The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
William P Johnson - One of the best experts on this subject based on the ideXlab platform.
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release of colloids from primary minimum contact under unfavorable conditions by perturbations in ionic strength and flow rate
Environmental Science & Technology, 2014Co-Authors: Eddy Pazmino, Jacob Trauscht, William P JohnsonAbstract:Colloid release from Surfaces in response to ionic strength and flow perturbations has been mechanistically simulated. However, these models do not address the mechanism by which colloid attachment occurs, at least in the presence of bulk colloid–collector repulsion (unfavorable conditions), which is a prevalent environmental condition. We test whether a mechanistic model that predicts colloid attachment under unfavorable conditions also predicts colloid release in response to reduced ionic strength (IS) and increased fluid velocity (conditions thought prevalent for mobilization of environmental colloids). The model trades in mean-field colloid–collector interaction for discrete representation of Surface Heterogeneity, which accounts for a combination of attractive and repulsive interactions simultaneously, and results in an attached colloid population (in primary minimum contact with the Surface) having a distribution of strengths of attraction. The model moderates equilibrium separation distance by incl...
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power law size distributed Heterogeneity explains colloid retention on soda lime glass in the presence of energy barriers
Langmuir, 2014Co-Authors: Eddy Pazmino, Jacob Trauscht, Brittany E Dame, William P JohnsonAbstract:This article concerns reading the nanoscale Heterogeneity thought responsible for colloid retention on Surfaces in the presence of energy barriers (unfavorable attachment conditions). We back out this Heterogeneity on glass Surfaces by comparing mechanistic simulations incorporating discrete Heterogeneity with colloid deposition experiments performed across a comprehensive set of experimental conditions. Original data is presented for attachment to soda lime glass for three colloid sizes (0.25, 1.1, and 1.95 μm microspheres) under a variety of ionic strengths and fluid velocities in an impinging jet system. A comparison of mechanistic particle trajectory simulations incorporating discrete Surface Heterogeneity represented by nanoscale zones of positive charge (heterodomains) indicates that a power law size distribution of heterodomains ranging in size from 120 to 60 nm in radius was able to explain the observed retention for all conditions examined. In contrast, uniform and random placement of single-size...
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Surface Heterogeneity on hemispheres in cell model yields all experimentally observed non straining colloid retention mechanisms in porous media in the presence of energy barriers
Langmuir, 2011Co-Authors: Eddy Pazmino, William P JohnsonAbstract:Many mechanisms of colloid retention in porous media under unfavorable conditions have been identified from experiments or theory, such as attachment at Surface heterogeneities, wedging at grain to grain contacts, retention via secondary energy minimum association in zones of low flow drag, and straining in pore throats too small to pass. However, no previously published model is capable of representing all of these mechanisms of colloid retention. In this work, we demonstrate that incorporation of Surface Heterogeneity into our hemispheres-in-cell model yields all experimentally observed non-straining retention mechanisms in porous media under unfavorable conditions. We also demonstrate that the predominance of any given retention mechanism depends on the coupled colloid-collector-flow interactions that are governed by parameters such as the size and spatial frequency of heterogeneous attractive domains, colloid size, and solution ionic strength. The force/torque balance-simulated retention is shown to d...
Zhangxin Chen - One of the best experts on this subject based on the ideXlab platform.
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model for Surface diffusion of adsorbed gas in nanopores of shale gas reservoirs
Industrial & Engineering Chemistry Research, 2015Co-Authors: Keliu Wu, Xiangfang Li, Chenchen Wang, Wei Yu, Zhangxin ChenAbstract:Surface diffusion plays a key role in gas mass transfer due to the majority of adsorbed gas within abundant nanopores of organic matter in shale gas reservoirs. Surface diffusion simulation is very complex as a result of high reservoir pressure, Surface Heterogeneity, and nonisothermal desorption in shale gas reservoirs. In this paper, a new model of Surface diffusion for adsorbed gas in shale gas reservoirs is established, which is based on a Hwang model derived under a low pressure condition and considers the effect of adsorbed gas coverage under high pressure. Additionally, this new model considers the effects of Surface Heterogeneity, isosteric sorption heat, and nonisothermal gas desorption. Results show that (1) the Surface diffusion coefficient increases with pressure and temperature, while it decreases with activation energy and gas molecular weight; (2) contributions of viscous flow, Knudsen diffusion, and Surface diffusion to the total gas mass transfer are varying during the development of shal...
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Model for Surface Diffusion of Adsorbed Gas in Nanopores of Shale Gas Reservoirs
2015Co-Authors: Chenchen Wang, Zhangxin ChenAbstract:Surface diffusion plays a key role in gas mass transfer due to the majority of adsorbed gas within abundant nanopores of organic matter in shale gas reservoirs. Surface diffusion simulation is very complex as a result of high reservoir pressure, Surface Heterogeneity, and nonisothermal desorption in shale gas reservoirs. In this paper, a new model of Surface diffusion for adsorbed gas in shale gas reservoirs is established, which is based on a Hwang model derived under a low pressure condition and considers the effect of adsorbed gas coverage under high pressure. Additionally, this new model considers the effects of Surface Heterogeneity, isosteric sorption heat, and nonisothermal gas desorption. Results show that (1) the Surface diffusion coefficient increases with pressure and temperature, while it decreases with activation energy and gas molecular weight; (2) contributions of viscous flow, Knudsen diffusion, and Surface diffusion to the total gas mass transfer are varying during the development of shale gas reservoirs, which are mainly controlled by nanopore-scale and pressure; (3) in micropores (pore radius of 50 nm), the contribution is less than 4.39%, which is negligible; in mesopores (2 nm < pore radius < 50 nm), the contribution is between micropores and macropores
Eddy Pazmino - One of the best experts on this subject based on the ideXlab platform.
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release of colloids from primary minimum contact under unfavorable conditions by perturbations in ionic strength and flow rate
Environmental Science & Technology, 2014Co-Authors: Eddy Pazmino, Jacob Trauscht, William P JohnsonAbstract:Colloid release from Surfaces in response to ionic strength and flow perturbations has been mechanistically simulated. However, these models do not address the mechanism by which colloid attachment occurs, at least in the presence of bulk colloid–collector repulsion (unfavorable conditions), which is a prevalent environmental condition. We test whether a mechanistic model that predicts colloid attachment under unfavorable conditions also predicts colloid release in response to reduced ionic strength (IS) and increased fluid velocity (conditions thought prevalent for mobilization of environmental colloids). The model trades in mean-field colloid–collector interaction for discrete representation of Surface Heterogeneity, which accounts for a combination of attractive and repulsive interactions simultaneously, and results in an attached colloid population (in primary minimum contact with the Surface) having a distribution of strengths of attraction. The model moderates equilibrium separation distance by incl...
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power law size distributed Heterogeneity explains colloid retention on soda lime glass in the presence of energy barriers
Langmuir, 2014Co-Authors: Eddy Pazmino, Jacob Trauscht, Brittany E Dame, William P JohnsonAbstract:This article concerns reading the nanoscale Heterogeneity thought responsible for colloid retention on Surfaces in the presence of energy barriers (unfavorable attachment conditions). We back out this Heterogeneity on glass Surfaces by comparing mechanistic simulations incorporating discrete Heterogeneity with colloid deposition experiments performed across a comprehensive set of experimental conditions. Original data is presented for attachment to soda lime glass for three colloid sizes (0.25, 1.1, and 1.95 μm microspheres) under a variety of ionic strengths and fluid velocities in an impinging jet system. A comparison of mechanistic particle trajectory simulations incorporating discrete Surface Heterogeneity represented by nanoscale zones of positive charge (heterodomains) indicates that a power law size distribution of heterodomains ranging in size from 120 to 60 nm in radius was able to explain the observed retention for all conditions examined. In contrast, uniform and random placement of single-size...
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Surface Heterogeneity on hemispheres in cell model yields all experimentally observed non straining colloid retention mechanisms in porous media in the presence of energy barriers
Langmuir, 2011Co-Authors: Eddy Pazmino, William P JohnsonAbstract:Many mechanisms of colloid retention in porous media under unfavorable conditions have been identified from experiments or theory, such as attachment at Surface heterogeneities, wedging at grain to grain contacts, retention via secondary energy minimum association in zones of low flow drag, and straining in pore throats too small to pass. However, no previously published model is capable of representing all of these mechanisms of colloid retention. In this work, we demonstrate that incorporation of Surface Heterogeneity into our hemispheres-in-cell model yields all experimentally observed non-straining retention mechanisms in porous media under unfavorable conditions. We also demonstrate that the predominance of any given retention mechanism depends on the coupled colloid-collector-flow interactions that are governed by parameters such as the size and spatial frequency of heterogeneous attractive domains, colloid size, and solution ionic strength. The force/torque balance-simulated retention is shown to d...
Georges Guiochon - One of the best experts on this subject based on the ideXlab platform.
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adsorption mechanisms and effect of temperature in reversed phase liquid chromatography meaning of the classical van t hoff plot in chromatography
Analytical Chemistry, 2006Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:The effect of temperature on the adsorption and retention behaviors of a low molecular weight compound (phenol) on a C18-bonded silica column (C18-Sunfire, Waters) from aqueous solutions of methanol (20%) or acetonitrile (15%) was investigated. The results of the measurements were interpreted successively on the basis of the linear (i.e., overall retention factors) and the nonlinear (i.e., adsorption isotherms, Surface Heterogeneity, saturation capacities, and equilibrium constants) chromatographic methods. The confrontation of these two approaches confirmed the impossibility of a sound physical interpretation of the conventional Van’t Hoff plot. The classical linear chromatography theory assumes that retention is determined by the equilibrium thermodynamics of analytes between a homogeneous stationary phase and a homogeneous mobile phase (although there may be two or several types of interactions). From values of the experimental retention factors in a temperature interval and estimates of the activity c...
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effect of the Surface Heterogeneity of the stationary phase on the range of concentrations for linear chromatography
Analytical Chemistry, 2005Co-Authors: Fabrice Gritti, Georges GuiochonAbstract:The range of sample sizes within which linear chromatographic behavior is achieved in a column depends on the Surface Heterogeneity of the RPLC adsorbents. Two widely different commercial adsorbents were tested, the end-capped XTerra-C18 and the non-end-capped Resolve-C18. Adsorption isotherm data of caffeine were acquired by frontal analysis. These data were modeled and used to calculate the adsorption energy distribution (AED). This double analysis informs on the degree of Surface Heterogeneity. The best adsorption isotherm models are the bi-Langmuir and the tetra-Langmuir isotherms for XTerra and Resolve, respectively. Their respective AEDs are bimodal and quadrimodal distributions. This interpretation of the results and the actual presence of a low density of high-energy adsorption sites on Resolve-C18 were validated by measuring the dependence of the peak retention times on the size of caffeine samples (20-μL volume, concentrations 10, 1, 0.1, 1 × 10-2, 1 × 10-3, 1 × 10-4, and 1 × 10-5 g/L). The expe...
Keliu Wu - One of the best experts on this subject based on the ideXlab platform.
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model for Surface diffusion of adsorbed gas in nanopores of shale gas reservoirs
Industrial & Engineering Chemistry Research, 2015Co-Authors: Keliu Wu, Xiangfang Li, Chenchen Wang, Wei Yu, Zhangxin ChenAbstract:Surface diffusion plays a key role in gas mass transfer due to the majority of adsorbed gas within abundant nanopores of organic matter in shale gas reservoirs. Surface diffusion simulation is very complex as a result of high reservoir pressure, Surface Heterogeneity, and nonisothermal desorption in shale gas reservoirs. In this paper, a new model of Surface diffusion for adsorbed gas in shale gas reservoirs is established, which is based on a Hwang model derived under a low pressure condition and considers the effect of adsorbed gas coverage under high pressure. Additionally, this new model considers the effects of Surface Heterogeneity, isosteric sorption heat, and nonisothermal gas desorption. Results show that (1) the Surface diffusion coefficient increases with pressure and temperature, while it decreases with activation energy and gas molecular weight; (2) contributions of viscous flow, Knudsen diffusion, and Surface diffusion to the total gas mass transfer are varying during the development of shal...
