Minimum Pore Diameter Research Articles

Thermoluminescence of the Films, Nanocomposites, and Solutions of the Silicon Organic Polymer Poly(di-n-hexyl silane)

A comparative study of low-temperature thermoluminescence (5–120 K) of silicon organic polymer poly(di-n-hexyl silane) films, nanocomposites (when the polymer is introduced into nanopores of silica МСМ-41 and SBA-15 with diameter of pores 2.8 and 10 nm) as well as solutions of polymer in tetrahydrofuran with different concentrations from 10–3 to 10–5 mol/L was carried out. It was shown that it is possible to control the number of charge carrier traps, as well as their energy distribution by changing the diameter of silica nanopores. It is established that maxima and FWHMs of the thermoluminescence curves of nanocomposites significantly depend on the pore diameter of the nanoporous silica. This result agrees with the data obtained in the investigation of polymer solutions. In the nanocomposite with a minimum pore diameter (2.8 nm), the number and depth of the traps as well as dispersion of their energy are significantly reduced compared to their values in the polymer film.

A modified model for spontaneous imbibition of wetting phase into fractal porous media

Fractal theory has been applied to characterize complex pore structure of sedimentary rocks and to model fluid flow through porous media. In recent years, several analytical models have been developed to simulate spontaneous imbibition of wetting phase into porous media with fractal geometry. In previous studies, spontaneous imbibition of wetting phase is considered as a piston-like displacement phenomenon which leads to similar rates of imbibition in capillaries with different diameters. However, imbibition rate of wetting phase is positively proportional to the square root of pore diameter based on the Lucas-Washburn equation. Therefore, we should expect faster imbibition of wetting phase in larger capillaries compared with smaller capillaries.In this paper, we extend the previous model by assuming non-piston-like imbibition in capillaries with different diameters. In our model, first the larger capillaries are filled by wetting phase, followed by smaller capillaries. We develop an analytical equation without considering hydrostatic pressure and a semi-analytical equation with considering hydrostatic pressure. We can apply actual boundary conditions in the proposed model, while the previous piston-like models are only valid before the wetting phase reaches top of the porous media in co-current spontaneous imbibition test. Moreover, the proposed model can be used to determine the minimum pore diameter of rock sample according to the equilibrium time in spontaneous imbibition tests.

Influence of a calcium hydroxide-based intracanal dressing on the quality of the root canal filling assessed by capillary flow porometry.

The objective of this study is to evaluate the influence of a calcium hydroxide intracanal dressing (CH) on the short- and long-term sealing ability of the root canal filling using capillary flow porometry (CFP). To verify the repeatability of the method, five obturated specimens were submitted to CFP. Measurements were repeated three times and compared with the non-parametric Friedman test. Forty-five instrumented palatal roots were randomly divided into three groups. Group 1: specimens were obturated in one step without placement of any dressing. Group 2: CH was placed and removed after 1week with syringe irrigation before obturation. Group 3: CH was placed and removed after 1week with ultrasonic activation before obturation. CFP measurements were conducted at 1week and 6months after obturation. The inter-group comparisons were performed using the Kruskal-Wallis test and the intra-group comparison over time using the Wilcoxon signed-rank test. Significance level was set at 0.05. In the five specimens, no difference could be detected between the consecutive measurements for minimum, mean flow, and maximum pore diameter indicating repeatability of the method. No difference in sealing ability could be detected neither between the 3 groups at 1week and at 6months nor within each group between the 1week and the 6months measurements. Placement of a CH did not affect significantly the short- and long-term sealing ability of the root canal filling. The use of an intermediary CH does not negatively influence the quality of the root canal filling.

Design and fabrication considerations for three dimensional scaffold structures

<p>Porous three dimensional structures have seen extensive investigation among design engineers for a wide range of novel applications. The fabrication of such designs would not be possible using traditional manufacturing approaches owing to the dimensional intricacy of such structures, but have now become a distinct possibility owing to the maturity of 3D printing technologies. In this study, we have examined the creation of novel unit cells from mathematic surface renderings as a basis for creating tailored porous structures, before realising the final designs through Fuse Deposition Modelling (FDM) 3D printing. We examined the use of Gyroid and Schwarz primitive (P) surfaces to create novel unit cells not typically found in design software libraries. We then transpose these structures into several test geometries comprising a cylinder, cuboid and tetrahedron, which will adequately test limits of design and fabrication in regular and irregularly shaped structures. It was found that the porosities of the resulting models could be adjusted through discrete dimensional changes in the unit cell and digital wrapping procedures. It was also found that models could be fabricated using FDM printing to a minimum pore diameter of approximately 1mm with a high degree of accuracy and repeatability. Ultimately this work will provide guidance to engineering's when creating porous structures and could find usefulness in applications where optimal material usage versus porosity are required, such as in high throughput 3D fluidic applications, such as heat exchangers and tissue engineered structures.</p>

A fractal model for real gas transport in porous shale

A model for real gas flow in shale gas matrices is proposed and consists of two main steps: (a) developing a microscopic (single pore) model for a real gas flow by generalizing our previously reported Extended Navier‐Stokes Equations (ENSE) method and (b) by using fractal theory concepts, up‐scaling the single pore model to the macroscopic scale. A prominent feature of the up‐scaled model is a predictor for the apparent permeability (AP). Both models are successfully validated with experimental data. The impact of the deviation of the gas behavior from ideality (real gas effect) on the gas transport mechanisms is investigated. The effect of the structural parameters (porosity Ф, the maximum pore diameter Dmax, and the minimum pore diameter Dmin) of the shale matrix on the apparent permeability is studied and a sensitivity analysis is performed to evaluate the significance of the parameters for gas transport. We find that (1) the real gas transport models for a single pore and porous shale matrix are both reliable and reasonable; (2) the real gas effect affects the thermodynamic parameters of the free gas and the adsorption and transport capacity of the adsorbed gas; (3) the real gas effect decreases the effective permeability for convective flow and surface diffusion; i.e., the derivation degree of the effective permeability for bulk diffusion and Knudsen diffusion increases with increasing pressure but presents a bathtub shape when the pore diameter is smaller than 10 nm; and (4) the apparent permeability increases with Ф, Dmax, and Dmin. It is more sensitive to Dmax, followed by the porosity. Dmin has a minor impact. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1430–1440, 2017

Study on mass transfer property of oxygen molecules and kinetic regimes of pressured pulverized coal combustion

The effects of pressure on diffusion of oxygen molecules during the coal combustion could not be ignored. The compressibility factor of real oxygen is investigated to evaluate the deviation between real and ideal oxygen, and obtain the mean free path of real oxygen. Comparing the Knudsen pore diameter with the minimum pore diameter, it is found that with the increase of pressure, Knudsen diffusion cannot exist at low pressure and may delay to occur at higher temperature. When pressure exceeds 3.5 MPa, no Knudsen diffusion occurs within the whole temperature range of our research. Comparing the diffusion rate at 1 MPa with the burning rate, one can conclude that the combustion mainly take place on the internal and external surfaces, and the reaction is controlled by the chemical kinetics below 1400 K. When themperature is between 1400 K and 1600 K, the reaction is controlled by both the diffusion and the chemical kinetics. When the temperature is more than 1600 K, the combustion primarily happens on the external surfaces and is controlled by the diffusion.

Quantification of Soil Pore Network Complexity with X-ray Computed Tomography and Gas Transport Measurements

Flow and transport of gases through soils are largely controlled by pore structural attributes. The quantification of pore network characteristics is therefore essential for accurate prediction of air permeability and gas diffusivity. In this study, the pore network characteristics of seven different soils subjected to 22 mo of field regeneration were quantified with X-ray computed tomography (CT) and compared with functional pore characteristics estimated from measurements of air permeability and gas diffusivity. Furthermore, predictive models for air permeability and gas diffusivity were developed based on CT-derived structural parameters and compared with previously proposed predictive models. Strong correlations between functional and pore geometry parameters were observed. The consideration of CT-derived air-filled porosity, pore network tortuosity and connectivity, and minimum equivalent pore diameter in predictive gas diffusivity and air permeability models significantly improved their performance. The obtained results suggest that the application of X-ray CT-derived pore-structural parameters has great potential for predicting gas diffusivity and air permeability.

Nanometer-Scale Pore Characteristics of Lacustrine Shale, Songliao Basin, NE China.

In shale, liquid hydrocarbons are accumulated mainly in nanometer-scale pores or fractures, so the pore types and PSDs (pore size distributions) play a major role in the shale oil occurrence (free or absorbed state), amount of oil, and flow features. The pore types and PSDs of marine shale have been well studied; however, research on lacustrine shale is rare, especially for shale in the oil generation window, although lacustrine shale is deposited widely around the world. To investigate the relationship between nanometer-scale pores and oil occurrence in the lacustrine shale, 10 lacustrine shale core samples from Songliao Basin, NE China were analyzed. Analyses of these samples included geochemical measurements, SEM (scanning electron microscope) observations, low pressure CO2 and N2 adsorption, and high-pressure mercury injection experiments. Analysis results indicate that: (1) Pore types in the lacustrine shale include inter-matrix pores, intergranular pores, organic matter pores, and dissolution pores, and these pores are dominated by mesopores and micropores; (2) There is no apparent correlation between pore volumes and clay content, however, a weak negative correlation is present between total pore volume and carbonate content; (3) Pores in lacustrine shale are well developed when the organic matter maturity (Ro) is >1.0% and the pore volume is positively correlated with the TOC (total organic carbon) content. The statistical results suggest that oil in lacustrine shale mainly occurs in pores with diameters larger than 40 nm. However, more research is needed to determine whether this minimum pore diameter for oil occurrence in lacustrine shale is widely applicable.

Atomic layer deposition-based tuning of the pore size in mesoporous thin films studied by in situ grazing incidence small angle X-ray scattering

Atomic layer deposition (ALD) enables the conformal coating of porous materials, making the technique suitable for pore size tuning at the atomic level, e.g., for applications in catalysis, gas separation and sensing. It is, however, not straightforward to obtain information about the conformality of ALD coatings deposited in pores with diameters in the low mesoporous regime (<10 nm). In this work, it is demonstrated that in situ synchrotron based grazing incidence small angle X-ray scattering (GISAXS) can provide valuable information on the change in density and internal surface area during ALD of TiO(2) in a porous titania film with small mesopores (3-8 nm). The results are shown to be in good agreement with in situ X-ray fluorescence data representing the evolution of the amount of Ti atoms deposited in the porous film. Analysis of both datasets indicates that the minimum pore diameter that can be achieved by ALD is determined by the size of the Ti-precursor molecule.

Permeability model for fractal porous media with rough surfaces

In this paper, a permeability model is derived for porous media, which are assumed to be comprised of a bundle of tortuous capillaries whose size distribution and roughness of surfaces follow the fractal scaling laws. The proposed model includes the effects of the fractal dimensions for size distributions of capillaries, for tortuosity of tortuous capillaries and for roughness of surfaces on the permeability. The analytical expression for permeability is a function of the relative roughness, the fractal dimensions for tortuosity and sizes of capillaries and for roughness of surfaces, as well as the microstructural parameters (such as the characteristic length, the maximum and minimum pore diameters and the fractal dimensions). The proposed model can properly reveal some mechanisms that affect the permeability. Every parameter in the proposed model has specific physical meaning. The ratio of the permeability ( $$ K_{\text{R}} $$ ) for rough capillaries to that (K) for smooth capillaries is found to be a function of the relative roughness and follows the quadruplicate power law, i.e., $$ K_{\text{R}} /K = (1 - \varepsilon )^{4} $$ , where $$ \varepsilon $$ is the relative roughness of surfaces of capillaries.

Diffusion behavior of Se(IV) and Re(VII) in GMZ bentonite

The diffusion behavior of HSeO3− and ReO4− was investigated in Gaomiaozi (GMZ) bentonite by the through-diffusion method. The effective diffusion coefficient De, porosity ε and rock capacity factor α were measured in order to evaluate the impact of porosity on anion diffusion in compacted bentonite. The De values of HSeO3− and ReO4− were (4.5–54)×10−12 and (3.0–53)×10−12m2/s at dry densities from 1300 to 1800kg/m3, respectively. HSeO3− sorbed on GMZ bentonite with a distribution coefficient Kd in the range of (1.4–1.8)×10−4m3/kg, whereas ReO4− showed little sorption. Moreover, the diffusion behavior of HSeO3- and ReO4- was similar to that of SeO32-and 99TcO4-. Since the minimum average pore diameter at a bulk dry density below 1800kg/m3 is much larger than that of anions, the constrictivity δ could be neglected. The De or the apparent diffusion coefficient Da was related to porosity ε by Archie's law and by a pore diffusion model with linear and logarithmic relations between τ and ε. The best fit was obtained by Archie's relation.

Analysis of permeability for transient two-phase flow in fractal porous media

A relative permeability model for transient two-phase flow in fractal porous media is derived based on the fractal characteristics of pore size distribution and the assumption that porous media consists of capillary bundles. The functions in this model are tortuosity fractal dimension, pore fractal dimension, and maximum and minimum pore diameters. Every parameter has clear physical meaning without the use of empirical constants. Good agreement between model predictions and experimental data is obtained, the sensitive parameters that influence the relative permeability are specified and their effects on relative permeability are discussed.

Investigation of Coronal Leakage of Root Fillings after Smear Layer Removal with EDTA or Er,Cr:YSGG Laser through Capillary Flow Porometry

No studies have been performed evaluating the marginal seal of root fillings after direct exposure of root canal (RC) walls to Er,Cr:YSGG laser irradiation. Therefore, 75 root filled teeth (5 × 15–cold lateral condensation) were analyzed for through-and-through leakage (TTL) using capillary flow porometry (CFP). The cleaning protocol determined the experimental groups: (1) irrigation with NaOCl 2.5% and EDTA 17% or standard protocol (SP), (2) SP + Er,Cr:YSGG lasing (dried RC), (3) NaOCl 2.5% + Er,Cr:YSGG lasing (dried RC), (4) SP + Er,Cr:YSGG lasing (wet RC), and (5) NaOCl 2.5% + Er,Cr:YSGG lasing (wet RC). Groups 6 to 10 consisted of the same filled teeth with resected apices. Resection was performed after the first CFP measurement. CFP was used to assess minimum, mean flow, and maximum pore diameters after 48 h. Statistics were performed using nonparametric tests (P > 0.05). Additional three roots per group were submitted to SEM of the RC walls. TTL was observed in all groups without statistically significant differences between the different groups for minimum, mean, and maximum pore diameter (P > 0.05). In this study, the use of EDTA and/or Er,Cr:YSGG laser did not reduce through-and-through leakage in nonresected and resected roots.

Tunable Porous Organic Crystals: Structural Scope and Adsorption Properties of Nanoporous Steroidal Ureas

Previous work has shown that certain steroidal bis-(N-phenyl)ureas, derived from cholic acid, form crystals in the P61 space group with unusually wide unidimensional pores. A key feature of the nanoporous steroidal urea (NPSU) structure is that groups at either end of the steroid are directed into the channels and may in principle be altered without disturbing the crystal packing. Herein we report an expanded study of this system, which increases the structural variety of NPSUs and also examines their inclusion properties. Nineteen new NPSU crystal structures are described, to add to the six which were previously reported. The materials show wide variations in channel size, shape, and chemical nature. Minimum pore diameters vary from ∼0 up to 13.1 Å, while some of the interior surfaces are markedly corrugated. Several variants possess functional groups positioned in the channels with potential to interact with guest molecules. Inclusion studies were performed using a relatively accessible tris-(N-phenyl)urea. Solvent removal was possible without crystal degradation, and gas adsorption could be demonstrated. Organic molecules ranging from simple aromatics (e.g., aniline and chlorobenzene) to the much larger squalene (Mw = 411) could be adsorbed from the liquid state, while several dyes were taken up from solutions in ether. Some dyes gave dichroic complexes, implying alignment of the chromophores in the NPSU channels. Notably, these complexes were formed by direct adsorption rather than cocrystallization, emphasizing the unusually robust nature of these organic molecular hosts.

Fractal analysis of dimensionless capillary pressure function

The dimensionless capillary pressure function J(SW) was used to eliminate the capillary pressure difference between different strata and to describe similar lithologic reservoirs. Based on the existing function J(SW) and the fractal geometry theory, a fractal model to describe the pore structure of the lithology is presented. The proposed fractal expression for the J(SW) function reveals that when the microstructural parameters (fractal dimension for pore area, the fractal dimension for tortuosity, and the ratio of the maximum pore diameter to the minimum pore diameter) are respectively equal or close for porous samples (with different permeabilities, porosities, interfacial tensions and wetting angles), the values of the J(SW)function vs. saturation coincide each other for wetting phase. In addition, a new dimensionless function G(SW), which is based on the ratio of the average capillary diameter to the critical capillary diameter, is proposed to describe the relationships among the structural parameters of similar lithological porous media and saturation as well as the dimensionless capillary pressure function J(SW).

Influence of Anodizing Parameters on Pore Diameter of Anodic Aluminium Oxide (AAO) Films Using Taguchi Design

Nanoporous anodic aluminium oxide (AAO) films were fabricated by using a two-step anodizing process of aluminium foils in oxalic acid electrolyte. The effect of synthesis conditions including applied voltage, electrolyte concentration and temperature on the pore diameter of AAO films was investigated. To reduce the number of experiments, the Taguchi L9 orthogonal array was adopted and the results were analyzed using minitab15 software. It was found that the pore size increased in direct proportion with the applied voltage. The proportion of the pore size with increasing electrolyte concentration was at first direct and then inverse and the maximum pore diameter was obtained in the case of 0.3 M. The pore size relation with increasing electrolyte temperature was at first inverse and then direct and the minimum pore diameter was seen at 10 ◦C. The diameter of the nanopores were predicted with the software in the range of 35–71 nm in different conditions of selected experimental parameters. Also, as a practical application of obtained AAO films, template-synthesis fabrication of polypyrrole nanowire arrays by electrochemical polymerization of pyrrole within the pores of the obtained AAO was successfully demonstrated.

Fabrication of Nanopores on Different Thickness Membranes

In recent years, solid-state nanopores have been widely used in biotechnology for detecting single molecules. Here, we studied the influence of membrane thickness and Focused Ion Beam action time on the diameter of silicon nitride nanppores. The results showed that on the 300 nm thick silicon nitride membrane, the minimum pore was 170 nm in diameter; while on thinner membranes with the thicknesses of 200nm and 100nm, the minimum pore diameters were 100nm and 30nm respectively. And on the membrane of a given thickness, the minimum diameter of nanopore is determined by the minimum action time. Therefore the 100 nm membrane thickness is ideal for milling small nanopores.

Transmembrane Serine Mutations reduce the Minimum Pore Diameter of Channelrhodopsin-2

Channelrhodopsin-2 (ChR2) is a microbial-type rhodopsin that, together with channelrhodopsin-1, mediates phototactic behavior in the green algae Chlamydomonas reinhardtii. Like all other microbial-type rhodopsins, ChR2 has seven transmembrane domains with the chromophore all-trans retinal bound to a single lysine residue. However, unlike other microbial-type rhodopsins, ChR2 functions as a non-selective cation channel and not an ion pump. A sequence alignment of ChR2 with the proton pump bacteriorhodopsin (bR) reveals that ChR2 lacks specific motifs within the transmembrane domains that facilitate non-covalent interactions and contribute to protein stability. Specifically, there are eight TM serine residues, which have a high propensity for forming inter- and intrahelical hydrogen-bonds, present in bR that are absent in ChR2. We hypothesized that the re-introduction of serine residues at homologous positions in ChR2 would facilitate hydrogen-bonding, thus reducing the pore diameter of ChR2. We measured kinetics, reversal potentials, and calculated permeability ratios of alkali metal solutions using two-electrode voltage clamp. Applying excluded volume theory, we determined the minimum pore diameter of wild-type and mutant ChR2. Three mutants had either reduced functionality or low surface expression. Furthermore, four ChR2 mutants were determined to have smaller pore diameters than wild-type ChR2 while one mutant was similar to the phenotype, but had two-fold slower kinetics. Lastly, we replaced an endogenous serine residue with alanine and observed an increase in the pore diameter. An analysis of experimental results shows that re-introducing serine residues into the transmembrane domain of ChR2 can restrict the pore diameter while the removal of a transmembrane serine results in a larger pore. We suggest that the pore restriction is caused by the formation of an inter- or intrahelical hydrogen-bond and that multiple positions along the intracellular side of the transmembrane domains contribute to cation permeability.

Re-Introduction of Transmembrane Serine Residues Reduce the Minimum Pore Diameter of Channelrhodopsin-2

Channelrhodopsin-2 (ChR2) is a microbial-type rhodopsin found in the green algae Chlamydomonas reinhardtii. Under physiological conditions, ChR2 is an inwardly rectifying cation channel that permeates a wide range of mono- and divalent cations. Although this protein shares a high sequence homology with other microbial-type rhodopsins, which are ion pumps, ChR2 is an ion channel. A sequence alignment of ChR2 with bacteriorhodopsin, a proton pump, reveals that ChR2 lacks specific motifs and residues, such as serine and threonine, known to contribute to non-covalent interactions within transmembrane domains. We hypothesized that reintroduction of the eight transmembrane serine residues present in bacteriorhodopsin, but not in ChR2, will restrict the conformational flexibility and reduce the pore diameter of ChR2. In this work, eight single serine mutations were created at homologous positions in ChR2. Additionally, an endogenous transmembrane serine was replaced with alanine. We measured kinetics, changes in reversal potential, and permeability ratios in different alkali metal solutions using two-electrode voltage clamp. Applying excluded volume theory, we calculated the minimum pore diameter of ChR2 constructs. An analysis of the results from our experiments show that reintroducing serine residues into the transmembrane domain of ChR2 can restrict the minimum pore diameter through inter- and intrahelical hydrogen bonds while the removal of a transmembrane serine results in a larger pore diameter. Therefore, multiple positions along the intracellular side of the transmembrane domains contribute to the cation permeability of ChR2.

Neck-size distributions of through-pores in polymer membranes

Abstract Capillary flow porometry (CFP) is used for measuring the most constricted part (bottleneck) of through-pores in synthetic membranes. In present work, a systematic study has been carried out to evaluate influence of membrane properties like tortuosity, intersecting pores and thickness on CFP. For evaluating CFP, the track-etched membranes were used as these membranes have cylindrical pores. The average, maximum and minimum pore diameters and pore-diameter distributions in the track-etched membranes were obtained by CFP, and compared with the values obtained by different techniques like atomic force microscopy (AFM), scanning electron microscopy (SEM) and molecular weight cut-off (MWCO). The internal architecture of pore in the track-etched membranes was studied by growing gold nano-rods in the pores. The gold nano-rods were grown in the membrane by electrodeposition using removable electrode (Hg). The transmission electron microscopy (TEM) of nano-gold rods were carried out after dissolution of the membranes in dichloromethane. The studies carried out in the present work showed that: (i) the CFP data remained practically independent of the membrane thickness and tortuosity, (ii) it measured the most constricted diameter of a pore independent of pore-architecture, and (iii) mean flow pore-diameters data were highly reproducible (±5%). The capability of CFP for assessing quality of the membrane was demonstrated using the pore-filled membrane samples having different amounts of the crosslinked poly- N -isopropylacrylamide (poly-NIPA). These samples were prepared by UV-initiator induced in situ photo-polymerization of NIPA in pores of the host microporous poly(propylene) membrane.