-01

In this study, one of the great challenges of inertial confinement fusion experiments is poor understanding of the effects of reactant heterogeneity on fusion reactions. The Marble campaign, conceived at Los Alamos National Laboratory, aims to gather new insights into this issue by utilizing target capsules containing polymer foams of variable pore sizes, tunable over an order of magnitude. Here, we describe recent and ongoing progress in the development of CH and CH/CD polymer foams in support of Marble. Hierarchical and tunable pore sizes have been achieved by utilizing a sacrificial porogen template within an open-celled poly(divinylbenzene) or poly(divinylbenzene-co-styrene) aerogelmore » matrix, resulting in low-density foams (~30 mg/ml) with continuous multimodal pore networks.« less

Tomographic analysis of reactive flow induced pore structure changes in column experiments

NASA Astrophysics Data System (ADS)

Cai, Rong; Lindquist, W. Brent; Um, Wooyong; Jones, Keith W.

2009-09-01

We utilize synchrotron X-ray computed micro-tomography to capture and quantify snapshots in time of dissolution and secondary precipitation in the microstructure of Hanford sediments exposed to simulated caustic waste in flow-column experiments. The experiment is complicated somewhat as logistics dictated that the column spent significant amounts of time in a sealed state (acting as a batch reactor). Changes accompanying a net reduction in porosity of 4% were quantified including: (1) a 25% net decrease in pores resulting from a 38% loss in the number of pores <10-4mm in volume and a 13% increase in the number of pores of larger size; and (2) a 38% decrease in the number of throats. The loss of throats resulted in decreased coordination number for pores of all sizes and significant reduction in the number of pore pathways.

Effect of pore geometry on the compressibility of a confined simple fluid

NASA Astrophysics Data System (ADS)

Dobrzanski, Christopher D.; Maximov, Max A.; Gor, Gennady Y.

2018-02-01

Fluids confined in nanopores exhibit properties different from the properties of the same fluids in bulk; among these properties is the isothermal compressibility or elastic modulus. The modulus of a fluid in nanopores can be extracted from ultrasonic experiments or calculated from molecular simulations. Using Monte Carlo simulations in the grand canonical ensemble, we calculated the modulus for liquid argon at its normal boiling point (87.3 K) adsorbed in model silica pores of two different morphologies and various sizes. For spherical pores, for all the pore sizes (diameters) exceeding 2 nm, we obtained a logarithmic dependence of fluid modulus on the vapor pressure. Calculation of the modulus at saturation showed that the modulus of the fluid in spherical pores is a linear function of the reciprocal pore size. The calculation of the modulus of the fluid in cylindrical pores appeared too scattered to make quantitative conclusions. We performed additional simulations at higher temperature (119.6 K), at which Monte Carlo insertions and removals become more efficient. The results of the simulations at higher temperature confirmed both regularities for cylindrical pores and showed quantitative difference between the fluid moduli in pores of different geometries. Both of the observed regularities for the modulus stem from the Tait-Murnaghan equation applied to the confined fluid. Our results, along with the development of the effective medium theories for nanoporous media, set the groundwork for analysis of the experimentally measured elastic properties of fluid-saturated nanoporous materials.

Synchrotron microtomographic quantification of geometrical soil pore characteristics affected by compaction

NASA Astrophysics Data System (ADS)

Udawatta, Ranjith P.; Gantzer, Clark J.; Anderson, Stephen H.; Assouline, Shmuel

2016-05-01

Soil compaction degrades soil structure and affects water, heat, and gas exchange as well as root penetration and crop production. The objective of this study was to use X-ray computed microtomography (CMT) techniques to compare differences in geometrical soil pore parameters as influenced by compaction of two different aggregate size classes. Sieved (diameter < 2 mm and < 0.5 mm) and repacked (1.51 and 1.72 Mg m-3) Hamra soil cores of 5 by 5 mm (average porosities were 0.44 and 0.35) were imaged at 9.6 μm resolution at the Argonne Advanced Photon Source (synchrotron facility) using X-ray CMT. Images of 58.9 mm3 volume were analyzed using 3-Dimensional Medial Axis (3-DMA) software. Geometrical characteristics of the spatial distributions of pore structures (pore radii, volume, connectivity, path length, and tortuosity) were numerically investigated. Results show that the coordination number (CN) distribution and path length (PL) measured from the medial axis were reasonably fit by exponential relationships P(CN) = 10-CN/Co and P(PL) = 10-PL/PLo, respectively, where Co and PLo are the corresponding characteristic constants. Compaction reduced porosity, average pore size, number of pores, and characteristic constants. The average pore radii (63.7 and 61 µm; p < 0.04), largest pore volume (1.58 and 0.58 mm3; p = 0.06), number of pores (55 and 50; p = 0.09), and characteristic coordination number (3.74 and 3.94; p = 0.02) were significantly different between the low-density than the high-density treatment. Aggregate size also influenced measured geometrical pore parameters. This analytical technique provides a tool for assessing changes in soil pores that affect hydraulic properties and thereby provides information to assist in assessment of soil management systems.

Impact of matric potential and pore size distribution on growth dynamics of filamentous and non-filamentous soil bacteria.

PubMed

Wolf, Alexandra B; Vos, Michiel; de Boer, Wietse; Kowalchuk, George A

2013-01-01

The filamentous growth form is an important strategy for soil microbes to bridge air-filled pores in unsaturated soils. In particular, fungi perform better than bacteria in soils during drought, a property that has been ascribed to the hyphal growth form of fungi. However, it is unknown if, and to what extent, filamentous bacteria may also display similar advantages over non-filamentous bacteria in soils with low hydraulic connectivity. In addition to allowing for microbial interactions and competition across connected micro-sites, water films also facilitate the motility of non-filamentous bacteria. To examine these issues, we constructed and characterized a series of quartz sand microcosms differing in matric potential and pore size distribution and, consequently, in connection of micro-habitats via water films. Our sand microcosms were used to examine the individual and competitive responses of a filamentous bacterium (Streptomyces atratus) and a motile rod-shaped bacterium (Bacillus weihenstephanensis) to differences in pore sizes and matric potential. The Bacillus strain had an initial advantage in all sand microcosms, which could be attributed to its faster growth rate. At later stages of the incubation, Streptomyces became dominant in microcosms with low connectivity (coarse pores and dry conditions). These data, combined with information on bacterial motility (expansion potential) across a range of pore-size and moisture conditions, suggest that, like their much larger fungal counterparts, filamentous bacteria also use this growth form to facilitate growth and expansion under conditions of low hydraulic conductivity. The sand microcosm system developed and used in this study allowed for precise manipulation of hydraulic properties and pore size distribution, thereby providing a useful approach for future examinations of how these properties influence the composition, diversity and function of soil-borne microbial communities.

Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes

NASA Astrophysics Data System (ADS)

Perrier, E. M. A.; Bird, N. R. A.; Rieutord, T. B.

2010-04-01

Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a Critical Filtration Size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.

Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes

NASA Astrophysics Data System (ADS)

Perrier, E. M. A.; Bird, N. R. A.; Rieutord, T. B.

2010-10-01

Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a critical filtration size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.

Effect of pore size on bone ingrowth into porous titanium implants fabricated by additive manufacturing: An in vivo experiment.

PubMed

Taniguchi, Naoya; Fujibayashi, Shunsuke; Takemoto, Mitsuru; Sasaki, Kiyoyuki; Otsuki, Bungo; Nakamura, Takashi; Matsushita, Tomiharu; Kokubo, Tadashi; Matsuda, Shuichi

2016-02-01

Selective laser melting (SLM) is an additive manufacturing technique with the ability to produce metallic scaffolds with accurately controlled pore size, porosity, and interconnectivity for orthopedic applications. However, the optimal pore structure of porous titanium manufactured by SLM remains unclear. In this study, we evaluated the effect of pore size with constant porosity on in vivo bone ingrowth in rabbits into porous titanium implants manufactured by SLM. Three porous titanium implants (with an intended porosity of 65% and pore sizes of 300, 600, and 900μm, designated the P300, P600, and P900 implants, respectively) were manufactured by SLM. A diamond lattice was adapted as the basic structure. Their porous structures were evaluated and verified using microfocus X-ray computed tomography. Their bone-implant fixation ability was evaluated by their implantation as porous-surfaced titanium plates into the cortical bone of the rabbit tibia. Bone ingrowth was evaluated by their implantation as cylindrical porous titanium implants into the cancellous bone of the rabbit femur for 2, 4, and 8weeks. The average pore sizes of the P300, P600, and P900 implants were 309, 632, and 956μm, respectively. The P600 implant demonstrated a significantly higher fixation ability at 2weeks than the other implants. After 4weeks, all models had sufficiently high fixation ability in a detaching test. Bone ingrowth into the P300 implant was lower than into the other implants at 4weeks. Because of its appropriate mechanical strength, high fixation ability, and rapid bone ingrowth, our results indicate that the pore structure of the P600 implant is a suitable porous structure for orthopedic implants manufactured by SLM. Copyright © 2015 Elsevier B.V. All rights reserved.

Influence of pore size distributions on decomposition of maize leaf residue: evidence from X-ray computed micro-tomography

NASA Astrophysics Data System (ADS)

Negassa, Wakene; Guber, Andrey; Kravchenko, Alexandra; Rivers, Mark

2014-05-01

Soil's potential to sequester carbon (C) depends not only on quality and quantity of organic inputs to soil but also on the residence time of the applied organic inputs within the soil. Soil pore structure is one of the main factors that influence residence time of soil organic matter by controlling gas exchange, soil moisture and microbial activities, thereby soil C sequestration capacity. Previous attempts to investigate the fate of organic inputs added to soil did not allow examining their decomposition in situ; the drawback that can now be remediated by application of X-ray computed micro-tomography (µ-CT). The non-destructive and non-invasive nature of µ-CT gives an opportunity to investigate the effect of soil pore size distributions on decomposition of plant residues at a new quantitative level. The objective of this study is to examine the influence of pore size distributions on the decomposition of plant residue added to soil. Samples with contrasting pore size distributions were created using aggregate fractions of five different sizes (<0.05, 0.05-0.1, 0.10-05, 0.5-1.0 and 1.0-2.0 mm). Weighted average pore diameters ranged from 10 µm (<0.05 mm fraction) to 104 µm (1-2 mm fraction), while maximum pore diameter were in a range from 29 µm (<0.05 mm fraction) to 568 µm (1-2 mm fraction) in the created soil samples. Dried pieces of maize leaves 2.5 mg in size (equivalent to 1.71 mg C g-1 soil) were added to half of the studied samples. Samples with and without maize leaves were incubated for 120 days. CO2 emission from the samples was measured at regular time intervals. In order to ensure that the observed differences are due to differences in pore structure and not due to differences in inherent properties of the studied aggregate fractions, we repeated the whole experiment using soil from the same aggregate size fractions but ground to <0.05 mm size. Five to six replicated samples were used for intact and ground samples of all sizes with and without leaves. Two replications of the intact aggregate fractions of all sizes with leaves were subjected to µ-CT scanning before and after incubation, whereas all the remaining replications of both intact and ground aggregate fractions of <0.05, 0.05-0.1, and 1.0-2.0 mm sizes with leaves were scanned with µ-CT after the incubation. The µ-CT image showed that approximately 80% of the leaves in the intact samples of large aggregate fractions (0.5-1.0 and 1.0-2.0 mm) was decomposed during the incubation, while only 50-60% of the leaves were decomposed in the intact samples of smaller sized fractions. Even lower percent of leaves (40-50%) was decomposed in the ground samples, with very similar leaf decomposition observed in all ground samples regardless of the aggregate fraction size. Consistent with µ-CT results, the proportion of decomposed leaf estimated with the conventional mass loss method was 48% and 60% for the <0.05 mm and 1.0-2.0 mm soil size fractions of intact aggregates, and 40-50% in ground samples, respectively. The results of the incubation experiment demonstrated that, while greater C mineralization was observed in samples of all size fractions amended with leaf, the effect of leaf presence was most pronounced in the smaller aggregate fractions (0.05-0.1 mm and 0.05 mm) of intact aggregates. The results of the present study unequivocally demonstrate that differences in pore size distributions have a major effect on the decomposition of plant residues added to soil. Moreover, in presence of plant residues, differences in pore size distributions appear to also influence the rates of decomposition of the intrinsic soil organic material.

Evolution of Micro-Pores in a Single-Crystal Nickel-Based Superalloy During Solution Heat Treatment

NASA Astrophysics Data System (ADS)

Li, Xiangwei; Wang, Li; Dong, Jiasheng; Lou, Langhong; Zhang, Jian

2017-06-01

Evolution of micro-pores in a third-generation single-crystal nickel-based superalloy during solution heat treatment at 1603 K (1330 °C) was investigated by X-ray computed tomography. 3D information including morphology, size, number, and volume fraction of micro-pores formed during solidification (S-pores) and solution (H-pores) was analyzed. The growth behaviors of both S-pores and H-pores can be related to the vacancy formation and diffusion during heat treatment.

Characterization of porosity in sulfide ore minerals: A USANS/SANS study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, F.; Zhao, J.; Etschmann, B. E.

Porosity plays a key role in the formation and alteration of sulfide ore minerals, yet our knowledge of the nature and formation of the residual pores is very limited. Herein, we report the application of ultra-small-angle neutron scattering and small-angle neutron scattering (USANS/SANS) to assess the porosity in five natural sulfide minerals (violarite, marcasite, pyrite, chalcopyrite, and bornite) possibly formed by hydrothermal mineral replacement reactions and two synthetic sulfide minerals (violarite and marcasite) prepared experimentally by mimicking natural hydrothermal conditions. USANS/SANS data showed very different pore size distributions for these minerals. Natural violarite and marcasite tend to possess less poresmore » in the small size range (<100 nm) compared with their synthetic counterparts. This phenomenon is consistent with a higher degree of pore healing or diagenetic compaction experienced by the natural violarite and marcasite. Surprisingly, nanometer-sized (<20 nm) pores were revealed for a natural pyrite cube from La Rioga, Spain, and the sample has a pore volume fraction of ~7.7%. Both chalcopyrite and bornite from the massive sulfide assemblage of the Olympic Dam deposit in Roxby Downs, South Australia, were found to be porous with a similar pore volume fraction (~15%), but chalcopyrite tends to have a higher proportion of nanometer-size pores centered at ~4 nm while bornite tends to have a broader pore size distribution. The specific surface area is generally low for these minerals ranging from 0.94 to 6.28 m2/g, and the surfaces are generally rough as surface fractal behavior was observed for all these minerals. This investigation has demonstrated that USANS/SANS is a very useful tool for analyzing porosity in ore minerals. We believe that with this quantified porosity information a deeper understanding of the complex fluid flow behavior within the porous minerals can be expected.« less

Polycation-Functionalized Nanoporous Silicon Particles for Gene Silencing on Breast Cancer Cells

PubMed Central

Zhang, Mingzhen; Xu, Rong; Xia, Xiaojun; Yang, Yong; Gu, Jianhua; Qin, Guoting; Liu, Xuewu; Ferrari, Mauro; Shen, Haifa

2013-01-01

Nanoporous silicon particles (pSi), with a pore size in the range of 20~60 nm, were modified with polyethyleimine (PEI) to yield pSi-PEI particles, which were subsequently complexed with siRNA. Thus, pSi-PEI/siRNA particles were fabricated, with the PEI/siRNA nanocomplexes mainly anchored inside the nanopore of the pSi particles. These hybrid particles were used as carriers to deliver siRNA to human breast cancer cells. Due to the gradual degradation of the pSi matrix under physiological conditions, the PEI/siRNA nanocomplexes were released from the pore interior in a sustained manner. Physicochemical characterization revealed that the released PEI/siRNA nanocomplexes exhibited well-defined spherical shape and narrow particle size distribution between 15 and 30 nm. Gene knockdown against the ataxia telangiectasia mutated (ATM) cancer gene showed dramatic gene silencing efficacy. Moreover, comprehensive biocompatibility studies were performed for the pSi-PEI/siRNA particles both in vitro and in vivo and demonstrated that the pSi-PEI particles exhibited significantly enhanced biocompatibility. As a consequence, PEI-modified porous silicon particles may have substantial potential as safe and effective siRNA delivery systems. PMID:24103653

Episodic tremor and slip explained by fluid-enhanced microfracturing and sealing

NASA Astrophysics Data System (ADS)

Bernaudin, M.; Gueydan, F.

2017-12-01

A combination of non-volcanic tremor and transient slow slip events behaviors is commonly observed at plate interface, between locked/seismogenic zone at low depths and stable/ductile creep zone at larger depths. This association defines Episodic Tremor and Slip, systematically highlighted by over-pressurized fluids and near failure shear stress conditions. Here we propose a new mechanical approach that provides for the first time a mechanical and field-based explanation of the observed association between non-volcanic tremor and slow slip events. In contrast with more classical rate-and-state models, this physical model uses a ductile rheology with grain size sensitivity, fluid-driven microfracturing and sealing (e.g. grain size reduction and grain growth) and related pore fluid pressure fluctuations. We reproduce slow slip events by transient ductile strain localization as a result of fluid-enhanced microfracturing and sealing. Moreover, occurrence of macrofracturing during transient strain localization and local increase in pore fluid pressure well simulate non-volcanic tremor. Our model provides therefore a field-based explanation of episodic tremor and slip and moreover predicts the depth and temperature ranges of their occurrence in subduction zones. It implies furthermore that non-volcanic tremor and slow slip events are physically related.

Characterization of the CO2 fluid adsorption in coal as a function of pressure using neutron scattering techniques (SANS and USANS)

USGS Publications Warehouse

Melnichenko, Y.B.; Radlinski, A.P.; Mastalerz, Maria; Cheng, G.; Rupp, J.

2009-01-01

Small angle neutron scattering techniques have been applied to investigate the phase behavior of CO2 injected into coal and possible changes in the coal pore structure that may result from this injection. Three coals were selected for this study: the Seelyville coal from the Illinois Basin (Ro = 0.53%), Baralaba coal from the Bowen Basin (Ro = 0.67%), and Bulli 4 coal from the Sydney Basin (Ro = 1.42%). The coals were selected from different depths to represent the range of the underground CO2 conditions (from subcritical to supercritical) which may be realized in the deep subsurface environment. The experiments were conducted in a high pressure cell and CO2 was injected under a range of pressure conditions, including those corresponding to in-situ hydrostatic subsurface conditions for each coal. Our experiments indicate that the porous matrix of all coals remains essentially unchanged after exposure to CO2 at pressures up to 200??bar (1??bar = 105??Pa). Each coal responds differently to the CO2 exposure and this response appears to be different in pores of various sizes within the same coal. For the Seelyville coal at reservoir conditions (16????C, 50??bar), CO2 condenses from a gas into liquid, which leads to increased average fluid density in the pores (??pore) with sizes (r) 1 ?? 105 ??? r ??? 1 ?? 104???? (??pore ??? 0.489??g/cm3) as well as in small pores with size between 30 and 300???? (??pore ??? 0.671??g/cm3). These values are by a factor of three to four higher than the density of bulk CO2 (??CO2) under similar thermodynamic conditions (??CO2 ??? 0.15??g/cm3). At the same time, in the intermediate size pores with r ??? 1000???? the average fluid density is similar to the density of bulk fluid, which indicates that adsorption does not occur in these pores. At in situ conditions for the Baralaba coal (35 OC, 100??bar), the average fluid density of CO2 in all pores is lower than that of the bulk fluid (??pore / ??CO2 ??? 0.6). Neutron scattering from the Bulli 4 coal did not show any significant variation with pressure, a phenomenon which we assign to the extremely small amount of porosity of this coal in the pore size range between 35 and 100,000????. ?? 2008 Elsevier B.V.

a New Method for Calculating Fractal Dimensions of Porous Media Based on Pore Size Distribution

NASA Astrophysics Data System (ADS)

Xia, Yuxuan; Cai, Jianchao; Wei, Wei; Hu, Xiangyun; Wang, Xin; Ge, Xinmin

Fractal theory has been widely used in petrophysical properties of porous rocks over several decades and determination of fractal dimensions is always the focus of researches and applications by means of fractal-based methods. In this work, a new method for calculating pore space fractal dimension and tortuosity fractal dimension of porous media is derived based on fractal capillary model assumption. The presented work establishes relationship between fractal dimensions and pore size distribution, which can be directly used to calculate the fractal dimensions. The published pore size distribution data for eight sandstone samples are used to calculate the fractal dimensions and simultaneously compared with prediction results from analytical expression. In addition, the proposed fractal dimension method is also tested through Micro-CT images of three sandstone cores, and are compared with fractal dimensions by box-counting algorithm. The test results also prove a self-similar fractal range in sandstone when excluding smaller pores.

The dissolution kinetics of major elements in municipal solid waste incineration bottom ash particles

NASA Astrophysics Data System (ADS)

Bendz, David; Tüchsen, Peter L.; Christensen, Thomas H.

2007-12-01

Leaching and tracer experiments in batches at L/S 20 were performed with 3-month-old MSWI bottom ash separated into eight different particle sizes. The time-dependent leaching of major elements (Ca 2+, K +, Na +, Cl - and SO 4- 2 ) was monitored for up to 747 h. Physical properties of the particles, the specific surface (BET), pore volume and pore volume distribution over pore sizes (BJH) were determined for all particle classes by N 2 adsorption/desorption experiments. Some common features of physical pore structure for all particles were revealed. The specific surface and the particle pore volume were found to be negatively correlated with particle size, ranging from 3.2 m 2/g to 25.7 m 2/g for the surface area and from 0.0086 cm 3/g to 0.091 cm 3/g for the pore volume. Not surprisingly, the specific surface area was found to be the major material parameter that governed the leaching behavior for all elements (Ca 2+, K +, Na +, Cl - and SO 4- 2 ) and particle sizes. The diffusion resistance was determined independently by separate tracer (tritium) experiments. Diffusion gave a significant contribution to the apparent leaching kinetics for all elements during the first 10-40 h (depending on the particle size) of leaching and surface reaction was the overall rate controlling mechanism at late times for all particle sizes. For Ca 2+ and SO 4- 2 , the coupled effect of diffusion resistance and the degree of undersaturation in the intra particle pore volume was found to be a major rate limiting dissolution mechanism for both early and late times. The solubility control in the intra particulate porosity may undermine any attempt to treat bottom ash by washing out the sulfate. Even for high liquid/solid ratios, the solubility in the intra-particular porosity will limit the release rate.

Sound absorption characteristics of aluminum foam with spherical cells

NASA Astrophysics Data System (ADS)

Li, Yunjie; Wang, Xinfu; Wang, Xingfu; Ren, Yuelu; Han, Fusheng; Wen, Cuie

2011-12-01

Aluminum foams were fabricated by an infiltration process. The foams possess spherical cells with a fixed porosity of 65% and varied pore sizes which ranged from 1.3 to 1.9 mm. The spherical cells are interconnected by small pores or pore openings on the cell walls that cause the foams show a characteristic of open cell structures. The sound absorption coefficient of the aluminum foams was measured by a standing wave tube and calculated by a transfer function method. It is shown that the sound absorption coefficient increases with an increase in the number of pore openings in the unit area or with a decrease of the diameter of the pore openings in the range of 0.3 to 0.4 mm. If backed with an air cavity, the resonant absorption peaks in the sound absorption coefficient versus frequency curves will be shifted toward lower frequencies as the cavity depth is increased. The samples with the same pore opening size but different pore size show almost the same absorption behavior, especially in the low frequency range. The present results are in good agreement with some theoretical predictions based on the acoustic impedance measurements of metal foams with circular apertures and cylindrical cavities and the principle of electroacoustic analogy.

Porosity characterization of fresh and altered stones by ultrasound velocity and mercury intrusion porosimetry

NASA Astrophysics Data System (ADS)

Scrivano, Simona; Gaggero, Laura; Gisbert Aguilar, Josep

2016-04-01

Porosity is the main physical feature dealing with rocks durability and storage capacity. The analysis of this parameter is key factor in predicting rock performances (Molina et al., 2011). There are several techniques that can be applied to acquire the widest information range possible about pores (e.g. size, shape, distribution), leading to a better understanding of decay processes and trapping capacity. The coupling of a detailed minero-petrographic analysis with physical measures such as ultrasounds and mercury intrusion porosimetry (MIP) proved to be a valid tool for understanding the porous network and its evolution during weathering processes. Both fresh and salt-weathered samples were analysed to investigate the modification triggered in the porous network by crystallization. The ageing process was induced using a Na2SO4 saturated saline solution with the partial continuous immersion method (Benavente et al., 2001). The study was addressed to four sedimentary lithotypes: 1) Arenaria Macigno, a greywacke made up of thickened clasts of quartz, plagioclase and K-feldspar cemented by micritic calcite and phyllosilicates; 2) Breccia Aurora, a calcareous breccia with nodules of compact limestone and micritic cement joints; 3) Rosso Verona, a biomicrite where the compact bio-micrite matrix is cut by clay minerals veins; and 4) Vicenza Stone, an organogenic limestone rich in micro- and macro foraminifera, algae, bryozoans and remains of echinoderms, with iron oxides. An appropriate description of the porous network variation and recognition of the origin of secondary porosity was attained. The study defined that the pore shape and distribution (anisotropy coefficient K) has a fluctuation up to the 50% after weathering treatments and pore-size distribution (defined in a range between 0,0025 - 75 μm), allowing modelling the mechanisms of water transport and evaluating decay susceptibility of these lithotypes. Molina E, Cultrone G, Sebastián E, Alonso FJ, Carrizo L, Gisbert J, et al. The pore system of sedimentary rocks as a key factor in the durability of building materials. Eng Geol 118 (2011) 110-21. D. Benavente, M.A. Garcia del Cura, A. Bernabeu, S. Ordonez. Quantification of salt weathering in porous stones using an experimental continuous partial immersion method. Eng Geol 59 (2001) 313-325.

3D Analysis of Porosity in a Ceramic Coating Using X-ray Microscopy

NASA Astrophysics Data System (ADS)

Klement, Uta; Ekberg, Johanna; Kelly, Stephen T.

2017-02-01

Suspension plasma spraying (SPS) is a new, innovative plasma spray technique using a feedstock consisting of fine powder particles suspended in a liquid. Using SPS, ceramic coatings with columnar microstructures have been produced which are used as topcoats in thermal barrier coatings. The microstructure contains a wide pore size range consisting of inter-columnar spacings, micro-pores and nano-pores. Hence, determination of total porosity and pore size distribution is a challenge. Here, x-ray microscopy (XRM) has been applied for describing the complex pore space of the coatings because of its capability to image the (local) porosity within the coating in 3D at a resolution down to 50 nm. The possibility to quantitatively segment the analyzed volume allows analysis of both open and closed porosity. For an yttria-stabilized zirconia coating with feathery microstructure, both open and closed porosity were determined and it could be revealed that 11% of the pore volumes (1.4% of the total volume) are closed pores. The analyzed volume was reconstructed to illustrate the distribution of open and closed pores in 3D. Moreover, pore widths and pore volumes were determined. The results on the complex pore space obtained by XRM are discussed in connection with other porosimetry techniques.

Capillary trapping quantification in sandstones using NMR relaxometry

NASA Astrophysics Data System (ADS)

Connolly, Paul R. J.; Vogt, Sarah J.; Iglauer, Stefan; May, Eric F.; Johns, Michael L.

2017-09-01

Capillary trapping of a non-wetting phase arising from two-phase immiscible flow in sedimentary rocks is critical to many geoscience scenarios, including oil and gas recovery, aquifer recharge and, with increasing interest, carbon sequestration. Here we demonstrate the successful use of low field 1H Nuclear Magnetic Resonance [NMR] to quantify capillary trapping; specifically we use transverse relaxation time [T2] time measurements to measure both residual water [wetting phase] content and the surface-to-volume ratio distribution (which is proportional to pore size] of the void space occupied by this residual water. Critically we systematically confirm this relationship between T2 and pore size by quantifying inter-pore magnetic field gradients due to magnetic susceptibility contrast, and demonstrate that our measurements at all water saturations are unaffected. Diffusion in such field gradients can potentially severely distort the T2-pore size relationship, rendering it unusable. Measurements are performed for nitrogen injection into a range of water-saturated sandstone plugs at reservoir conditions. Consistent with a water-wet system, water was preferentially displaced from larger pores while relatively little change was observed in the water occupying smaller pore spaces. The impact of cyclic wetting/non-wetting fluid injection was explored and indicated that such a regime increased non-wetting trapping efficiency by the sequential occupation of the most available larger pores by nitrogen. Finally the replacement of nitrogen by CO2 was considered; this revealed that dissolution of paramagnetic minerals from the sandstone caused by its exposure to carbonic acid reduced the in situ bulk fluid T2 relaxation time on a timescale comparable to our core flooding experiments. The implications of this for the T2-pore size relationship are discussed.

Microporous alumina ceramic membranes

DOEpatents

Anderson, M.A.; Guangyao Sheng.

1993-05-04

Several methods are disclosed for the preparation microporous alumina ceramic membranes. For the first time, porous alumina membranes are made which have mean pore sizes less than 100 Angstroms and substantially no pores larger than that size. The methods are based on improved sol-gel techniques.

Microporous alumina ceramic membranes

DOEpatents

Anderson, Marc A.; Sheng, Guangyao

1993-01-01

Several methods are disclosed for the preparation microporous alumina ceramic membranes. For the first time, porous alumina membranes are made which have mean pore sizes less than 100 Angstroms and substantially no pores larger than that size. The methods are based on improved sol-gel techniques.

A universal model for nanoporous carbon supercapacitors applicable to diverse pore regimes, carbon materials, and electrolytes.

PubMed

Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent

2008-01-01

Supercapacitors, commonly called electric double-layer capacitors (EDLCs), are emerging as a novel type of energy-storage device with the potential to substitute batteries in applications that require high power densities. In response to the latest experimental breakthrough in nanoporous carbon supercapacitors, we propose a heuristic theoretical model that takes pore curvature into account as a replacement for the EDLC model, which is based on a traditional parallel-plate capacitor. When the pore size is in the mesopore regime (2-50 nm), counterions enter mesoporous carbon materials and approach the pore wall to form an electric double-cylinder capacitor (EDCC); in the micropore regime (<2 nm), solvated/desolvated counterions line up along the pore axis to form an electric wire-in-cylinder capacitor (EWCC). In the macropore regime (>50 nm) at which pores are large enough so that pore curvature is no longer significant, the EDCC model can be reduced naturally to the EDLC model. We present density functional theory calculations and detailed analyses of available experimental data in various pore regimes, which show the significant effects of pore curvature on the supercapacitor properties of nanoporous carbon materials. It is shown that the EDCC/EWCC model is universal for carbon supercapacitors with diverse carbon materials, including activated carbon materials, template carbon materials, and novel carbide-derived carbon materials, and with diverse electrolytes, including organic electrolytes, such as tetraethylammonium tetrafluoroborate (TEABF(4)) and tetraethylammonium methylsulfonate (TEAMS) in acetonitrile, aqueous H(2)SO(4) and KOH electrolytes, and even an ionic liquid electrolyte, such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI). The EDCC/EWCC model allows the supercapacitor properties to be correlated with pore size, specific surface area, Debye length, electrolyte concentration and dielectric constant, and solute ion size It may lend support for the systematic optimization of the properties of carbon supercapacitors through experiments. On the basis of the insight obtained from the new model, we also discuss the effects of the kinetic solvation/desolvation process, multimodal (versus unimodal) pore size distribution, and exohedral (versus endohedral) capacitors on the electrochemical properties of supercapacitors.

Determination of size distribution and encapsulation efficiency of liposome-encapsulated hemoglobin blood substitutes using asymmetric flow field-flow fractionation coupled with multi-angle static light scattering.

PubMed

Arifin, Dian R; Palmer, Andre F

2003-01-01

In this study, we investigated the size distribution, encapsulation efficiency, and oxygen affinity of liposome-encapsulated tetrameric hemoglobin (LEHb) dispersions and correlated the data with the variation in extruder membrane pore size, ionic strength of the extrusion buffer, and hemoglobin (Hb) concentration. Asymmetric flow field-flow fractionation (AFFF) in series with multi-angle static light scattering (MASLS) was used to study the LEHb size distribution. We also introduced a novel method to measure the encapsulation efficiency using a differential interferometric refractive index (DIR) detector coupled to the AFFF-MASLS system. This technique was nondestructive toward the sample and easy to implement. LEHbs were prepared by extrusion using a lipid combination of dimyristoyl-phosphatidylcholine, cholesterol, and dimyristoyl-phosphatidylglycerol in a 10:9:1 molar ratio. Five initial Hb concentrations (50, 100, 150, 200, and 300 mg Hb per mL of buffer) extruded through five different membrane pore diameters (400, 200, 100, 80, and 50 nm) were studied. Phosphate buffered saline (PBS) and phosphate buffer (PB) both at pH 7.3 were used as extrusion buffers. Despite the variation, extrusion through 400-nm pore diameter membranes produced LEHbs smaller than the pore size, extrusion through 200-nm membranes produced LEHbs with diameters close to the pore diameter, and extrusion through 100-, 80-, and 50-nm membranes produced LEHbs larger than the pore sizes. We found that the choice of extrusion buffer had the greatest effect on the LEHb size distribution compared to either Hb concentration or extruder membrane pore size. Extrusion in PBS produced larger LEHbs and more monodisperse LEHb dispersions. However, LEHbs extruded in PB generally had higher Hb encapsulation efficiencies and lower methemoglobin (metHb) levels. The choice of extrusion buffer also affected how the encapsulation efficiency correlated with Hb concentration, extruder pore size, and the metHb level. The most optimum encapsulation efficiency and amount of Hb entrapped were achieved at the highest Hb concentration and the largest pore size for both extrusion buffers (62.38% and 187.14 mg Hb/mL of LEHb dispersion extruded in PBS, and 69.98% and 209.94 mg Hb/mL of LEHb dispersion extruded in PB). All LEHbs displayed good oxygen-carrying properties as indicated by their P(50) and cooperativity coefficients. LEHbs extruded in PB had an average P(50) of 23.04 mmHg and an average Hill number of 2.29, and those extruded in PBS had average values of 27.25 mmHg and 2.49. These oxygen-binding properties indicate that LEHbs possess strong potential as artificial blood substitutes. In addition, the metHb levels in PB-LEHb dispersions are significantly low even in the absence of antioxidants such as N-acetyl-L-cysteine.

Manufacturing of Open-Cell Zn-22Al-2Cu Alloy Foams by a Centrifugal-Replication Process

NASA Astrophysics Data System (ADS)

Sánchez, A.; Cruz, A.; Rivera, J. E.; Romero, J. A.; Suárez, M. A.; Gutiérrez, V. H.

2018-01-01

Centrifugal force was used to produce open-cell Zn-22Al-2Cu alloy foams by the replication method. Three different sizes (0.50, 0.69, and 0.95 mm) of NaCl spherical particles were used as space holders. A relatively low infiltration pressure was required to infiltrate completely the liquid metal into the three pore sizes, and it was determined based on the centrifugation system parameters. The infiltration pressure required was decreased when the diameter of the particle was increased. The porosity of the foam was increased from 58 to 63 pct, when the pore size was increased from 0.50 to 0.95 mm, while the relative density was decreased from 0.42 to 0.36. The NaCl preform was preheated to avoid the freezing and to keep the rheological properties of the melt. The centrifugal-replication method is a suitable technique for the fabrication of open-cell Zn-Al-Cu alloy foams with small pore size. The compressive mechanical properties of the open-cell Zn-22Al-2Cu foams increased when the pore size decreased.

Modelling the physical properties of glasslike carbon foams

NASA Astrophysics Data System (ADS)

Letellier, M.; Macutkevic, J.; Bychanok, D.; Kuzhir, P.; Delgado-Sanchez, C.; Naguib, H.; Ghaffari Mosanenzadeh, S.; Fierro, V.; Celzard, A.

2017-07-01

In this work, model alveolar materials - carbon cellular and/or carbon reticulated foams - were produced in order to study and to model their physical properties. It was shown that very different morphologies could be obtained whereas the constituting vitreous carbon from which they were made remained exactly the same. Doing so, the physical properties of these foams were expected to depend neither on the composition nor on the carbonaceous texture but only on the porous structure, which could be tuned for the first time for having a constant pore size in a range of porosities, or a range of pore sizes at fixed porosity. The physical properties were then investigated through mechanical, acoustic, thermal and electromagnetic measurements. The results demonstrate the roles played by bulk density and cell size on all physical properties. Whereas some of the latter strongly depend on porosity and/or pore size, others are independent of pore size. It is expected that these results apply to many other kinds of rigid foams used in a broad range of different applications. The present results therefore open the route to their optimisation.

Control of both particle and pore size in nanoporous palladium alloy powders

DOE PAGES

Jones, Christopher G.; Cappillino, Patrick J.; Stavila, Vitalie; ...

2014-07-15

Energy storage materials often involve chemical reactions with bulk solids. Porosity within the solids can enhance reaction rates. The porosity can be either within or between individual particles of the material. Greater control of the size and uniformity of both types of pore should lead to enhancements of charging and discharging rates in energy storage systems. Furthermore, to control both particle and pore size in nanoporous palladium (Pd)-based hydrogen storage materials, first we created uniformly sized copper particles of about 1 μm diameter by the reduction of copper sulfate with ascorbic acid. In turn, these were used as reducing agentsmore » for tetrachloropalladate in the presence of a block copolymer surfactant. The copper reductant particles are geometrically self-limiting, so the resulting Pd particles are of similar size. The surfactant induces formation of 10 nm-scale pores within the particles. Some residual copper is alloyed with the Pd, reducing hydrogen storage capacity; use of a more reactive Pd salt can mitigate this. The reaction is conveniently performed in gram-scale batches.« less

Determination by Small-angle X-ray Scattering of Pore Size Distribution in Nanoporous Track-etched Polycarbonate Membranes

NASA Astrophysics Data System (ADS)

Jonas, A. M.; Legras, R.; Ferain, E.

1998-03-01

Nanoporous track-etched membranes with narrow pore size distributions and average pore size diameters tunable from 100 to 1000 Åare produced by the chemical etching of latent tracks in polymer films after irradiation by a beam of accelerated heavy ions. Nanoporous membranes are used for highly demanding filtration purposes, or as templates to obtain metallic or polymeric nanowires (L. Piraux et al., Nucl. Instr. Meth. Phys. Res. 1997, B131, 357). Such applications call for developments in nanopore size characterization techniques. In this respect, we report on the characterization by small-angle X-ray scattering (SAXS) of nanopore size distribution (nPSD) in polycarbonate track-etched membranes. The obtention of nPSD requires inverting an ill-conditioned inhomogeneous equation. We present different numerical routes to overcome the amplification of experimental errors in the resulting solutions, including a regularization technique allowing to obtain the nPSD without a priori knowledge of its shape. The effect of deviations from cylindrical pore shape on the resulting distributions are analyzed. Finally, SAXS results are compared to results obtained by electron microscopy and conductometry.

Solute mixing regulates heterogeneity of mineral precipitation in porous media: Effect of Solute Mixing on Precipitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cil, Mehmet B.; Xie, Minwei; Packman, Aaron I.

Synchrotron X-ray microtomography was used to track the spatiotemporal evolution of mineral precipitation and the consequent alteration of the pore structure. Column experiments were conducted by injecting CaCl2 and NaHCO3 solutions into granular porous media either as a premixed supersaturated solution (external mixing) or as separate solutions that mixed within the specimen (internal mixing). The two mixing modes produced distinct mineral growth patterns. While internal mixing promoted transverse heterogeneity with precipitation at the mixing zone, external mixing favored relatively homogeneous precipitation along the flow direction. The impact of precipitation on pore water flow and permeability was assessed via 3-D flowmore » simulations, which indicated anisotropic permeability evolution for both mixing modes. Under both mixing modes, precipitation decreased the median pore size and increased the skewness of the pore size distribution. Such similar pore-scale evolution patterns suggest that the clogging of individual pores depends primarily on local supersaturation state and pore geometry.« less

Water nano-filtration device

DOEpatents

Judkins, Roddie R [Knoxville, TN

2009-02-03

A water filter includes a porous support characterized by a mean porosity in the range of 20 to 50% and a mean pore size of 2 to 5 .mu.m; and a carbon filter membrane disposed thereon which is characterized by a mean particle size of no more than 50 .mu.m and a mean pore size of no more than 7.2 .mu.m.

Variations of permeability and pore size distribution of porous media with pressure.

PubMed

Chen, Quan; Kinzelbach, Wolfgang; Ye, Chaohui; Yue, Yong

2002-01-01

Porosity and permeability of porous and fractured geological media decrease with the exploitation of formation fluids such as petroleum, natural gas, or ground water. This may result in ground subsidence and a decrease of recovery of petroleum, natural gas, or ground water. Therefore, an evaluation of the behavior of permeability and porosity under formation fluid pressure changes is important to petroleum and ground water industries. This study for the first time establishes a method, which allows for the measurement of permeability, porosity, and pore size distribution of cores simultaneously. From the observation of the pore size distribution by low-field nuclear magnetic resonance (NMR) relaxation time spectrometry the mechanisms of pressure-dependent porosity and permeability change can be derived. This information cannot be obtained by traditional methods. As the large-size pores or fractures contribute significantly to the permeability, their change consequently leads to a large permeability change. The contribution of fractures to permeability is even larger than that of pores. Thus, the permeability of the cores with fractures decreased more than that of cores without fractures during formation pressure decrease. Furthermore, it did not recover during formation pressure increase. It can be concluded that in fractures, mainly plastic deformation takes place, while matrix pores mainly show elastic deformation. Therefore, it is very important to keep an appropriate formation fluid pressure during the exploitation of ground water and petroleum in a fractured formation.

Effect of excess pore pressure on the long runout of debris flows over low gradient channels: A case study of the Dongyuege debris flow in Nu River, China

NASA Astrophysics Data System (ADS)

Zhou, Zhen-Hua; Ren, Zhe; Wang, Kun; Yang, Kui; Tang, Yong-Jun; Tian, Lin; Xu, Ze-Min

2018-05-01

Debris flows with long reaches are one of the major natural hazards to human life and property on alluvial fans, as shown by the debris flow that occurred in the Dongyuege (DYG) Gully in August 18, 2010, and caused 96 deaths. The travel distance and the runout distance of the DYG large-scale tragic debris flow were 11 km and 9 km, respectively. In particular, the runout distance over the low gradient channel (channel slope < 5°) upstream of the depositional fan apex reached up to 3.3 km. The build-up and maintenance of excess pore pressure in the debris-flow mass might have played a crucial role in the persistence and long runout of the bouldery viscous debris flow. Experiments to measure pore pressure and pore water escape have been carried out by reconstituting the debris flow bodies with the DYG debris flow deposit. The slurrying of the debris is governed by solid volumetric concentration (SVC), and the difference between the lower SVC limit and the upper SVC limit can be defined as debris flow index (Id). Peak value (Kp) and rate of dissipation (R) of relative excess pore pressure are dependent on SVC. Further, the SVC that gives the lowest rate of dissipation is regarded as the optimum SVC (Cvo). The dissipation response of excess pore pressure can be characterized by the R value under Cvo at a given moment (i.e., 0.5 h, 1 h or 2 h later after peak time). The results reveal that a relatively high level of excess pore pressure developed within the DYG debris-flow mass and had a strong persistence capability. Further research shows that the development, peak value and dissipation of excess pore pressure in a mixture of sediment and water are related to the maximum grain size (MGS), gradation and mineralogy of clay-size particles of the sediment. The layer-lattice silicates in clay particles can be the typical clay minerals, including kaolinite, montmorillonite and illite, and also the unrepresentative clay minerals such as muscovite and chlorite. Moreover, small woody debris can also contribute to the slurrying of sediments and maintenance of debris flows in well vegetated mountainous areas and the boulders suspended in debris flows can elevate excess pore pressure and extend debris-flow mobility. The parameters, including Id, Kp, R and etc., are affected by the intrinsic properties of debris. They, therefore, can reflect the slurrying susceptibility of sediments, and can also be applied to the research on the occurrence mechanisms and risk assessment of other debris flows.

MEASUREMENT AND CONTROL OF FOULING IN FINE PORE DIFFUSER SYSTEMS

EPA Science Inventory

The purpose of the study was two-fold: First, to define the efficiency of various methods of cleaning fine pore diffusers and, second, to develop a methodology that could be used to evaluate the efficiency of the cleaning techniques. Dirty fine pore domes from the North Texas Mu...

Free energies of stable and metastable pores in lipid membranes under tension.

PubMed

den Otter, Wouter K

2009-11-28

The free energy profile of pore formation in a lipid membrane, covering the entire range from a density fluctuation in an intact bilayer to a large tension-stabilized pore, has been calculated by molecular dynamics simulations with a coarse-grained lipid model. Several fixed elongations are used to obtain the Helmholtz free energy as a function of pore size for thermodynamically stable, metastable, and unstable pores, and the system-size dependence of these elongations is discussed. A link to the Gibbs free energy at constant tension, commonly known as the Litster model, is established by a Legendre transformation. The change of genus upon pore formation is exploited to estimate the saddle-splay modulus or Gaussian curvature modulus of the membrane leaflets. Details are provided of the simulation approach, which combines the potential of mean constraint force method with a reaction coordinate based on the local lipid density.

Catalytic nanoporous membranes

DOEpatents

Pellin, Michael J; Hryn, John N; Elam, Jeffrey W

2013-08-27

A nanoporous catalytic membrane which displays several unique features Including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity. Also provided is a method for producing a catalytic membrane having flow-through pores and discreet catalytic clusters adhering to the inside surfaces of the pores.

Pore Formation During Solidification of Aluminum: Reconciliation of Experimental Observations, Modeling Assumptions, and Classical Nucleation Theory

NASA Astrophysics Data System (ADS)

Yousefian, Pedram; Tiryakioğlu, Murat

2018-02-01

An in-depth discussion of pore formation is presented in this paper by first reinterpreting in situ observations reported in the literature as well as assumptions commonly made to model pore formation in aluminum castings. The physics of pore formation is reviewed through theoretical fracture pressure calculations based on classical nucleation theory for homogeneous and heterogeneous nucleation, with and without dissolved gas, i.e., hydrogen. Based on the fracture pressure for aluminum, critical pore size and the corresponding probability of vacancies clustering to form that size have been calculated using thermodynamic data reported in the literature. Calculations show that it is impossible for a pore to nucleate either homogeneously or heterogeneously in aluminum, even with dissolved hydrogen. The formation of pores in aluminum castings can only be explained by inflation of entrained surface oxide films (bifilms) under reduced pressure and/or with dissolved gas, which involves only growth, avoiding any nucleation problem. This mechanism is consistent with the reinterpretations of in situ observations as well as the assumptions made in the literature to model pore formation.

Metalloporphyrin-based porous polymers prepared via click chemistry for size-selective adsorption of protein.

PubMed

Zhu, Dailian; Qin, Cunqi; Ao, Shanshi; Su, Qiuping; Sun, Xiying; Jiang, Tengfei; Pei, Kemei; Ni, Huagang; Ye, Peng

2018-08-01

Zinc porphyrin-based porous polymers (PPs-Zn) with different pore sizes were prepared by controlling the reaction condition of click chemistry, and the protein adsorption in PPs-Zn and the catalytic activity of immobilized enzyme were investigated. PPs-Zn-1 with 18 nm and PPS-Zn-2 with 90 nm of pore size were characterized by FTIR, NMR and nitrogen absorption experiments. The amount of adsorbed protein in PPs-Zn-1 was more than that in PPs-Zn-2 for small size proteins, such as lysozyme, lipase and bovine serum albumin (BSA). And for large size proteins including myosin and human fibrinogen (HFg), the amount of adsorbed protein in PPs-Zn-1 was less than that in PPs-Zn-2. The result indicates that the protein adsorption is size-selective in PPs-Zn. Both the protein size and the pore size have a significant effect on the amount of adsorbed protein in the PPs-Zn. Lipase and lysozyme immobilized in PPs-Zn exhibited excellent reuse stability.

Distribution of transvascular pathway sizes through the pulmonary microvascular barrier.

PubMed

McNamee, J E

1987-01-01

Mathematical models of solute and water exchange in the lung have been helpful in understanding factors governing the volume flow rate and composition of pulmonary lymph. As experimental data and models become more encompassing, parameter identification becomes more difficult. Pore sizes in these models should approach and eventually become equivalent to actual physiological pathway sizes as more complex and accurate models are tried. However, pore sizes and numbers vary from model to model as new pathway sizes are added. This apparent inconsistency of pore sizes can be explained if it is assumed that the pulmonary blood-lymph barrier is widely heteroporous, for example, being composed of a continuous distribution of pathway sizes. The sieving characteristics of the pulmonary barrier are reproduced by a log normal distribution of pathway sizes (log mean = -0.20, log s.d. = 1.05). A log normal distribution of pathways in the microvascular barrier is shown to follow from a rather general assumption about the nature of the pulmonary endothelial junction.

The Pressure-Dependence of the Size of Extruded Vesicles

PubMed Central

Patty, Philipus J.; Frisken, Barbara J.

2003-01-01

Variations in the size of vesicles formed by extrusion through small pores are discussed in terms of a simple model. Our model predicts that the radius should decrease as the square root of the applied pressure, consistent with data for vesicles extruded under various conditions. The model also predicts dependencies on the pore size used and on the lysis tension of the vesicles being extruded that are consistent with our data. The pore size was varied by using track-etched polycarbonate membranes with average pore diameters ranging from 50 to 200 nm. To vary the lysis tension, vesicles made from POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine), mixtures of POPC and cholesterol, and mixtures of POPC and C16-ceramide were studied. The lysis tension, as measured by an extrusion-based technique, of POPC:cholesterol vesicles is higher than that of pure POPC vesicles whereas POPC:ceramide vesicles have lower lysis tensions than POPC vesicles. PMID:12885646

Engineering multi-stage nanovectors for controlled degradation and tunable release kinetics

PubMed Central

Martinez, Jonathan O.; Chiappini, Ciro; Ziemys, Arturas; Faust, Ari M.; Kojic, Milos; Liu, Xuewu; Ferrari, Mauro; Tasciotti, Ennio

2013-01-01

Nanovectors hold substantial promise in abating the off-target effects of therapeutics by providing a means to selectively accumulate payloads at the target lesion, resulting in an increase in the therapeutic index. A sophisticated understanding of the factors that govern the degradation and release dynamics of these nanovectors is imperative to achieve these ambitious goals. In this work, we elucidate the relationship that exists between variations in pore size and the impact on the degradation, loading, and release of multistage nanovectors. Larger pored vectors displayed faster degradation and higher loading of nanoparticles, while exhibiting the slowest release rate. The degradation of these particles was characterized to occur in a multi-step progression where they initially decreased in size leaving the porous core isolated, while the pores gradually increased in size. Empirical loading and release studies of nanoparticles along with diffusion modeling revealed that this prolonged release was modulated by the penetration within the porous core of the vectors regulated by their pore size. PMID:23911070

Do Surface Porosity and Pore Size Influence Mechanical Properties and Cellular Response to PEEK?

PubMed

Torstrick, F Brennan; Evans, Nathan T; Stevens, Hazel Y; Gall, Ken; Guldberg, Robert E

2016-11-01

Despite its widespread use in orthopaedic implants such as soft tissue fasteners and spinal intervertebral implants, polyetheretherketone (PEEK) often suffers from poor osseointegration. Introducing porosity can overcome this limitation by encouraging bone ingrowth; however, the corresponding decrease in implant strength can potentially reduce the implant's ability to bear physiologic loads. We have previously shown, using a single pore size, that limiting porosity to the surface of PEEK implants preserves strength while supporting in vivo osseointegration. However, additional work is needed to investigate the effect of pore size on both the mechanical properties and cellular response to PEEK. (1) Can surface porous PEEK (PEEK-SP) microstructure be reliably controlled? (2) What is the effect of pore size on the mechanical properties of PEEK-SP? (3) Do surface porosity and pore size influence the cellular response to PEEK? PEEK-SP was created by extruding PEEK through NaCl crystals of three controlled ranges: 200 to 312, 312 to 425, and 425 to 508 µm. Micro-CT was used to characterize the microstructure of PEEK-SP. Tensile, fatigue, and interfacial shear tests were performed to compare the mechanical properties of PEEK-SP with injection-molded PEEK (PEEK-IM). The cellular response to PEEK-SP, assessed by proliferation, alkaline phosphatase activity, vascular endothelial growth factor production, and calcium content of osteoblast, mesenchymal stem cell, and preosteoblast (MC3T3-E1) cultures, was compared with that of machined smooth PEEK and Ti6Al4V. Micro-CT analysis showed that PEEK-SP layers possessed pores that were 284 ± 35 µm, 341 ± 49 µm, and 416 ± 54 µm for each pore size group. Porosity and pore layer depth ranged from 61% to 69% and 303 to 391 µm, respectively. Mechanical testing revealed tensile strengths > 67 MPa and interfacial shear strengths > 20 MPa for all three pore size groups. All PEEK-SP groups exhibited > 50% decrease in ductility compared with PEEK-IM and demonstrated fatigue strength > 38 MPa at one million cycles. All PEEK-SP groups also supported greater proliferation and cell-mediated mineralization compared with smooth PEEK and Ti6Al4V. The PEEK-SP formulations evaluated in this study maintained favorable mechanical properties that merit further investigation into their use in load-bearing orthopaedic applications and supported greater in vitro osteogenic differentiation compared with smooth PEEK and Ti6Al4V. These results are independent of pore sizes ranging 200 µm to 508 µm. PEEK-SP may provide enhanced osseointegration compared with current implants while maintaining the structural integrity to be considered for several load-bearing orthopaedic applications such as spinal fusion or soft tissue repair.

Three-dimensional culture of rat calvarial osteoblasts in porous biodegradable polymers

NASA Technical Reports Server (NTRS)

Ishaug-Riley, S. L.; Crane-Kruger, G. M.; Yaszemski, M. J.; Mikos, A. G.

1998-01-01

Neonatal rat calvarial osteoblasts were cultured in 90% porous, 75:25 poly(DL-lactic-co-glycolic acid) (PLGA) foam scaffolds for up to 56 days to examine the effects of the cell seeding density, scaffold pore size, and foam thickness on the proliferation and function of the cells in this three-dimensional environment. Osteoblasts were seeded at either 11.1 x 10(5) or 22.1 x 10(5) cells per cm2 onto PLGA scaffolds having pore sizes in the range of 150-300 or 500-710 microm with a thickness of either 1.9 or 3.2 mm. After 1 day in culture, 75.6 and 68.6% of the seeded cells attached and proliferated on the 1.9 mm thick scaffolds of 150-300 microm pore size for the low and high seeding densities, respectively. The number of osteoblasts continued to increase throughout the study and eventually leveled off near 56 days, as indicated by a quantitative DNA assay. Osteoblast/foam constructs with a low cell seeding density achieved comparable DNA content and alkaline phosphatase (ALPase) activity after 14 days, and mineralization results after 56 days to those with a high cell seeding density. A maximum penetration depth of osseous tissue of 220+/-40 microm was reached after 56 days in the osteoblast/foam constructs of 150-300 microm pore size initially seeded with a high cell density. For constructs of 500-710 microm pore size, the penetration depth was 190+/-40 microm under the same conditions. Scaffold pore size and thickness did not significantly affect the proliferation or function of osteoblasts as demonstrated by DNA content, ALPase activity, and mineralized tissue formation. These data show that comparable bone-like tissues can be engineered in vitro over a 56 day period using different rat calvarial osteoblast seeding densities onto biodegradable polymer scaffolds with pore sizes in the range of 150-710 microm. When compared with the results of a previous study where similar polymer scaffolds were seeded and cultured with marrow stromal cells, this study demonstrates that PLGA foams are suitable substrates for osteoblast growth and differentiated function independent of cell source.

Tunable sustained intravitreal drug delivery system for daunorubicin using oxidized porous silicon

PubMed Central

Hou, Huiyuan; Nieto, Alejandra; Ma, Feiyan; Freeman, William R.; Sailor, Michael J.; Cheng, Lingyun

2014-01-01

Daunorubicin (DNR) is an effective inhibitor of an array of proteins involved in neovascularization, including VEGF and PDGF. These growth factors are directly related to retina scar formation in many devastating retinal diseases. Due to the short vitreous half-life and narrow therapeutic window, ocular application of DNR is limited. It has been shown that a porous silicon (pSi) based delivery system can extend DNR vitreous residence from a few days to 3 months. In this study we investigated the feasibility of altering the pore size of the silicon particles to regulate the payload release. Modulation of the etching parameters allowed control of the nano-pore size from 15 nm to 95 nm. In vitro studies showed that degradation of pSi O2 increased with increasing pore size and the degradation of pSi O2 was approximately constant for a given particle type. The degradation of pSi O2 with 43 nm pores was significantly greater than the other two particles with smaller pores, judged by observed and normalized mean Si concentration of the dissolution samples (44.2±8.9 vs 25.7±5.6 or 21.2±4.2 µg/mL, p<0.0001). In vitro dynamic DNR release revealed that pSiO2-CO2H:DNR (Porous silicon dioxide with covalent loading of daunorubicin) with large pores (43 nm) yielded a significantly higher DNR level than particles with 15 or 26 nm pores (13.5±6.9 ng/mL vs. 2.3±1.6 ng/mL and 1.1±0.9 ng/mL, p<0.0001). After two months of in vitro dynamic release, 54% of the pSiO2-CO2H:DNR particles still remained in the dissolution chamber by weight. In vivo drug release study demonstrated that free DNR in vitreous at post-injection day 14 was 66.52 ng/mL for 95 nm pore size pSiO2-CO2H:DNR, 10.76 ng/mL for 43 nm pSi O2-CO2 H:DNR, and only 1.05 ng/mL for 15 nm pSi O2-CO2 H:DNR. Pore expansion from 15 nm to 95 nm led to a 63 folds increase of DNR release (p<0.0001) and a direct correlation between the pore size and the drug levels in the living eye vitreous was confirmed. The present study demonstrates the feasibility of regulating DNR release from pSi O2 covalently loaded with DNR by engineering the nano-pore size of pSi. PMID:24424270

Tunable sustained intravitreal drug delivery system for daunorubicin using oxidized porous silicon.

PubMed

Hou, Huiyuan; Nieto, Alejandra; Ma, Feiyan; Freeman, William R; Sailor, Michael J; Cheng, Lingyun

2014-03-28

Daunorubicin (DNR) is an effective inhibitor of an array of proteins involved in neovascularization, including VEGF and PDGF. These growth factors are directly related to retina scar formation in many devastating retinal diseases. Due to the short vitreous half-life and narrow therapeutic window, ocular application of DNR is limited. It has been shown that a porous silicon (pSi) based delivery system can extend DNR vitreous residence from a few days to 3months. In this study we investigated the feasibility of altering the pore size of the silicon particles to regulate the payload release. Modulation of the etching parameters allowed control of the nano-pore size from 15nm to 95nm. In vitro studies showed that degradation of pSiO2 increased with increasing pore size and the degradation of pSiO2 was approximately constant for a given particle type. The degradation of pSiO2 with 43nm pores was significantly greater than the other two particles with smaller pores, judged by observed and normalized mean Si concentration of the dissolution samples (44.2±8.9 vs 25.7±5.6 or 21.2±4.2μg/mL, p<0.0001). In vitro dynamic DNR release revealed that pSiO2-CO2H:DNR (porous silicon dioxide with covalent loading of daunorubicin) with large pores (43nm) yielded a significantly higher DNR level than particles with 15 or 26nm pores (13.5±6.9ng/mL vs. 2.3±1.6ng/mL and 1.1±0.9ng/mL, p<0.0001). After two months of in vitro dynamic release, 54% of the pSiO2-CO2H:DNR particles still remained in the dissolution chamber by weight. In vivo drug release study demonstrated that free DNR in the vitreous at post-injection day 14 was 66.52ng/mL for 95nm pore size pSiO2-CO2H:DNR, 10.76ng/mL for 43nm pSiO2-CO2H:DNR, and only 1.05ng/mL for 15nm pSiO2-CO2H:DNR. Pore expansion from 15nm to 95nm led to a 63 fold increase of DNR release (p<0.0001) and a direct correlation between the pore size and the drug levels in the living eye vitreous was confirmed. The present study demonstrates the feasibility of regulating DNR release from pSiO2 covalently loaded with DNR by engineering the nano-pore size of pSi. Copyright © 2014 Elsevier B.V. All rights reserved.

Isoreticular metal-organic frameworks, process for forming the same, and systematic design of pore size and functionality therein, with application for gas storage

DOEpatents

Yaghi, Omar M.; Eddaoudi, Mohamed; Li, Hailian; Kim, Jaheon; Rosi, Nathaniel

2007-03-27

The ability to design and construct solid-state materials with pre-determined structures is a grand challenge in chemistry. An inventive strategy based on reticulating metal ions and organic carboxylate links into extended networks has been advanced to a point that has allowed the design of porous structures in which pore size and functionality can be varied systematically. MOF-5, a prototype of a new class of porous materials and one that is constructed from octahedral Zn--O--C clusters and benzene links, was used to demonstrate that its 3-D porous system can be functionalized with the organic groups, --Br, --NH2, --OC₃H₇, --OC₅H₁₁, --H₄C₂, and --H₄C₄, and its pore size expanded with the long molecular struts biphenyl, tetrahydropyrene, pyrene, and terphenyl. The ability to direct the formation of the octahedral clusters in the presence of a desired carboxylate link is an essential feature of this strategy, which resulted in the design of an isoreticular (having the same framework topology) series of sixteen well-defined materials whose crystals have open space representing up to 91.1% of the crystal volume, and homogeneous periodic pores that can be incrementally varied from 3.8 to 28.8 angstroms. Unlike the unpredictable nature of zeolite and other molecular sieve syntheses, the deliberate control exercised at the molecular level in the design of these crystals is expected to have tremendous implications on materials properties and future technologies. Indeed, data indicate that members of this series represent the first monocrystalline mesoporous organic/inorganic frameworks, and exhibit the highest capacity for methane storage (155 cm³/cm³ at 36 atm) and the lowest densities (0.41 to 0.21 g/cm³) attained to date for any crystalline material at room temperature.

Differences in Purinergic Amplification of Osmotic Cell Lysis by the Pore-Forming RTX Toxins Bordetella pertussis CyaA and Actinobacillus pleuropneumoniae ApxIA: the Role of Pore Size

PubMed Central

Fiser, Radovan; Linhartova, Irena; Osicka, Radim; Bumba, Ladislav; Hewlett, Erik L.; Benz, Roland; Sebo, Peter

2013-01-01

A large subgroup of the repeat in toxin (RTX) family of leukotoxins of Gram-negative pathogens consists of pore-forming hemolysins. These can permeabilize mammalian erythrocytes (RBCs) and provoke their colloid osmotic lysis (hemolytic activity). Recently, ATP leakage through pannexin channels and P2X receptor-mediated opening of cellular calcium and potassium channels were implicated in cell permeabilization by pore-forming toxins. In the study described here, we examined the role played by purinergic signaling in the cytolytic action of two RTX toxins that form pores of different sizes. The cytolytic potency of ApxIA hemolysin of Actinobacillus pleuropneumoniae, which forms pores about 2.4 nm wide, was clearly reduced in the presence of P2X7 receptor antagonists or an ATP scavenger, such as pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS), Brilliant Blue G, ATP oxidized sodium salt, or hexokinase. In contrast, antagonists of purinergic signaling had no impact on the hemolytic potency of the adenylate cyclase toxin-hemolysin (CyaA) of Bordetella pertussis, which forms pores of 0.6 to 0.8 nm in diameter. Moreover, the conductance of pores formed by ApxIA increased with the toxin concentration, while the conductance of the CyaA single pore units was constant at various toxin concentrations. However, the P2X7 receptor antagonist PPADS inhibited in a concentration-dependent manner the exacerbated hemolytic activity of a CyaA-ΔN489 construct (lacking 489 N-terminal residues of CyaA), which exhibited a strongly enhanced pore-forming propensity (>20-fold) and also formed severalfold larger conductance units in planar lipid bilayers than intact CyaA. These results point to a pore size threshold of purinergic amplification involvement in cell permeabilization by pore-forming RTX toxins. PMID:24082076

Adsorption of Poly(methyl methacrylate) on Concave Al2O3 Surfaces in Nanoporous Membranes

PubMed Central

Nunnery, Grady; Hershkovits, Eli; Tannenbaum, Allen; Tannenbaum, Rina

2009-01-01

The objective of this study was to determine the influence of polymer molecular weight and surface curvature on the adsorption of polymers onto concave surfaces. Poly(methyl methacrylate) (PMMA) of various molecular weights was adsorbed onto porous aluminum oxide membranes having various pore sizes, ranging from 32 to 220 nm. The surface coverage, expressed as repeat units per unit surface area, was observed to vary linearly with molecular weight for molecular weights below ~120 000 g/mol. The coverage was independent of molecular weight above this critical molar mass, as was previously reported for the adsorption of PMMA on convex surfaces. Furthermore, the coverage varied linearly with pore size. A theoretical model was developed to describe curvature-dependent adsorption by considering the density gradient that exists between the surface and the edge of the adsorption layer. According to this model, the density gradient of the adsorbed polymer segments scales inversely with particle size, while the total coverage scales linearly with particle size, in good agreement with experiment. These results show that the details of the adsorption of polymers onto concave surfaces with cylindrical geometries can be used to calculate molecular weight (below a critical molecular weight) if pore size is known. Conversely, pore size can also be determined with similar adsorption experiments. Most significantly, for polymers above a critical molecular weight, the precise molecular weight need not be known in order to determine pore size. Moreover, the adsorption developed and validated in this work can be used to predict coverage also onto surfaces with different geometries. PMID:19415910

Evaluation of a High-Resolution Benchtop Micro-CT Scanner for Application in Porous Media Research

NASA Astrophysics Data System (ADS)

Tuller, M.; Vaz, C. M.; Lasso, P. O.; Kulkarni, R.; Ferre, T. A.

2010-12-01

Recent advances in Micro Computed Tomography (MCT) provided the motivation to thoroughly evaluate and optimize scanning, image reconstruction/segmentation and pore-space analysis capabilities of a new generation benchtop MCT scanner and associated software package. To demonstrate applicability to soil research the project was focused on determination of porosities and pore size distributions of two Brazilian Oxisols from segmented MCT-data. Effects of metal filters and various acquisition parameters (e.g. total rotation, rotation step, and radiograph frame averaging) on image quality and acquisition time are evaluated. Impacts of sample size and scanning resolution on CT-derived porosities and pore-size distributions are illustrated.

Pore size distribution and supercritical hydrogen adsorption in activated carbon fibers

NASA Astrophysics Data System (ADS)

Purewal, J. J.; Kabbour, H.; Vajo, J. J.; Ahn, C. C.; Fultz, B.

2009-05-01

Pore size distributions (PSD) and supercritical H2 isotherms have been measured for two activated carbon fiber (ACF) samples. The surface area and the PSD both depend on the degree of activation to which the ACF has been exposed. The low-surface-area ACF has a narrow PSD centered at 0.5 nm, while the high-surface-area ACF has a broad distribution of pore widths between 0.5 and 2 nm. The H2 adsorption enthalpy in the zero-coverage limit depends on the relative abundance of the smallest pores relative to the larger pores. Measurements of the H2 isosteric adsorption enthalpy indicate the presence of energy heterogeneity in both ACF samples. Additional measurements on a microporous, coconut-derived activated carbon are presented for reference.

Pore size distribution and supercritical hydrogen adsorption in activated carbon fibers.

PubMed

Purewal, J J; Kabbour, H; Vajo, J J; Ahn, C C; Fultz, B

2009-05-20

Pore size distributions (PSD) and supercritical H2 isotherms have been measured for two activated carbon fiber (ACF) samples. The surface area and the PSD both depend on the degree of activation to which the ACF has been exposed. The low-surface-area ACF has a narrow PSD centered at 0.5 nm, while the high-surface-area ACF has a broad distribution of pore widths between 0.5 and 2 nm. The H2 adsorption enthalpy in the zero-coverage limit depends on the relative abundance of the smallest pores relative to the larger pores. Measurements of the H2 isosteric adsorption enthalpy indicate the presence of energy heterogeneity in both ACF samples. Additional measurements on a microporous, coconut-derived activated carbon are presented for reference.

Influence of pore structure on carbon retention/loss in soil macro-aggregates

NASA Astrophysics Data System (ADS)

Quigley, Michelle; Kravchenko, Alexandra; Rivers, Mark

2017-04-01

Carbon protection within soil macro-aggregates is an important component of soil carbon sequestration. Pores, as the transportation network for microorganisms, water, air and nutrients within macro-aggregates, are among the factors controlling carbon protection through restricting physical accessibility of carbon to microorganisms. The understanding of how the intra-aggregate pore structure relates to the degree of carbon physical protection, however, is currently lacking. This knowledge gap can lead to potentially inaccurate models and predictions of soil carbon's fate and storage in future changing climates. This study utilized the natural isotopic difference between C3 and C4 plants to trace the location of newly added carbon within macro-aggregates before and after decomposition and explored how location of this carbon relates to characteristics of intra-aggregate pores. To mimic the effect of decomposition, aggregates were incubated at 23˚ C for 28 days. Computed micro-tomographic images were used to determine pore characteristics at 6 μm resolution before and after incubation. Soil (0-10 cm depth) from a 20 year continuous corn (C4 plant) experiment was used. Two soil treatments were considered: 1) "destroyed-structure", where 1 mm sieved soil was used and 2) "intact-structure", where intact blocks of soil were used. Cereal rye (Secale cereale L.) (C3 plant) was grown in the planting boxes (2 intact, 3 destroyed, and one control) for three months in a greenhouse. From each box, ˜5 macro-aggregates of ˜5 mm size were collected for a total of 27 macro-aggregates. Half of the aggregates were cut into 5-11 sections, with relative positions of the sections within the aggregate recorded, and analyzed for δ13C. The remaining aggregates were incubated and then subjected to cutting and δ13C analysis. While there were no significant differences between the aggregate pore size distributions of the two treatments, the roles that specific pores sizes played in carbon protect were disparate. In intact-structure aggregates, prior to incubation, there was no association between carbon distribution and pores. After incubation, significant correlations (α=0.05) were observed between abundance of 6-40 μm pores and both soil organic carbon (SOC) and δ13C. Sections containing more 6-40 μm pores also had increased amounts of SOC (r2=0.23) with higher presence of C4 carbon (r2=0.27). This indicates preferential preservation of older carbon in the pores of this size range. Prior to incubation, destroyed-structure aggregates had higher amounts of C3 carbon associated with 40-95 μm pores (r2=0.14), pointing to a greater presence of newly added carbon within these pores. However, after incubation there was a significant loss of SOC from these pores (r2=0.22) and, specifically, the loss of C3 carbon (r2=0.16). In the studied soil, pores of 6-40 μm size range appeared to control the preservation of older carbon, while 40-95 μm pores controlled the fate of newly added carbon. Older carbon preservation in 6-40 μm pores was mostly observed in macro-aggregates from the soil with intact structure, while the associations between 40-95 μm pores and gains and losses of newly added carbon were primarily observed in the macro-aggregates that were formed anew in the sieved soil during the plant growing experiment.

Physically based estimation of soil water retention from textural data: General framework, new models, and streamlined existing models

USGS Publications Warehouse

Nimmo, J.R.; Herkelrath, W.N.; Laguna, Luna A.M.

2007-01-01

Numerous models are in widespread use for the estimation of soil water retention from more easily measured textural data. Improved models are needed for better prediction and wider applicability. We developed a basic framework from which new and existing models can be derived to facilitate improvements. Starting from the assumption that every particle has a characteristic dimension R associated uniquely with a matric pressure ?? and that the form of the ??-R relation is the defining characteristic of each model, this framework leads to particular models by specification of geometric relationships between pores and particles. Typical assumptions are that particles are spheres, pores are cylinders with volume equal to the associated particle volume times the void ratio, and that the capillary inverse proportionality between radius and matric pressure is valid. Examples include fixed-pore-shape and fixed-pore-length models. We also developed alternative versions of the model of Arya and Paris that eliminate its interval-size dependence and other problems. The alternative models are calculable by direct application of algebraic formulas rather than manipulation of data tables and intermediate results, and they easily combine with other models (e.g., incorporating structural effects) that are formulated on a continuous basis. Additionally, we developed a family of models based on the same pore geometry as the widely used unsaturated hydraulic conductivity model of Mualem. Predictions of measurements for different suitable media show that some of the models provide consistently good results and can be chosen based on ease of calculations and other factors. ?? Soil Science Society of America. All rights reserved.

Rapid Prototyping of Patterned Multifunctional Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

FAN,HONGYOU; LU,YUNFENG; LOPEZ,GABRIEL P.

2000-07-18

The ability to engineer ordered arrays of objects on multiple length scales has potential for applications such as microelectronics, sensors, wave guides, and photonic lattices with tunable band gaps. Since the invention of surfactant templated mesoporous sieves in 1992, great progress has been made in controlling different mesophases in the form of powders, particles, fibers, and films. To date, although there have been several reports of patterned mesostructures, materials prepared have been limited to metal oxides with no specific functionality. For many of the envisioned applications of hierarchical materials in micro-systems, sensors, waveguides, photonics, and electronics, it is necessary tomore » define both form and function on several length scales. In addition, the patterning strategies utilized so far require hours or even days for completion. Such slow processes are inherently difficult to implement in commercial environments. The authors present a series of new methods of producing patterns within seconds. Combining sol-gel chemistry, Evaporation-Induced Self-Assembly (EISA), and rapid prototyping techniques like pen lithography, ink-jet printing, and dip-coating on micro-contact printed substrates, they form hierarchically organized silica structures that exhibit order and function on multiple scales: on the molecular scale, functional organic moieties are positioned on pore surfaces, on the mesoscale, mono-sized pores are organized into 1-, 2-, or 3-dimensional networks, providing size-selective accessibility from the gas or liquid phase, and on the macroscale, 2-dimensional arrays and fluidic or photonic systems may be defined. These rapid patterning techniques establish for the first time a link between computer-aided design and rapid processing of self-assembled nanostructures.« less

Transport of Brownian spheroidal nanoparticles in near-wall vascular flows for cancer therapy

NASA Astrophysics Data System (ADS)

Lin, Tiras Y.; Shah, Preyas N.; Smith, Bryan R.; Shaqfeh, Eric S. G.

2016-11-01

The microenvironment local to a tumor is characterized by a leaky vasculature induced by angiogenesis from tumor growth. Small pores form in the blood vessel walls, and these pores provide a pathway for cancer-ameliorating nanoparticle drug carriers. Using both simulations and microfluidics experiments, we investigate the extravasation of nanoparticles through pores. Using Brownian dynamics simulations, we evolve the stochastic equations for both point particles and finite-size spheroids of varying aspect ratio. We investigate the effect of wall shear flow and pore suction flow (Sampson flow) on the extravasation process. We consider pores of two types: physiologically relevant short pores with a length equal to the particle size and long pores which are relevant to diffusion through membranes. Additionally, we perform microfluidics experiments in which the extravasation rates of various nanoparticles tagged with fluorescent dye through pores are measured. In particular, using fluorometry we measure the flux of nanoparticles across a track-etched membrane, which separates two chambers. Our preliminary results indicate that the flux measured from experiment agrees reasonably with the simulations done with long pores, and we discuss the effect of pore length on extravasation. T.Y.L. is supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

Comparison of Polytetrafluoroethylene Flat-Sheet Membranes with Different Pore Sizes in Application to Submerged Membrane Bioreactor

PubMed Central

Nittami, Tadashi; Hitomi, Tetsuo; Matsumoto, Kanji; Nakamura, Kazuho; Ikeda, Takaharu; Setoguchi, Yoshihiro; Motoori, Manabu

2012-01-01

This study focused on phase separation of activated sludge mixed liquor by flat-sheet membranes of polytetrafluoroethylene (PTFE). A 20 liter working volume lab-scale MBR incorporating immersed PTFE flat-sheet membrane modules with different pore sizes (0.3, 0.5 and 1.0 μm) was operated for 19 days treating a synthetic wastewater. The experiment was interrupted twice at days 5 and 13 when the modules were removed and cleaned physically and chemically in sequence. The pure water permeate flux of each membrane module was measured before and after each cleaning step to calculate membrane resistances. Results showed that fouling of membrane modules with 0.3 μm pore size was more rapid than other membrane modules with different pore sizes (0.5 and 1.0 μm). On the other hand, it was not clear whether fouling of the 0.5 μm membrane module was more severe than that of the 1.0 μm membrane module. This was partly because of the membrane condition after chemical cleaning, which seemed to determine the fouling of those modules over the next period. When irreversible resistance (Ri) i.e., differences in membrane resistance before use and after chemical cleaning was high, the transmembrane pressure increased quickly during the next period irrespective of membrane pore size. PMID:24958174

Effect of Fe- and Si-Enriched Secondary Precipitates and Surface Roughness on Pore Formation on Aluminum Plate Surfaces During Anodizing

NASA Astrophysics Data System (ADS)

Zhu, Yuanzhi; Wang, Shizhi; Yang, Qingda; Zhou, Feng

2014-09-01

Two twin roll casts (TRCs) and one hot rolled (HR) AA 1235 aluminum alloy plates with different microstructures are prepared. The plates were electrolyzed in a 1.2 wt% HCl solution with a voltage of 21 V and a current of 1.9 mA. The shape, size, and number of pores formed on the surfaces of these plates were analyzed and correlated with the microstructures of the plates. It is found that pores are easier to form on the alloy plates containing subgrains with a lower dislocation density inside the subgrains, rather than along the grain boundaries. Furthermore, Fe- and Si-enriched particles in the AA1235 aluminum alloys lead to the formation of pores on the surface during electrolyzing; the average precipitate sizes of 4, 3.5, and 2 μm in Alloy 1#, Alloy 2# and Alloy 3# result in the average pore sizes of 3.78, 2.76, and 1.9 μm on the surfaces of the three alloys, respectively; The G.P zone in the alloy also facilitates the surface pore formation. High-surface roughness enhances the possibility of entrapping more lubricants into the plate surface, which eventually blocks the formation of the pores on the surface of the aluminum plates in the following electrolyzing process.

Atomic layer deposition of nanoporous biomaterials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narayan, R. J.; Adiga, S. P.; Pellin, M. J.

2010-03-01

Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials.more » Nanoporous alumina, also known as anodic aluminum oxide (AAO), is a nanomaterial that exhibits several unusual properties, including high pore densities, straight pores, small pore sizes, and uniform pore sizes. In 1953, Keller et al. showed that anodizing aluminum in acid electrolytes results in a thick layer of nearly cylindrical pores, which are arranged in a close-packed hexagonal cell structure. More recently, Matsuda & Fukuda demonstrated preparation of highly ordered platinum and gold nanohole arrays using a replication process. In this study, a negative structure of nanoporous alumina was initially fabricated and a positive structure of a nanoporous metal was subsequently fabricated. Over the past fifteen years, nanoporous alumina membranes have been used as templates for growth of a variety of nanostructured materials, including nanotubes, nanowires, nanorods, and nanoporous membranes.« less

A molecular theory for optimal blue energy extraction by electrical double layer expansion

DOE PAGES

Kong, Xian; Gallegos, Alejandro; Lu, Diannan; ...

2015-08-19

We proposed the electrical double layer expansion (CDLE) as a promising alternative to reverse electrodialysis (RED) and pressure retarded osmosis (PRO) processes for extracting osmotic power generated by the salinity difference between freshwater and seawater. The performance of the CDLE process is sensitive to the configuration of porous electrodes and operation parameters for ion extraction and release cycles. In our work, we use a classical density functional theory (CDFT) to examine how the electrode pore size and charging/discharging potentials influence the thermodynamic efficiency of the CDLE cycle. The existence of an optimal charging potential that maximizes the energy output formore » a given pore configuration is predicted, which varies substantially with the pore size, especially when it is smaller than 2 nm. Finally, the thermodynamic efficiency is maximized when the electrode has a pore size about twice the ion diameter.« less

Bio-inspired Murray materials for mass transfer and activity

NASA Astrophysics Data System (ADS)

Zheng, Xianfeng; Shen, Guofang; Wang, Chao; Li, Yu; Dunphy, Darren; Hasan, Tawfique; Brinker, C. Jeffrey; Su, Bao-Lian

2017-04-01

Both plants and animals possess analogous tissues containing hierarchical networks of pores, with pore size ratios that have evolved to maximize mass transport and rates of reactions. The underlying physical principles of this optimized hierarchical design are embodied in Murray's law. However, we are yet to realize the benefit of mimicking nature's Murray networks in synthetic materials due to the challenges in fabricating vascularized structures. Here we emulate optimum natural systems following Murray's law using a bottom-up approach. Such bio-inspired materials, whose pore sizes decrease across multiple scales and finally terminate in size-invariant units like plant stems, leaf veins and vascular and respiratory systems provide hierarchical branching and precise diameter ratios for connecting multi-scale pores from macro to micro levels. Our Murray material mimics enable highly enhanced mass exchange and transfer in liquid-solid, gas-solid and electrochemical reactions and exhibit enhanced performance in photocatalysis, gas sensing and as Li-ion battery electrodes.

Pore-scale modeling of Capillary Penetration of Wetting Liquid into 3D Fibrous Media: A Critical Examination of Equivalent Capillary Concept

NASA Astrophysics Data System (ADS)

Palakurthi, Nikhil Kumar; Ghia, Urmila; Comer, Ken

2013-11-01

Capillary penetration of liquid through fibrous porous media is important in many applications such as printing, drug delivery patches, sanitary wipes, and performance fabrics. Historically, capillary transport (with a distinct liquid propagating front) in porous media is modeled using capillary-bundle theory. However, it is not clear if the capillary model (Washburn equation) describes the fluid transport in porous media accurately, as it assumes uniformity of pore sizes in the porous medium. The present work investigates the limitations of the applicability of the capillary model by studying liquid penetration through virtual fibrous media with uniform and non-uniform pore-sizes. For the non-uniform-pore fibrous medium, the effective capillary radius of the fibrous medium was estimated from the pore-size distribution curve. Liquid penetration into the 3D virtual fibrous medium at micro-scale was simulated using OpenFOAM, and the numerical results were compared with the Washburn-equation capillary-model predictions. Preliminary results show that the Washburn equation over-predicts the height rise in the early stages (purely inertial and visco-inertial stages) of capillary transport.

Mesoporous silica as the enzyme carrier for organophosphate detection and/or detoxification

NASA Astrophysics Data System (ADS)

Frančič, Nina; Nedeljko, Polonca; Lobnik, Aleksandra

2013-05-01

In the past decade, interest in mesoporous materials has developed dramatically since they can be useful in a number of applications, including adsorption and sensor technology. Mesoporous materials are a class of nanostrustures with well-defined mesoscale (2-50 nm) pores, surface areas up to 1000 m2/g and large pore volumes (~1.0 mL/g). In general, ordered mesoporous materials are formed from solution by co-assembly and cross-linking of network-forming inorganic species (typically oxides) in the presence of structure-directing agents (SDAs) [1]. The SDAs are typically surfactants or blockcopolymers that self-organize into mesoscale (2-50 nm) structures, according to the solution composition and processing conditions used [2]. Owing to their structural properties and regular morphology, mesoporous silicas (MPS) are promising materials for applications in the immobilization processes or as supports for bulky bio-molecules, such as enzymes. We report on the synthesis of mesoporous silica (MPS) particles and their potential use for immobilization of the enzyme hexahistidine tagged OPH (His6-OPH). Particle characterization points out a strong influence of the synthesis parameters (addition of ethyl acetate). BET results show a high specific surface area (300-450 m2/g) and an appropriate pore size distribution ranging from 10 to 40 nm. Immobilization of the enzyme His6-OPH, with the size of 72 kDa and isoelectric point (pI) of 8.5, was carried out in MPS particles of spherical morphology. Preliminary results indicate significant potential in use of encapsulated enzyme His6-OPH for the purpose of bio-sensing or in the detoxification processes of organophosphates.

Surface area and pore size characteristics of nanoporous gold subjected to thermal, mechanical, or surface modification studied using gas adsorption isotherms, cyclic voltammetry, thermogravimetric analysis, and scanning electron microscopy

PubMed Central

Tan, Yih Horng; Davis, Jason A.; Fujikawa, Kohki; Ganesh, N. Vijaya; Demchenko, Alexei V.

2012-01-01

Nitrogen adsorption/desorption isotherms are used to investigate the Brunauer, Emmett, and Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size distribution of physically modified, thermally annealed, and octadecanethiol functionalized np-Au monoliths. We present the full adsorption-desorption isotherms for N2 gas on np-Au, and observe type IV isotherms and type H1 hysteresis loops. The evolution of the np-Au under various thermal annealing treatments was examined using scanning electron microscopy (SEM). The images of both the exterior and interior of the thermally annealed np-Au show that the porosity of all free standing np-Au structures decreases as the heat treatment temperature increases. The modification of the np-Au surface with a self-assembled monolayer (SAM) of C18-SH (coverage of 2.94 × 1014 molecules cm−2 based from the decomposition of the C18-SH using thermogravimetric analysis (TGA)), was found to reduce the strength of the interaction of nitrogen gas with the np-Au surface, as reflected by a decrease in the ‘C’ parameter of the BET equation. From cyclic voltammetry studies, we found that the surface area of the np-Au monoliths annealed at elevated temperatures followed the same trend with annealing temperature as found in the BET surface area study and SEM morphology characterization. The study highlights the ability to control free-standing nanoporous gold monoliths with high surface area, and well-defined, tunable pore morphology. PMID:22822294

The pore structure and fractal characteristics of shales with low thermal maturity from the Yuqia Coalfield, northern Qaidam Basin, northwestern China

NASA Astrophysics Data System (ADS)

Hou, Haihai; Shao, Longyi; Li, Yonghong; Li, Zhen; Zhang, Wenlong; Wen, Huaijun

2018-03-01

The continental shales from the Middle Jurassic Shimengou Formation of the northern Qaidam Basin, northwestern China, have been investigated in recent years because of their shale gas potential. In this study, a total of twenty-two shale samples were collected from the YQ-1 borehole in the Yuqia Coalfield, northern Qaidam Basin. The total organic carbon (TOC) contents, pore structure parameters, and fractal characteristics of the samples were investigated using TOC analysis, low-temperature nitrogen adsorption experiments, and fractal analysis. The results show that the average pore size of the Shimengou shales varied from 8.149 nm to 20.635 nm with a mean value of 10.74 nm, which is considered mesopore-sized. The pores of the shales are mainly inkbottle- and slit-shaped. The sedimentary environment plays an essential role in controlling the TOC contents of the low maturity shales, with the TOC values of shales from deep to semi-deep lake facies (mean: 5.23%) being notably higher than those of the shore-shallow lake facies (mean: 0.65%). The fractal dimensions range from 2.4639 to 2.6857 with a mean of 2.6122, higher than those of marine shales, which indicates that the pore surface was rougher and the pore structure more complex in these continental shales. The fractal dimensions increase with increasing total pore volume and total specific surface area, and with decreasing average pore size. With increasing TOC contents in shales, the fractal dimensions increase first and then decrease, with the highest value occurring at 2% of TOC content, which is in accordance with the trends between the TOC and both total specific surface area and total pore volume. The pore structure complexity and pore surface roughness of these low-maturity shales would be controlled by the combined effects of both sedimentary environments and the TOC contents.

Synchrotron Microtomographic Quantification of Geometrical Soil Pore Characteristics Affected by Compaction

NASA Astrophysics Data System (ADS)

Udawatta, Ranjith; Gantzer, Clark; Anderson, Stephen; Assouline, Shmuel

2015-04-01

Soil compaction degrades soil structure and affects water, heat, and gas exchange as well as root penetration and crop production. The objective of this study was to use X-ray computed microtomography (CMT) techniques to compare differences in geometrical soil pore parameters as influenced by compaction of two different aggregate size classes. Sieved (diam. < 2mm and < 0.5mm) and repacked (1.51 and 1.72 Mg m-3) Hamra soil cores of 5- by 5-mm (average porosities were 0.44 and 0.35) were imaged at 9.6-micrometer resolution at the Argonne Advanced Photon Source (synchrotron facility) using X-ray computed microtomography. Images of 58.9 mm3 volume were analyzed using 3-Dimensional Medial Axis (3DMA) software. Geometrical characteristics of the spatial distributions of pore structures (pore radii, volume, connectivity, path length, and tortuosity) were numerically investigated. Results show that the coordination number (CN) distribution and path length (PL) measured from the medial axis were reasonably fit by exponential relationships P(CN)=10-CN/Co and P(PL)=10-PL/PLo, respectively, where Co and PLo are the corresponding characteristic constants. Compaction reduced porosity, average pore size, number of pores, and characteristic constants. The average pore radii (64 and 61 μm; p<0.04), largest pore volume (1.6 and 0.6 mm3; p=0.06), number of pores (55 and 50; p=0.09), characteristic coordination number (6.3 and 6.0; p=0.09), and characteristic path length number (116 and 105; p=0.001) were significantly greater in the low density than the high density treatment. Aggregate size also influenced measured geometrical pore parameters. This analytical technique provides a tool for assessing changes in soil pores that affect hydraulic properties and thereby provides information to assist in assessment of soil management systems.

Synchrotron microtomographic quantification of geometrical soil pore characteristics affected by compaction

NASA Astrophysics Data System (ADS)

Udawatta, R. P.; Gantzer, C. J.; Anderson, S. H.; Assouline, S.

2015-07-01

Soil compaction degrades soil structure and affects water, heat, and gas exchange as well as root penetration and crop production. The objective of this study was to use X-ray computed microtomography (CMT) techniques to compare differences in geometrical soil pore parameters as influenced by compaction of two different aggregate size classes. Sieved (diam. < 2 mm and < 0.5 mm) and repacked (1.51 and 1.72 Mg m-3) Hamra soil cores of 5- by 5 mm (average porosities were 0.44 and 0.35) were imaged at 9.6-micrometer resolution at the Argonne Advanced Photon Source (synchrotron facility) using X-ray computed microtomography. Images of 58.9 mm3 volume were analyzed using 3-Dimensional Medial Axis (3DMA) software. Geometrical characteristics of the spatial distributions of pore structures (pore radii, volume, connectivity, path length, and tortuosity) were numerically investigated. Results show that the coordination number (CN) distribution and path length (PL) measured from the medial axis were reasonably fit by exponential relationships P(CN) = 10-CN/Co and P(PL) = 10-PL/PLo, respectively, where Co and PLo are the corresponding characteristic constants. Compaction reduced porosity, average pore size, number of pores, and characteristic constants. The average pore radii (63.7 and 61 μm; p < 0.04), largest pore volume (1.58 and 0.58 mm3; p = 0.06), number of pores (55 and 50; p = 0.09), characteristic coordination number (6.32 and 5.94; p = 0.09), and characteristic path length number (116 and 105; p = 0.001) were significantly greater in the low density than the high density treatment. Aggregate size also influenced measured geometrical pore parameters. This analytical technique provides a tool for assessing changes in soil pores that affect hydraulic properties and thereby provides information to assist in assessment of soil management systems.

Growth of nanostructures with controlled diameter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pfefferle, Lisa; Haller, Gary; Ciuparu, Dragos

2009-02-03

Transition metal-substituted MCM-41 framework structures with a high degree of structural order and a narrow pore diameter distribution were reproducibly synthesized by a hydrothermal method using a surfactant and an anti-foaming agent. The pore size and the mesoporous volume depend linearly on the surfactant chain length. The transition metals, such as cobalt, are incorporated substitutionally and highly dispersed in the silica framework. Single wall carbon nanotubes with a narrow diameter distribution that correlates with the pore diameter of the catalytic framework structure were prepared by a Boudouard reaction. Nanostructures with a specified diameter or cross-sectional area can therefore be predictablymore » prepared by selecting a suitable pore size of the framework structure.« less

Pore size and concentration effect of mesoporous silica nanoparticles on the coefficient of thermal expansion and optical transparency of poly(ether sulfone) films.

PubMed

Vo, Nhat Tri; Patra, Astam K; Kim, Dukjoon

2017-01-18

Mesoporous silica nanoparticles (MSNs) with uniform size (<50 nm) yet with different pore diameters were synthesized, and used as fillers in poly(ether sulfone) (PES) films in order to decrease their coefficient of thermal expansion (CTE) without sacrificing optical transparency. Here, both CTE and optical transparency of the MSN/PES nanocomposite films gradually decreased with increasing MSN concentration. The PES films containing MSNs with larger pores showed the best performance in CTE and optical transparency. While the CTE decreased by 32.3% with increasing MSN content up to 0.5 wt%, the optical transparency decreased by only less than 6.9% because of the small and uniform particle size of less than 50 nm, which minimizes light scattering. This pore size effect is more clearly observed via an annealing process, which enables the polymer chains to slowly move and fill in the free volume in the pores of the MSN, and thus restricts the thermal motion. The effect of the silica nanoparticles was investigated not only on the thermal stability but also on the mechanical stability. We expect the MSNs synthesized in this study to be used as a promising filler to enhance the thermal and mechanical stability of the PES substrate without sacrificing its optical transparency.

Organic-inorganic hybrid mesoporous silicas: functionalization, pore size, and morphology control.

PubMed

Park, Sung Soo; Ha, Chang-Sik

2006-01-01

Topological design of mesoporous silica materials, pore architecture, pore size, and morphology are currently major issues in areas such as catalytic conversion of bulky molecules, adsorption, host-guest chemistry, etc. In this sense, we discuss the pore size-controlled mesostructure, framework functionalization, and morphology control of organic-inorganic hybrid mesoporous silicas by which we can improve the applicability of mesoporous materials. First, we explain that the sizes of hexagonal- and cubic-type pores in organic-inorganic hybrid mesoporous silicas are well controlled from 24.3 to 98.0 A by the direct micelle-control method using an organosilica precursor and surfactants with different alkyl chain lengths or triblock copolymers as templates and swelling agents incorporated in the formed micelles. Second, we describe that organic-inorganic hybrid mesoporous materials with various functional groups form various external morphologies such as rod, cauliflower, film, rope, spheroid, monolith, and fiber shapes. Third, we discuss that transition metals (Ti and Ru) and rare-earth ions (Eu(3+) and Tb(3+)) are used to modify organic-inorganic hybrid mesoporous silica materials. Such hybrid mesoporous silica materials are expected to be applied as excellent catalysts for organic reactions, photocatalysis, optical devices, etc. c) 2006 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

A Facile and Eco-friendly Route to Fabricate Poly(Lactic Acid) Scaffolds with Graded Pore Size.

PubMed

Scaffaro, Roberto; Lopresti, Francesco; Botta, Luigi; Maio, Andrea; Sutera, Fiorenza; Mistretta, Maria Chiara; La Mantia, Francesco Paolo

2016-10-17

Over the recent years, functionally graded scaffolds (FGS) gaineda crucial role for manufacturing of devices for tissue engineering. The importance of this new field of biomaterials research is due to the necessity to develop implants capable of mimicking the complex functionality of the various tissues, including a continuous change from one structure or composition to another. In this latter context, one topic of main interest concerns the design of appropriate scaffolds for bone-cartilage interface tissue. In this study, three-layered scaffolds with graded pore size were achieved by melt mixing poly(lactic acid) (PLA), sodium chloride (NaCl) and polyethylene glycol (PEG). Pore size distributions were controlled by NaCl granulometry and PEG solvation. Scaffolds were characterized from a morphological and mechanical point of view. A correlation between the preparation method, the pore architecture and compressive mechanical behavior was found. The interface adhesion strength was quantitatively evaluated by using a custom-designed interfacial strength test. Furthermore, in order to imitate the human physiology, mechanical tests were also performed in phosphate buffered saline (PBS) solution at 37 °C. The method herein presented provides a high control of porosity, pore size distribution and mechanical performance, thus offering the possibility to fabricate three-layered scaffolds with tailored properties by following a simple and eco-friendly route.

Characterization and Quantification of the Pore Structures of the Shale Oil Reservoir Formations in Multiscale

NASA Astrophysics Data System (ADS)

Liu, K.; Ostadhassan, M.

2016-12-01

Due to the fast development of hydraulic fracturing and horizontal drilling, shale formations now are one important resource of energy in North America. Characterizing the pore structure of these shale formations is of critical importance in understanding the original oil/gas in place and also the flow properties of the rock matrix. Pore with different properties such as pore size and pore shape can impact the physical, mechanical and chemical properties including strength, elastic modulus, permeability and conductivity. Nowadays, image analysis has been a robust method to quantify the pore information from the porous medium.SEM has been one of the most useful tools to study the pore microstructures due to its high depth of focus which can provide detailed topographical information about the surface. The suitable difference between solid matrix and pores due to the different gray level pixels can be used to study the pore structures.In this paper, we characterized and quantified the pore structures of rock samples from Middle Bakken Formation which is a typical unconventional reservoir in North America. High resolution SEM images of five samples we chose based on the gamma logs were derived after sample preparation. After determining the threshold of the images, we extracted the pore spaces. Then we analyzed the pore structures properties such as pore size distributions and pore shape distributions of the five samples and compared based on their mineral compositions. After that, we analyzed their heterogeneity and isotropy properties which have been identified as an important factor affecting reservoir productivity. Finally, we studied the impact of scale effect on the pore structures characterization.

Hydraulic characterisation of iron-oxide-coated sand and gravel based on nuclear magnetic resonance relaxation mode analyses

NASA Astrophysics Data System (ADS)

Costabel, Stephan; Weidner, Christoph; Müller-Petke, Mike; Houben, Georg

2018-03-01

The capability of nuclear magnetic resonance (NMR) relaxometry to characterise hydraulic properties of iron-oxide-coated sand and gravel was evaluated in a laboratory study. Past studies have shown that the presence of paramagnetic iron oxides and large pores in coarse sand and gravel disturbs the otherwise linear relationship between relaxation time and pore size. Consequently, the commonly applied empirical approaches fail when deriving hydraulic quantities from NMR parameters. Recent research demonstrates that higher relaxation modes must be taken into account to relate the size of a large pore to its NMR relaxation behaviour in the presence of significant paramagnetic impurities at its pore wall. We performed NMR relaxation experiments with water-saturated natural and reworked sands and gravels, coated with natural and synthetic ferric oxides (goethite, ferrihydrite), and show that the impact of the higher relaxation modes increases significantly with increasing iron content. Since the investigated materials exhibit narrow pore size distributions, and can thus be described by a virtual bundle of capillaries with identical apparent pore radius, recently presented inversion approaches allow for estimation of a unique solution yielding the apparent capillary radius from the NMR data. We found the NMR-based apparent radii to correspond well to the effective hydraulic radii estimated from the grain size distributions of the samples for the entire range of observed iron contents. Consequently, they can be used to estimate the hydraulic conductivity using the well-known Kozeny-Carman equation without any calibration that is otherwise necessary when predicting hydraulic conductivities from NMR data. Our future research will focus on the development of relaxation time models that consider pore size distributions. Furthermore, we plan to establish a measurement system based on borehole NMR for localising iron clogging and controlling its remediation in the gravel pack of groundwater wells.

Laboratory characterization of shale pores

NASA Astrophysics Data System (ADS)

Nur Listiyowati, Lina

2018-02-01

To estimate the potential of shale gas reservoir, one needs to understand the characteristics of pore structures. Characterization of shale gas reservoir microstructure is still a challenge due to ultra-fine grained micro-fabric and micro level heterogeneity of these sedimentary rocks. The sample used in the analysis is a small portion of any reservoir. Thus, each measurement technique has a different result. It raises the question which methods are suitable for characterizing pore shale. The goal of this paper is to summarize some of the microstructure analysis tools of shale rock to get near-real results. The two analyzing pore structure methods are indirect measurement (MIP, He, NMR, LTNA) and direct observation (SEM, TEM, Xray CT). Shale rocks have a high heterogeneity; thus, it needs multiscale quantification techniques to understand their pore structures. To describe the complex pore system of shale, several measurement techniques are needed to characterize the surface area and pore size distribution (LTNA, MIP), shapes, size and distribution of pore (FIB-SEM, TEM, Xray CT), and total porosity (He pycnometer, NMR). The choice of techniques and methods should take into account the purpose of the analysis and also the time and budget.

Characterizing the surface charge of synthetic nanomembranes by the streaming potential method

PubMed Central

Datta, Subhra; Conlisk, A. T.; Kanani, Dharmesh M.; Zydney, Andrew L.; Fissell, William H.; Roy, Shuvo

2010-01-01

The inference of the surface charge of polyethylene glycol (PEG)-coated and uncoated silicon membranes with nanoscale pore sizes from streaming potential measurements in the presence of finite electric double layer (EDL) effects is studied theoretically and experimentally. The developed theoretical model for inferring the pore wall surface charge density from streaming potential measurements is applicable to arbitrary pore cross-sectional shapes and accounts for the effect of finite salt concentration on the ionic mobilities and the thickness of the deposited layer of PEG. Theoretical interpretation of the streaming potential data collected from silicon membranes having nanoscale pore sizes, with/without pore wall surface modification with PEG, indicates that finite electric double layer (EDL) effects in the pore-confined electrolyte significantly affect the interpretation of the membrane charge and that surface modification with PEG leads to a reduction in the pore wall surface charge density. The theoretical model is also used to study the relative significance of the following uniquely nanoscale factors affecting the interpretation of streaming potential in moderate to strongly charged pores: altered net charge convection by applied pressure differentials, surface-charge effects on ionic conduction, and electroosmotic convection of charges. PMID:20462592

Origin and heterogeneity of pore sizes in the Mount Simon Sandstone and Eau Claire Formation: Implications for multiphase fluid flow

DOE PAGES

Mozley, Peter S.; Heath, Jason E.; Dewers, Thomas A.; ...

2016-01-01

The Mount Simon Sandstone and Eau Claire Formation represent a principal reservoir - caprock system for wastewater disposal, geologic CO 2 storage, and compressed air energy storage (CAES) in the Midwestern United States. Of primary concern to site performance is heterogeneity in flow properties that could lead to non-ideal injectivity and distribution of injected fluids (e.g., poor sweep efficiency). Using core samples from the Dallas Center Structure, Iowa, we investigate pore structure that governs flow properties of major lithofacies of these formations. Methods include gas porosimetry and permeametry, mercury intrusion porosimetry, thin section petrography, and X-ray diffraction. The lithofacies exhibitmore » highly variable intra- and inter-informational distributions of pore throat and body sizes. Based on pore-throat size, samples fall into four distinct groups. Micropore-throat dominated samples are from the Eau Claire Formation, whereas the macropore-, mesopore-, and uniform-dominated samples are from the Mount Simon Sandstone. Complex paragenesis governs the high degree of pore and pore-throat size heterogeneity, due to an interplay of precipitation, non-uniform compaction, and later dissolution of cements. Furthermore, the cement dissolution event probably accounts for much of the current porosity in the unit. The unusually heterogeneous nature of the pore networks in the Mount Simon Sandstone indicates that there is a greater-than-normal opportunity for reservoir capillary trapping of non-wetting fluids — as quantified by CO 2 and air column heights — which should be taken into account when assessing the potential of the reservoir-caprock system for CO 2 storage and CAES.« less

Study on extrusion process of SiC ceramic matrix

NASA Astrophysics Data System (ADS)

Dai, Xiao-Yuan; Shen, Fan; Ji, Jia-You; Wang, Shu-Ling; Xu, Man

2017-11-01

In this thesis, the extrusion process of SiC ceramic matrix has been systematically studied.The effect of different cellulose content on the flexural strength and pore size distribution of SiC matrix was discussed.Reselts show that with the increase of cellulose content, the flexural strength decreased.The pore size distribution in the sample was 1um-4um, and the 1um-2um concentration was more concentrated. It is found that the cellulose content has little effect on the pore size distribution.When the cellulose content is 7%, the flexural strength of the sample is 40.9Mpa. At this time, the mechanical properties of the sample are the strongest.

Correlation Study of PVDF Membrane Morphology with Protein Adsorption: Quantitative Analysis by FTIR/ATR Technique

NASA Astrophysics Data System (ADS)

Ideris, N.; Ahmad, A. L.; Ooi, B. S.; Low, S. C.

2018-05-01

Microporous PVDF membranes were used as protein capture matrices in immunoassays. Because the most common labels in immunoassays were detected based on the colour change, an understanding of how protein concentration varies on different PVDF surfaces was needed. Herein, the correlation between the membrane pore size and protein adsorption was systematically investigated. Five different PVDF membrane morphologies were prepared and FTIR/ATR was employed to accurately quantify the surface protein concentration on membranes with small pore sizes. SigmaPlot® was used to find a suitable curve fit for protein adsorption and membrane pore size, with a high correlation coefficient, R2, of 0.9971.

Pore-scale Modeling of CO2 Local Trapping in Heterogeneous Porous Media with Inter-granular Cements

NASA Astrophysics Data System (ADS)

Wang, D.; Li, Y.

2017-12-01

Based on pore-scale modeling of CO2/brine multiphase flow in heterogeneous porous media with inter-granular cements, we numerically analyze the effects of cement-modified pore structure on CO2 local trapping. Results indicate: 1) small pore throat is the main reason for causing CO2 local trapping in front of low-porosity layers (namely dense layers) formed by inter-granular cements; 2) in the case of the same pore throat size, the smaller particle size can increase the number of flow paths for CO2 plume and equivalently enhances local permeability, which may counteract the impediment of high capillary pressure on CO2 migration to some extent and consequently disables CO2 local capillary trapping; 3) the isolated pores by inter-granular cements can lead to dramatic reduction of CO2 saturation inside the dense layers, whereas the change of connectivity of some pores due to the cements can increase CO2 accumulation in front of the dense layers by lowering the displacement area of CO2 plume.

Micro- and nano-X-ray computed-tomography: A step forward in the characterization of the pore network of a leached cement paste

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bossa, Nathan, E-mail: bossanathan@gmail.com; INERIS, Parc Technologique Alata, BP2, 60550 Verneuil-en-Halatte; iCEINT, CNRS, Duke Univ. International Consortium for the Environmental Implications of Nanotechnology, Aix-en-Provence

2015-01-15

Pore structure of leached cement pastes (w/c = 0.5) was studied for the first time from micro-scale down to the nano-scale by combining micro- and nano-X-ray computed tomography (micro- and nano-CT). This allowed assessing the 3D heterogeneity of the pore network along the cement profile (from the core to the altered layer) of almost the entire range of cement pore size, i.e. from capillary to gel pores. We successfully quantified an increase of porosity in the altered layer at both resolutions. Porosity is increasing from 1.8 to 6.1% and from 18 to 58% at the micro-(voxel = 1.81 μm) andmore » nano-scale (voxel = 63.5 nm) respectively. The combination of both CT allowed to circumvent weaknesses inherent of both investigation scales. In addition the connectivity and the channel size of the pore network were also evaluated to obtain a complete 3D pore network characterization at both scales.« less

Osteogenic differentiation of dura mater stem cells cultured in vitro on three-dimensional porous scaffolds of poly(ε-caprolactone) fabricated via co-extrusion and gas foaming

PubMed Central

Aronin, C.E. Petrie; Cooper, J.A.; Sefcik, L.S.; Tholpady, S.S.; Ogle, R.C.; Botchwey, E.A.

2008-01-01

A novel scaffold fabrication method utilizing both polymer blend extrusion and gas foaming techniques to control pore size distribution is presented. Seventy five per cent of all pores produced using polymer blend extrusion alone were less than 50 μm. Introducing a gas technique provided better control of pore size distribution, expanding the range from 0-50 to 0-350 μm. Varying sintering time, annealing temperature and foaming pressure also helped reduced the percentage of pore sizes below 50 μm. Scaffolds chosen for in vitro cellular studies had a pore size distribution of 0-300 μm, average pore size 66 ± 17 μm, 0.54 ± 0.02% porosity and 98% interconnectivity, measured by micro computed tomography (microCT) analysis. The ability of the scaffolds to support osteogenic differentiation and cranial defect repair was evaluated by static and dynamic (0.035 ± 0.006 m s-1 terminal velocity) cultivation with dura mater stem cells (DSCs). In vitro studies showed minimal increases in proliferation over 28 days in culture in osteogenic media. Alkaline phosphatase expression remained constant throughout the study. Moderate increases in matrix deposition, as assessed by histochemical staining and microCT analysis, occurred at later time points, days 21 and 28. Although constructs cultured dynamically showed greater mineralization than static conditions, these trends were not significant. It remains unclear whether bioreactor culture of DSCs is advantageous for bone tissue engineering applications. However, these studies show that polycaprolactone (PCL) scaffolds alone, without the addition of other co-polymers or ceramics, support long-term attachment and mineralization of DSCs throughout the entire porous scaffold. PMID:18434267

Confinement effects on dipolar relaxation by translational dynamics of liquids in porous silica glasses

NASA Astrophysics Data System (ADS)

Korb, J.-P.; Xu, Shu; Jonas, J.

1993-02-01

A theory of dipolar relaxation by translational diffusion of a nonwetting liquid confined in model porous media is presented. We obtain expressions of the rates of spin-lattice relaxation 1/T1, spin-spin relaxation 1/T2, and spin-lattice relaxation in the rotating frame 1/T1ρ, which depend on the average pore size d. The frequency variations of these rates are intermediate between the two-dimensional and three-dimensional results. At small frequency they vary logarithmically for small d and tend progressively to a constant with increasing d. For small pore sizes we obtain quadratic confinement dependences of these rates (∝1/d2), at variance with the linear (∝1/d) relation coming from the biphasic fast exchange model usually applied for a wetting liquid in porous media. We apply such a theory to the 1H NMR relaxation of methylcyclohexane liquid in sol-gel porous silica glasses with a narrow pore-size distribution. The experiments confirm the theoretical predictions for very weak interacting solvent in porous silica glasses of pore sizes varying in the range of 18.4-87.2 Å and in the bulk. At the limit of small pores, the logarithmic frequency dependencies of 1/T1ρ and 1/T1 observed over several decades of frequency are interpreted with a model of unbounded two-dimensional diffusion in a layered geometry. The leveling off of the 1/T1ρ low-frequency dependence is interpreted in terms of the bounded two-dimensional diffusion due to the finite length L of the pores. An estimate of a finite size of L=100 Å is in excellent agreement with the experimental results of the transmission electron microscopy study of platinium-carbon replicated xerogels.

Joint inversion of NMR and SIP data to estimate pore size distribution of geomaterials

NASA Astrophysics Data System (ADS)

Niu, Qifei; Zhang, Chi

2018-03-01

There are growing interests in using geophysical tools to characterize the microstructure of geomaterials because of the non-invasive nature and the applicability in field. In these applications, multiple types of geophysical data sets are usually processed separately, which may be inadequate to constrain the key feature of target variables. Therefore, simultaneous processing of multiple data sets could potentially improve the resolution. In this study, we propose a method to estimate pore size distribution by joint inversion of nuclear magnetic resonance (NMR) T2 relaxation and spectral induced polarization (SIP) spectra. The petrophysical relation between NMR T2 relaxation time and SIP relaxation time is incorporated in a nonlinear least squares problem formulation, which is solved using Gauss-Newton method. The joint inversion scheme is applied to a synthetic sample and a Berea sandstone sample. The jointly estimated pore size distributions are very close to the true model and results from other experimental method. Even when the knowledge of the petrophysical models of the sample is incomplete, the joint inversion can still capture the main features of the pore size distribution of the samples, including the general shape and relative peak positions of the distribution curves. It is also found from the numerical example that the surface relaxivity of the sample could be extracted with the joint inversion of NMR and SIP data if the diffusion coefficient of the ions in the electrical double layer is known. Comparing to individual inversions, the joint inversion could improve the resolution of the estimated pore size distribution because of the addition of extra data sets. The proposed approach might constitute a first step towards a comprehensive joint inversion that can extract the full pore geometry information of a geomaterial from NMR and SIP data.

Changes in pore structure of coal caused by coal-to-gas bioconversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Rui; Liu, Shimin; Bahadur, Jitendra

Microbial enhanced coalbed methane (ME-CBM) recovery is critically examined as a viable technology for natural gas recovery from coalbed methane (CBM) reservoirs. Since the majority of gas-in-place (GIP) is stored as an adsorbed phase in fine pores of coal matrix, the nano-pore structure directly influences gas storage and transport properties. Only limited studies have quantified the alteration of the nano-pore structure due to ME-CBM treatment. This study examines the evolution of the pore structure using a combination of small angle X-ray scattering (SAXS), low-pressure N 2 and CO 2 adsorption (LPGA) and high-pressure methane adsorption methods. The results show thatmore » the surface fractal dimension decreases for the two bioconverted coals compared to the untreated coal. After bio-treatment, the mesopore surface area and pore volume decrease with the average pore diameter increases, while the micropore surface area increases with pore volume decreases. Both inaccessible meso-/micropore size distributions decrease after bioconversion, while the accessible micropore size distribution increases, making a portion of closed micropore network accessible. In addition, the methane adsorption capacities increase after bio-treatment, which is confirmed by the increase of micropore surface area. A conceptual physical model of methanogenesis is proposed based on the evolution of the pore structure.« less

Changes in pore structure of coal caused by coal-to-gas bioconversion

DOE PAGES

Zhang, Rui; Liu, Shimin; Bahadur, Jitendra; ...

2017-06-19

Microbial enhanced coalbed methane (ME-CBM) recovery is critically examined as a viable technology for natural gas recovery from coalbed methane (CBM) reservoirs. Since the majority of gas-in-place (GIP) is stored as an adsorbed phase in fine pores of coal matrix, the nano-pore structure directly influences gas storage and transport properties. Only limited studies have quantified the alteration of the nano-pore structure due to ME-CBM treatment. This study examines the evolution of the pore structure using a combination of small angle X-ray scattering (SAXS), low-pressure N 2 and CO 2 adsorption (LPGA) and high-pressure methane adsorption methods. The results show thatmore » the surface fractal dimension decreases for the two bioconverted coals compared to the untreated coal. After bio-treatment, the mesopore surface area and pore volume decrease with the average pore diameter increases, while the micropore surface area increases with pore volume decreases. Both inaccessible meso-/micropore size distributions decrease after bioconversion, while the accessible micropore size distribution increases, making a portion of closed micropore network accessible. In addition, the methane adsorption capacities increase after bio-treatment, which is confirmed by the increase of micropore surface area. A conceptual physical model of methanogenesis is proposed based on the evolution of the pore structure.« less

Effects of Pore Distributions on Ductility of Thin-Walled High Pressure Die-Cast Magnesium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Kyoo Sil; Li, Dongsheng; Sun, Xin

2013-06-01

In this paper, a microstructure-based three-dimensional (3D) finite element modeling method is adopted to investigate the effects of porosity in thin-walled high pressure die-cast (HPDC) Magnesium alloys on their ductility. For this purpose, the cross-sections of AM60 casting samples are first examined using optical microscope and X-ray tomography to obtain the general information on the pore distribution features. The experimentally observed pore distribution features are then used to generate a series of synthetic microstructure-based 3D finite element models with different pore volume fractions and pore distribution features. Shear and ductile damage models are adopted in the finite element analyses tomore » induce the fracture by element removal, leading to the prediction of ductility. The results in this study show that the ductility monotonically decreases as the pore volume fraction increases and that the effect of ‘skin region’ on the ductility is noticeable under the condition of same local pore volume fraction in the center region of the sample and its existence can be beneficial for the improvement of ductility. The further synthetic microstructure-based 3D finite element analyses are planned to investigate the effects of pore size and pore size distribution.« less

Four-flux model of the light scattering in porous varnish and paint layers: towards understanding the visual appearance of altered blanched easel oil paintings

NASA Astrophysics Data System (ADS)

Genty-Vincent, Anaïs; Van Song, Théo Phan; Andraud, Christine; Menu, Michel

2017-07-01

Blanching of easel oil paintings is a recurring alteration that can affect the varnish layer and also the paint layer itself, and strongly alter the visual appearance. Our examinations by field emission gun scanning electron microscopy (FEG-SEM) of altered and unaltered samples revealed the presence of spherical pores in the altered layers, with a pore size ranging from few nanometers to few micrometers. The aim of the present study is to corroborate that the visual appearance modification can be explained by light scattering theories (Mie or Rayleigh depending on the pore size of the considered layer). The four-flux model was used to resolve the radiative transfer equation (RTE) and model the light scattering in porous varnish layers as well as in porous green earth and raw umber oil paint layers. It enables to highlight that the pore size has an important impact on the visual appearance of the altered layer (color and opacity modification). The pore concentration and the thickness of the altered part affect, however, only the opacity. This work points out that the blanching of easel oil paintings is due to light scattering by the pores, which is an important result toward the proposal of adapted and durable future conservation treatments.

Substantial Expansion of Detectable Size Range in Ionic Current Sensing through Pores by Using a Microfluidic Bridge Circuit.

PubMed

Yasaki, Hirotoshi; Yasui, Takao; Yanagida, Takeshi; Kaji, Noritada; Kanai, Masaki; Nagashima, Kazuki; Kawai, Tomoji; Baba, Yoshinobu

2017-10-11

Measuring ionic currents passing through nano- or micropores has shown great promise for the electrical discrimination of various biomolecules, cells, bacteria, and viruses. However, conventional measurements have shown there is an inherent limitation to the detectable particle volume (1% of the pore volume), which critically hinders applications to real mixtures of biomolecule samples with a wide size range of suspended particles. Here we propose a rational methodology that can detect samples with the detectable particle volume of 0.01% of the pore volume by measuring a transient current generated from the potential differences in a microfluidic bridge circuit. Our method substantially suppresses the background ionic current from the μA level to the pA level, which essentially lowers the detectable particle volume limit even for relatively large pore structures. Indeed, utilizing a microscale long pore structure (volume of 5.6 × 10 4 aL; height and width of 2.0 × 2.0 μm; length of 14 μm), we successfully detected various samples including polystyrene nanoparticles (volume: 4 aL), bacteria, cancer cells, and DNA molecules. Our method will expand the applicability of ionic current sensing systems for various mixed biomolecule samples with a wide size range, which have been difficult to measure by previously existing pore technologies.

Cell wall microstructure, pore size distribution and absolute density of hemp shiv

PubMed Central

Lawrence, M.; Ansell, M. P.; Hussain, A.

2018-01-01

This paper, for the first time, fully characterizes the intrinsic physical parameters of hemp shiv including cell wall microstructure, pore size distribution and absolute density. Scanning electron microscopy revealed microstructural features similar to hardwoods. Confocal microscopy revealed three major layers in the cell wall: middle lamella, primary cell wall and secondary cell wall. Computed tomography improved the visualization of pore shape and pore connectivity in three dimensions. Mercury intrusion porosimetry (MIP) showed that the average accessible porosity was 76.67 ± 2.03% and pore size classes could be distinguished into micropores (3–10 nm) and macropores (0.1–1 µm and 20–80 µm). The absolute density was evaluated by helium pycnometry, MIP and Archimedes' methods. The results show that these methods can lead to misinterpretation of absolute density. The MIP method showed a realistic absolute density (1.45 g cm−3) consistent with the density of the known constituents, including lignin, cellulose and hemi-cellulose. However, helium pycnometry and Archimedes’ methods gave falsely low values owing to 10% of the volume being inaccessible pores, which require sample pretreatment in order to be filled by liquid or gas. This indicates that the determination of the cell wall density is strongly dependent on sample geometry and preparation. PMID:29765652

Mouthpart conduit sizes of fluid-feeding insects determine the ability to feed from pores

DOE PAGES

Lehnert, Matthew S.; Bennett, Andrew; Reiter, Kristen E.; ...

2017-01-04

Fluid-feeding insects, such as butterflies, moths, and flies (20% of all animal species), are faced with the common selection pressure of having to remove and feed on trace amounts of fluids from porous surfaces. Insects able to acquire fluids that are confined to pores during drought conditions would have an adaptive advantage and increased fitness over other individuals. Here we performed feeding trials using solutions with magnetic nanoparticles to show that butterflies and flies have mouthparts adapted to pull liquids from porous surfaces using capillary action as the governing principle. In addition, the ability to feed on the liquids collectedmore » from pores depends on a relationship between the diameter of the mouthpart conduits and substrate pore size diameter; insects with mouthpart conduit diameters larger than the pores cannot successfully feed, thus there is a limiting substrate pore size from which each species can acquire liquids for fluid uptake. In conclusion, given that natural selection independently favored mouthpart architectures that support these methods of fluid uptake (Diptera and Lepidoptera share a common ancestor 280 mya that had chewing mouthparts), we suggest that the convergence of this mechanism advocates this as an optimal strategy for pulling trace amounts of fluids from porous surfaces.« less

Mouthpart conduit sizes of fluid-feeding insects determine the ability to feed from pores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lehnert, Matthew S.; Bennett, Andrew; Reiter, Kristen E.

Fluid-feeding insects, such as butterflies, moths, and flies (20% of all animal species), are faced with the common selection pressure of having to remove and feed on trace amounts of fluids from porous surfaces. Insects able to acquire fluids that are confined to pores during drought conditions would have an adaptive advantage and increased fitness over other individuals. Here we performed feeding trials using solutions with magnetic nanoparticles to show that butterflies and flies have mouthparts adapted to pull liquids from porous surfaces using capillary action as the governing principle. In addition, the ability to feed on the liquids collectedmore » from pores depends on a relationship between the diameter of the mouthpart conduits and substrate pore size diameter; insects with mouthpart conduit diameters larger than the pores cannot successfully feed, thus there is a limiting substrate pore size from which each species can acquire liquids for fluid uptake. In conclusion, given that natural selection independently favored mouthpart architectures that support these methods of fluid uptake (Diptera and Lepidoptera share a common ancestor 280 mya that had chewing mouthparts), we suggest that the convergence of this mechanism advocates this as an optimal strategy for pulling trace amounts of fluids from porous surfaces.« less

Cell wall microstructure, pore size distribution and absolute density of hemp shiv

NASA Astrophysics Data System (ADS)

Jiang, Y.; Lawrence, M.; Ansell, M. P.; Hussain, A.

2018-04-01

This paper, for the first time, fully characterizes the intrinsic physical parameters of hemp shiv including cell wall microstructure, pore size distribution and absolute density. Scanning electron microscopy revealed microstructural features similar to hardwoods. Confocal microscopy revealed three major layers in the cell wall: middle lamella, primary cell wall and secondary cell wall. Computed tomography improved the visualization of pore shape and pore connectivity in three dimensions. Mercury intrusion porosimetry (MIP) showed that the average accessible porosity was 76.67 ± 2.03% and pore size classes could be distinguished into micropores (3-10 nm) and macropores (0.1-1 µm and 20-80 µm). The absolute density was evaluated by helium pycnometry, MIP and Archimedes' methods. The results show that these methods can lead to misinterpretation of absolute density. The MIP method showed a realistic absolute density (1.45 g cm-3) consistent with the density of the known constituents, including lignin, cellulose and hemi-cellulose. However, helium pycnometry and Archimedes' methods gave falsely low values owing to 10% of the volume being inaccessible pores, which require sample pretreatment in order to be filled by liquid or gas. This indicates that the determination of the cell wall density is strongly dependent on sample geometry and preparation.

Adsorption of pharmaceuticals to microporous activated carbon treated with potassium hydroxide, carbon dioxide, and steam.

PubMed

Fu, Heyun; Yang, Liuyan; Wan, Yuqiu; Xu, Zhaoyi; Zhu, Dongqiang

2011-01-01

Adsorption of sulfapyridine, tetracycline, and tylosin to a commercial microporous activated carbon (AC) and its potassium hydroxide (KOH)-, CO-, and steam-treated counterparts (prepared by heating at 850°C) was studied to explore efficient adsorbents for the removal of selected pharmaceuticals from water. Phenol and nitrobenzene were included as additional adsorbates, and nonporous graphite was included as a model adsorbent. The activation treatments markedly increased the specific surface area and enlarged the pore sizes of the mesopores of AC (with the strongest effects shown on the KOH-treated AC). Adsorption of large-size tetracycline and tylosin was greatly enhanced, especially for the KOH-treated AC (more than one order of magnitude), probably due to the alleviated size-exclusion effect. However, the treatments had little effect on adsorption of low-size phenol and nitrobenzene due to the predominance of micropore-filling effect in adsorption and the nearly unaffected content of small micropores causative to such effect. These hypothesized mechanisms on pore-size dependent adsorption were further tested by comparing surface area-normalized adsorption data and adsorbent pore size distributions with and without the presence of adsorbed antibiotics. The findings indicate that efficient adsorption of bulky pharmaceuticals to AC can be achieved by enlarging the adsorbent pore size through suitable activation treatments. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Three-dimensional {Co(3+)-Zn2+} and {Co(3+)-Cd2+} networks originated from carboxylate-rich building blocks: syntheses, structures, and heterogeneous catalysis.

PubMed

Kumar, Girijesh; Gupta, Rajeev

2013-10-07

The present work shows the utilization of Co(3+) complexes appended with either para- or meta-arylcarboxylic acid groups as the molecular building blocks for the construction of three-dimensional {Co(3+)-Zn(2+)} and {Co(3+)-Cd(2+)} heterobimetallic networks. The structural characterizations of these networks show several interesting features including well-defined pores and channels. These networks function as heterogeneous and reusable catalysts for the regio- and stereoselective ring-opening reactions of various epoxides and size-selective cyanation reactions of assorted aldehydes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Chandan K.; Singh, Jayant K., E-mail: jayantks@iitk.ac.in

Three-stage pseudo-supercritical transformation path and multiple-histogram reweighting technique are employed for the determination of solid-liquid coexistence of the Lennard-Jones (12-6) fluid, in a structureless cylindrical pore of radius, R, ranging from 4 to 20 molecular diameters. The Gibbs free energy difference is evaluated using thermodynamic integration method by connecting solid and liquid phases under confinement via one or more intermediate states without any first order phase transition among them. The thermodynamic melting temperature, T{sub m}, is found to oscillate for pore size, R < 8, which is in agreement with the behavior observed for the melting temperature in slit pores.more » However, T{sub m} for almost all pore sizes is less than the bulk case, which is contrary to the behavior seen for the slit pore. The oscillation in T{sub m} decays at around pore radius R = 8, and beyond that shift in the melting temperature with respect to the bulk case is in line with the prediction of the Gibbs-Thomson equation.« less

Catalytic nanoporous membranes

DOEpatents

Pellin, Michael J [Naperville, IL; Hryn, John N [Naperville, IL; Elam, Jeffrey W [Elmhurst, IL

2009-12-01

A nanoporous catalytic membrane which displays several unique features including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity.

Physiologic upper limits of pore size of different blood capillary types and another perspective on the dual pore theory of microvascular permeability.

PubMed

Sarin, Hemant

2010-08-11

Much of our current understanding of microvascular permeability is based on the findings of classic experimental studies of blood capillary permeability to various-sized lipid-insoluble endogenous and non-endogenous macromolecules. According to the classic small pore theory of microvascular permeability, which was formulated on the basis of the findings of studies on the transcapillary flow rates of various-sized systemically or regionally perfused endogenous macromolecules, transcapillary exchange across the capillary wall takes place through a single population of small pores that are approximately 6 nm in diameter; whereas, according to the dual pore theory of microvascular permeability, which was formulated on the basis of the findings of studies on the accumulation of various-sized systemically or regionally perfused non-endogenous macromolecules in the locoregional tissue lymphatic drainages, transcapillary exchange across the capillary wall also takes place through a separate population of large pores, or capillary leaks, that are between 24 and 60 nm in diameter. The classification of blood capillary types on the basis of differences in the physiologic upper limits of pore size to transvascular flow highlights the differences in the transcapillary exchange routes for the transvascular transport of endogenous and non-endogenous macromolecules across the capillary walls of different blood capillary types. The findings and published data of studies on capillary wall ultrastructure and capillary microvascular permeability to lipid-insoluble endogenous and non-endogenous molecules from the 1950s to date were reviewed. In this study, the blood capillary types in different tissues and organs were classified on the basis of the physiologic upper limits of pore size to the transvascular flow of lipid-insoluble molecules. Blood capillaries were classified as non-sinusoidal or sinusoidal on the basis of capillary wall basement membrane layer continuity or lack thereof. Non-sinusoidal blood capillaries were further sub-classified as non-fenestrated or fenestrated based on the absence or presence of endothelial cells with fenestrations. The sinusoidal blood capillaries of the liver, myeloid (red) bone marrow, and spleen were sub-classified as reticuloendothelial or non-reticuloendothelial based on the phago-endocytic capacity of the endothelial cells. The physiologic upper limit of pore size for transvascular flow across capillary walls of non-sinusoidal non-fenestrated blood capillaries is less than 1 nm for those with interendothelial cell clefts lined with zona occludens junctions (i.e. brain and spinal cord), and approximately 5 nm for those with clefts lined with macula occludens junctions (i.e. skeletal muscle). The physiologic upper limit of pore size for transvascular flow across the capillary walls of non-sinusoidal fenestrated blood capillaries with diaphragmed fenestrae ranges between 6 and 12 nm (i.e. exocrine and endocrine glands); whereas, the physiologic upper limit of pore size for transvascular flow across the capillary walls of non-sinusoidal fenestrated capillaries with open 'non-diaphragmed' fenestrae is approximately 15 nm (kidney glomerulus). In the case of the sinusoidal reticuloendothelial blood capillaries of myeloid bone marrow, the transvascular transport of non-endogenous macromolecules larger than 5 nm into the bone marrow interstitial space takes place via reticuloendothelial cell-mediated phago-endocytosis and transvascular release, which is the case for systemic bone marrow imaging agents as large as 60 nm in diameter. The physiologic upper limit of pore size in the capillary walls of most non-sinusoidal blood capillaries to the transcapillary passage of lipid-insoluble endogenous and non-endogenous macromolecules ranges between 5 and 12 nm. Therefore, macromolecules larger than the physiologic upper limits of pore size in the non-sinusoidal blood capillary types generally do not accumulate within the respective tissue interstitial spaces and their lymphatic drainages. In the case of reticuloendothelial sinusoidal blood capillaries of myeloid bone marrow, however, non-endogenous macromolecules as large as 60 nm in diameter can distribute into the bone marrow interstitial space via the phago-endocytic route, and then subsequently accumulate in the locoregional lymphatic drainages of tissues following absorption into the lymphatic drainage of periosteal fibrous tissues, which is the lymphatic drainage of myeloid bone marrow. When the ultrastructural basis for transcapillary exchange across the capillary walls of different capillary types is viewed in this light, it becomes evident that the physiologic evidence for the existence of aqueous large pores ranging between 24 and 60 nm in diameter in the capillary walls of blood capillaries, is circumstantial, at best.

Impact of pore size on the sorption of uranyl under seawater conditions

DOE PAGES

Mayes, Richard T.; Gorka, Joanna; Dai, Sheng

2016-04-05

The extraction of uranium from seawater has received significant interest recently, because of the possibility of a near-limitless supply of uranium to fuel the nuclear power industry. While sorbent development has focused primarily on polymeric sorbents, nanomaterials represent a new area that has the potential to surpass the current polymeric sorbents, because of the high surface areas that are possible. Mesoporous carbon materials are a stable, high-surface-area material capable of extracting various chemical species from a variety of environments. Herein, we report the use of a dual templating process to understand the effect of pore size on the adsorption ofmore » uranyl ions from a uranyl brine consisting of seawater-relevant sodium, chloride, and bicarbonate ions. It was found that pore size played a more significant role in the effective use of the grafted polymer, leading to higher uranium capacities than the surface area. Furthermore, the pore size must be tailored to meet the demands of the extraction medium and analyte metal to achieve efficacy as an adsorbent.« less

Influence of surface treatments on micropore structure and hydrogen adsorption behavior of nanoporous carbons.

PubMed

Kim, Byung-Joo; Park, Soo-Jin

2007-07-15

The scope of this work was to control the pore sizes of porous carbons by various surface treatments and to investigate the relation between pore structures and hydrogen adsorption capacity. The effects of various surface treatments (i.e., gas-phase ozone, anodic oxidation, fluorination, and oxygen plasma) on the micropore structures of porous carbons were investigated by N(2)/77 K isothermal adsorption. The hydrogen adsorption capacity was measured by H(2) isothermal adsorption at 77 K. In the result, the specific surface area and micropore volume of all of the treated samples were slightly decreased due to the micropore filling or pore collapsing behaviors. It was also found that in F(2)-treated carbons the center of the pore size distribution was shifted to left side, meaning that the average size of the micropores decreased. The F(2)- and plasma-treated samples showed higher hydrogen storage capacities than did the other samples, the F(2)-treated one being the best, indicating that the micropore size of the porous carbons played a key role in the hydrogen adsorption at 77 K.

Performance of Granular Starch with Controlled Pore Size during Hydrolysis with Digestive Enzymes.

PubMed

Benavent-Gil, Yaiza; Rosell, Cristina M

2017-12-01

Studies on porous starch have been directed to explore different industrial applications as bio-adsorbents of a variety of compounds. However, the analysis of starch digestibility is essential for food application. The objective of this study was to determine the impact of porous structure on in vitro starch digestibility. Porous starches were obtained using a range of concentrations of amyloglucosidase (AMG), α-amylase (AM), cyclodextrin-glycosyltransferase (CGTase) or branching enzyme (BE). Porous starches exhibited major content of digestible starch (DS) that increased with the intensity of the enzymatic treatment, and very low amount of resistant starch (RS). Porous starches behaved differently during in vitro hydrolysis depending on their enzymatic treatment. AMG was the unique treatment that increased the digestive amylolysis and estimated glycemic index, whereas AM, CGTase and BE reduced them. A significant relationship was found between the pore size and the severity of the amylolysis, suggesting that a specific pore size is required for the accessibility of the digestive amylase. Therefore, pore size in the starch surface was a limiting factor for digestion of starch granules.

Analytical electron tomography mapping of the SiCporeoxidation at the nanoscale

NASA Astrophysics Data System (ADS)

Florea, Ileana; Ersen, Ovidiu; Hirlimann, Charles; Roiban, Lucian; Deneuve, Adrien; Houllé, Matthieu; Janowska, Izabela; Nguyen, Patrick; Pham, Charlotte; Pham-Huu, Cuong

2010-12-01

Silicon carbide is a ceramic material that has been widely studied because of its potential applications, ranging from electronics to heterogeneous catalysis. Recently, a new type of SiC materials with a medium specific surface area and thermal conductivity, called β-SiC, has attracted overgrowing interest as a new class of catalyst support in several catalytic reactions. A primary electron tomography study, performed in usual mode, has revealed a dual surface structure defined by two types of porosities made of networks of connected channels with sizes larger than 50 nm and ink-bottled pores with sizes spanning from 4 to 50 nm. Depending on the solvent nature, metal nanoparticles could be selectively deposited inside one of the two porosities, a fact that illustrates a selective wetting titration of the two types of surfaces by different liquids. The explaining hypothesis that has been put forward was that this selectivity against solvents is related to the pore surface oxidation degree of the two types of pores. A new technique of analytical electron tomography, where the series of projections used to reconstruct the volume of an object is recorded in energy filtered mode (EFTEM), has been implemented to map the poreoxidation state and to correlate it with the morphology and the accessibility of the porous network. Applied, for the first time, at a nanoscale resolution, this technique allowed us to obtain 3D elemental maps of different elements present in the analysed porous grains, in particular oxygen; we found thus that the interconnected channelpores are more rapidly oxidized than the ink-bottled ones. Alternatively, our study highlights the great interest of this method that opens the way for obtaining precise information on the chemical composition of a 3D surface at a nanometer scale.Silicon carbide is a ceramic material that has been widely studied because of its potential applications, ranging from electronics to heterogeneous catalysis. Recently, a new type of SiC materials with a medium specific surface area and thermal conductivity, called β-SiC, has attracted overgrowing interest as a new class of catalyst support in several catalytic reactions. A primary electron tomography study, performed in usual mode, has revealed a dual surface structure defined by two types of porosities made of networks of connected channels with sizes larger than 50 nm and ink-bottled pores with sizes spanning from 4 to 50 nm. Depending on the solvent nature, metal nanoparticles could be selectively deposited inside one of the two porosities, a fact that illustrates a selective wetting titration of the two types of surfaces by different liquids. The explaining hypothesis that has been put forward was that this selectivity against solvents is related to the pore surface oxidation degree of the two types of pores. A new technique of analytical electron tomography, where the series of projections used to reconstruct the volume of an object is recorded in energy filtered mode (EFTEM), has been implemented to map the poreoxidation state and to correlate it with the morphology and the accessibility of the porous network. Applied, for the first time, at a nanoscale resolution, this technique allowed us to obtain 3D elemental maps of different elements present in the analysed porous grains, in particular oxygen; we found thus that the interconnected channelpores are more rapidly oxidized than the ink-bottled ones. Alternatively, our study highlights the great interest of this method that opens the way for obtaining precise information on the chemical composition of a 3D surface at a nanometer scale. Electronic supplementary information (ESI) available: SI-1-SI-4. See DOI: 10.1039/c0nr00449a

Effect of freezing conditions on β-Tricalcium Phosphate /Camphene scaffold with micro sized particles fabricated by freeze casting.

PubMed

Singh, Gurdev; Soundarapandian, S

2018-03-01

The long standing need of the implant manufacturing industries is to fabricate multi-matrix, customized porous scaffold as cost-effectively. In recent years, freeze casting has shown greater opportunity in the fabrication of porous scaffolds (tricalcium phosphate, hydroxyapatite, bioglass, alumina, etc.) such as at ease and good control over pore size, porosity, a range of materials and economic feasibility. In particular, tricalcium phosphate (TCP) has proved as it possesses good biocompatible (osteoinduction, osteoconduction, etc.) and biodegradability hence beta-tricalcium phosphate (β-TCP, particle size of 10µm) was used as base material and camphene was used as a freezing vehicle in this study. Both freezing conditions such as constant freezing temperature (CFT) and constant freezing rate (CFR) were used for six different conditional samples (CFT: 30, 35 and 40vol% solid loading; similarly CFR: 30, 35 and 40vol% solid loading) to study and understand the effect of various properties (pore size, porosity and compressive strength) of the freeze-cast porous scaffold. It was observed that the average size of the pore was varying linearly as from lower to higher when the solid loading was varying higher to lower. With the help of scanning electron micrographs (SEM), it was observed that the average size of pore during CFR (9.7/ 6.5/ 4.9µm) was comparatively higher than the process of CFT (6.0/ 4.8/ 2.6µm) with respect to the same solid loading (30/ 35/ 40vol%) conditions. From the Gas pycnometer analysis, it was found that the porosity in both freezing conditions (CFT, CFR) were almost near values such as 32.8% and 28.5%. Further to be observed that with the increase in solid loading, the total porosity value has decreased due to the reduction in the concentration of the freezing vehicle. Hence, the freezing vehicle was found as responsible for the formation of appropriate size and orientation of pores during freeze casting. The compressive strength (CS) testing was clearly indicated that the CS was majorly depending on the size of pore which was depending on solid loading. The CS of CFT-based samples (smaller pore sizes and higher resistance to the propagation of crack) were higher due to the higher solid content (pore size) in compared with CFR-based samples on the similar solid loading conditions. As evidently, it was noted that the CFT-based sample with 40% solid loading has given the compressive strength which has come in the range of cancellous bone. The positive note was that the ratio of Ca/P has come as 1.68 (natural bone) after sintering and that was the required value recommended by the food and drug administration (FDI) for manufacturing of bone implants. Copyright © 2017 Elsevier Ltd. All rights reserved.

Pore space connectivity and porosity using CT scans of tropical soils

NASA Astrophysics Data System (ADS)

Previatello da Silva, Livia; de Jong Van Lier, Quirijn

2015-04-01

Microtomography has been used in soil physics for characterization and allows non-destructive analysis with high-resolution, yielding a three-dimensional representation of pore space and fluid distribution. It also allows quantitative characterization of pore space, including pore size distribution, shape, connectivity, porosity, tortuosity, orientation, preferential pathways and is also possible predict the saturated hydraulic conductivity using Darcy's equation and a modified Poiseuille's equation. Connectivity of pore space is an important topological property of soil. Together with porosity and pore-size distribution, it governs transport of water, solutes and gases. In order to quantify and analyze pore space (quantifying connectivity of pores and porosity) of four tropical soils from Brazil with different texture and land use, undisturbed samples were collected in São Paulo State, Brazil, with PVC ring with 7.5 cm in height and diameter of 7.5 cm, depth of 10 - 30 cm from soil surface. Image acquisition was performed with a CT system Nikon XT H 225, with technical specifications of dual reflection-transmission target system including a 225 kV, 225 W high performance Xray source equipped with a reflection target with pot size of 3 μm combined with a nano-focus transmission module with a spot size of 1 μm. The images were acquired at specific energy level for each soil type, according to soil texture, and external copper filters were used in order to allow the attenuation of low frequency X-ray photons and passage of one monoenergetic beam. This step was performed aiming minimize artifacts such as beam hardening that may occur during the attenuation in the material interface with different densities within the same sample. Images were processed and analyzed using ImageJ/Fiji software. Retention curve (tension table and the pressure chamber methods), saturated hydraulic conductivity (constant head permeameter), granulometry, soil density and particle density were also performed in laboratory and results were compared with images analyzes.

Comparison of fouling characteristics in different pore-sized submerged ceramic membrane bioreactors.

PubMed

Jin, Le; Ong, Say Leong; Ng, How Yong

2010-12-01

Membrane fouling, the key disadvantage that inevitably occurs continuously in the membrane bioreactor (MBR), baffles the wide-scale application of MBR. Ceramic membrane, which possesses high chemical and thermal resistance, has seldom been used in MBR to treat municipal wastewater. Four ceramic membranes with the same materials but different pore sizes, ranging from 80 to 300 nm, were studied in parallel using four lab-scale submerged MBRs (i.e., one type of ceramic membrane in one MBR). Total COD and ammonia nitrogen removal efficiencies were observed to be consistently above 94.5 and 98%, respectively, in all submerged ceramic membrane bioreactors. The experimental results showed that fouling was mainly affected by membrane's microstructure, surface roughness and pore sizes. Ceramic membrane with the roughest surface and biggest pore size (300 nm) had the highest fouling potential with respect to the TMP profile. The 80 nm membrane with a smoother surface and relatively uniform smaller pore openings experienced least membrane fouling with respect to TMP increase. The effects of the molecular weight distribution, particle size distribution and other biomass characteristics such as extracellular polymeric substances, zeta potential and capillary suction time, were also investigated in this study. Results showed that no significant differences of these attributes were observed. These observations indicate that the membrane surface properties are the dominant factors leading to different fouling potential in this study. Copyright © 2010 Elsevier Ltd. All rights reserved.

The Description of Shale Reservoir Pore Structure Based on Method of Moments Estimation

PubMed Central

Li, Wenjie; Wang, Changcheng; Shi, Zejin; Wei, Yi; Zhou, Huailai; Deng, Kun

2016-01-01

Shale has been considered as good gas reservoir due to its abundant interior nanoscale pores. Thus, the study of the pore structure of shale is of great significance for the evaluation and development of shale oil and gas. To date, the most widely used approaches for studying the shale pore structure include image analysis, radiation and fluid invasion methods. The detailed pore structures can be studied intuitively by image analysis and radiation methods, but the results obtained are quite sensitive to sample preparation, equipment performance and experimental operation. In contrast, the fluid invasion method can be used to obtain information on pore size distribution and pore structure, but the relative simple parameters derived cannot be used to evaluate the pore structure of shale comprehensively and quantitatively. To characterize the nanoscale pore structure of shale reservoir more effectively and expand the current research techniques, we proposed a new method based on gas adsorption experimental data and the method of moments to describe the pore structure parameters of shale reservoir. Combined with the geological mixture empirical distribution and the method of moments estimation principle, the new method calculates the characteristic parameters of shale, including the mean pore size (x¯), standard deviation (σ), skewness (Sk) and variation coefficient (c). These values are found by reconstructing the grouping intervals of observation values and optimizing algorithms for eigenvalues. This approach assures a more effective description of the characteristics of nanoscale pore structures. Finally, the new method has been applied to analyze the Yanchang shale in the Ordos Basin (China) and Longmaxi shale from the Sichuan Basin (China). The results obtained well reveal the pore characteristics of shale, indicating the feasibility of this new method in the study of the pore structure of shale reservoir. PMID:26992168

The Description of Shale Reservoir Pore Structure Based on Method of Moments Estimation.

PubMed

Li, Wenjie; Wang, Changcheng; Shi, Zejin; Wei, Yi; Zhou, Huailai; Deng, Kun

2016-01-01

Shale has been considered as good gas reservoir due to its abundant interior nanoscale pores. Thus, the study of the pore structure of shale is of great significance for the evaluation and development of shale oil and gas. To date, the most widely used approaches for studying the shale pore structure include image analysis, radiation and fluid invasion methods. The detailed pore structures can be studied intuitively by image analysis and radiation methods, but the results obtained are quite sensitive to sample preparation, equipment performance and experimental operation. In contrast, the fluid invasion method can be used to obtain information on pore size distribution and pore structure, but the relative simple parameters derived cannot be used to evaluate the pore structure of shale comprehensively and quantitatively. To characterize the nanoscale pore structure of shale reservoir more effectively and expand the current research techniques, we proposed a new method based on gas adsorption experimental data and the method of moments to describe the pore structure parameters of shale reservoir. Combined with the geological mixture empirical distribution and the method of moments estimation principle, the new method calculates the characteristic parameters of shale, including the mean pore size (mean), standard deviation (σ), skewness (Sk) and variation coefficient (c). These values are found by reconstructing the grouping intervals of observation values and optimizing algorithms for eigenvalues. This approach assures a more effective description of the characteristics of nanoscale pore structures. Finally, the new method has been applied to analyze the Yanchang shale in the Ordos Basin (China) and Longmaxi shale from the Sichuan Basin (China). The results obtained well reveal the pore characteristics of shale, indicating the feasibility of this new method in the study of the pore structure of shale reservoir.

Relative permeability of hydrate-bearing sediments from percolation theory and critical path analysis: theoretical and experimental results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daigle, Hugh; Rice, Mary Anna; Daigle, Hugh

Relative permeabilities to water and gas are important parameters for accurate modeling of the formation of methane hydrate deposits and production of methane from hydrate reservoirs. Experimental measurements of gas and water permeability in the presence of hydrate are difficult to obtain. The few datasets that do exist suggest that relative permeability obeys a power law relationship with water or gas saturation with exponents ranging from around 2 to greater than 10. Critical path analysis and percolation theory provide a framework for interpreting the saturation-dependence of relative permeability based on percolation thresholds and the breadth of pore size distributions, whichmore » may be determined easily from 3-D images or gas adsorption-desorption hysteresis. We show that the exponent of the permeability-saturation relationship for relative permeability to water is related to the breadth of the pore size distribution, with broader pore size distributions corresponding to larger exponents. Relative permeability to water in well-sorted sediments with narrow pore size distributions, such as Berea sandstone or Toyoura sand, follows percolation scaling with an exponent of 2. On the other hand, pore-size distributions determined from argon adsorption measurements we performed on clays from the Nankai Trough suggest that relative permeability to water in fine-grained intervals may be characterized by exponents as large as 10 as determined from critical path analysis. We also show that relative permeability to the gas phase follows percolation scaling with a quadratic dependence on gas saturation, but the threshold gas saturation for percolation changes with hydrate saturation, which is an important consideration in systems in which both hydrate and gas are present, such as during production from a hydrate reservoir. Our work shows how measurements of pore size distributions from 3-D imaging or gas adsorption may be used to determine relative permeabilities.« less

Generalized network modeling of capillary-dominated two-phase flow

NASA Astrophysics Data System (ADS)

Raeini, Ali Q.; Bijeljic, Branko; Blunt, Martin J.

2018-02-01

We present a generalized network model for simulating capillary-dominated two-phase flow through porous media at the pore scale. Three-dimensional images of the pore space are discretized using a generalized network—described in a companion paper [A. Q. Raeini, B. Bijeljic, and M. J. Blunt, Phys. Rev. E 96, 013312 (2017), 10.1103/PhysRevE.96.013312]—which comprises pores that are divided into smaller elements called half-throats and subsequently into corners. Half-throats define the connectivity of the network at the coarsest level, connecting each pore to half-throats of its neighboring pores from their narrower ends, while corners define the connectivity of pore crevices. The corners are discretized at different levels for accurate calculation of entry pressures, fluid volumes, and flow conductivities that are obtained using direct simulation of flow on the underlying image. This paper discusses the two-phase flow model that is used to compute the averaged flow properties of the generalized network, including relative permeability and capillary pressure. We validate the model using direct finite-volume two-phase flow simulations on synthetic geometries, and then present a comparison of the model predictions with a conventional pore-network model and experimental measurements of relative permeability in the literature.

Water storage capacities of soil under four different land uses in Hawaii

Treesearch

Teruo Yamamoto; Paul Duffy

1963-01-01

Soil pore volume and pore size were correlated with land use or vegetation cover type. The top foot of forest soils had more large pores and higher water-holding capacities than that of soils under cultivation, in pasture land, or in idle grassland.

Ionic Liquid/Metal-Organic Framework Composites: From Synthesis to Applications.

PubMed

Kinik, Fatma Pelin; Uzun, Alper; Keskin, Seda

2017-07-21

Metal-organic frameworks (MOFs) have been widely studied for different applications owing to their fascinating properties such as large surface areas, high porosities, tunable pore sizes, and acceptable thermal and chemical stabilities. Ionic liquids (ILs) have been recently incorporated into the pores of MOFs as cavity occupants to change the physicochemical properties and gas affinities of MOFs. Several recent studies have shown that IL/MOF composites show superior performances compared with pristine MOFs in various fields, such as gas storage, adsorption and membrane-based gas separation, catalysis, and ionic conductivity. In this review, we address the recent advances in syntheses of IL/MOF composites and provide a comprehensive overview of their applications. Opportunities and challenges of using IL/MOF composites in many applications are reviewed and the requirements for the utilization of these composite materials in real industrial processes are discussed to define the future directions in this field. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reticular synthesis of porous molecular 1D nanotubes and 3D networks.

PubMed

Slater, A G; Little, M A; Pulido, A; Chong, S Y; Holden, D; Chen, L; Morgan, C; Wu, X; Cheng, G; Clowes, R; Briggs, M E; Hasell, T; Jelfs, K E; Day, G M; Cooper, A I

2017-01-01

Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of 'reticular synthesis', in which multiple building blocks can be assembled according to a common assembly motif. Here we apply a chiral recognition strategy to a new family of tubular covalent cages to create both 1D porous nanotubes and 3D diamondoid pillared porous networks. The diamondoid networks are analogous to MOFs prepared from tetrahedral metal nodes and linear ditopic organic linkers. The crystal structures can be rationalized by computational lattice-energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the 'node and strut' principles of reticular synthesis to molecular crystals.

Reticular synthesis of porous molecular 1D nanotubes and 3D networks

NASA Astrophysics Data System (ADS)

Slater, A. G.; Little, M. A.; Pulido, A.; Chong, S. Y.; Holden, D.; Chen, L.; Morgan, C.; Wu, X.; Cheng, G.; Clowes, R.; Briggs, M. E.; Hasell, T.; Jelfs, K. E.; Day, G. M.; Cooper, A. I.

2017-01-01

Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of 'reticular synthesis', in which multiple building blocks can be assembled according to a common assembly motif. Here we apply a chiral recognition strategy to a new family of tubular covalent cages to create both 1D porous nanotubes and 3D diamondoid pillared porous networks. The diamondoid networks are analogous to MOFs prepared from tetrahedral metal nodes and linear ditopic organic linkers. The crystal structures can be rationalized by computational lattice-energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the 'node and strut' principles of reticular synthesis to molecular crystals.

Polyelectrolyte layer-by-layer deposition in cylindrical nanopores.

PubMed

Lazzara, Thomas D; Lau, K H Aaron; Abou-Kandil, Ahmed I; Caminade, Anne-Marie; Majoral, Jean-Pierre; Knoll, Wolfgang

2010-07-27

Layer-by-layer (LbL) deposition of polyelectrolytes within nanopores in terms of the pore size and the ionic strength was experimentally studied. Anodic aluminum oxide (AAO) membranes, which have aligned, cylindrical, nonintersecting pores, were used as a model nanoporous system. Furthermore, the AAO membranes were also employed as planar optical waveguides to enable in situ monitoring of the LbL process within the nanopores by optical waveguide spectroscopy (OWS). Structurally well-defined N,N-disubstituted hydrazine phosphorus-containing dendrimers of the fourth generation, with peripherally charged groups and diameters of approximately 7 nm, were used as the model polyelectrolytes. The pore diameter of the AAO was varied between 30-116 nm and the ionic strength was varied over 3 orders of magnitude. The dependence of the deposited layer thickness on ionic strength within the nanopores is found to be significantly stronger than LbL deposition on a planar surface. Furthermore, deposition within the nanopores can become inhibited even if the pore diameter is much larger than the diameter of the G4-polyelectrolyte, or if the screening length is insignificant relative to the dendrimer diameter at high ionic strengths. Our results will aid in the template preparation of polyelectrolyte multilayer nanotubes, and our experimental approach may be useful for investigating theories regarding the partitioning of nano-objects within nanopores where electrostatic interactions are dominant. Furthermore, we show that the enhanced ionic strength dependence of polyelectrolyte transport within the nanopores can be used to selectively deposit a LbL multilayer atop a nanoporous substrate.

Habitable pore space and survival ofRhizobium leguminosarum biovartrifolii introduced into soil.

PubMed

Postma, J; van Veen, J A

1990-03-01

The hypothesis that the population size of introduced bacteria is affected by habitable pore space was studied by varying moisture content and bulk density in sterilized, as well as in natural loamy sand and silt loam. The soils were inoculated withRhizobium leguminosarum biovartrifolii and established and maintained at soil water potentials between -5 and -20 kPa (pF 1.7 and 2.3). Rhizobial cells were enumerated when population sizes were expected to be more or less stable. In sterilized soils, the rhizobial numbers were not affected or decreased only slightly when water potentials increased from -20 to -5 kPa. In natural soils, the decrease in rhizobial numbers with increasing water potentials was more pronounced. Bulk density had only minor effects on the population sizes of rhizobia or total bacteria. Soil water retention curves of both soils were used to calculate volume and surface area of pores from different diameter classes, and an estimation of the habitable pore space was made. Combining these values of the theoretical habitable pore space with the measured rhizobial numbers showed that only 0.37 and 0.44% of the habitable pore space was occupied in the sterilized loamy sand and silt loam, respectively. The situation in natural soil is more complicated, since a whole variety of microorganisms is present. Nevertheless, it was suggested that, in general, pore space does not limit proliferation and growth of soil microorganisms.

Building solids inside nano-space: from confined amorphous through confined solvate to confined 'metastable' polymorph.

PubMed

Nartowski, K P; Tedder, J; Braun, D E; Fábián, L; Khimyak, Y Z

2015-10-14

The nanocrystallisation of complex molecules inside mesoporous hosts and control over the resulting structure is a significant challenge. To date the largest organic molecule crystallised inside the nano-pores is a known pharmaceutical intermediate - ROY (259.3 g mol(-1)). In this work we demonstrate smart manipulation of the phase of a larger confined pharmaceutical - indomethacin (IMC, 357.8 g mol(-1)), a substance with known conformational flexibility and complex polymorphic behaviour. We show the detailed structural analysis and the control of solid state transformations of encapsulated molecules inside the pores of mesoscopic cellular foam (MCF, pore size ca. 29 nm) and controlled pore glass (CPG, pore size ca. 55 nm). Starting from confined amorphous IMC we drive crystallisation into a confined methanol solvate, which upon vacuum drying leads to the stabilised rare form V of IMC inside the MCF host. In contrast to the pure form, encapsulated form V does not transform into a more stable polymorph upon heating. The size of the constraining pores and the drug concentration within the pores determine whether the amorphous state of the drug is stabilised or it recrystallises into confined nanocrystals. The work presents, in a critical manner, an application of complementary techniques (DSC, PXRD, solid-state NMR, N2 adsorption) to confirm unambiguously the phase transitions under confinement and offers a comprehensive strategy towards the formation and control of nano-crystalline encapsulated organic solids.

Mercury porosimetry for comparing piece-wise hydraulic properties with full range pore characteristics of soil aggregates and porous rocks

NASA Astrophysics Data System (ADS)

Turturro, Antonietta Celeste; Caputo, Maria C.; Gerke, Horst H.

2017-04-01

Unsaturated hydraulic properties are essential in the modeling of water and solute movement in the vadose zone. Since standard hydraulic techniques are limited to specific moisture ranges, maybe affected by air entrapment, wettability problems, limitations due to water vapor pressure, and are depending on the initial saturation, the continuous maximal drying curves of the complete hydraulic functions can mostly not reflect the basic pore size distribution. The aim of this work was to compare the water retention curves of soil aggregates and porous rocks with their porosity characteristics. Soil aggregates of Haplic Luvisols from Loess L (Hneveceves, Czech Republic) and glacial Till T (Holzendorf, Germany) and two lithotypes of porous rock C (Canosa) and M (Massafra), Italy, were analyzed using, suction table, evaporation, psychrometry methods, and the adopted Quasi-Steady Centrifuge method for determination of unsaturated hydraulic conductivity. These various water-based techniques were applied to determine the piece-wise retention and the unsaturated hydraulic conductivity functions in the range of pore water saturations. The pore-size distribution was determined with the mercury intrusion porosimetry (MIP). MIP results allowed assessing the volumetric mercury content at applied pressures up to 420000 kPa. Greater intrusion and porosity values were found for the porous rocks than for the soil aggregates. Except for the aggregate samples from glacial till, maximum liquid contents were always smaller than porosity. Multimodal porosities and retention curves were observed for both porous rocks and aggregate soils. Two pore-size peaks with pore diameters of 0.135 and 27.5 µm, 1.847 and 19.7 µm, and 0.75 and 232 µm were found for C, M and T, respectively, while three peaks of 0.005, 0.392 and 222 µm were identified for L. The MIP data allowed describing the retention curve in the entire mercury saturation range as compared to water retention curves that required combining several methods for limited suction ranges. Although the soil aggregates and porous rocks differed in pore geometries and pore size distributions, MIP provided additional information for characterizing the relation between pore structure and hydraulic properties for both.

Effect of nitric acid treatment on activated carbon derived from oil palm shell

NASA Astrophysics Data System (ADS)

Allwar, Allwar; Hartati, Retno; Fatimah, Is

2017-03-01

The primary object of this work is to study the effect of nitric acid on the porous and morphology structure of activated carbon. Production of activated carbon from oil palm shell was prepared with pyrolysis process at temperature 900°C and by introduction of 10 M nitric acid. Determination of surface area, pore volume and pore size distribution of activated carbon was conducted by the N2 adsorption-desorption isotherm at 77 K. Morphology structure and elemental micro-analysis of activated carbon were estimated by Scanning Electron Microscopy (SEM) and energy dispersive X-ray (EDX), respectively. The result shows that activated carbon after treating with nitric acid proved an increasing porous characteristics involving surface area, pore volume and pore size distribution. It also could remove the contaminants including metals and exhibit an increasing of pores and crevices all over the surface.

Pore-network model of evaporation-induced salt precipitation in porous media: The effect of correlations and heterogeneity

NASA Astrophysics Data System (ADS)

Dashtian, Hassan; Shokri, Nima; Sahimi, Muhammad

2018-02-01

Salt transport and precipitation in porous media constitute a set of complex and fascinating phenomena that are of considerable interest to several important problems, ranging from storage of CO2 in geological formations, to soil fertility, and protection of pavements and roads, as well as historical monuments. The phenomena occur at the pore scale and are greatly influenced by the heterogeneity of the pore space morphology. We present a pore-network (PN) model to study the phenomena. Vapor diffusion, capillary effect at the brine-vapor interface, flow of brine, and transport of salt and its precipitation in the pores that plug the pores partially or completely are all accounted for. The drying process is modeled by the invasion percolation, while transport of salt in brine is accounted for by the convective-diffusion equation. We demonstrate that the drying patterns, the clustering and connectivity of the pore throats in which salt precipitation occurs, the saturation distribution, and the drying rate are all strongly dependent upon the pore-size distribution, the correlations among the pore sizes, and the anisotropy of the pore space caused by stratification that most natural porous media contain. In particular, if the strata are more or less parallel to the direction of injection of the gas that dries out the pore space (air, for example) and/or causes salt precipitation (CO2, for example), the drying rate increases significantly. Moreover, salt tends to precipitate in clusters of neighboring pores that are parallel to the open surface of the porous medium.

Adsorption of polypropylene from dilute solutions on a zeolite column packing.

PubMed

Macko, Tibor; Pasch, Harald; Denayer, Joeri F

2005-01-01

Faujasite type zeolite CBV-780 was tested as adsorbent for isotactic polypropylene by liquid chromatography. When cyclohexane, cyclohexanol, n-decanol, n-dodecanol, diphenylmethane, or methylcyclohexane was used as mobile phase, polypropylene was fully or partially retained within the column packing. This is the first series of sorbent-solvent systems to show a pronounced retention of isotactic polypropylene. According to the hydrodynamic volumes of polypropylene in solution, macromolecules of polypropylene should be fully excluded from the pore volume of the sorbent. Sizes of polypropylene macromolecules in linear conformations, however, correlate with the pore size of the column packing used. It is presumed that the polypropylene chains partially penetrate into the pores and are retained due to the high adsorption potential in the narrow pores.

Modeling the interaction of ultrasound with pores

NASA Technical Reports Server (NTRS)

Lu, Yichi; Wadley, Haydn N. G.; Parthasarathi, Sanjai

1991-01-01

Factors that affect ultrasonic velocity sensing of density during consolidation of metal powders are examined. A comparison is made between experimental results obtained during the final stage of densification and the predictions of models that assume either a spherical or a spheroidal pore shape. It is found that for measurements made at low frequencies during the final stage of densification, relative density (pore fraction) and pore shape are the two most important factors determining the ultrasonic velocity, the effect of pore size is negligible.

An emerging pore-making strategy: confined swelling-induced pore generation in block copolymer materials.

PubMed

Wang, Yong; Li, Fengbin

2011-05-17

Block copolymers (BCPs) composed of two or more thermodynamically incompatible homopolymers self-assemble into periodic microdomains. Exposing self-assembled BCPs with solvents selective to one block causes a swelling of the domains composed of this block. Strong swelling in the confinement imposed by the matrix of the other glassy block leads to well-defined porous structures via morphology reconstruction. This confined swelling-induced pore-making process has emerged recently as a new strategy to produce porous materials due to synergic advantages that include extreme simplicity, high pore regularity, involvement of no chemical reactions, no weight loss, reversibility of the pore forming process, etc. The mechanism, kinetics, morphology, and governing parameters of the confined swelling-induced pore-making process in BCP thin films are discussed, and the main applications of nanoporous thin films in the fields of template synthesis, surface patterning, and guidance for the areal arrangements of nanomaterials and biomolecules are summarized. Recent, promising results of extending this mechanism to produce BCP nanofibers or nanotubes and bulk materials with well-defined porosity, which makes this strategy also attractive to researchers outside the nanocommunity, are also presented. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

LONG-TERM PERFORMANCE CHARACTERISTICS OF FINE PORE CERAMIC DIFFUSERS AT MONROE, WISCONSIN

EPA Science Inventory

A study of the fine pore aeration system at the Monroe, Wisconsin wastewater treatment plant was conducted to monitor, over a 2-year period, the oxygen transfer efficiency (OTE) and fouling tendencies of four different effective pore size ceramic discs. The plant treats a mixtur...

Synthesis and characterization of high-surface-area millimeter-sized silica beads with hierarchical multi-modal pore structure by the addition of agar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Yosep; Choi, Junhyun; Tong, Meiping, E-mail: tongmeiping@iee.pku.edu.cn

2014-04-01

Millimeter-sized spherical silica foams (SSFs) with hierarchical multi-modal pore structure featuring high specific surface area and ordered mesoporous frameworks were successfully prepared using aqueous agar addition, foaming and drop-in-oil processes. The pore-related properties of the prepared spherical silica (SSs) and SSFs were systematically characterized by field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), small-angle X-ray diffraction (SAXRD), Hg intrusion porosimetry, and N{sub 2} adsorption–desorption isotherm measurements. Improvements in the BET surface area and total pore volume were observed at 504 m{sup 2} g{sup −1} and 5.45 cm{sup 3} g{sup −1}, respectively, after an agar addition and foaming process. Despitemore » the increase in the BET surface area, the mesopore wall thickness and the pore size of the mesopores generated from the block copolymer with agar addition were unchanged based on the SAXRD, TEM, and BJH methods. The SSFs prepared in the present study were confirmed to have improved BET surface area and micropore volume through the agar loading, and to exhibit interconnected 3-dimensional network macropore structure leading to the enhancement of total porosity and BET surface area via the foaming process. - Highlights: • Millimeter-sized spherical silica foams (SSFs) are successfully prepared. • SSFs exhibit high BET surface area and ordered hierarchical pore structure. • Agar addition improves BET surface area and micropore volume of SSFs. • Foaming process generates interconnected 3-D network macropore structure of SSFs.« less

Developing a Novel Hydrogen Sponge with Ideal Binding Energy and High Surface Area for Practical Hydrogen Storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chung, T. C. Mike

This Phase I (5 quarters) research project was to examine the validity of a new class of boron-containing polymer (B-polymer) frameworks, serving as the adsorbents for the practical onboard H2 storage applications. Three B-polymer frameworks were synthesized and investigated, which include B-poly(butyenylstyrene) (B-PBS) framework (A), B-poly(phenyldiacetyene) (B-PPDA) framework (B), and B-poly(phenyltriacetylene) (B-PPTA) framework (C). They are 2-D polymer structures with the repeating cyclic units that spontaneously form open morphology and the B-doped (p-type) π-electrons delocalized surfaces. The ideal B-polymer framework shall exhibit open micropores (pore size in the range of 1-1.5nm) with high surface area (>3000 m 2/g), and themore » B-dopants in the conjugated framework shall provide high surface energy for interacting with H 2 molecules (an ideal H 2 binding energy in the range of 15-25 kJ/mol). The pore size distribution and H2 binding energy were investigated at both Penn State and NREL laboratories. So far, the experimental results show the successful synthesis of B-polymer frameworks with the relatively well-defined planar (2-D) structures. The intrinsically formed porous morphology exhibits a broad pore size distribution (in the range of 0.5-10 nm) with specific surface area (~1000 m 2/g). The miss-alignment between 2-D layers may block some micropore channels and limit gas diffusion throughout the entire matrix. In addition, the 2-D planar conjugated structure may also allow free π-electrons delocalization throughout the framework, which significantly reduces the acidity of B-moieties (electron-deficiency).The resulting 2-D B-polymer frameworks only exhibit a small increase of H 2 binding energy in the range of 8-9 KJ/mole (quite constant over the whole sorption range).« less

Ultrasonic Inspection and Fatigue Evaluation of Critical Pore Size in Welds.

DTIC Science & Technology

1981-09-01

Boiler and Pressure Vessel Code ) 20...Five porosity levels were produced that parallelled ASME boiler and pressure vessel code specification (Section VIII). Appendix IV of the pressure...Figure 2 shows porosity charts (ASME Boiler and Pressure Vessel Code ) which classify and designate the number and size of pores in any six inch length

Effect of porosity variation on the electrochemical behavior of vertically aligned multi-walled carbon nanotubes.

PubMed

Raut, Akshay S; Parker, Charles B; Stoner, Brian R; Glass, Jeffrey T

2012-06-01

Electrochemical charge storage characteristics of vertically aligned multi-walled carbon nanotubes (MWCNTs) as a function of varying diameter and spacing are reported. It was observed that the specific capacitance of the MWCNTs increased as both diameter and inter-tube spacing decreased. The MWCNT films with 229 nm inter-MWCNT spacing exhibited specific capacitance of 228 F/g versus 70 F/g for 506 nm spacing, when tested in a non-aqueous electrolyte. Further, a trend in specific capacitance versus pore size is proposed. Coupled with previously reported trends observed in the sub-10 nm pore size regime, this is expected to offer better understanding of electrochemical behavior of porous carbon materials over a wide range of pore sizes.

Scalability of transport parameters with pore sizes in isodense disordered media

NASA Astrophysics Data System (ADS)

Reginald, S. William; Schmitt, V.; Vallée, R. A. L.

2014-09-01

We study light multiple scattering in complex disordered porous materials. High internal phase emulsion-based isodense polystyrene foams are designed. Two types of samples, exhibiting different pore size distributions, are investigated for different slab thicknesses varying from L = 1 \\text{mm} to 10 \\text{mm} . Optical measurements combining steady-state and time-resolved detection are used to characterize the photon transport parameters. Very interestingly, a clear scalability of the transport mean free path \\ellt with the average size of the pores S is observed, featuring a constant velocity of the transport energy in these isodense structures. This study strongly motivates further investigations into the limits of validity of this scalability as the scattering strength of the system increases.

Extension of the thermal porosimetry method to high gas pressure for nanoporosimetry estimation

NASA Astrophysics Data System (ADS)

Jannot, Y.; Degiovanni, A.; Camus, M.

2018-04-01

Standard pore size determination methods like mercury porosimetry, nitrogen sorption, microscopy, or X-ray tomography are not suited to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization has been developed in a previous study. This method has been used with air pressure varying from 10-1 to 105 Pa for materials having a thermal conductivity less than 0.05 W m-1 K-1 at atmospheric pressure. It enables the estimation of pore size distribution between 100 nm and 1 mm. In this paper, we present a new experimental device enabling thermal conductivity measurement under gas pressure up to 106 Pa, enabling the estimation of the volume fraction of pores having a 10 nm diameter. It is also demonstrated that the main thermal conductivity models (parallel, series, Maxwell, Bruggeman, self-consistent) lead to the same estimation of the pore size distribution as the extended parallel model (EPM) presented in this paper and then used to process the experimental data. Three materials with thermal conductivities at atmospheric pressure ranging from 0.014 W m-1 K-1 to 0.04 W m-1 K-1 are studied. The thermal conductivity measurement results obtained with the three materials are presented, and the corresponding pore size distributions between 10 nm and 1 mm are presented and discussed.

Three-Dimensional Scaffolds for Tissue Engineering Applications: Role of Porosity and Pore Size

PubMed Central

Loh, Qiu Li

2013-01-01

Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate damaged tissues or organs. These scaffolds serve to mimic the actual in vivo microenvironment where cells interact and behave according to the mechanical cues obtained from the surrounding 3D environment. Hence, the material properties of the scaffolds are vital in determining cellular response and fate. These 3D scaffolds are generally highly porous with interconnected pore networks to facilitate nutrient and oxygen diffusion and waste removal. This review focuses on the various fabrication techniques (e.g., conventional and rapid prototyping methods) that have been employed to fabricate 3D scaffolds of different pore sizes and porosity. The different pore size and porosity measurement methods will also be discussed. Scaffolds with graded porosity have also been studied for their ability to better represent the actual in vivo situation where cells are exposed to layers of different tissues with varying properties. In addition, the ability of pore size and porosity of scaffolds to direct cellular responses and alter the mechanical properties of scaffolds will be reviewed, followed by a look at nature's own scaffold, the extracellular matrix. Overall, the limitations of current scaffold fabrication approaches for tissue engineering applications and some novel and promising alternatives will be highlighted. PMID:23672709

Variation in aluminum, iron, and particle concentrations in oxic groundwater samples collected by use of tangential-flow ultrafiltration with low-flow sampling

NASA Astrophysics Data System (ADS)

Szabo, Zoltan; Oden, Jeannette H.; Gibs, Jacob; Rice, Donald E.; Ding, Yuan

2002-02-01

Particulates that move with ground water and those that are artificially mobilized during well purging could be incorporated into water samples during collection and could cause trace-element concentrations to vary in unfiltered samples, and possibly in filtered samples (typically 0.45-um (micron) pore size) as well, depending on the particle-size fractions present. Therefore, measured concentrations may not be representative of those in the aquifer. Ground water may contain particles of various sizes and shapes that are broadly classified as colloids, which do not settle from water, and particulates, which do. In order to investigate variations in trace-element concentrations in ground-water samples as a function of particle concentrations and particle-size fractions, the U.S. Geological Survey, in cooperation with the U.S. Air Force, collected samples from five wells completed in the unconfined, oxic Kirkwood-Cohansey aquifer system of the New Jersey Coastal Plain. Samples were collected by purging with a portable pump at low flow (0.2-0.5 liters per minute and minimal drawdown, ideally less than 0.5 foot). Unfiltered samples were collected in the following sequence: (1) within the first few minutes of pumping, (2) after initial turbidity declined and about one to two casing volumes of water had been purged, and (3) after turbidity values had stabilized at less than 1 to 5 Nephelometric Turbidity Units. Filtered samples were split concurrently through (1) a 0.45-um pore size capsule filter, (2) a 0.45-um pore size capsule filter and a 0.0029-um pore size tangential-flow filter in sequence, and (3), in selected cases, a 0.45-um and a 0.05-um pore size capsule filter in sequence. Filtered samples were collected concurrently with the unfiltered sample that was collected when turbidity values stabilized. Quality-assurance samples consisted of sequential duplicates (about 25 percent) and equipment blanks. Concentrations of particles were determined by light scattering.

The Effect of Various Acids to the Gelation Process to the Silica Gel Characteristic Using Organic Silica

NASA Astrophysics Data System (ADS)

Rahman, NA; Widiyastuti, W.; Sigit, D.; Ajiza, M.; Sujana, W.

2018-01-01

Bagasse ash is solid waste of cane sugar industry which contain of silica more than 51%. Some previous study of silica gel from bagasse ash have been conducted often and been applied. This study concerns about the effect of various acid used in the process of gelation to the characteristic of silica gel produced. Then, this silica gel will be used as adsorbent. As that, the silica gel must fulfill the requirements of adsorbent, as have good pores characteristics, fit in mesoporous size so that adsorbent diffusion process is not disturbed. A fitted pores size of silica gel can be prepared by managing acid concentration used. The effect of acid, organic acid (tartaric acid) and inorganic acid (hydrochloric acid), is investigated in detail. The acid is added into sodium silicate solution in that the gel is formed, the pores structures can be investigated with BET, the crystal form is analyzed with XRD and the pore structure is analyzed visually with SEM. By managing the acid concentration added, it gets the effect of acid to the pore structure of silica gel. The bigger concentration is, the bigger the pore’s size of silica gel produced.

Structure and properties of clinical coralline implants measured via 3D imaging and analysis.

PubMed

Knackstedt, Mark Alexander; Arns, Christoph H; Senden, Tim J; Gross, Karlis

2006-05-01

The development and design of advanced porous materials for biomedical applications requires a thorough understanding of how material structure impacts on mechanical and transport properties. This paper illustrates a 3D imaging and analysis study of two clinically proven coral bone graft samples (Porites and Goniopora). Images are obtained from X-ray micro-computed tomography (micro-CT) at a resolution of 16.8 microm. A visual comparison of the two images shows very different structure; Porites has a homogeneous structure and consistent pore size while Goniopora has a bimodal pore size and a strongly disordered structure. A number of 3D structural characteristics are measured directly on the images including pore volume-to-surface-area, pore and solid size distributions, chord length measurements and tortuosity. Computational results made directly on the digitized tomographic images are presented for the permeability, diffusivity and elastic modulus of the coral samples. The results allow one to quantify differences between the two samples. 3D digital analysis can provide a more thorough assessment of biomaterial structure including the pore wall thickness, local flow, mechanical properties and diffusion pathways. We discuss the implications of these results to the development of optimal scaffold design for tissue ingrowth.

Foam flow in a model porous medium: I. The effect of foam coarsening.

PubMed

Jones, S A; Getrouw, N; Vincent-Bonnieu, S

2018-05-09

Foam structure evolves with time due to gas diffusion between bubbles (coarsening). In a bulk foam, coarsening behaviour is well defined, but there is less understanding of coarsening in confined geometries such as porous media. Previous predictions suggest that coarsening will cause foam lamellae to move to low energy configurations in the pore throats, resulting in greater capillary resistance when restarting flow. Foam coarsening experiments were conducted in both a model-porous-media micromodel and in a sandstone core. In both cases, foam was generated by coinjecting surfactant solution and nitrogen. Once steady state flow had been achieved, the injection was stopped and the system sealed off. In the micromodel, the foam coarsening was recorded using time-lapse photography. In the core flood, the additional driving pressure required to reinitiate flow after coarsening was measured. In the micromodel the bubbles coarsened rapidly to the pore size. At the completion of coarsening the lamellae were located in minimum energy configurations in the pore throats. The wall effect meant that the coarsening did not conform to the unconstricted growth laws. The coreflood tests also showed coarsening to be a rapid process. The additional driving pressure to restart flow reached a maximum after just 2 minutes.

Cystic fibrosis transmembrane conductance regulator: temperature-dependent cysteine reactivity suggests different stable conformers of the conduction pathway.

PubMed

Liu, Xuehong; Dawson, David C

2011-11-29

Cysteine scanning has been widely used to identify pore-lining residues in mammalian ion channels, including the cystic fibrosis transmembrane conductance regulator (CFTR). These studies, however, have been typically conducted at room temperature rather than human body temperature. Reports of substantial effects of temperature on gating and anion conduction in CFTR channels as well as an unexpected pattern of cysteine reactivity in the sixth transmembrane segment (TM6) prompted us to investigate the effect of temperature on the reactivity of cysteines engineered into TM6 of CFTR. We compared reaction rates at temperatures ranging from 22 to 37 °C for cysteines placed on either side of an apparent size-selective accessibility barrier previously defined by comparing reactivity toward channel-permeant and channel-impermeant, thiol-directed reagents. The results indicate that the reactivity of cysteines at three positions extracellular to the position of the accessibility barrier, 334, 336, and 337, is highly temperature-dependent. At 37 °C, cysteines at these positions were highly reactive toward MTSES(-), whereas at 22 °C, the reaction rates were 2-6-fold slower to undetectable. An activation energy of 157 kJ/mol for the reaction at position 337 is consistent with the hypothesis that, at physiological temperature, the extracellular portion of the CFTR pore can adopt conformations that differ significantly from those that can be accessed at room temperature. However, the position of the accessibility barrier defined empirically by applying channel-permeant and channel-impermeant reagents to the extracellular aspect of the pore is not altered. The results illuminate previous scanning results and indicate that the assay temperature is a critical variable in studies designed to use chemical modification to test structural models for the CFTR anion conduction pathway.

Characterization of the enhancement effect of Na2CO3 on the sulfur capture capacity of limestones.

PubMed

Laursen, Karin; Kern, Arnt A; Grace, John R; Lim, C Jim

2003-08-15

It has been known for a long time that certain additives (e.g., NaCl, CaCl2, Na2CO3, Fe2O3) can increase the sulfur dioxide capture-capacity of limestones. In a recent study we demonstrated that very small amounts of Na2CO3 can be very beneficial for producing sorbents of very high sorption capacities. This paper explores what contributes to these significant increases. Mercury porosimetry measurements of calcined limestone samples reveal a change in the pore-size from 0.04-0.2 microm in untreated samples to 2-10 microm in samples treated with Na2CO3--a pore-size more favorable for penetration of sulfur into the particles. The change in pore-size facilitates reaction with lime grains throughout the whole particle without rapid plugging of pores, avoiding premature change from a fast chemical reaction to a slow solid-state diffusion controlled process, as seen for untreated samples. Calcination in a thermogravimetric reactor showed that Na2CO3 increased the rate of calcination of CaCO3 to CaO, an effect which was slightly larger at 825 degrees C than at 900 degrees C. Peak broadening analysis of powder X-ray diffraction data of the raw, calcined, and sulfated samples revealed an unaffected calcite size (approximately 125-170 nm) but a significant increase in the crystallite size for lime (approximately 60-90 nm to approximately 250-300 nm) and less for anhydrite (approximately 125-150 nm to approximately 225-250 nm). The increase in the crystallite and pore-size of the treated limestones is attributed to an increase in ionic mobility in the crystal lattice due to formation of vacancies in the crystals when Ca is partly replaced by Na.

Nanoporous anodic aluminum oxide with a long-range order and tunable cell sizes by phosphoric acid anodization on pre-patterned substrates

PubMed Central

Surawathanawises, Krissada; Cheng, Xuanhong

2014-01-01

Nanoporous anodic aluminum oxide (AAO) has been explored for various applications due to its regular cell arrangement and relatively easy fabrication processes. However, conventional two-step anodization based on self-organization only allows the fabrication of a few discrete cell sizes and formation of small domains of hexagonally packed pores. Recent efforts to pre-pattern aluminum followed with anodization significantly improve the regularity and available pore geometries in AAO, while systematic study of the anodization condition, especially the impact of acid composition on pore formation guided by nanoindentation is still lacking. In this work, we pre-patterned aluminium thin films using ordered monolayers of silica beads and formed porous AAO in a single-step anodization in phosphoric acid. Controllable cell sizes ranging from 280 nm to 760 nm were obtained, matching the diameters of the silica nanobead molds used. This range of cell size is significantly greater than what has been reported for AAO formed in phosphoric acid in the literature. In addition, the relationships between the acid concentration, cell size, pore size, anodization voltage and film growth rate were studied quantitatively. The results are consistent with the theory of oxide formation through an electrochemical reaction. Not only does this study provide useful operational conditions of nanoindentation induced anodization in phosphoric acid, it also generates significant information for fundamental understanding of AAO formation. PMID:24535886

[Preparation of nano-nacre artificial bone].

PubMed

Chen, Jian-ting; Tang, Yong-zhi; Zhang, Jian-gang; Wang, Jian-jun; Xiao, Ying

2008-12-01

To assess the improvements in the properties of nano-nacre artificial bone prepared on the basis of nacre/polylactide acid composite artificial bone and its potential for clinical use. The compound of nano-scale nacre powder and poly-D, L-lactide acid (PDLLA) was used to prepare the cylindrical hollow artificial bone, whose properties including raw material powder scale, pore size, porosity and biomechanical characteristics were compared with another artificial bone made of micron-scale nacre powder and PDLLA. Scanning electron microscope showed that the average particle size of the nano-nacre powder was 50.4-/+12.4 nm, and the average pore size of the artificial bone prepared using nano-nacre powder was 215.7-/+77.5 microm, as compared with the particle size of the micron-scale nacre powder of 5.0-/+3.0 microm and the pore size of the resultant artificial bone of 205.1-/+72.0 microm. The porosities of nano-nacre artificial bone and the micron-nacre artificial bone were (65.4-/+2.9)% and (53.4-/+2.2)%, respectively, and the two artificial bones had comparable compressive strength and Young's modulus, but the flexural strength of the nano-nacre artificial bone was lower than that of the micro-nacre artificial bone. The nano-nacre artificial bone allows better biodegradability and possesses appropriate pore size, porosity and biomechanical properties for use as a promising material in bone tissue engineering.

Pore-scale modeling of saturated permeabilities in random sphere packings.

PubMed

Pan, C; Hilpert, M; Miller, C T

2001-12-01

We use two pore-scale approaches, lattice-Boltzmann (LB) and pore-network modeling, to simulate single-phase flow in simulated sphere packings that vary in porosity and sphere-size distribution. For both modeling approaches, we determine the size of the representative elementary volume with respect to the permeability. Permeabilities obtained by LB modeling agree well with Rumpf and Gupte's experiments in sphere packings for small Reynolds numbers. The LB simulations agree well with the empirical Ergun equation for intermediate but not for small Reynolds numbers. We suggest a modified form of Ergun's equation to describe both low and intermediate Reynolds number flows. The pore-network simulations agree well with predictions from the effective-medium approximation but underestimate the permeability due to the simplified representation of the porous media. Based on LB simulations in packings with log-normal sphere-size distributions, we suggest a permeability relation with respect to the porosity, as well as the mean and standard deviation of the sphere diameter.

Reactive Melt Infiltration of Silicon-Niobium Alloys in Microporous Carbons

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1994-01-01

Studies of the reactive melt infiltration of silicon-niobium alloys in microporous carbon preforms prepared by the pyrolysis of a polymer precursor have been carried out using modeling, Differential Thermal Analysis (DTA), and melt infiltration. Mercury porosimetry results indicate a very narrow pore size distribution with virtually all the porosity within the carbon preforms open to infiltrants. The morphology and amount of the residual phases (niobium disilicide and silicon) in the infiltrated material can be tailored according to requirements by careful control of the properties (pore size and pore volume) of the porous carbon preforms and alloy composition. The average room temperature four-point flexural strength of a reaction-formed silicon carbide material (made by the infiltration of medium pore size carbon preform with Si - 5 at. % Nb alloy) is 290 +/- 40 MPa (42 +/- 6 ksi) and the fracture toughness is 3.7 +/- 0.3 MPa square root of m. The flexural strength decreases at high temperatures due to relaxation of residual thermal stresses and the presence of free silicon in the material.

Bio-inspired Murray materials for mass transfer and activity

PubMed Central

Zheng, Xianfeng; Shen, Guofang; Wang, Chao; Li, Yu; Dunphy, Darren; Hasan, Tawfique; Brinker, C. Jeffrey; Su, Bao-Lian

2017-01-01

Both plants and animals possess analogous tissues containing hierarchical networks of pores, with pore size ratios that have evolved to maximize mass transport and rates of reactions. The underlying physical principles of this optimized hierarchical design are embodied in Murray's law. However, we are yet to realize the benefit of mimicking nature's Murray networks in synthetic materials due to the challenges in fabricating vascularized structures. Here we emulate optimum natural systems following Murray's law using a bottom-up approach. Such bio-inspired materials, whose pore sizes decrease across multiple scales and finally terminate in size-invariant units like plant stems, leaf veins and vascular and respiratory systems provide hierarchical branching and precise diameter ratios for connecting multi-scale pores from macro to micro levels. Our Murray material mimics enable highly enhanced mass exchange and transfer in liquid–solid, gas–solid and electrochemical reactions and exhibit enhanced performance in photocatalysis, gas sensing and as Li-ion battery electrodes. PMID:28382972

Visualizing feasible operating ranges within tissue engineering systems using a "windows of operation" approach: a perfusion-scaffold bioreactor case study.

PubMed

McCoy, Ryan J; O'Brien, Fergal J

2012-12-01

Tissue engineering approaches to developing functional substitutes are often highly complex, multivariate systems where many aspects of the biomaterials, bio-regulatory factors or cell sources may be controlled in an effort to enhance tissue formation. Furthermore, success is based on multiple performance criteria reflecting both the quantity and quality of the tissue produced. Managing the trade-offs between different performance criteria is a challenge. A "windows of operation" tool that graphically represents feasible operating spaces to achieve user-defined levels of performance has previously been described by researchers in the bio-processing industry. This paper demonstrates the value of "windows of operation" to the tissue engineering field using a perfusion-scaffold bioreactor system as a case study. In our laboratory, perfusion bioreactor systems are utilized in the context of bone tissue engineering to enhance the osteogenic differentiation of cell-seeded scaffolds. A key challenge of such perfusion bioreactor systems is to maximize the induction of osteogenesis but minimize cell detachment from the scaffold. Two key operating variables that influence these performance criteria are the mean scaffold pore size and flow-rate. Using cyclooxygenase-2 and osteopontin gene expression levels as surrogate indicators of osteogenesis, we employed the "windows of operation" methodology to rapidly identify feasible operating ranges for the mean scaffold pore size and flow-rate that achieved user-defined levels of performance for cell detachment and differentiation. Incorporation of such tools into the tissue engineer's armory will hopefully yield a greater understanding of the highly complex systems used and help aid decision making in future translation of products from the bench top to the market place. Copyright © 2012 Wiley Periodicals, Inc.

Ultrafast selective transport of alkali metal ions in metal organic frameworks with subnanometer pores

PubMed Central

Zhang, Huacheng; Hou, Jue; Hu, Yaoxin; Wang, Peiyao; Ou, Ranwen; Jiang, Lei; Liu, Jefferson Zhe; Freeman, Benny D.; Hill, Anita J.; Wang, Huanting

2018-01-01

Porous membranes with ultrafast ion permeation and high ion selectivity are highly desirable for efficient mineral separation, water purification, and energy conversion, but it is still a huge challenge to efficiently separate monatomic ions of the same valence and similar sizes using synthetic membranes. We report metal organic framework (MOF) membranes, including ZIF-8 and UiO-66 membranes with uniform subnanometer pores consisting of angstrom-sized windows and nanometer-sized cavities for ultrafast selective transport of alkali metal ions. The angstrom-sized windows acted as ion selectivity filters for selection of alkali metal ions, whereas the nanometer-sized cavities functioned as ion conductive pores for ultrafast ion transport. The ZIF-8 and UiO-66 membranes showed a LiCl/RbCl selectivity of ~4.6 and ~1.8, respectively, which are much greater than the LiCl/RbCl selectivity of 0.6 to 0.8 measured in traditional porous membranes. Molecular dynamics simulations suggested that ultrafast and selective ion transport in ZIF-8 was associated with partial dehydration effects. This study reveals ultrafast and selective transport of monovalent ions in subnanometer MOF pores and opens up a new avenue to develop unique MOF platforms for efficient ion separations in the future. PMID:29487910

Ultrafast selective transport of alkali metal ions in metal organic frameworks with subnanometer pores.

PubMed

Zhang, Huacheng; Hou, Jue; Hu, Yaoxin; Wang, Peiyao; Ou, Ranwen; Jiang, Lei; Liu, Jefferson Zhe; Freeman, Benny D; Hill, Anita J; Wang, Huanting

2018-02-01

Porous membranes with ultrafast ion permeation and high ion selectivity are highly desirable for efficient mineral separation, water purification, and energy conversion, but it is still a huge challenge to efficiently separate monatomic ions of the same valence and similar sizes using synthetic membranes. We report metal organic framework (MOF) membranes, including ZIF-8 and UiO-66 membranes with uniform subnanometer pores consisting of angstrom-sized windows and nanometer-sized cavities for ultrafast selective transport of alkali metal ions. The angstrom-sized windows acted as ion selectivity filters for selection of alkali metal ions, whereas the nanometer-sized cavities functioned as ion conductive pores for ultrafast ion transport. The ZIF-8 and UiO-66 membranes showed a LiCl/RbCl selectivity of ~4.6 and ~1.8, respectively, which are much greater than the LiCl/RbCl selectivity of 0.6 to 0.8 measured in traditional porous membranes. Molecular dynamics simulations suggested that ultrafast and selective ion transport in ZIF-8 was associated with partial dehydration effects. This study reveals ultrafast and selective transport of monovalent ions in subnanometer MOF pores and opens up a new avenue to develop unique MOF platforms for efficient ion separations in the future.

Capillary pressure-saturation relationships for porous granular materials: Pore morphology method vs. pore unit assembly method

NASA Astrophysics Data System (ADS)

Sweijen, Thomas; Aslannejad, Hamed; Hassanizadeh, S. Majid

2017-09-01

In studies of two-phase flow in complex porous media it is often desirable to have an estimation of the capillary pressure-saturation curve prior to measurements. Therefore, we compare in this research the capability of three pore-scale approaches in reproducing experimentally measured capillary pressure-saturation curves. To do so, we have generated 12 packings of spheres that are representative of four different glass-bead packings and eight different sand packings, for which we have found experimental data on the capillary pressure-saturation curve in the literature. In generating the packings, we matched the particle size distributions and porosity values of the granular materials. We have used three different pore-scale approaches for generating the capillary pressure-saturation curves of each packing: i) the Pore Unit Assembly (PUA) method in combination with the Mayer and Stowe-Princen (MS-P) approximation for estimating the entry pressures of pore throats, ii) the PUA method in combination with the hemisphere approximation, and iii) the Pore Morphology Method (PMM) in combination with the hemisphere approximation. The three approaches were also used to produce capillary pressure-saturation curves for the coating layer of paper, used in inkjet printing. Curves for such layers are extremely difficult to determine experimentally, due to their very small thickness and the presence of extremely small pores (less than one micrometer in size). Results indicate that the PMM and PUA-hemisphere method give similar capillary pressure-saturation curves, because both methods rely on a hemisphere to represent the air-water interface. The ability of the hemisphere approximation and the MS-P approximation to reproduce correct capillary pressure seems to depend on the type of particle size distribution, with the hemisphere approximation working well for narrowly distributed granular materials.

Dependence of cell adhesion on extracellular matrix materials formed on pore bridge boundaries by nanopore opening and closing geometry.

PubMed

Kim, Sueon; Han, Dong Yeol; Chen, Zhenzhong; Lee, Won Gu

2018-04-30

In this study, we report experimental results for characterization of the growth and formation of pore bridge materials that modified the adhesion structures of cells cultured on nanomembranes with opening and closing geometry. To perform the proof-of-concept experiments, we fabricated two types of anodized alumina oxide substrates with single-sided opening (i.e., one side open, but closed at the other side) and double-sided opening (i.e., both sides open). In our experiment, we compared the densities of pores formed and of bridge materials which differently act as connective proteins depending on the size of pores. The results show that the pore opening geometry can be used to promote the net contact force between pores, resulting in the growth and formation of pore bridge materials before and after cell culture. The results also imply that the bridge materials can be used to attract the structural protrusion of filopodia that can promote the adhesion of cell-to-cell and cell-to-pore bridge. It is observed that the shape and size of cellular structures of filopodia depend on the presence of pore bridge materials. Overall, this observation brought us a significant clue that cells cultured on nanopore substrates would change the adhesion property depending on not only the formation of nanopores formed on the surface of topological substrates, but also that of pore bridge materials by its morphological growth.

Investigating the relative permeability behavior of microporosity-rich carbonates and tight sandstones with multiscale pore network models

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Stappen, Jeroen Van; Kock, Tim De; Boever, Wesley De; Boone, Marijn A.; Hoorebeke, Luc Van; Cnudde, Veerle

2016-11-01

The relative permeability behavior of rocks with wide ranges of pore sizes is in many cases still poorly understood and is difficult to model at the pore scale. In this work, we investigate the capillary pressure and relative permeability behavior of three outcrop carbonates and two tight reservoir sandstones with wide, multimodal pore size distributions. To examine how the drainage and imbibition properties of these complex rock types are influenced by the connectivity of macropores to each other and to zones with unresolved small-scale porosity, we apply a previously presented microcomputed-tomography-based multiscale pore network model to these samples. The sensitivity to the properties of the small-scale porosity is studied by performing simulations with different artificial sphere-packing-based networks as a proxy for these pores. Finally, the mixed-wet water-flooding behavior of the samples is investigated, assuming different wettability distributions for the microporosity and macroporosity. While this work is not an attempt to perform predictive modeling, it seeks to qualitatively explain the behavior of the investigated samples and illustrates some of the most recent developments in multiscale pore network modeling.

3D hierarchically porous Cu-BiOCl nanocomposite films: one-step electrochemical synthesis, structural characterization and nanomechanical and photoluminescent properties

NASA Astrophysics Data System (ADS)

Guerrero, Miguel; Pané, Salvador; Nelson, Bradley J.; Baró, Maria Dolors; Roldán, Mònica; Sort, Jordi; Pellicer, Eva

2013-11-01

Three-dimensional (3D) hierarchically porous composite Cu-BiOCl films have been prepared by a facile one-step galvanostatic electrodeposition process from acidic electrolytic solutions containing Cu(ii) and Bi(iii) chloride salts and Triton X-100. The films show spherical, micron-sized pores that spread over the whole film thickness. In turn, the pore walls are made of randomly packed BiOCl nanoplates that are assembled leaving micro-nanopore voids beneath. It is believed that Cu grows within the interstitial spaces between the hydrogen bubbles produced from the reduction of H+ ions. Then, the BiOCl sheets accommodate in the porous network defined by the Cu building blocks. The presence of Cu tends to enhance the mechanical stability of the composite material. The resulting porous Cu-BiOCl films exhibit homogeneous and stable-in-time photoluminescent response arising from the BiOCl component that spreads over the entire 3D porous structure, as demonstrated by confocal scanning laser microscopy. A broad-band emission covering the entire visible range, in the wavelength interval 450-750 nm, is obtained. The present work paves the way for the facile and controlled preparation of a new generation of photoluminescent membranes.Three-dimensional (3D) hierarchically porous composite Cu-BiOCl films have been prepared by a facile one-step galvanostatic electrodeposition process from acidic electrolytic solutions containing Cu(ii) and Bi(iii) chloride salts and Triton X-100. The films show spherical, micron-sized pores that spread over the whole film thickness. In turn, the pore walls are made of randomly packed BiOCl nanoplates that are assembled leaving micro-nanopore voids beneath. It is believed that Cu grows within the interstitial spaces between the hydrogen bubbles produced from the reduction of H+ ions. Then, the BiOCl sheets accommodate in the porous network defined by the Cu building blocks. The presence of Cu tends to enhance the mechanical stability of the composite material. The resulting porous Cu-BiOCl films exhibit homogeneous and stable-in-time photoluminescent response arising from the BiOCl component that spreads over the entire 3D porous structure, as demonstrated by confocal scanning laser microscopy. A broad-band emission covering the entire visible range, in the wavelength interval 450-750 nm, is obtained. The present work paves the way for the facile and controlled preparation of a new generation of photoluminescent membranes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03491g

Characterization of the porosity of human dental enamel and shear bond strength in vitro after variable etch times: initial findings using the BET method.

PubMed

Nguyen, Trang T; Miller, Arthur; Orellana, Maria F

2011-07-01

(1) To quantitatively characterize human enamel porosity and surface area in vitro before and after etching for variable etching times; and (2) to evaluate shear bond strength after variable etching times. Specifically, our goal was to identify the presence of any correlation between enamel porosity and shear bond strength. Pore surface area, pore volume, and pore size of enamel from extracted human teeth were analyzed by Brunauer-Emmett-Teller (BET) gas adsorption before and after etching for 15, 30, and 60 seconds with 37% phosphoric acid. Orthodontic brackets were bonded with Transbond to the samples with variable etch times and were subsequently applied to a single-plane lap shear testing system. Pore volume and surface area increased after etching for 15 and 30 seconds. At 60 seconds, this increase was less pronounced. On the contrary, pore size appears to decrease after etching. No correlation was found between variable etching times and shear strength. Samples etched for 15, 30, and 60 seconds all demonstrated clinically viable shear strength values. The BET adsorption method could be a valuable tool in enhancing our understanding of enamel characteristics. Our findings indicate that distinct quantitative changes in enamel pore architecture are evident after etching. Further testing with a larger sample size would have to be carried out for more definitive conclusions to be made.

Particle seeding enhances interconnectivity in polymeric scaffolds foamed using supercritical CO(2).

PubMed

Collins, Niki J; Bridson, Rachel H; Leeke, Gary A; Grover, Liam M

2010-03-01

Foaming using supercritical CO(2) is a well-known process for the production of polymeric scaffolds for tissue engineering. However, this method typically leads to scaffolds with low pore interconnectivity, resulting in insufficient mass transport and a heterogeneous distribution of cells. In this study, microparticulate silica was added to the polymer during processing and the effects of this particulate seeding on the interconnectivity of the pore structure and pore size distribution were investigated. Scaffolds comprising polylactide and a range of silica contents (0-50 wt.%) were produced by foaming with supercritical CO(2). Scaffold structure, pore size distributions and interconnectivity were assessed using X-ray computed microtomography. Interconnectivity was also determined through physical measurements. It was found that incorporation of increasing quantities of silica particles increased the interconnectivity of the scaffold pore structure. The pore size distribution was also reduced through the addition of silica, while total porosity was found to be largely independent of silica content. Physical measurements and those derived from X-ray computed microtomography were comparable. The conclusion drawn was that the architecture of foamed polymeric scaffolds can be advantageously manipulated through the incorporation of silica microparticles. The findings of this study further establish supercritical fluid foaming as an important tool in scaffold production and show how a previous limitation can be overcome. Copyright 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A 2D Micromodel Study of Fines Migration and Clogging Behavior in Porous Media: Implications of Fines on Methane Extraction from Hydrate-Bearing Sediments

NASA Astrophysics Data System (ADS)

Cao, S. C.; Jang, J.; Waite, W. F.; Jafari, M.; Jung, J.

2017-12-01

Fine-grained sediment, or "fines," exist nearly ubiquitously in natural sediment, even in the predominantly coarse-grained sediments that host gas hydrates. Fines within these sandy sediments can play a crucial role during gas hydrate production activities. During methane extraction, several processes can alter the mobility and clogging potential of fines: 1) fluid flow as the formation is depressurized to release methane from hydrate; 2) pore-fluid chemistry shifts as pore-fluid brine freshens due to pure water released from dissociating hydrate; 3) the presence of a moving gas/water interface as gas evolves from dissociating hydrate and moves through the reservoir toward the production well. To evaluate fines migration and clogging behavior changes resulting from methane gas production and pore-water freshening during hydrate dissociation, 2D micromodel experiments have been conducted on a selection of pure fines, pore-fluids, and micromodel pore-throat sizes. Additionally, tests have been run with and without an invading gas phase (CO2) to test the significance of a moving meniscus on fines mobility and clogging. The endmember fine particles chosen for this research include silica silt, mica, calcium carbonate, diatoms, kaolinite, illite, and bentonite (primarily made of montmorillonite). The pore fluids include deionized water, sodium chloride brine (2M concentration), and kerosene. The microfluidic pore models, used as porous media analogs, were fabricated with pore-throat widths of 40, 60, and 100 µm. Results from this research show that in addition to the expected dependence of clogging on the ratio of particle-to-pore-throat size, pore-fluid chemistry is also a significant factor because the interaction between a particular type of fine and pore fluid influences that fine's capacity to cluster, clump together and effectively increase its particle "size" relative to the pore-throat width. The presence of a moving gas/fluid meniscus increases the clogging potential regardless of fine type as the advancing meniscus tends to gather and concentrate the fines. Results show the need to identify both the type and concentration of fines prior to evaluating whether a system's clogging potential will increase or decrease as pore waters freshen during methane extraction from hydrate.

Influence of system size on the properties of a fluid adsorbed in a nanopore: Physical manifestations and methodological consequences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puibasset, Joël, E-mail: puibasset@cnrs-orleans.fr; Kierlik, Edouard, E-mail: edouard.kierlik@upmc.fr; Tarjus, Gilles, E-mail: tarjus@lptl.jussieu.fr

Hysteresis and discontinuities in the isotherms of a fluid adsorbed in a nanopore in general hamper the determination of equilibrium thermodynamic properties, even in computer simulations. A way around this has been to consider both a reservoir of small size and a pore of small extent in order to restrict the fluctuations of density and approach a classical van der Waals loop. We assess this suggestion by thoroughly studying through Monte Carlo simulations and density functional theory the influence of system size on the equilibrium configurations of the adsorbed fluid and on the resulting isotherms. We stress the importance ofmore » pore-symmetry-breaking states that even for modest pore sizes lead to discontinuous isotherms and we discuss the physical relevance of these states and the methodological consequences for computing thermodynamic quantities.« less

Investigation of pore size and energy distributions by statistical physics formalism applied to agriculture products

NASA Astrophysics Data System (ADS)

Aouaini, Fatma; Knani, Salah; Yahia, Manel Ben; Bahloul, Neila; Ben Lamine, Abdelmottaleb; Kechaou, Nabil

2015-12-01

In this paper, we present a new investigation that allows determining the pore size distribution (PSD) in a porous medium. This PSD is achieved by using the desorption isotherms of four varieties of olive leaves. This is by the means of statistical physics formalism and Kelvin's law. The results are compared with those obtained with scanning electron microscopy. The effect of temperature on the distribution function of pores has been studied. The influence of each parameter on the PSD is interpreted. A similar function of adsorption energy distribution, AED, is deduced from the PSD.

Fabrication and characterization of microsieve electrode array (µSEA) enabling cell positioning on 3D electrodes

NASA Astrophysics Data System (ADS)

Schurink, B.; Tiggelaar, R. M.; Gardeniers, J. G. E.; Luttge, R.

2017-01-01

Here the fabrication and characterization of a novel microelectrode array for electrophysiology applications is described, termed a micro sieve electrode array (µSEA). This silicon based µSEA device allows for hydrodynamic parallel positioning of single cells on 3D electrodes realized on the walls of inverted pyramidal shaped pores. To realize the µSEA, a previously realized silicon sieving structure is provided with a patterned boron doped poly-silicon, connecting the contact electrodes with the 3D sensing electrodes in the pores. A LPCVD silicon-rich silicon nitride layer was used as insulation. The selective opening of this insulation layer at the ends of the wiring lines allows to generate well-defined contact and sensing electrodes according to the layout used in commercial microelectrode array readers. The main challenge lays in the simultaneously selective etching of material at both the planar surface (contact electrode) as well as in the sieving structure containing the (3D) pores (sensing electrodes). For the generation of 3D electrodes in the pores a self-aligning technique was developed using the pore geometry to our advantage. This technique, based on sacrificial layer etching, allows for the fine tuning of the sensing electrode surface area and thus supports the positioning and coupling of single cells on the electrode surface in relation to the cell size. Furthermore, a self-aligning silicide is formed on the sensing electrodes to favour the electrical properties. Experiments were performed to demonstrate the working principle of the µSEA using different types of neuronal cells. Capture efficiency in the pores was  >70% with a 70% survival rate of the cell maintained for up to 14 DIV. The TiSi2-boron-doped-poly-silicon sensing electrodes of the µSEA were characterized, which indicated noise levels of  <15 µV and impedance values of 360 kΩ. These findings potentially allow for future electrophysiological measurements using the µSEA.

Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy.

PubMed

Karlsson, Johan; Atefyekta, Saba; Andersson, Martin

2015-01-01

The osseointegration capacity of bone-anchoring implants can be improved by the use of drugs that are administrated by an inbuilt drug delivery system. However, to attain superior control of drug delivery and to have the ability to administer drugs of varying size, including proteins, further material development of drug carriers is needed. Mesoporous materials have shown great potential in drug delivery applications to provide and maintain a drug concentration within the therapeutic window for the desired period of time. Moreover, drug delivery from coatings consisting of mesoporous titania has shown to be promising to improve healing of bone-anchoring implants. Here we report on how the delivery of an osteoporosis drug, alendronate, can be controlled by altering pore size and surface energy of mesoporous titania thin films. The pore size was varied from 3.4 nm to 7.2 nm by the use of different structure-directing templates and addition of a swelling agent. The surface energy was also altered by grafting dimethylsilane to the pore walls. The drug uptake and release profiles were monitored in situ using quartz crystal microbalance with dissipation (QCM-D) and it was shown that both pore size and surface energy had a profound effect on both the adsorption and release kinetics of alendronate. The QCM-D data provided evidence that the drug delivery from mesoporous titania films is controlled by a binding-diffusion mechanism. The yielded knowledge of release kinetics is crucial in order to improve the in vivo tissue response associated to therapeutic treatments.

Bone bonding strength of diamond-structured porous titanium-alloy implants manufactured using the electron beam-melting technique.

PubMed

Hara, Daisuke; Nakashima, Yasuharu; Sato, Taishi; Hirata, Masanobu; Kanazawa, Masayuki; Kohno, Yusuke; Yoshimoto, Kensei; Yoshihara, Yusuke; Nakamura, Akihiro; Nakao, Yumiko; Iwamoto, Yukihide

2016-02-01

The present study examined the bone bonding strength of diamond-structured porous titanium-alloy (Porous-Ti-alloy) manufactured using the electron beam-melting technique in comparison with fiber mesh-coated or rough-surfaced implants. Cylindrical implants with four different pore sizes (500, 640, 800, and 1000μm) of Porous-Ti-alloy, titanium fiber mesh (FM), and surfaces roughened by titanium arc spray (Ti-spray) were implanted into the distal femur of rabbits. Bone bonding strength and histological bone ingrowth were evaluated at 4 and 12weeks after implantation. The bone bonding strength of Porous-Ti-alloy implants (640μm pore size) increased over time from 541.4N at 4weeks to 704.6N at 12weeks and was comparable to that of FM and Ti-spray implants at both weeks. No breakage of the porous structure after mechanical testing was found with Porous-Ti-alloy implants. Histological bone ingrowth that increased with implantation time occurred along the inner structure of Porous-Ti-alloy implants. There was no difference in bone ingrowth in Porous-Ti-alloy implants with pore sizes among 500, 640, and 800μm; however, less bone ingrowth was observed with the 1000μm pore size. These results indicated Porous-Ti-alloy implants with pore size under 800μm provided biologically active and mechanically stable surface for implant fixation to bone, and had potential advantages for weight bearing orthopedic implants such as acetabular cups. Copyright © 2015 Elsevier B.V. All rights reserved.

Disposable, Autonomic, Energy-Converting Ion Channel Sensor Materials

DTIC Science & Technology

2018-07-02

variant forms well-defined pores _____________________________ 26 4.2. Another pore-forming peptide, Ceratotoxin A, displays alamethicin-like activity ...bilayer recordings to examine the activity of these compounds on the single-pore level. We plan to use modified CtxA for targeted cell killing...strongly dependent on entropy of activation . Tethering is one strategy towards achieving this goal. A manuscript regarding this work is currently in

An investigation into the effects of pore connectivity on T2 NMR relaxation

NASA Astrophysics Data System (ADS)

Ghomeshi, Shahin; Kryuchkov, Sergey; Kantzas, Apostolos

2018-04-01

Nuclear Magnetic Resonance (NMR) is a powerful technique used to characterize fluids and flow in porous media. The NMR relaxation curves are closely related to pore geometry, and the inversion of the NMR relaxometry data is known to give useful information with regards to pore size distribution (PSD) through the relative amplitudes of the fluids stored in the small and large pores. While this information is crucial, the main challenge for the successful use of the NMR measurements is the proper interpretation of the measured signals. Natural porous media patterns consist of complex pore structures with many interconnected or "coupled" regions, as well as isolated pores. This connectivity along the throats changes the relaxation distribution and in order to properly interpret this data, a thorough understanding of the effects of pore connectivity on the NMR relaxation distribution is warranted. In this paper we address two main points. The first pertains to the fact that there is a discrepancy between the relaxation distribution obtained from experiments, and the ones obtained from solving the mathematical models of diffusion process in the digitized images of the pore space. There are several reasons that may attribute to this such as the lack of a proper incorporation of surface roughness into the model. However, here we are more interested in the effects of pore connectivity and to understand why the typical NMR relaxation distribution obtained from experiments are wider, while the numerical simulations predict that a wider NMR relaxation distribution may indicate poor connectivity. Secondly, by not taking into account the pore coupling effects, from our experience in interpreting the data, we tend to underestimate the pore volume of small pores and overestimate the amplitudes in the large pores. The role of pore coupling becomes even more prominent in rocks with small pore sizes such as for example in shales, clay in sandstones, and in the microstructures of carbonates.

4D Imaging of Salt Precipitation during Evaporation from Saline Porous Media Influenced by the Particle Size Distribution

NASA Astrophysics Data System (ADS)

Norouzi Rad, M.; Shokri, N.

2014-12-01

Understanding the physics of water evaporation from saline porous media is important in many processes such as evaporation from porous media, vegetation, plant growth, biodiversity in soil, and durability of building materials. To investigate the effect of particle size distribution on the dynamics of salt precipitation in saline porous media during evaporation, we applied X-ray micro-tomography technique. Six samples of quartz sand with different grain size distributions were used in the present study enabling us to constrain the effects of particle and pore sizes on salt precipitation patterns and dynamics. The pore size distributions were computed using the pore-scale X-ray images. The packed beds were saturated with NaCl solution of 3 Molal and the X-ray imaging was continued for one day with temporal resolution of 30 min resulting in pore scale information about the evaporation and precipitation dynamics. Our results show more precipitation at the early stage of the evaporation in the case of sand with the larger particle size due to the presence of fewer evaporation sites at the surface. The presence of more preferential evaporation sites at the surface of finer sands significantly modified the patterns and thickness of the salt crust deposited on the surface such that a thinner salt crust was formed in the case of sand with smaller particle size covering larger area at the surface as opposed to the thicker patchy crusts in samples with larger particle sizes. Our results provide new insights regarding the physics of salt precipitation in porous media during evaporation.

Transverse thermal conductivity of porous materials made from aligned nano- and microcylindrical pores

NASA Astrophysics Data System (ADS)

Prasher, Ravi

2006-09-01

Nanoporous and microporous materials made from aligned cylindrical pores play important roles in present technologies and will play even bigger roles in future technologies. The insight into the phonon thermal conductivity of these materials is important and relevant in many technologies and applications. Since the mean free path of phonons can be comparable to the pore size and interpore distance, diffusion-approximation based effective medium models cannot be used to predict the thermal conductivity of these materials. Strictly speaking, the Boltzmann transport equation (BTE) must be solved to capture the ballistic nature of thermal transport; however, solving BTE in such a complex network of pores is impractical. As an alternative, we propose an approximate ballistic-diffusive microscopic effective medium model for predicting the thermal conductivity of phonons in two-dimensional nanoporous and microporous materials made from aligned cylindrical pores. The model captures the size effects due to the pore diameter and the interpore distance and reduces to diffusion-approximation based models for macroporous materials. The results are in good agreement with experimental data.

Silica incorporated membrane for wastewater based filtration

NASA Astrophysics Data System (ADS)

Fernandes, C. S.; Bilad, M. R.; Nordin, N. A. H. M.

2017-10-01

Membrane technology has long been applied for waste water treatment industries due to its numerous advantages compared to other conventional processes. However, the biggest challenge in pressure driven membrane process is membrane fouling. Fouling decreases the productivity and efficiency of the filtration, reduces the lifespan of the membrane and reduces the overall efficiency of water treatment processes. In this study, a novel membrane material is developed for water filtration. The developed membrane incorporates silica nanoparticles mainly to improve its structural properties. Membranes with different loadings of silica nanoparticles were applied in this study. The result shows an increase in clean water permeability and filterability of the membrane for treating activated sludge, microalgae solution, secondary effluent and raw sewage as feed. Adding silica into the membrane matrix does not significantly alter contact angle and membrane pore size. We believe that silica acts as an effective pore forming agent that increases the number of pores without significantly altering the pore sizes. A higher number of small pores on the surface of the membrane could reduce membrane fouling because of a low specific loading imposed to individual pores.

Tailoring Pore Size of Nitrogen-Doped Hollow Carbon Nanospheres for Confi ning Sulfur in Lithium–Sulfur Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Weidong; Wang, Chong M.; Zhang, Quiglin

Three types of nitrogen-doped hollow carbon spheres with different pore sized porous shells are prepared to investigate the performance of sulfur confinement. The reason that why no sulfur is observed in previous research is determined and it is successfully demonstrated that the sulfur/polysulfide will overflow the porous carbon during the lithiation process.

Passage of Campylobacter jejuni and Campylobacter coli subtypes through 0.45 and 0.65 µm pore size nitro-cellulose filters

USDA-ARS?s Scientific Manuscript database

Campylobacter can be difficult to recover from complex samples due to overgrowth by background bacteria. A 0.45 or 0.65 µm pore size filter overlaid on agar plates can be used as a means to separate Campylobacter from confounding non-Campylobacter cells, facilitating detection on solid plating medi...

Iron films deposited on porous alumina substrates

NASA Astrophysics Data System (ADS)

Yamada, Yasuhiro; Tanabe, Kenichi; Nishida, Naoki; Kobayashi, Yoshio

2016-12-01

Iron films were deposited on porous alumina substrates using an arc plasma gun. The pore sizes (120 - 250 nm) of the substrates were controlled by changing the temperature during the anodic oxidation of aluminum plates. Iron atoms penetrated into pores with diameters of less than 160 nm, and were stabilized by forming γ-Fe, whereas α-Fe was produced as a flat plane covering the pores. For porous alumina substrates with pore sizes larger than 200 nm, the deposited iron films contained many defects and the resulting α-Fe had smaller hyperfine magnetic fields. In addition, only a very small amount of γ-Fe was obtained. It was demonstrated that the composition and structure of an iron film can be affected by the surface morphology of the porous alumina substrate on which the film is grown.

Micropore analysis of polymer networks by gas sorption and 129Xe NMR spectroscopy: toward a better understanding of intrinsic microporosity.

PubMed

Weber, Jens; Schmidt, Johannes; Thomas, Arne; Böhlmann, Winfried

2010-10-05

The microporosity of two microporous polymer networks is investigated in detail. Both networks are based on a central spirobifluorene motif but have different linker groups, namely, imide and thiophene units. The microporosity of the networks is based on the "polymers of intrinsic microporosity (PIM)" design strategy. Nitrogen, argon, and carbon dioxide were used as sorbates in order to analyze the microporosity in greater detail. The gas sorption data was analyzed with respect to important parameters such as specific surface area, pore volume, and pore size (distribution). It is shown that the results can be strongly model dependent and swelling effects have to be regarded. (129)Xe NMR was used as an independent technique for the estimation of the average pore size of the polymer networks. The results indicate that both networks are mainly ultramicroporous (pore sizes < 0.8 nm) in the dry state, which was not expected based on the molecular design. Phase separation and network defects might influence the overall network morphology strongly. Finally, the observed swelling indicates that this "soft" microporous matter might have a different micropore size in the solvent swollen/filled state that in the dry state.

Solvent evaporation induced graphene powder with high volumetric capacitance and outstanding rate capability for supercapacitors

NASA Astrophysics Data System (ADS)

Zhang, Xiaozhe; Raj, Devaraj Vasanth; Zhou, Xufeng; Liu, Zhaoping

2018-04-01

Graphene-based electrode materials for supercapacitors usually suffer from poor volumetric performance due to the low density. The enhancement of volumetric capacitance by densification of graphene materials, however, is usually accompanied by deterioration of rate capability, as the huge contraction of pore size hinders rapid diffusion of electrolytes. Thus, it is important to develop suitable pore size in graphene materials, which can sustain fast ion diffusion and avoid excessive voids to acquire high density simultaneously for supercapacitor applications. Accordingly, we propose a simple solvent evaporation method to control the pore size of graphene powders by adjusting the surface tension of solvents. Ethanol is used instead of water to reduce the shrinkage degree of graphene powder during solvent evaporation process, due to its lower surface tension comparing with water. Followed by the assistance of mechanical compression, graphene powder having high compaction density of 1.30 g cm-3 and a large proportion of mesopores in the pore size range of 2-30 nm is obtained, which delivers high volumetric capacitance of 162 F cm-3 and exhibits outstanding rate performance of 76% capacity retention at a high current density of 100 A g-1 simultaneously.

Effect of Pore Size and Porosity on the Biomechanical Properties and Cytocompatibility of Porous NiTi Alloys

PubMed Central

Jian, Yu-Tao; Yang, Yue; Tian, Tian; Stanford, Clark; Zhang, Xin-Ping; Zhao, Ke

2015-01-01

Five types of porous Nickel-Titanium (NiTi) alloy samples of different porosities and pore sizes were fabricated. According to compressive and fracture strengths, three groups of porous NiTi alloy samples underwent further cytocompatibility experiments. Porous NiTi alloys exhibited a lower Young’s modulus (2.0 GPa ~ 0.8 GPa). Both compressive strength (108.8 MPa ~ 56.2 MPa) and fracture strength (64.6 MPa ~ 41.6 MPa) decreased gradually with increasing mean pore size (MPS). Cells grew and spread well on all porous NiTi alloy samples. Cells attached more strongly on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cell adhesion on porous NiTi alloys was correlated negatively to MPS (277.2 μm ~ 566.5 μm; p < 0.05). More cells proliferated on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cellular ALP activity on all porous NiTi alloy samples was higher than on control group and blank group (p < 0.05). The porous NiTi alloys with optimized pore size could be a potential orthopedic material. PMID:26047515

Analysis of variability in additive manufactured open cell porous structures.

PubMed

Evans, Sam; Jones, Eric; Fox, Pete; Sutcliffe, Chris

2017-06-01

In this article, a novel method of analysing build consistency of additively manufactured open cell porous structures is presented. Conventionally, methods such as micro computed tomography or scanning electron microscopy imaging have been applied to the measurement of geometric properties of porous material; however, high costs and low speeds make them unsuitable for analysing high volumes of components. Recent advances in the image-based analysis of open cell structures have opened up the possibility of qualifying variation in manufacturing of porous material. Here, a photogrammetric method of measurement, employing image analysis to extract values for geometric properties, is used to investigate the variation between identically designed porous samples measuring changes in material thickness and pore size, both intra- and inter-build. Following the measurement of 125 samples, intra-build material thickness showed variation of ±12%, and pore size ±4% of the mean measured values across five builds. Inter-build material thickness and pore size showed mean ranges higher than those of intra-build, ±16% and ±6% of the mean material thickness and pore size, respectively. Acquired measurements created baseline variation values and demonstrated techniques suitable for tracking build deviation and inspecting additively manufactured porous structures to indicate unwanted process fluctuations.

Methods to control ectomycorrhizal colonization: effectiveness of chemical and physical barriers.

PubMed

Teste, François P; Karst, Justine; Jones, Melanie D; Simard, Suzanne W; Durall, Daniel M

2006-12-01

We conducted greenhouse experiments using Douglas-fir (Pseudotsuga menziesii var. glauca) seedlings where chemical methods (fungicides) were used to prevent ectomycorrhizal colonization of single seedlings or physical methods (mesh barriers) were used to prevent formation of mycorrhizal connections between neighboring seedlings. These methods were chosen for their ease of application in the field. We applied the fungicides, Topas (nonspecific) and Senator (ascomycete specific), separately and in combination at different concentrations and application frequencies to seedlings grown in unsterilized forest soils. Additionally, we assessed the ability of hyphae to penetrate mesh barriers of various pore sizes (0.2, 1, 20, and 500 microm) to form mycorrhizas on roots of neighboring seedlings. Ectomycorrhizal colonization was reduced by approximately 55% with the application of Topas at 0.5 g l(-1). Meshes with pore sizes of 0.2 and 1 microm were effective in preventing the formation of mycorrhizas via hyphal growth across the mesh barriers. Hence, meshes in this range of pore sizes could also be used to prevent the formation of common mycorrhizal networks in the field. Depending on the ecological question of interest, Topas or the employment of mesh with pore sizes <1 microm are suitable for restricting mycorrhization in the field.

Microfabricated biocapsules for the immunoisolation of pancreatic islets of Langerhans

NASA Astrophysics Data System (ADS)

Desai, Tejal Ashwin

1998-08-01

A silicon-based microfabricated biocapsule was developed and evaluated for use in the immunoisolation of transplanted cells, specifically pancreatic islets of Langerhans for the treatment of Type I diabetes. The transplantation of cells with specific functions is a promising therapy for a wide variety of pathologies including diabetes, Parkinson's, and hemophilia. Such transplanted cells, however, are sensitive to both cellular and humoral immune rejection as well as damage by autoimmune activity, without chronic immunosuppression. The research presented in this dissertation investigated whether microfabricated silicon-based biocapsules, with uniform membrane pore sizes in the tens of nanometer range, could provide an immunoprotective environment for pancreatic islets and other insulin-secreting cell lines, while maintaining cell viability and functionality. By utilizing fabrication techniques commonly employed in the microelectronics industry (MEMS), membranes were fabricated with precisely controlled and uniform pore sizes, allowing the optimization of biocapsule membrane parameters for the encapsulation of specific hormone-secreting cell types. The biocapsule-forming process employed bulk micromachining to define cell-containing chambers within single crystalline silicon wafers. These chambers interface with the surrounding biological environment through polycrystalline silicon filter membranes, which were surface micromachined to present a high density of uniform pores to allow sufficient permeability to oxygen, glucose, and insulin. Both in vitro and in vivo experiments established the biocompatibility of the microfabricated biocapsule, and demonstrated that encapsulated cells could live and function normally in terms of insulin-secretion within microfabricated environments for extended periods of time. This novel research shows the potential of using microfabricated biocapsules for the encapsulation of several different cell xenografts. The semipermeability of microfabricated biocapsules, their biocompatibility, along with their thermal and chemical stability, may provide an improved encapsulation device for the immunoisolation of cell xenografts in hormone-replacement and cell-based therapies.

Hybrid braided 3-D scaffold for bioartificial liver assist devices.

PubMed

Hoque, M E; Mao, H Q; Ramakrishna, S

2007-01-01

Three-dimensional ex vivo hepatocyte culture is a tissue-engineering approach to improve the treatment of liver disease. The extracorporeal bioartificial liver (BAL) assists devices that are used in patients until they either recover or receive a liver transplant. The 3-D scaffold plays a key role in the design of bioreactor that is the most important component of the BAL. Presently available 3-D scaffolds used in BAL have shown good performance. However, existing scaffolds are considered to be less than ideal in terms of high-density cultures of hepatocytes maintaining long-term metabolic functions. This study aims to develop a 3-D hybrid scaffold for a BAL support system that would facilitate high-density hepatocyte anchorage with long-term metabolic functions. The scaffolds were fabricated by interlacing polyethylene terephthalate (PET) fibers onto the polysulfone hollow fibers utilizing a modern microbraiding technique. Scaffolds with various pore sizes and porosities were developed by varying braiding angle which was controlled by the gear ratio of the microbraiding machine. The morphological characteristics (pore size and porosity) of the scaffolds were found to be regulated by the gear ratio. Smaller braiding angle yields larger pore and higher porosity. On the other hand, a larger braiding angle causes smaller pore and lower porosity. In hepatocyte culture it was investigated how the morphological characteristics (pore size and porosity) of scaffolds influenced the cell anchorage and metabolic functions. Scaffolds with larger pores and higher porosity resulted in more cell anchorage and higher cellular functions, like albumin and urea secretion, compared to that of smaller pores and lower porosity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Jian; Vemuri, Rama S.; Estevez, Luis

Metal–organic frameworks (MOFs) are found to be promising sorbents for adsorption cooling applications. Using organic ligands with 1, 2, and 3 phenylene rings, we construct moisture-stable Ni-MOF-74 members with adjustable pore apertures. These pore-engineered materials exhibit excellent sorption capabilities towards water and fluorocarbons. The adsorption patterns for these materials differ significantly and are attributed to variances in the hydrophobic/hydrophilic pore character, associated with differences in pore size. Complementary ex situ characterizations and in situ FTIR spectra are deployed to understand the correlations between the mechanisms of gas loadings and the pore environment of the MOFs.

Enhanced viability of corneal epithelial cells for efficient transport/storage using a structurally modified calcium alginate hydrogel.

PubMed

Wright, Bernice; Cave, Richard A; Cook, Joseph P; Khutoryanskiy, Vitaliy V; Mi, Shengli; Chen, Bo; Leyland, Martin; Connon, Che J

2012-05-01

Therapeutic limbal epithelial stem cells could be managed more efficiently if clinically validated batches were transported for 'on-demand' use. In this study, corneal epithelial cell viability in calcium alginate hydrogels was examined under cell culture, ambient and chilled conditions for up to 7 days. Cell viability improved as gel internal pore size increased, and was further enhanced with modification of the gel from a mass to a thin disc. Ambient storage conditions were optimal for supporting cell viability in gel discs. Cell viability in gel discs was significantly enhanced with increases in pore size mediated by hydroxyethyl cellulose. Our novel methodology of controlling alginate gel shape and pore size together provides a more practical and economical alternative to established corneal tissue/cell storage methods.

Water Desalination Using Nanoporous Single-Layer Graphene with Tunable Pore Size

DOE PAGES

Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; ...

2015-03-23

Graphene has great potential to serve as a separation membrane due to its unique properties such as chemical and mechanical stability, flexibility and most importantly its one-atom thickness. In this study, we demonstrate first experimental evidence of the use of single-layer porous graphene as a desalination membrane. Nanometer-sized pores are introduced into single layer graphene using a convenient oxygen plasma etching process that permits tuning of the pore size. The resulting porous graphene membrane exhibited high rejection of salt ions and rapid water transport, thus functioning as an efficient water desalination membrane. Salt rejection selectivity of nearly 100% and exceptionallymore » high water fluxes exceeding 105 g m-2 s-1 at 40 C were measured using saturated water vapor as a driving force.« less

Fabrication of Controllable Pore and Particle Size of Mesoporous Silica Nanoparticles via a Liquid-phase Synthesis Method and Its Absorption Characteristics

NASA Astrophysics Data System (ADS)

Nandiyanto, Asep Bayu Dani; Iskandar, Ferry; Okuyama, Kikuo

2011-12-01

Monodisperse spherical mesoporous silica nanoparticles were successfully synthesized using a liquid-phase synthesis method. The result showed particles with controllable pore size from several to tens nanometers with outer diameter of several tens nanometers. The ability in the control of pore size and outer diameter was altered by adjusting the precursor solution ratios. In addition, we have conducted the adsorption ability of the prepared particles. The result showed that large organic molecules were well-absorbed to the prepared silica porous particles, in which this result was not obtained when using commercial dense silica particle and/or hollow silica particle. With this result, the prepared mesoporous silica particles may be used efficiently in various applications, such as sensors, pharmaceuticals, environmentally sensitive pursuits, etc.

A Model for Hydraulic Properties Based on Angular Pores with Lognormal Size Distribution

NASA Astrophysics Data System (ADS)

Durner, W.; Diamantopoulos, E.

2014-12-01

Soil water retention and unsaturated hydraulic conductivity curves are mandatory for modeling water flow in soils. It is a common approach to measure few points of the water retention curve and to calculate the hydraulic conductivity curve by assuming that the soil can be represented as a bundle of capillary tubes. Both curves are then used to predict water flow at larger spatial scales. However, the predictive power of these curves is often very limited. This can be very easily illustrated if we measure the soil hydraulic properties (SHPs) for a drainage experiment and then use these properties to predict the water flow in the case of imbibition. Further complications arise from the incomplete wetting of water at the solid matrix which results in finite values of the contact angles between the solid-water-air interfaces. To address these problems we present a physically-based model for hysteretic SHPs. This model is based on bundles of angular pores. Hysteresis for individual pores is caused by (i) different snap-off pressures during filling and emptying of single angular pores and (ii) by different advancing and receding contact angles for fluids that are not perfectly wettable. We derive a model of hydraulic conductivity as a function of contact angle by assuming flow perpendicular to pore cross sections and present closed-form expressions for both the sample scale water retention and hydraulic conductivity function by assuming a log-normal statistical distribution of pore size. We tested the new model against drainage and imbibition experiments for various sandy materials which were conducted with various liquids of differing wettability. The model described both imbibition and drainage experiments very well by assuming a unique pore size distribution of the sample and a zero contact angle for the perfectly wetting liquid. Eventually, we see the possibility to relate the particle size distribution with a model which describes the SHPs.

Nanometre-sized pores in coal: Variations between coal basins and coal origin

USGS Publications Warehouse

Sakurovs, Richard; Koval, Lukas; Grigore, Mihaela; Sokolava, Anna; Ruppert, Leslie F.; Melnichenko, Yuri B.

2018-01-01

We have used small angle neutron scattering (SANS) to investigate the differences in methane and hexane penetration in pores in bituminous coal samples from the U.S., Canada, South Africa, and China, and maceral concentrates from Australian coals. This work is an extension of previous work that showed consistent differences between the extent of penetration by methane into 10–20 nm size pores in inertinite in bituminous coals from Australia, North America and Poland.In this study we have confirmed that there are differences in the response of inertinite to methane and hexane penetration in coals sourced from different coal basins. Inertinite in Permian Australian coals generally has relatively high numbers of pores in the 2.5–250 nm size range and the pores are highly penetrable by methane and hexane; coals sourced from Western Canada had similar penetrability to these Australian coals. However, the penetrability of methane and hexane into inertinite from the Australian Illawarra Coal Measures (also Permian) is substantially less than that of the other Australian coals; there are about 80% fewer 12 nm pores in Illawarra inertinite compared to the other Australian coals examined. The inertinite in coals sourced from South Africa and China had accessibility intermediate between the Illawarra coals and the other Australian coals.The extent of hexane penetration was 10–20% less than CD4 penetration into the same coal and this difference was most pronounced in the 5–50 nm pore size range. Hexane and methane penetrability into the coals showed similar trends with inertinite content.The observed variations in inertinite porosity between coals from different coal regions and coal basins may explain why previous studies differ in their observations of the relationships between gas sorption behavior, permeability, porosity, and maceral composition. These variations are not simply a demarcation between Northern and Southern Hemisphere coals.

Numerical Simulation of the Freeze-Thaw Behavior of Mortar Containing Deicing Salt Solution

PubMed Central

Esmaeeli, Hadi S.; Farnam, Yaghoob; Bentz, Dale P.; Zavattieri, Pablo D.; Weiss, Jason

2016-01-01

This paper presents a one-dimensional finite difference model that is developed to describe the freeze-thaw behavior of an air-entrained mortar containing deicing salt solution. A phenomenological model is used to predict the temperature and the heat flow for mortar specimens during cooling and heating. Phase transformations associated with the freezing/melting of water/ice or transition of the eutectic solution from liquid to solid are included in this phenomenological model. The lever rule is used to calculate the quantity of solution that undergoes the phase transformation, thereby simulating the energy released/absorbed during phase transformation. Undercooling and pore size effects are considered in the numerical model. To investigate the effect of pore size distribution, this distribution is considered using the Gibbs-Thomson equation in a saturated mortar specimen. For an air-entrained mortar, the impact of considering pore size (and curvature) on freezing was relatively insignificant; however the impact of pore size is much more significant during melting. The fluid inside pores smaller than 5 nm (i.e., gel pores) has a relatively small contribution in the macroscopic freeze-thaw behavior of mortar specimens within the temperature range used in this study (i.e., +24 °C to −35 °C), and can therefore be neglected for the macroscopic freeze-thaw simulations. A heat sink term is utilized to simulate the heat dissipation during phase transformations. Data from experiments performed using a low-temperature longitudinal guarded comparative calorimeter (LGCC) on mortar specimens fully saturated with various concentration NaCl solutions or partially saturated with water is compared to the numerical results and a promising agreement is generally obtained. PMID:28082830

Neutron Scattering Studies of Liquid on or Confined in Nano- and Mesoporous Carbons, Including Carbide-Derived Carbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wesolowski, David J

2014-07-01

This project involved the synthesis of microporous graphitic-carbon powders with subnanometer average pore size, and very narrow pore size distributions, and the use of these materials in experimental studies of pore-fluid structure and dynamics. Samples of carbide-derived carbon powder, synthesized by extraction of the metal cations from TiC by a high temperature chlorination process, followed by high temperature vacuum annealing, were prepared by Ranjan Dash and his associates at CRADA partner Y-Carbon, Inc. The resulting material had average pore sizes ranging from 5 to 8 . These powders were used in two experiments conducted by researchers involved in the Energymore » Frontier Research Center Directed by David J. Wesolowski at ORNL, the Fluid Interface Reactions, Structures and Transport (FIRST) Center. FIRST-funded researchers at Drexel University collaborated with scientists at the Paul Scherrer Institute, Switzerland, to measure the expansion and contraction of the microporous carbon particles during charging and discharging of supercapactor electrodes composed of these particles (Hantell et al., 2011, Electrochemistry Communications, v. 13, pp. 1221-1224.) in an electrolyte composed of tetraethylammonium tetrafluoroborate dissolved in acetonitrile. In the second experiment, researchers at Oak Ridge National Laboratory and Drexel University conducted quasielastic neutron scattering studies of the diffusional dynamics of water imbibed into the micropores of the same material (Chathoth et al., 2011, EuroPhysics Journal, v. 95, pp. 56001/1-6). These studies helped to establish the role of pores approaching the size of the solvent and dissolved ions in altering diffusional dynamics, ion transport and physical response of conducting substrates to ion desolvation and entry into subnamometer pores.« less

Facial skin pores: a multiethnic study

PubMed Central

Flament, Frederic; Francois, Ghislain; Qiu, Huixia; Ye, Chengda; Hanaya, Tomoo; Batisse, Dominique; Cointereau-Chardon, Suzy; Seixas, Mirela Donato Gianeti; Dal Belo, Susi Elaine; Bazin, Roland

2015-01-01

Skin pores (SP), as they are called by laymen, are common and benign features mostly located on the face (nose, cheeks, etc) that generate many aesthetic concerns or complaints. Despite the prevalence of skin pores, related literature is scarce. With the aim of describing the prevalence of skin pores and anatomic features among ethnic groups, a dermatoscopic instrument, using polarized lighting, coupled to a digital camera recorded the major features of skin pores (size, density, coverage) on the cheeks of 2,585 women in different countries and continents. A detection threshold of 250 μm, correlated to clinical scorings by experts, was input into a specific software to further allow for automatic counting of the SP density (N/cm2) and determination of their respective sizes in mm2. Integrating both criteria also led to establishing the relative part of the skin surface (as a percentage) that is actually covered by SP on cheeks. The results showed that the values of respective sizes, densities, and skin coverage: 1) were recorded in all studied subjects; 2) varied greatly with ethnicity; 3) plateaued with age in most cases; and 4) globally refected self-assessment by subjects, in particular those who self-declare having “enlarged pores” like Brazilian women. Inversely, Chinese women were clearly distinct from other ethnicities in having very low density and sizes. Analyzing the present results suggests that facial skin pore’s morphology as perceived by human eye less result from functional criteria of associated appendages such as sebaceous glands. To what extent skin pores may be viewed as additional criteria of a photo-altered skin is an issue to be further addressed. PMID:25733918

Numerical Simulation of the Freeze-Thaw Behavior of Mortar Containing Deicing Salt Solution.

PubMed

Esmaeeli, Hadi S; Farnam, Yaghoob; Bentz, Dale P; Zavattieri, Pablo D; Weiss, Jason

2017-02-01

This paper presents a one-dimensional finite difference model that is developed to describe the freeze-thaw behavior of an air-entrained mortar containing deicing salt solution. A phenomenological model is used to predict the temperature and the heat flow for mortar specimens during cooling and heating. Phase transformations associated with the freezing/melting of water/ice or transition of the eutectic solution from liquid to solid are included in this phenomenological model. The lever rule is used to calculate the quantity of solution that undergoes the phase transformation, thereby simulating the energy released/absorbed during phase transformation. Undercooling and pore size effects are considered in the numerical model. To investigate the effect of pore size distribution, this distribution is considered using the Gibbs-Thomson equation in a saturated mortar specimen. For an air-entrained mortar, the impact of considering pore size (and curvature) on freezing was relatively insignificant; however the impact of pore size is much more significant during melting. The fluid inside pores smaller than 5 nm (i.e., gel pores) has a relatively small contribution in the macroscopic freeze-thaw behavior of mortar specimens within the temperature range used in this study (i.e., +24 °C to -35 °C), and can therefore be neglected for the macroscopic freeze-thaw simulations. A heat sink term is utilized to simulate the heat dissipation during phase transformations. Data from experiments performed using a low-temperature longitudinal guarded comparative calorimeter (LGCC) on mortar specimens fully saturated with various concentration NaCl solutions or partially saturated with water is compared to the numerical results and a promising agreement is generally obtained.

Pore-scale simulations of drainage in granular materials: Finite size effects and the representative elementary volume

NASA Astrophysics Data System (ADS)

Yuan, Chao; Chareyre, Bruno; Darve, Félix

2016-09-01

A pore-scale model is introduced for two-phase flow in dense packings of polydisperse spheres. The model is developed as a component of a more general hydromechanical coupling framework based on the discrete element method, which will be elaborated in future papers and will apply to various processes of interest in soil science, in geomechanics and in oil and gas production. Here the emphasis is on the generation of a network of pores mapping the void space between spherical grains, and the definition of local criteria governing the primary drainage process. The pore space is decomposed by Regular Triangulation, from which a set of pores connected by throats are identified. A local entry capillary pressure is evaluated for each throat, based on the balance of capillary pressure and surface tension at equilibrium. The model reflects the possible entrapment of disconnected patches of the receding wetting phase. It is validated by a comparison with drainage experiments. In the last part of the paper, a series of simulations are reported to illustrate size and boundary effects, key questions when studying small samples made of spherical particles be it in simulations or experiments. Repeated tests on samples of different sizes give evolution of water content which are not only scattered but also strongly biased for small sample sizes. More than 20,000 spheres are needed to reduce the bias on saturation below 0.02. Additional statistics are generated by subsampling a large sample of 64,000 spheres. They suggest that the minimal sampling volume for evaluating saturation is one hundred times greater that the sampling volume needed for measuring porosity with the same accuracy. This requirement in terms of sample size induces a need for efficient computer codes. The method described herein has a low algorithmic complexity in order to satisfy this requirement. It will be well suited to further developments toward coupled flow-deformation problems in which evolution of the microstructure require frequent updates of the pore network.

Ultrafiltration and nanofiltration membrane fouling by natural organic matter: Mechanisms and mitigation by pre-ozonation and pH.

PubMed

Yu, Wenzheng; Liu, Teng; Crawshaw, John; Liu, Ting; Graham, Nigel

2018-08-01

The fouling of ultrafiltration (UF) and nanofiltration (NF) membranes during the treatment of surface waters continues to be of concern and the particular role of natural organic matter (NOM) requires further investigation. In this study the effect of pH and surface charge on membrane fouling during the treatment of samples of a representative surface water (Hyde Park recreational lake) were evaluated, together with the impact of pre-ozonation. While biopolymers in the surface water could be removed by the UF membrane, smaller molecular weight (MW) fractions of NOM were poorly removed, confirming the importance of membrane pore size. For NF membranes the removal of smaller MW fractions (800 Da-10 kDa) was less than expected from their pore size; however, nearly all of the hydrophobic, humic-type substances could be removed by the hydrophilic NF membranes for all MW distributions (greater than 90%). The results indicated the importance of the charge and hydrophilic nature of the NOM. Thus, the hydrophilic NF membrane could remove the hydrophobic organic matter, but not the hydrophilic substances. Increasing charge effects (more negative zeta potentials) with increasing solution pH were found to enhance organics removal and reduce fouling (flux decline), most likely through greater membrane surface repulsion. Pre-ozonation of the surface water increased the hydrophilic fraction and anionic charge of NOM and altered their size distributions. This resulted in a decreased fouling (less flux decline) for the UF and smaller pore NF, but a slight increase in fouling for the larger pore NF. The differences in the NF behavior are believed to relate to the relative sizes of ozonated organic fractions and the NF pores; a similar size of ozonated organic fractions and the NF pores causes significant membrane fouling. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Impact of geometrical properties on permeability and fluid phase distribution in porous media

NASA Astrophysics Data System (ADS)

Lehmann, P.; Berchtold, M.; Ahrenholz, B.; Tölke, J.; Kaestner, A.; Krafczyk, M.; Flühler, H.; Künsch, H. R.

2008-09-01

To predict fluid phase distribution in porous media, the effect of geometric properties on flow processes must be understood. In this study, we analyze the effect of volume, surface, curvature and connectivity (the four Minkowski functionals) on the hydraulic conductivity and the water retention curve. For that purpose, we generated 12 artificial structures with 800 3 voxels (the units of a 3D image) and compared them with a scanned sand sample of the same size. The structures were generated with a Boolean model based on a random distribution of overlapping ellipsoids whose size and shape were chosen to fulfill the criteria of the measured functionals. The pore structure of sand material was mapped with X-rays from synchrotrons. To analyze the effect of geometry on water flow and fluid distribution we carried out three types of analysis: Firstly, we computed geometrical properties like chord length, distance from the solids, pore size distribution and the Minkowski functionals as a function of pore size. Secondly, the fluid phase distribution as a function of the applied pressure was calculated with a morphological pore network model. Thirdly, the permeability was determined using a state-of-the-art lattice-Boltzmann method. For the simulated structure with the true Minkowski functionals the pores were larger and the computed air-entry value of the artificial medium was reduced to 85% of the value obtained from the scanned sample. The computed permeability for the geometry with the four fitted Minkowski functionals was equal to the permeability of the scanned image. The permeability was much more sensitive to the volume and surface than to curvature and connectivity of the medium. We conclude that the Minkowski functionals are not sufficient to characterize the geometrical properties of a porous structure that are relevant for the distribution of two fluid phases. Depending on the procedure to generate artificial structures with predefined Minkowski functionals, structures differing in pore size distribution can be obtained.

Physically-based model of soil hydraulic properties accounting for variable contact angle and its effect on hysteresis

NASA Astrophysics Data System (ADS)

Diamantopoulos, Efstathios; Durner, Wolfgang

2013-09-01

The description of soil water movement in the unsaturated zone requires the knowledge of the soil hydraulic properties, i.e. the water retention and the hydraulic conductivity function. A great amount of parameterizations for this can be found in the literature, the majority of which represent the complex pore space of soils as a bundle of cylindrical capillary tubes of various sizes. The assumption of zero contact angles between water and surface of the grains is also made. However, these assumptions limit the predictive capabilities of these models, leading often to errors in the prediction of water dynamics in soils. We present a pore-scale analysis for equilibrium liquid configuration in angular pores taking pore-scale hysteresis and the effect of contact angle into account. Furthermore, we propose a derivation of the hydraulic conductivity function, again as a function of the contact angle. An additional parameter was added to the conductivity function in order take into account effects which are not included in the analysis. Finally, we upscale our model from the pore to the sample scale by assuming a gamma statistical distribution of the pore sizes. Closed-form expressions are derived for both water retention and conductivity functions. The new model was tested against experimental data from multistep inflow/outflow (MSI/MSO) experiments for a sandy material. They were conducted using ethanol and water as the wetting liquid. Ethanol was assumed to form a zero contact angle with the soil grains. By keeping constant the parameters fitted from the ethanol MSO experiment we could predict the ethanol MSI dynamics based on our theory. Furthermore, by keeping constant the pore size distribution parameters from the ethanol experiments we could also predict very well the water dynamics for the MSO experiment. Lastly, we could predict the imbibition dynamics for the water MSI experiment by introducing a finite value of the contact angle. Most importantly, the predictions for both ethanol and water MSI/MSO dynamics were made by assuming a unique pore-size distribution.

Application of real rock pore-threat statistics to a regular pore network model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rakibul, M.; Sarker, H.; McIntyre, D.

2011-01-01

This work reports the application of real rock statistical data to a previously developed regular pore network model in an attempt to produce an accurate simulation tool with low computational overhead. A core plug from the St. Peter Sandstone formation in Indiana was scanned with a high resolution micro CT scanner. The pore-throat statistics of the three-dimensional reconstructed rock were extracted and the distribution of the pore-throat sizes was applied to the regular pore network model. In order to keep the equivalent model regular, only the throat area or the throat radius was varied. Ten realizations of randomly distributed throatmore » sizes were generated to simulate the drainage process and relative permeability was calculated and compared with the experimentally determined values of the original rock sample. The numerical and experimental procedures are explained in detail and the performance of the model in relation to the experimental data is discussed and analyzed. Petrophysical properties such as relative permeability are important in many applied fields such as production of petroleum fluids, enhanced oil recovery, carbon dioxide sequestration, ground water flow, etc. Relative permeability data are used for a wide range of conventional reservoir engineering calculations and in numerical reservoir simulation. Two-phase oil water relative permeability data are generated on the same core plug from both pore network model and experimental procedure. The shape and size of the relative permeability curves were compared and analyzed and good match has been observed for wetting phase relative permeability but for non-wetting phase, simulation results were found to be deviated from the experimental ones. Efforts to determine petrophysical properties of rocks using numerical techniques are to eliminate the necessity of regular core analysis, which can be time consuming and expensive. So a numerical technique is expected to be fast and to produce reliable results. In applied engineering, sometimes quick result with reasonable accuracy is acceptable than the more time consuming results. Present work is an effort to check the accuracy and validity of a previously developed pore network model for obtaining important petrophysical properties of rocks based on cutting-sized sample data.« less

Application of real rock pore-throat statistics to a regular pore network model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarker, M.R.; McIntyre, D.; Ferer, M.

2011-01-01

This work reports the application of real rock statistical data to a previously developed regular pore network model in an attempt to produce an accurate simulation tool with low computational overhead. A core plug from the St. Peter Sandstone formation in Indiana was scanned with a high resolution micro CT scanner. The pore-throat statistics of the three-dimensional reconstructed rock were extracted and the distribution of the pore-throat sizes was applied to the regular pore network model. In order to keep the equivalent model regular, only the throat area or the throat radius was varied. Ten realizations of randomly distributed throatmore » sizes were generated to simulate the drainage process and relative permeability was calculated and compared with the experimentally determined values of the original rock sample. The numerical and experimental procedures are explained in detail and the performance of the model in relation to the experimental data is discussed and analyzed. Petrophysical properties such as relative permeability are important in many applied fields such as production of petroleum fluids, enhanced oil recovery, carbon dioxide sequestration, ground water flow, etc. Relative permeability data are used for a wide range of conventional reservoir engineering calculations and in numerical reservoir simulation. Two-phase oil water relative permeability data are generated on the same core plug from both pore network model and experimental procedure. The shape and size of the relative permeability curves were compared and analyzed and good match has been observed for wetting phase relative permeability but for non-wetting phase, simulation results were found to be deviated from the experimental ones. Efforts to determine petrophysical properties of rocks using numerical techniques are to eliminate the necessity of regular core analysis, which can be time consuming and expensive. So a numerical technique is expected to be fast and to produce reliable results. In applied engineering, sometimes quick result with reasonable accuracy is acceptable than the more time consuming results. Present work is an effort to check the accuracy and validity of a previously developed pore network model for obtaining important petrophysical properties of rocks based on cutting-sized sample data. Introduction« less

A New Dual-Pore Formation Factor Model: A Percolation Network Study and Comparison to Experimental Data

NASA Astrophysics Data System (ADS)

Tang, Y. B.; Li, M.; Bernabe, Y.

2014-12-01

We modeled the electrical transport behavior of dual-pore carbonate rocks in this paper. Based on experimental data of a carbonate reservoir in China, we simply considered the low porosity samples equivalent to the matrix (micro-pore system) of the high porosity samples. For modeling the bimodal porous media, we considered that the matrix is homogeneous and interconnected. The connectivity and the pore size distribution of macro-pore system are varied randomly. Both pore systems are supposed to act electrically in parallel, connected at the nodes, where the fluid exchange takes place, an approach previously used by Bauer et al. (2012). Then, the effect of the properties of matrix, the pore size distribution and connectivity of macro-pore system on petrophysical properties of carbonates can be investigated. We simulated electrical current through networks in three-dimensional simple cubic (SC) and body-center cubic (BCC) with different coordination numbers and different pipe radius distributions of macro-pore system. Based on the simulation results, we found that the formation factor obeys a "universal" scaling relationship (i.e. independent of lattice type), 1/F∝eγz, where γ is a function of the normalized standard deviation of the pore radius distribution of macro-pore system and z is the coordination number of macro-pore system. This relationship is different from the classic "universal power law" in percolation theory. A formation factor model was inferred on the basis of the scaling relationship mentioned above and several scale-invariant quantities (such as hydraulic radius rH and throat length l of macro-pore). Several methods were developed to estimate corresponding parameters of the new model with conventional core analyses. It was satisfactorily tested against experimental data, including some published experimental data. Furthermore, the relationship between water saturation and resistivity in dual-pore carbonates was discussed based on the new model.

Multiscale Analysis of Soil Porosity from Hg Injection Curves in Soils from Minas Gerais, Brazil

NASA Astrophysics Data System (ADS)

Vidal Vázquez, E.; Miranda, J. G. V.; Paz-Ferreiro, J.

2012-04-01

The soil pore space is a continuum extremely variable in size, including structures smaller than nanometres and as large as macropores or cracks with millimetres or even centimetres size. Pore size distributions (PSDs) affects important soil functions, such as transmission and storage of water, and root growth. Direct and indirect measurements of PSDs are currently used to characterize soil structure. Mercury injection porosimetry is useful for assessing equivalent pore size diameters in the range from about 0,5 nm to 100 μm. Here, the multifractal formalism was employed to describe Hg injection curves measured in duplicate samples collected on 54 horizons from 19 profiles in Minas Gerais state, Brazil. Ten of the studied profiles were classified as Ferralsols (Latosols, Oxisols). Besides these, other wide different soil groups were sampled, including Nitisol, Acrisol, Alisol, Luvisol, Planosol, Cambisol, Andosol and Leptosol. Clay content varied from 4 to 86% and pore volume in the range from 100 to 0.005 μm was between 5.52 a 53.76 cm3100g-1. All the horizons taken on Ferralsols and Nitisols as well as in Bt argic horizons from Acrisol Alisol, Luvisol and Planosol clearly showed a bimodal pore size distribution. Pore volume in the range from 100 to 0.005 μm and microporosity (0,2-0.005 μm) showed a significant relationship with clay content an Al2O3. All the Hg injection data sets studied soil showed remarkably good scaling trends and could be fitted reasonably well with multifractal models. The capacity dimensions, D0, was not significantly different from the Euclidean dimension. The entropy dimension, D1, varied from 0.590 to 0.946 , whereas the Hölder exponent of order zero, α0was between 1.027 and 1.451, and these two parameters showed a lineal negatives relationship, as expected. The highest D1 values, ranging from 0.913 to 0.980, were obtained for the Leptosol, whereas the lowest D1 values, ranging from 0.641 to 0.766 corresponded to the Nitisol. This results reflect that most of the measure concentrated in a small size domain for the horizons sampled from the Nitisol, whereas for the Leptosol the measure was more evenly distributed. In general, multifractal indices have been found to be useful for assessing differences in pore size distributions of the studied soil types.