Pore Surface Roughness Research Articles

Knudsen self- and Fickian diffusion in rough nanoporous media

The effect of pore surface roughness on Knudsen diffusion in nanoporous media is investigated by dynamic Monte Carlo simulations and analytical calculations. A conceptual difference is found between the roughness dependence of the macroscopic, transport diffusivity and the microscopic, self-diffusivity, which is reminiscent of diffusion in zeolites, where a similar difference arises due to adsorption effects and intermolecular interactions. Because of the dependence of the self-diffusivity on molecular residence times, self-diffusion may be roughness dependent, while transport diffusion is not. Detailed proofs are given. The differences become significant when the pore surface is rough down to molecular scales, as is the case, e.g., for many common sol–gel materials. Simulations are in good agreement with analytical calculations for several tested rough, fractal pore structures. These results are important for the interpretation of experimental diffusion measurements and for the study of diffusion-reaction processes in nanoporous catalysts with a rough internal surface.

How Pore Size and Surface Roughness Affect Diffusion Barrier Continuity on Porous Low-k Films

The structural features that affect continuity of ultrathin diffusion barriers on porous low-dielectric-constant (k) thin films has been investigated. The dimensions of interconnected nanopores in a series of Dow Corning XLK films are found to increase as the dielectric constant becomes smaller. The minimum thickness required for tantalum (Ta) to form a continuous barrier layer is affected by the pore size and surface roughness of the porous low-k films according to positronium annihilation lifetime spectroscopy analysis. The films with large pores require thick barrier layers to form effective diffusion barriers. The surface roughness of the porous films as observed by atomic force microscopy has a significant influence on the continuity of diffusion barriers. © 2003 The Electrochemical Society. All rights reserved.

Characterization of molecularly imprinted composite membranes using an atomic force microscope

AbstractAtomic force microscopy (AFM) has been used to investigate the surface structure of molecularly imprinted polyethersulphone (PES) membranes and to quantify pore size and surface roughness. Molecularly imprinted polymeric (MIP) membranes were developed using photoinitiated copolymerization of 2‐hydroxyethyl methacrylate as functional monomer and trimethylopropane trimethacrylate as crosslinker in the presence of adenosine 3′ : 5″‐cyclic monophosphate as template, followed by deposition of a MIP layer on the surface of (PES) microfiltration membranes. Atomic force microscopy images clearly indicate that a consistent increase in the degree of modification leads to a systematic decrease in pore size and an increase in surface roughness. These results show a good correlation with the filtration data of cAMP solutions. Thus, it was shown that direct AFM quantification of key parameters of imprinted membrane structure provide useful guidelines for the development of novel MIP composite membranes. Copyright © 2002 John Wiley & Sons, Ltd.

Pore surface fractal dimension of sol–gel-derived Al2O3–SiO2 membranes

Pore surface roughness change in composite Al2O3–SiO2 membranes induced by chemical composition and sintering process has been investigated by the analysis of surface fractal dimension. Fractal features are analyzed from N2 adsorption–desorption measurements. It was found that an increase in the surface fractal dimension occurs while silica content increases at the composite membranes with different molar ratio of alumina to silica sintering at 600 °C. The surface fractal dimension of membrane with 40 mol% silica content slightly increases while sintering from 200 to 600 °C due to shrinkage and increase of mass fractal dimension of silica clusters, but decreases at the temperature of 800 °C, attributable to the smoothing of clusters and the collapse of pores located between clusters.

Effect of rain on the macroporosity at the soil surface

SummaryRain falling on soil causes slaking, mechanical disruption of aggregates and compaction. Too few data exist to predict the changes likely to occur in particular soil, landscape and management conditions. Experiments with simulated rain were set up to study and to model mathematically the changes of the pore system within the surface layer of a soil when rain was applied on a field cropped with maize. Macroporosity, pore‐size and pore‐shape distributions, and the pore volume were measured by image analysis of thin sections and the fractal dimensions of the pore surface roughness were estimated. The general trends of changes in porosity indicated the presence of two different sets of processes at the surface (0–3 cm) and in the layer immediately underneath (3–6 cm). In both layers most of the variation in macroporosity was due to a loss of elongated porosity. A theoretical approach recently developed to link rain and erosion to sealing properties was extended to describing the effect of rain on the elongated porosity and the pore volume fractal dimension in these two layers. The resulting set of equations describe in detail the evolution of soil porosity near the soil surface. Our approach could be useful when modelling the effects of sealing processes in soil erosion.

Saturated hydraulic conductivity prediction from microscopic pore geometry measurements and neural network analysis

Traditional models to describe hydraulic properties in soils are constrained by the assumption of cylindrical capillarity to account for the geometry of the pore space. This study was conducted to develop a new methodology to directly measure the porosity and its microscopic characteristics. The methodology is based on the analysis of binary images collected with a backscattered electron detector from thin sections of soils. Pore surface area, perimeter, roughness, circularity, and maximum and average diameter were quantified in 36 thin sections prepared from undisturbed soils. Saturated hydraulic conductivity Ksat, particle size distribution, particle density, bulk density, and chemical properties were determined on the same cores. We used the Kozeny‐Carman equation and neural network and bootstrap analysis to predict a formation factor from microscopic, macroscopic, and chemical data. The predicted Ksat was in excellent agreement with the measured Ksat (R2=0.91) when a hydraulic radius rH defined as pore area divided by pore perimeter and the formation factor were included in the Kozeny‐Carman equation.

Size Effects of Exchange Cation on the Pore Structure and Surface Fractality of Montmorillonite

Ca-montmorillonites were exchanged with both metal cations (manganese and copper) and organic cations (tetramethylammonium (TMA) and hexadecyltrimethylammonium (HDTMA)) to study the cation size effects on the pore structure and surface roughness of montmorillonite based on the classical and fractal analysis of their nitrogen adsorption isotherms. The surface fractal dimension D was calculated from their nitrogen isotherms with the aid of the recently proposed Neimark equation. The decrease of BET surface area of montmorillonite induced by the larger size of exchange cation was interpreted with both the coverture of some surface roughness (surface screening effect) and the inhibition of nitrogen molecule into some pores (pore blocking effect). The pore blocking effect was examined with the changes of mean pore size. Meanwhile, the D value was used to examine whether or not the surface screening effect existed. It was concluded that the combination of classical and fractal analyses of nitrogen isotherms may facilitate our understanding of the evolution of pore and surface structures of clay exchanged with different cations.

Preparation of a palladium alloy composite membrane supported in a porous stainless steel by vacuum electrodeposition

Pinhole-free palladium/nickel (Pd/Ni) alloy membranes deposited on a porous stainless steel (SUS) support have been fabricated. The deposition was made by vacuum electrodeposition technique which could produce the alloy film less than 1 μm thick. This technique allows for the Pd/Ni alloy by employing Pd/Ni complex reagent, and typical Pd/Ni plating had compositions of 78% Pd and 22% Ni. In order to make the surface smooth and enhance the adhesive bond between the top layer and the substrate, a nascent porous SUS disk was treated sequently with submicron nickel powder and CuCN solution. The important parameters that can affect deposition were pore size, defects, and surface roughness of substrate. The membranes were characterized by permeation experiments with hydrogen and nitrogen at temperatures ranging from 623 to 823 K and pressures from 10.3 to 51.7 cmHg. The composite membranes prepared in this technique yielded excellent separation performance for hydrogen: hydrogen permeance of 5.79×10 −2 cm 3/cm 2 cmHg s and hydrogen/nitrogen (H 2/N 2) selectivity was 4700 at 823 K.

Prediction of the Saturated Hydraulic Conductivity‐Porosity Dependence Using Fractals

AbstractFractal theory has been used to quantify morphological properties of pore systems in soil, but predictive capabilities of the derived fractal dimensions have remained largely untested. The objective of this study was to use morphologically derived fractal dimensions to predict an exponent N in a power law relation between saturated hydraulic conductivity, Ksat, and porosity. A Kozeny‐Carman equation was used to derive N as a function of two fractal dimensions (pore volume, Dv, and pore surface roughness, Ds) and a connectivity parameter, α. The α parameter was used as a matching factor between fitted and calculated N values. Values of Dy and Ds characterizing pores in both undisturbed and packed soil were obtained from images with pixel sizes of 0.06 and 0.29 mm. Porosity was measured on the 0.29‐mm pixel images, while Ksat was measured in undisturbed cores and packed soil columns. Also, published data on porosity, Ksat, and Dv and Ds from dye‐stained patterns of four undisturbed soils were used. Lower coefficients of variation and lower absolute values of α were obtained with fractal dimensions from the 0.06‐mm pixel images. Values of α were related to parameters from probability distributions of hydraulic radii as calculated from the 0.06‐mm pixel images, and to the connectivity of pores as inferred from dye‐stained patterns. Fractal characterization of pore structure proved useful for predicting N, but predictions would probably be improved by considering only flow‐active pores in the calculation of a fractal dimension. Methods to obtain such fractal dimensions were suggested.

Fractal dimensions for volume and surface of interaggregate pores — scale effects

Geometrical attributes of pore systems in soil have shown fractal scaling. Scaling in natural materials is inherently statistical, i.e., fractal dimensions may change with scale. While fractal dimensions characterizing pore surface roughness, D s, or scaling of pore sizes, D v, have been reported, seldom are both measurements made at more than one scale. We examine a scale effect on D v and D s values, and relationships between fractal dimensions of both properties. Natural and artificial types of soil structure were studied in a Normania soil. Natural soil structure was sampled from experiments involving: (l) three primary tillage tools, sampled immediately after tillage; and (2) three tillage systems, sampled after consolidation. Artificial soil structure was formed in columns packed with aggregate assemblies that included two single aggregate-size fractions, and two mixtures of six aggregate-size fractions (each covering two ranges) made to obtain fractal aggregate-size distributions. Block-like samples from all sources were resin-impregnated in situ and a face was cut and polished. Images of UV-illuminated faces were obtained at three magnifications and then pooled into two groups. A box-counting technique was applied to area and outline of pores to obtain D v-box, and D s-box, respectively; D s was also calculated from area-perimeter relations ( D s- AP ). Box-count data showed two segments; D v-box and D s-box were evaluated in relation to each segment and to D s- AP . Coefficients of determination in the relation D s- AP vs D s-box were relatively low, indicating discrepancies between the two methods. Fractal dimensions were not scale-invariant. Values of D s-box for aggregate assemblies decreased with resolution, especially for single aggregate-size fractions. Values of D v-box were more influenced by aggregate size than resolution. Both D s-box and D v-box varied with resolution for freshly tilled soil. For somewhat consolidated soil, variations in values of both fractal dimensions were related to tillage systems. Values of D s-box and D v-box were highly correlated, with linear relations depending on magnification and type of soil structure.

Atomic Force Microscope Studies of Membranes: Surface Pore Structures of Diaflo Ultrafiltration Membranes

Noncontact atomic force microscopy (AFM) has been used to investigate the surface pore structure of eight Diaflo ultrafiltration membranes covering a range of nominal molecular weight cutoff (MWCO) from 3000 to 300,000 and manufactured from three different polymer types. Excellent high resolution images were obtained. Analysis of the pore images gave quantitative information on the surface pore structure, in particular the pore size distribution and surface roughness. Such data is compared to that obtained by other techniques. Noncontact AFM is a facile and informative means of studying the surface structure of porous materials such as synthetic membranes.

A Correlation for Miscible Flood Displacement Efficiency in the San Andres With NMR Relaxation

ABSTRACT A set of San Andres crystalline dolomite cores was examined for the relationship between pore attributes discernible from NMR relaxation and miscible flooding displacement efficiency. A strong correlation was observed between the inferred abundance of long relaxation time components and laboratory measured residual oil to a multicontact miscible displacement process. NMR relaxation time distribution proved to be a simple, noninvasive, nondestructive indicator of flow performance in the 12 San Andres dolomite samples examined. Spin-lattice relaxation measurements were conducted on clean, brine saturated core end pieces from plugs taken adjacent to those used for flow displacement studies. Sample data were deconvoluted into a distribution of relaxation times, which is intimately related to surface-to-volume ratio distribution. The median relaxation time was determined to be the most sensitive statistic to convey flow performance. Residual oil saturation was adequately represented by a power law function of the median relaxation time. Relaxation time is recognized to be a function of pore size, shape, surface roughness, and mineral composition. It was determined through direct observation by scanning electron microscopy that variation between samples was principally due to pore size distribution. Samples with larger mean pore size were observed to be less efficiently swept. Larger pores within a distribution are envisioned to bias individual fluid flow pathways, causing significant stranding of oil.

Flow phenomena in rocks: from continuum models to fractals, percolation, cellular automata, and simulated annealing

In this paper, theoretical and experimental approaches to flow, hydrodynamic dispersion, and miscible and immiscible displacement processes in reservoir rocks are reviewed and discussed. Both macroscopically homogeneous and heterogeneous rocks are considered. The latter are characterized by large-scale spatial variations and correlations in their effective properties and include rocks that may be characterized by several distinct degrees of porosity, a well-known example of which is a fractured rock with two degrees of porosity---those of the pores and of the fractures. First, the diagenetic processes that give rise to the present reservoir rocks are discussed and a few geometrical models of such processes are described. Then, measurement and characterization of important properties, such as pore-size distribution, pore-space topology, and pore surface roughness, and morphological properties of fracture networks are discussed. It is shown that fractal and percolation concepts play important roles in the characterization of rocks, from the smallest length scale at the pore level to the largest length scales at the fracture and fault scales. Next, various structural models of homogeneous and heterogeneous rock are discussed, and theoretical and computer simulation approaches to flow, dispersion, and displacement in such systems are reviewed. Two different modeling approaches to these phenomena are compared. The first approach is based on the classical equations of transport supplemented with constitutive equations describing the transport and other important coefficients and parameters. These are called the continuum models. The second approach is based on network models of pore space and fractured rocks; it models the phenomena at the smallest scale, a pore or fracture, and then employs large-scale simulation and modern concepts of the statistical physics of disordered systems, such as scaling and universality, to obtain the macroscopic properties of the system. The fundamental roles of the interconnectivity of the rock and its wetting properties in dispersion and two-phase flows, and those of microscopic and macroscopic heterogeneities in miscible displacements are emphasized. Two important conceptual advances for modeling fractured rocks and studying flow phenomena in porous media are also discussed. The first, based on cellular automata, can in principle be used for computing macroscopic properties of flow phenomena in any porous medium, regardless of the complexity of its structure. The second, simulated annealing, borrowed from optimization processes and the statistical mechanics of spin glasses, is used for finding the optimum structure of a fractured reservoir that honors a limited amount of experimental data.

"Honey, I Shrunk the Pores!"

Introduction When I was young, my parents instilled in me a curiosity about the physical nature of the world. I remember Dad, an avid reader of "The Country Guide," explaining the enormous power or a prairie thunderstorm by telling me "an inch of rainfall on all acre of land is over one hundred tons of water." To bring this analogy closer to our own business, it still amazes me that a reservoir one foot thick with ten per cent porosity will also hold almost one hundred tons of oil per acre of land. Sometimes we get so bogged down by the details of our business, we don't have time to think about some of nature's simple wonders. With thoughts like these in mind, it's neat to take a closer look at a parameter which is taken very much for granted: porosity. To ost of us, the only thing which matters is the absolute value of porosity, and obviously the higher the better! Some interestinghenomena pop to light, however, when one really visualizes things on a pore-scale. With that in mind, let's take closer look at some porous systems from the inside... Conventional Pore Systems Let's quickly review some basic geometric concepts, focussing at the pore-scale. Table 1 shows how Archie(1) and Lucia(2) classified carbonate pore sizes: a typical "medium"-sized pore is about 50 microns (0.002 inches). Pore throats, the inter-pore connections which determine permeability, are much smaller, often in the 1-10 micron range. Obviously, it takes an enormous number of these pores to form a reservoir. We also know that the size of the individual pores may not have much impact on the total porosity. Figure 1 shows the porosity resulting from a cubic arrangement of spherical grains is 48%, regardless of the size of the grains.owever, for a given porosity, the pore system surface area increases as the average pore size decreases (Table 2). The surface areas in Table 2 assume pores are spherical: however, in reality their shapes are much more complex. As a result, urface areas in reservoir rocks may be 100 times higher than shown in Table 2 due to tile dramatic effects of surface roughness.good example is Donaldson's work(3), which showed the TABLE 1: Pore size classifications. Table Available In Full Paper. TABLE 2: Ways to make 11% porosity in 1 m3 of rock. Table Available In Full Paper. surface area of many common reservoir rocks to be about 1 m2/gm. These large surface areas are rather startling at first glance. Imagine one cubic metre or oil-saturated rock with 11% porosity. Table 2 shows the resulting 0.11 m3 of oil would be spread over 10,000m2; accounting for pore surface roughness the area would actually be about 1,000,000 m2. To put it in more real terms, this would be like spreading a couple of cups of oil across the surface of a foothall field. Is it any wonder that oilfield recoveries average only about 25%?

Roughness of soil pore surface and its effect on available habitat space of microarthropods

Like the majority of natural objects, soil pores can be described by means of fractal geometry. Since the area of a fractal surface depends on the scale of measurement, the amount of available pore area for different size classes of non-burrowing soil animals should depend on the fractal dimension of the soil pore surface following the relationship A( δ)≈ δ 2− D s , were A is the area measured on scale δ, and D s is the fractal dimension of the surface. We estimated D s by photographing and digitizing thin sections of various Austrian soils. Images were analyzed using the area-perimeter method following the relationship P∼ A D p/2 , where P is the perimeter of an intersected soil pore measured at any convenient scale, A is its sectional area, and D p is the fractal dimension of the boundary line. D p/2 can be recovered by a linear regression in a plot of In P against In A. Under the assumption of isotropy adding 1 to D p yields the estimate of the fractal dimension of soil pore surface. Our estimates of D s≈2.3 suggest that a decrease in an order-of-magnitude of body length will increase available habitat-space approximately 4 times. We discuss the usefulness of the measurement of pore-wall roughness for predicting a size-class abundance/body size relationship in soil micro-arthropod communities.

Surface pore structures of micro- and ultrafiltration membranes imaged with the atomic force microscope

In this paper we present images of the surface of various microfiltration (MF) and ultrafiltration (UF) membranes obtained with an atomic force microscope (AFM) operating in air. The AFM works with an optical lever system and uses microfabricated cantilevers to minimize forces between tip and membrane surface. Three track-etched MF membranes with pores between 100 nm and 10 nm were used to demonstrate that the AFM can image openings in this range of size. The influence of the tip shape on the measured pore structure is discussed. Eight UF membranes with cutoff between 5,000 and 100,000 show wide variations in surface roughness, size and shape of pores, and homogenity. Most surfaces were found to have a network-like fine structure, in good agreement with field emission scanning electron micrographs. Surface pore characteristics like pore diameter, mean pore distance and pore density have been determined from image analysis. Pore sizes of the UF membranes were found to be between 7.2 and 36.6 nm, pore densities range from 88 to 482 pores/μm 2 and are much higher than for the MF membranes. The porosity is less than 7% for both MF and UF membranes.

Hydrodynamics of particulate motion in porous media.

We develop a general model for flow suspended particles in a porous medium. The model can take into account the effects of the morphology of the porous medium (including pore surface roughness and fractality), the chemistry of the flowing fluid, and all important forces between the particles and the pore surface. If surface deposition and pore plugging by size exclusion take place, the process is a percolation phenomenon which may belong to a different universality class than that of random percolation. The model is applied to two classes of problems, flow of solid, electrically charged colloidal particles, and that of stable emulsion droplets in a porous medium.

ChemInform Abstract: Application of Ion‐Scattering Spectroscopy to Catalyst Characterization

Abstract The study of surfaces has evolved in the last decade from a virtually dormant field to one that is vibrant with new ideas and technologies. In the past, the only useful information to be gained from surface techniques was physical in nature, i.e., surface area determination, pore size distributions, film thickness, and surface roughness. No chemical information could be obtained. Today, with the advent of spectroscopic methods, it is possible to gather a variety of information regarding the chemical nature of the surface. Examples of such information include oxidation state determinations, structural effects, and elemental and atomic analysis.

Wettability and Adsorption Characteristics of Crude-Oil Asphaltene and Polar Fractions

This study relates the chemical composition of the polar compounds of crude oil to the wettability of rock/oil/brine systems. Adsorption properties of polar and asphaltene fractions were evaluated to determine their effects on wettability. Polar compound fractions were found to cause an oil-wet state on Berea sandstone, but the effects were not a function of the polar-fraction concentration. The concentration of nitrogen/sulfur compounds in six crude-oil polar fractions correlated with the wettability of the polar fractions on Berea sandstone. Langmuir-type adsorption on Berea sandstone was observed in adsorption studies of the asphaltene and polar fractions. Additional analysis with brien-saturated Berea sandstone resulted in adsorption values up to three times less than that for dry Berea. The amount of polar fraction adsorbed on brine-saturated berea sandstone correlated with crude-oil wettability.

Application of Ion-Scattering Spectroscopy to Catalyst Characterization

Abstract The study of surfaces has evolved in the last decade from a virtually dormant field to one that is vibrant with new ideas and technologies. In the past, the only useful information to be gained from surface techniques was physical in nature, i.e., surface area determination, pore size distributions, film thickness, and surface roughness. No chemical information could be obtained. Today, with the advent of spectroscopic methods, it is possible to gather a variety of information regarding the chemical nature of the surface. Examples of such information include oxidation state determinations, structural effects, and elemental and atomic analysis.