Calculated Pore Radius Research Articles

Characterization of wood micromorphology from gas permeability measurements

This paper presents a method for identifying wood morphological parameters from gas apparent permeability measurements. The apparent permeability at a given mean pressure is typically determined from the pressure relaxation kinetics when the gas permeates through the wood sample between two compartments which have different initial pressures. Using the proposed set-up, apparent permeability values ranging from 10−10 to 10−18 m2 can be measured with a mean gas pressure varying from 2 bar down to 35 mbar. Morphological and topological parameters are then identified from the variations in apparent permeability as a function of the mean gas pressure using a pore network model. The network consists of elements such as pipes or orifices connected in series or in parallel. The rarefied gas flow is described in each element by an appropriate model, and the unknowns are determined by an inverse method. This approach was first applied to track-etched polycarbonate membranes for validation purposes. The calculated pore radius and pore density values were compared to observations by environmental scanning electron microscopy. Softwood specimens were then investigated. The mean radius of the pores controlling permeability in the longitudinal and tangential directions was determined and found to be in good agreement with literature data.

Pore radius estimation based on organic solute molecular shape and effects of pressure on pore radius for a reverse osmosis membrane

The pore radius of a reverse osmosis membrane was evaluated by considering the molecular shape of uncharged organic solutes. Molecular shape was approximated by a rectangular parallelepiped; molecular length ( L) and molecular width ( MWd) were used as shape parameters. The steric partition factor of a solute was calculated from L and MWd, and the Stokes radius and diffusivity were estimated from MWd. Twenty-four alcohols and polyhydric alcohols were used as probe solutes, and pore radius was estimated by both non-spherical and spherical models: a uniform pore-size model was used. The non-spherical model gave better correspondence between calculated and observed rejections for ES10 membrane, and the calculated pore radius (0.506 nm) was larger than that obtained by the spherical model (0.301 nm). The effect of applied pressure (0.2–1.0 MPa) on the pore radius was examined with the non-spherical model. The results indicated that the pore radius slightly increased with applied pressure, suggesting that the pore was slightly enlarged by increasing the applied pressure.

Effect of molecular shape on rejection of uncharged organic compounds by nanofiltration membranes and on calculated pore radii

We examined the effects of molecular shape on the rejection of uncharged organic compounds by nanofiltration membranes and on pore radii calculated for those membranes. Molecular shape was approximated by a rectangular parallelepiped; molecular length ( L) and molecular width ( MWd) were used as shape parameters. The steric partition factor of a solute was calculated from L and MWd, and the Stokes radius and diffusivity were estimated from MWd. Twenty-four alcohols and polyhydric alcohols were used as probe compounds, and pore radius was estimated by both non-spherical and spherical models within a uniform pore-size model or log-normal pore-size distribution model. The uniform pore/non-spherical model gave better correspondence between the calculated and observed rejections for NTR-729HF membranes, and the calculated pore radius (0.634 nm) was larger than that from the spherical model (0.387 nm). Similar results were obtained from previous rejection data. In the case of the non-spherical model, employing a log-normal pore-size distribution model did not improve the correspondence between observed and calculated rejections. The logarithm of the product of calculated solute permeability and pore length log( B* Δ x) was correlated linearly with MWd. Molecular width is thus a major factor controlling solute permeation.

Developing thin film composite poly(piperazine-amide) and poly(vinyl-alcohol) nanofiltration membranes

In this work, two different thin film composite (TFC) nanofiltration (NF) membranes were fabricated for water softening: (i) poly(piperazine-amide) and (ii) poly(vinyl-alcohol) (PVA) nanofiltration membranes. The nanofiltration performance of membranes was evaluated by cross flow filtration using NaCl (1 g/l) and MgSO 4 (1 g/l) solution at 5 and 10 bar, 25 °C and 10 l/min. The morphological and hydrophilicity studies were carried out with scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle, respectively. Thin film composite poly(piperazine-amide) nanofiltration membrane was prepared by interfacial polymerization of piperazine (PIP) with trimesoyl chloride (TMC). The SEM and AFM studies indicated that a rough and dense film was formed on the polyethersulfone (PES) support membrane by interfacial polymerization. The water permeability of this membrane was 53 and 101 kg m − 2 h − 1 (during salt solution filtration), 57 and 126 kg m − 2 h − 1 (during pure water filtration) at 5 and 10 bar. Moreover, the rejection to the MgSO 4 as divalent salt (78 and 70%) was high compared to the NaCl as monovalent salt (44 and 35%). In second type, thin film composite poly(vinyl-alcohol) (PVA) nanofiltration membrane was prepared by dip coating and cross-linking with glutaraldehyde. In the case of PVA membrane, a thick and smooth film was formed. This membrane shows the water permeability of 60 and 109 kg m − 2 h − 1 (during salt solution filtration), 69 and 135 kg m − 2 h − 1 (during pure water filtration) and the rejection of 25 and 20% for NaCl and 72 and 63% for MgSO 4 at two different pressures. Moreover, these two NF membranes exhibited structural and performance stabilities. The calculated pore radius and thickness-to-porosity (Δ X / A K) ratio by the modified Nernst–Plank equation confirmed the obtained results of rejection data of the synthesized membranes.

Nafion-117 Behavior during Cation Separation from Spent Chromium Plating Solutions

This study investigated the behavior of Nafion-117 ion-exchange membranes that are commonly used as the separator in electrolytic regeneration of spent chromium plating solutions. In the co-presence of Cu2+, Ni2+, and Fe3+ impurities (∼0.01−0.1 M) in ∼0.5−2.0 M H2CrO4, the exchange equivalents of Ni2+ by Nafion-117 was double that of Cu2+ (0.02 mmol of H+/(g of Nafion)) but smaller than that (∼0.03−0.15 mmol of H+/(g of Nafion)) of Fe3+, exhibiting the order Fe3+ ≥ Ni2+ ≥ Cu2+ in Nafion affinity. The water content (∼41%) of a Nafion-117 membrane soaked in 2 M H2CrO4 was greater than those (∼35−38%) in the contaminated 2 M chromic acid solutions, whereas the porosity (0.24) of the former was smaller than those (0.29−0.37) of the latter. For the Nafion-117 in 2 M chromic acid solutions with/without cation impurities, (1) the tortuosity coefficient of Fe3+ was about 1.8 times that of Cu2+ or Ni2+, (2) the calculated pore radius was 3.2 nm for a multiimpurity case (0.1 M Cu(II), Fe(III), Ni(II), and Cr(III) e...

Curvature-Driven Pore Growth in Charged Membranes during Charge-Pulse and Voltage-Clamp Experiments

We find that curvature-driven growth of pores in electrically charged membranes correctly reproduces charge-pulse experiments. Our model, consisting of a Langevin equation for the time dependence of the pore radius coupled to an ordinary differential equation for the number of pores, captures the statistics of the pore population and its effect on the membrane conductance. The calculated pore radius is a linear, and not an exponential, function of time, as observed experimentally. Two other important features of charge-pulse experiments are recovered: pores reseal for low and high voltages but grow irreversibly for intermediate values of the voltage. Our set of coupled ordinary differential equations is equivalent to the partial differential equation used previously to study pore dynamics, but permits the study of longer timescales necessary for the simulations of voltage-clamp experiments. An effective phase diagram for such experiments is obtained.

Effect of changing intestinal flow rate on a measurement of intestinal permeability

Background/Aims: The flow rate of fluid through the proximal small intestine varies widely under normal physiological conditions. The aim of this study was to assess the effect of changes in flow rate on the passive permeability of the aqueous paracellular pathway of the human jejunum. Methods: Normal subjects were studied in vivo during constant perfusion of 30-cm loops of jejunum at flow rates of 5, 10, or 20 mL/min. The permeability ratio of l-xylose/urea was used to assess apparent permeability of the mucosa and to calculate the average pore radius of the aqueous pathway for passive diffusion. Results: Increasing jejunal flow rate from 5 to 20 mL/min significantly decreased the l-xylose/urea permeability ratio from 0.35 to 0.23 and decreased average calculated pore radius of the diffusion pathway from 13 Å to 8 Å. Conclusions: Increases in flow rate in the normal physiological range decrease the estimated pore size of normal healthy jejunal mucosa. Because increasing flow rate is known to increase exposure of luminal fluid to the intervillus space, the results of this study are best explained by postulating that cells lining the sides of villi are less permeable than cells lining the villus tips.

A Ce-Hf oxide porous glass and glass-ceramic

Substitution of the binary CeO2-HfO2 mixture for SiO2 in the ternary Na2O-SO2-B2O3 system resulted after melting in glassy and/or crystalline materials, depending on subsequent heat treatments. At least one of the phases present was water soluble. Quenching, heat treating, leaching and sintering altered the state of this ceramic. Crystalline forms found were cubic CeO2, monoclinic Ce(BO2)3 and monoclinic HfO2. Specific surface areas of the leached materials were from 120-233 m2 g−1 with a calculated pore radii from 1.3–2.5 nm.

Structure parameters of molecules and media evaluated by chromatographic partition: I. Controlled-pore glasses

Polystyrene, dextran and sodium dodecyl sulphate—protein data for eleven controlled-pore glasses have been used to validate the expression K D = ( b − R e/ R x) 2 derived from a geometrical exclusion model for cylindrical pores. The calculated pore radii ( R x) agreed well with mercury-intrusion values, and the crucial role of Stokes′ radius ( R e) was confirmed by comparison with Casassa's formulations [E.F. Casassa and Y. Tagami, Macromolecules, 2 (1969) 14; E.F. Casassa, J. Polym. Sci., Part B, 5 (1967) 773]. From theory it was demonstrated that for any molecule, R e = A M x where A and x are defined, structure-specific constants. Thus, linear K D( M) functions were derived and tested, by which one is able to distinguish between coils. rods and ellipsoids, ideal and real solvents, and to determine bond lengths, expansion, gyration radii, axial ratios and diffusion coefficients. The characteristic shape of the empirical K D:log M curves derives directly from the linear K D( M) function.

Alkali resistant non-silicate porous glass-like material

Substitution of the end-member oxides in the ternary sodium borosilicate system has been studied. Replacing SiO2 with a combination of alkali resistant oxides, Th, Zr, Ce with or without Y2O3, was found to produce glasses which, after heat treatment, decomposed into two immiscible microphases, one of which was water soluble. The structure of the leached material or material sintered after leaching (ThO2, ZrO2, CeO2, Y2O3 or ThO2, ZrO2, CeO2) was predominantly glass-like. Some Na2O and B2O3 may be expected to remain unleached in the pores as has been observed in silica-based material. However, no evidence of this in crystalline form was found during X-ray diffraction analysis. The specific surface areas of the materials so formed ranged between 58 and 315 m2 g−1, having calculated pore radii of between 0.8 and 13.6 nm. Alkali resistance of up to 1.96×10−2 mg dm−2 and water resistance between 5 and 16.18 mg Na2Og−1 were measured.

Some comments on the applicability of gas permeation methods to characterize porous membranes based on improved experimental accuracy and data handling

The measurement of the gas permeability coefficient as a function of the mean pressure across a membrane can be used to determine a mean pore radius of the membrane. This method has been applied by several authors to characterize microporous and asymmetric ultrafiltration or hyperfiltration membranes. This paper shows how the data acquisition and handling are improved. Experiments are performed on microporous Millipore membranes with a nominal pore radius of 50 nm and on ultrafiltration merebranes of poly(2,6-dimethyl-1,4-phenyleneoxide) with an expectedly sharp pore-size distribution around 2 nm. For the Millipore membrane an unexpected dependence of the calculated pore radius on the type of gas used in the experiment has been found. Measurements on the ultrafiltration membranes indicate that the viscous flow contribution to the permeability coefficient cannot be determined with sufficient accuracy. It is concluded that application of the gas permeation method has some limitations which were not previously recognized.

Permeability of connective tissue linings isolated from implanted capsules; implications for interstitial pressure measurements.

Quantification of the permeability of connective tissue linings isolated from implanted capsules was achieved by two types of experiments. The objective of the first type was to determine the restriction offered by the lining to diffusion of 125I-labeled human serum albumin. The restricted diffusion coefficient of albumin with respect to the connective tissue lining the luminal capsule surface (internal lining) averaged 3.0 times 10-7 plus or minus 0.4 times 10-7 cm2/sec in ten experiments indicating that the rate if migration of albumin across the structure was 35% of its free diffusion rate in water. In contrast, the albumin diffusion coefficient obtained for the abluminal (external) lining suggested that diffusion of albumin through this structure was 73% of the free diffusion rate in water. The objective of the second type of experiment was to determine solute reflection coefficients for inulin, serum albumin, and gamma-globulin with respect to the internal and external linings. For the internal lining, the reflection coefficients were: inulin 0.07, albumin0.23, and gamma-globulin 0.53. The external lining showed greater leakiness as evidenced by its lower reflection coefficient for a given molecule and its higher hydraulic conductivity. An equivalent pore calculation resulted in a calculated pore radius of 250-350 angstrom for the internal lining and a calculated pore radius of 500-600 angstrom for the external lining. The ineffectiveness of the leaky capsule lining in transmitting oncotic pressure suggests that under normal conditions the capsule measures interstitial hydrostatic pressure rather than oncotic pressure.