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Grant S Heffelfinger - One of the best experts on this subject based on the ideXlab platform.
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Transport diffusion of liquid water and methanol through membranes
The Journal of Chemical Physics, 2002Co-Authors: Qinxin Zhang, Grant S Heffelfinger, Jie Zheng, Abhijit V. Shevade, Luzheng Zhang, Stevin H. Gehrke, Shaoyi JiangAbstract:In this work, we carried out Dual-Control-Volume grand canonical molecular dynamics simulations of the transport diffusion of liquid water and methanol to vacuum under a fixed chemical potential gradient through a slit pore consisting of Au(111) surfaces covered by −CH3 or −OH terminated self-assembled monolayers (SAMs). Methanol and water are selected as model fluid molecules because water represents a strongly polar molecule while methanol is intermediate between nonpolar and strongly polar molecules. Surface hydrophobicity is adjusted by varying the terminal group of −CH3 (hydrophobic) or −OH (hydrophilic) of SAMs. We observed for the first time from simulations the convex and concave interfaces of fluids transporting across the slit pores. Results show that the characteristics of the interfaces are determined by the interactions between fluid molecules and surfaces. The objective of this work is to provide a fundamental understanding of how these interactions affect transport diffusion.
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direct molecular simulation of gradient driven diffusion of large molecules using constant pressure
Journal of Chemical Physics, 1999Co-Authors: Aidan P Thompson, Grant S HeffelfingerAbstract:Dual Control Volume grand canonical molecular dynamics (DCV-GCMD) is a boundary-driven nonequilibrium molecular-dynamics technique for simulating gradient-driven diffusion in multicomponent systems. Two Control Volumes are established at opposite ends of the simulation box. Constant temperature and chemical potential of diffusing species are imposed in the Control Volumes (i.e., constant-μ1⋯μn−1μnVT). This results in stable chemical potential gradients and steady-state diffusion fluxes in the region between the Control Volumes. We present results and detailed analysis for a new constant-pressure variant of the DCV-GCMD method in which one of the diffusing species for which a steady-state diffusion flux exists does not have to be inserted or deleted. Constant temperature, pressure, and chemical potential of all diffusing species except one are imposed in the Control Volumes (i.e., constant-μ1⋯μn−1NnPT). The constant-pressure method can be applied to situations in which insertion and deletion of large molec...
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massively parallel Dual Control Volume grand canonical molecular dynamics with ladera ii gradient driven diffusion through polymers
Molecular Physics, 1998Co-Authors: D M Ford, Grant S HeffelfingerAbstract:This paper, the second part of a series, extends the capabilities of the LADERA FORTRAN code for massively parallel Dual Control Volume grand canonical molecular dynamics (DCVGCMD). DCV-GCMD is a hybrid of two more common molecular simulation techniques (grand canonical Monte Carlo and molecular dynamics) which allows the direct molecularlevel modelling of diffusion under a chemical potential gradient. The present version of the code, LADERA-B has the capability of modelling systems with explicit intramolecular interactions such as bonds, angles, and dihedral rotations. The utility of the new code for studying gradient-driven diffusion of small molecules through polymers is demonstrated by applying it to two model systems. LADERA-B includes another new feature, which is the use of neighbour lists in force calculations. This feature increases the speed of the code but presents several challenges in the parallel hybrid algorithm. There is discussion on how these problems were addressed and how our implement...
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massively parallel Dual Control Volume grand canonical molecular dynamics with ladera i gradient driven diffusion in lennard jones fluids
Molecular Physics, 1998Co-Authors: Grant S Heffelfinger, D M FordAbstract:A new algorithm to enable the implementation of Dual Control Volume grand canonical molecular dynamics (DCV-GCMD) on massively parallel (MP) architectures is presented. DCVGCMD can be thought of as hybridization of molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) and was developed recently to make possible the simulation of gradient-driven diffusion. The method has broad application to such problems as membrane separations, drug delivery systems, diffusion in polymers and zeolites, etc. The massively parallel algorithm for the DCV-GCMD method has been implemented in a code named LADERA which employs the short range Lennard-Jones potential for pure fluids and multicomponent mixtures including bulk and confined (single pore as well as amorphous solid materials) systems. Like DCV-GCMD, LADERA's MP algorithm can be thought of as a hybridization of two different algorithms, spatial MD and spatial GCMC. The DCV-GCMD method is described fully followed by the DCV-GCMD parallel algorithm employed in ...
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gradient driven diffusion using Dual Control Volume grand canonical molecular dynamics dcv gcmd
MRS Proceedings, 1995Co-Authors: Frank Van Swol, Grant S HeffelfingerAbstract:Recently we developed a new nonequilibrium molecular simulation method [1] that allows the direct study of interdiffusion in multicomponent mixtures. The method combines stochastic insertion and deletion moves characteristic of grand canonical (GC) simulations with molecular dynamics (MD) to Control the chemical potential μi of a species i. Restricting the insertions and deletions to two separate Control Volumes (CV’s) one can apply different μi’ s in distinct locations, and thus create chemical potential gradients. DCV-GCMD can be used to study transient phenomena such as the filling of micropores or used in steady-state mode to determine the diffusion coefficients in multicomponent fluid mixtures. We report on the effects of molecular interactions and demonstrate how in a sufficiently nonideal ternary mixture this can lead to up-hill or reverse diffusion. In addition we introduce a novel extension of DCV-GCMD that is specifically designed for the study of gradient-driven diffusion of molecules that are simply too large to be inserted and deleted.
Tina M Nenoff - One of the best experts on this subject based on the ideXlab platform.
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effect of pressure membrane thickness and placement of Control Volumes on the flux of methane through thin silicalite membranes a Dual Control Volume grand canonical molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Marcus G Martin, Aidan P Thompson, Tina M NenoffAbstract:The flux of methane through the straight channels of thin silicalite membranes is studied via Dual Control Volume grand canonical molecular dynamics. The adsorption layers on the surfaces of the thin membranes are found to provide a significant resistance to the flux of methane. This strong surface effect for thin membranes requires that the Control Volumes (where insertions and deletions are performed) must be placed far enough away from the membrane surface that they do not overlap with the surface adsorption layer. The permeance (flux/pressure drop) of methane through the surface layer is shown to be insensitive to both the average pressure and the pressure drop. In contrast, the permeance through the interior of the membrane increases with decreasing average pressure. These results are explained using a model which treats the transport through the surface barrier as driven by the pressure gradient and transport through the zeolite as driven by the chemical potential gradient. A new force field named D...
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effect of pressure membrane thickness and placement of Control Volumes on the flux of methane through thin silicalite membranes a Dual Control Volume grand canonical molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Marcus G Martin, Aidan P Thompson, Tina M NenoffAbstract:The flux of methane through the straight channels of thin silicalite membranes is studied via Dual Control Volume grand canonical molecular dynamics. The adsorption layers on the surfaces of the thin membranes are found to provide a significant resistance to the flux of methane. This strong surface effect for thin membranes requires that the Control Volumes (where insertions and deletions are performed) must be placed far enough away from the membrane surface that they do not overlap with the surface adsorption layer. The permeance (flux/pressure drop) of methane through the surface layer is shown to be insensitive to both the average pressure and the pressure drop. In contrast, the permeance through the interior of the membrane increases with decreasing average pressure. These results are explained using a model which treats the transport through the surface barrier as driven by the pressure gradient and transport through the zeolite as driven by the chemical potential gradient. A new force field named DACNIS is presented which accurately describes the adsorption isotherms of methane and ethane in silicalite.
Abbas Firoozabadi - One of the best experts on this subject based on the ideXlab platform.
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phase behavior and flow in shale nanopores from molecular simulations
Fluid Phase Equilibria, 2016Co-Authors: Zhehui Jin, Abbas FiroozabadiAbstract:Abstract Phase behavior and flow in shale nanopores, due to fluid heterogeneity, cannot be described by bulk and continuum-based formulations. The interactions between fluid and rock molecules are important in both phase behavior and flow. As a result, frameworks from bulk equations of state in phase behavior, and continuum mechanisms and Klinkenberg slippage in flow may become inapplicable. Recently, we have studied both phase behavior and flow in nanopores using density functional theory and various molecular simulations. This work addresses a number of issues related to the adsorption of mixtures of hydrocarbons, carbon dioxide and water as well as methane flow at different pressure conditions in nanopores. For flow, we use the Dual Control Volume-grand canonical molecular dynamics (DCV-GCMD) simulation as in our previous work. We use a smaller pressure difference between high and low pressure reservoirs connected to the nanopores. We find that similar to our past work, the flux of methane in the slit pores can be two orders of magnitude higher than the results from the Hagen-Poiseuille equation.
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Flow of methane in shale nanopores at low and high pressure by molecular dynamics simulations
The Journal of chemical physics, 2015Co-Authors: Zhehui Jin, Abbas FiroozabadiAbstract:Flow in shale nanopores may be vastly different from that in the conventional permeable media. In large pores and fractures, flow is governed by viscosity and pressure-driven. Convection describes the process. Pores in some shale media are in nanometer range. At this scale, continuum flow mechanism may not apply. Knudsen diffusion and hydrodynamic expressions such as the Hagen-Poiseuille equation and their modifications have been used to compute flow in nanopores. Both approaches may have drawbacks and can significantly underestimate molecular flux in nanopores. In this work, we use the Dual Control Volume-grand canonical molecular dynamics simulations to investigate methane flow in carbon nanopores at low and high pressure conditions. Our simulations reveal that methane flow in a slit pore width of 1–4 nm can be more than one order of magnitude greater than that from Knudsen diffusion at low pressure and the Hagen-Poiseuille equation at high pressure. Knudsen diffusion and Hagen-Poiseuille equations do not account for surface adsorption and mobility of the adsorbed molecules, and inhomogeneous fluid density distributions. Mobility of molecules in the adsorbed layers significantly increases molecular flux. Molecular velocity profiles in nanopores deviate significantly from the Navier-Stokes hydrodynamic predictions. Our molecular simulation results are in agreement with the enhanced flow measurements in carbon nanotubes.
Marcus G Martin - One of the best experts on this subject based on the ideXlab platform.
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effect of pressure membrane thickness and placement of Control Volumes on the flux of methane through thin silicalite membranes a Dual Control Volume grand canonical molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Marcus G Martin, Aidan P Thompson, Tina M NenoffAbstract:The flux of methane through the straight channels of thin silicalite membranes is studied via Dual Control Volume grand canonical molecular dynamics. The adsorption layers on the surfaces of the thin membranes are found to provide a significant resistance to the flux of methane. This strong surface effect for thin membranes requires that the Control Volumes (where insertions and deletions are performed) must be placed far enough away from the membrane surface that they do not overlap with the surface adsorption layer. The permeance (flux/pressure drop) of methane through the surface layer is shown to be insensitive to both the average pressure and the pressure drop. In contrast, the permeance through the interior of the membrane increases with decreasing average pressure. These results are explained using a model which treats the transport through the surface barrier as driven by the pressure gradient and transport through the zeolite as driven by the chemical potential gradient. A new force field named D...
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effect of pressure membrane thickness and placement of Control Volumes on the flux of methane through thin silicalite membranes a Dual Control Volume grand canonical molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Marcus G Martin, Aidan P Thompson, Tina M NenoffAbstract:The flux of methane through the straight channels of thin silicalite membranes is studied via Dual Control Volume grand canonical molecular dynamics. The adsorption layers on the surfaces of the thin membranes are found to provide a significant resistance to the flux of methane. This strong surface effect for thin membranes requires that the Control Volumes (where insertions and deletions are performed) must be placed far enough away from the membrane surface that they do not overlap with the surface adsorption layer. The permeance (flux/pressure drop) of methane through the surface layer is shown to be insensitive to both the average pressure and the pressure drop. In contrast, the permeance through the interior of the membrane increases with decreasing average pressure. These results are explained using a model which treats the transport through the surface barrier as driven by the pressure gradient and transport through the zeolite as driven by the chemical potential gradient. A new force field named DACNIS is presented which accurately describes the adsorption isotherms of methane and ethane in silicalite.
Aidan P Thompson - One of the best experts on this subject based on the ideXlab platform.
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effect of pressure membrane thickness and placement of Control Volumes on the flux of methane through thin silicalite membranes a Dual Control Volume grand canonical molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Marcus G Martin, Aidan P Thompson, Tina M NenoffAbstract:The flux of methane through the straight channels of thin silicalite membranes is studied via Dual Control Volume grand canonical molecular dynamics. The adsorption layers on the surfaces of the thin membranes are found to provide a significant resistance to the flux of methane. This strong surface effect for thin membranes requires that the Control Volumes (where insertions and deletions are performed) must be placed far enough away from the membrane surface that they do not overlap with the surface adsorption layer. The permeance (flux/pressure drop) of methane through the surface layer is shown to be insensitive to both the average pressure and the pressure drop. In contrast, the permeance through the interior of the membrane increases with decreasing average pressure. These results are explained using a model which treats the transport through the surface barrier as driven by the pressure gradient and transport through the zeolite as driven by the chemical potential gradient. A new force field named DACNIS is presented which accurately describes the adsorption isotherms of methane and ethane in silicalite.
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effect of pressure membrane thickness and placement of Control Volumes on the flux of methane through thin silicalite membranes a Dual Control Volume grand canonical molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Marcus G Martin, Aidan P Thompson, Tina M NenoffAbstract:The flux of methane through the straight channels of thin silicalite membranes is studied via Dual Control Volume grand canonical molecular dynamics. The adsorption layers on the surfaces of the thin membranes are found to provide a significant resistance to the flux of methane. This strong surface effect for thin membranes requires that the Control Volumes (where insertions and deletions are performed) must be placed far enough away from the membrane surface that they do not overlap with the surface adsorption layer. The permeance (flux/pressure drop) of methane through the surface layer is shown to be insensitive to both the average pressure and the pressure drop. In contrast, the permeance through the interior of the membrane increases with decreasing average pressure. These results are explained using a model which treats the transport through the surface barrier as driven by the pressure gradient and transport through the zeolite as driven by the chemical potential gradient. A new force field named D...
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direct molecular simulation of gradient driven diffusion of large molecules using constant pressure
Journal of Chemical Physics, 1999Co-Authors: Aidan P Thompson, Grant S HeffelfingerAbstract:Dual Control Volume grand canonical molecular dynamics (DCV-GCMD) is a boundary-driven nonequilibrium molecular-dynamics technique for simulating gradient-driven diffusion in multicomponent systems. Two Control Volumes are established at opposite ends of the simulation box. Constant temperature and chemical potential of diffusing species are imposed in the Control Volumes (i.e., constant-μ1⋯μn−1μnVT). This results in stable chemical potential gradients and steady-state diffusion fluxes in the region between the Control Volumes. We present results and detailed analysis for a new constant-pressure variant of the DCV-GCMD method in which one of the diffusing species for which a steady-state diffusion flux exists does not have to be inserted or deleted. Constant temperature, pressure, and chemical potential of all diffusing species except one are imposed in the Control Volumes (i.e., constant-μ1⋯μn−1NnPT). The constant-pressure method can be applied to situations in which insertion and deletion of large molec...
