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Patrice Malfreyt - One of the best experts on this subject based on the ideXlab platform.

  • Test-area surface tension calculation of the graphene-methane interface: Fluctuations and commensurability
    Journal of Chemical Physics, 2017
    Co-Authors: H. D. D'oliveira, Patrice Malfreyt, X. Davoy, E. Arche, Aziz Ghoufi
    Abstract:

    The surface tension (gamma) of methane on a graphene monolayer is calculated by using the test-area approach. By using a united atom model to describe methane molecules, strong fluctuations of surface tension as a function of the surface area of the graphene are evidenced. In contrast with the Liquid-Vapor Interfaces, the use of a larger cutoff does not fully erase the fluctuations in the surface tension. Counterintuitively, the description of methane and graphene from the Optimized Potentials for Liquid Simulations all-atom model and a flexible model, respectively, led to a lessening in the surface tension fluctuations. This result suggests that the origin of fluctuations in gamma is due to a model-effect rather than size-effects. We show that the molecular origin of these fluctuations is the result of a commensurable organization between both graphene and methane. This commensurable structure can be avoided by describing methane and graphene from a flexible force field. Although differences in gamma with respect to the model have been often reported, it is the first time that the model drastically affects the physics of a system. Published by AIP Publishing.

  • Bulk and Liquid–Vapor Interface of Pyrrolidinium-Based Ionic Liquids: A Molecular Simulation Study
    Journal of Physical Chemistry B, 2014
    Co-Authors: Xavier Paredes, Josefa Fernández, Agílio A. H. Pádua, Patrice Malfreyt, Friedrich Malberg, Barbara Kirchner, Alfonso S. Pensado
    Abstract:

    Using molecular dynamics simulations, we have studied the structure of three 1-butyl-1-methylpyrrolidinium ionic liquids whose anions are triflate, bis(trifluoromethanesulfonyl)imide, and tris(pentafluoroethyl)trifluorophosphate. The structure of the bulk phase of the three ionic liquids has been interpreted using radial and spatial distribution functions and structure factors that allows us to characterize the morphology of the polar and nonpolar domains present in this family of liquids. The size of the polar regions depends on the anion size, whereas the morphology of the nonpolar domains is anion-independent. Furthermore, the surface ordering properties of the ionic liquids and charge and density profiles were also studied using molecular simulations. The surface tension of the liquid–vapor Interfaces of these ionic liquids was also predicted from our molecular simulations. In addition, microscopic structural analysis of orientational ordering at the interface and density profiles along the direction ...

  • Bulk and Liquid-Vapor Interface of Pyrrolidinium-Based Ionic Liquids: A Molecular Simulation Study.
    Journal of Physical Chemistry B, 2014
    Co-Authors: Xavier Paredes, Josefa Fernández, Agílio A. H. Pádua, Patrice Malfreyt, Friedrich Malberg, Barbara Kirchner, Alfonso S. Pensado
    Abstract:

    Using molecular dynamics simulations, we have studied the structure of three 1-butyl-1-methylpyrrolidinium ionic liquids whose anions are triflate, bis(trifluoromethanesulfonyl)imide, and tris(pentafluoroethyl)trifluorophosphate. The structure of the bulk phase of the three ionic liquids has been interpreted using radial and spatial distribution functions and structure factors that allows us to characterize the morphology of the polar and nonpolar domains present in this family of liquids. The size of the polar regions depends on the anion size, whereas the morphology of the nonpolar domains is anion-independent. Furthermore, the surface ordering properties of the ionic liquids and charge and density profiles were also studied using molecular simulations. The surface tension of the Liquid-Vapor Interfaces of these ionic liquids was also predicted from our molecular simulations. In addition, microscopic structural analysis of orientational ordering at the interface and density profiles along the direction normal to the interface suggest that the alkyl chains of the cation tend to protrude toward the vacuum, and the presence of the interface leads to a strong organization of the liquid phase in the region close to the interface. In the interfacial area, the polar regions of the ionic liquids are more structured than those in the bulk phase, whereas the opposite behavior is observed for the nonpolar regions.

  • Recent advances in Many Body Dissipative Particles Dynamics simulations of Liquid-Vapor Interfaces
    The European Physical Journal E, 2013
    Co-Authors: Aziz Ghoufi, Janine Emile, Patrice Malfreyt
    Abstract:

    Many Body Dissipative Particles Dynamics (MDPD) simulation is a novel promising mesoscopic method to model the Liquid-Vapor Interfaces. Based upon works of Paganobarraga and Frenkel (J. Chem. Phys. 15, 5015 (2001)) and Trofimov (J. Chem. Phys. 117, 9383 (2002)) and of Warren (Phys. Rev. E 68, 066702 (2003)) this method has been critically reviewed during this last decade. We propose here to give an overview of the Many Body Dissipative Particles Dynamic simulation within the framework of the Liquid-Vapor Interfaces. We recall the theoretical background of MDPD and we present some recent results of systems of interest such as water Liquid-Vapor Interfaces and salt effect on water surface tension. Additionally we discuss the ability of MDPD to capture the mechanisms at the mesoscopic scale through the formation of micelles and the coalescence of a nanodroplet water on water surface.

  • calculation of the surface tension and pressure components from a non exponential perturbation method of the thermodynamic route
    Journal of Chemical Physics, 2012
    Co-Authors: Aziz Ghoufi, Patrice Malfreyt
    Abstract:

    Surface tension is probably the most important interfacial property and a large number of techniques have been devoted to its calculation. Usually, this calculation is carried out using mechanical or thermodynamic definitions. The mechanical route uses an arbitrary choice to affect the contribution of the pairwise force. To overcome this arbitrariness, a thermodynamic route based on the area perturbation (test-area (TA) method) has been developed for the calculation of surface tension. The volume perturbation (VP) method provides an original route to compute the components of the pressure tensor. These two routes are developed from the perturbation theory leading to working expressions using exponential averages of energy. The use of exponential averages makes the calculation strongly dependent on the occurrence of low values of ΔU. Additionally, the decomposition of the energy to obtain local surface tension is nontrivial. From the explicit derivation of the partition function the exponential average is avoided providing an interesting alternative to TA, VP, and mechanical methods. To make a consistent comparison, we study the profiles of the surface tension along the direction normal to the surface for the different definitions and techniques in the cases of Liquid-Vapor Interfaces of acids gases, binary, and apolar systems.

Markus Tuller - One of the best experts on this subject based on the ideXlab platform.

  • hydraulic conductivity of variably saturated porous media film and corner flow in angular pore space
    Water Resources Research, 2001
    Co-Authors: Markus Tuller, Dani Or
    Abstract:

    Many models for hydraulic conductivity of partially saturated porous media rely on oversimplified representation of the pore space as a bundle of cylindrical capillaries and disregard flow in liquid films. Recent progress in modeling liquid behavior in angular pores of partially saturated porous media offers an alternative framework. We assume that equilibrium Liquid-Vapor Interfaces provide well-defined and stable boundaries for slow laminar film and corner flow regimes in pore space comprised of angular pores connected to slit-shaped spaces. Knowledge of liquid configuration in the assumed geometry facilitates calculation of average liquid velocities in films and corners and enables derivation of pore-scale hydraulic conductivity as a function of matric potential. The pore-scale model is statistically upscaled to represent hydraulic conductivity for a sample of porous medium. Model parameters for the analytical sample-scale expressions are estimated from measured liquid retention data and other measurable medium properties. Model calculations illustrate the important role of film flow, whose contribution dominates capillary flow (in full pores and corners) at relatively high matric potentials (approximately −100 to −300 J kg−1, or −1 to 3 bars). The crossover region between film and capillary flow is marked by a significant change in the slope of the hydraulic conductivity function as often observed in measurements. Model predictions are compared with the widely applied van Genuchten–Mualem model and yield reasonable agreement with measured retention and hydraulic conductivity data over a wide range of soil textural classes.

  • liquid retention and interfacial area in variably saturated porous media upscaling from single pore to sample scale model
    Water Resources Research, 1999
    Co-Authors: Markus Tuller
    Abstract:

    A new model for liquid configuration in angular pore space considering both capillary and adsorptive contributions was proposed as an alternative to the conventional bundle of capillaries representation. In this study we develop a statistical framework for upscaling pore-scale processes to represent a sample-scale response of variably saturated porous medium. The representation of pore size distribution by the gamma distribution enables derivation of closed-form expressions for sample-scale liquid retention and Liquid-Vapor interfacial area. The statistical framework calculates the expected values of liquid configuration as a function of pore geometry and chemical potential considerations. Media properties are used to estimate upscaling parameters by matching model predictions with measured retention data subject to specific surface area constraint. Additionally, a method for estimating liquid-solid adsorption behavior for the medium is proposed. Model predictions compare favorably with measured retention data, yielding a similar close fit as obtained with the van Genuchten parametric model. Liquid-Vapor interfacial area as a function of chemical potential is readily calculated using the estimated retention parameters. Model calculations of Liquid-Vapor interfacial area for sand show reasonable agreement with measurements obtained with surface-active tracers. The contribution of liquid films dominates the total Liquid-Vapor interfacial area and often surpasses the capillary contribution (curved menisci) by several orders of magnitude. This illustrates potential limitations in using cylindrical pore network modeling of interfacial area for multiphase flow predictions. The detailed picture of liquid vapor Interfaces provides a sound basis for unsaturated hydraulic conductivity calculations in the sample cross section (i.e., neglecting network effects) and offers insights into microbial habitats and related exchange processes in partially saturated porous media.

Alfonso S. Pensado - One of the best experts on this subject based on the ideXlab platform.

  • Bulk and Liquid–Vapor Interface of Pyrrolidinium-Based Ionic Liquids: A Molecular Simulation Study
    Journal of Physical Chemistry B, 2014
    Co-Authors: Xavier Paredes, Josefa Fernández, Agílio A. H. Pádua, Patrice Malfreyt, Friedrich Malberg, Barbara Kirchner, Alfonso S. Pensado
    Abstract:

    Using molecular dynamics simulations, we have studied the structure of three 1-butyl-1-methylpyrrolidinium ionic liquids whose anions are triflate, bis(trifluoromethanesulfonyl)imide, and tris(pentafluoroethyl)trifluorophosphate. The structure of the bulk phase of the three ionic liquids has been interpreted using radial and spatial distribution functions and structure factors that allows us to characterize the morphology of the polar and nonpolar domains present in this family of liquids. The size of the polar regions depends on the anion size, whereas the morphology of the nonpolar domains is anion-independent. Furthermore, the surface ordering properties of the ionic liquids and charge and density profiles were also studied using molecular simulations. The surface tension of the liquid–vapor Interfaces of these ionic liquids was also predicted from our molecular simulations. In addition, microscopic structural analysis of orientational ordering at the interface and density profiles along the direction ...

  • Bulk and Liquid-Vapor Interface of Pyrrolidinium-Based Ionic Liquids: A Molecular Simulation Study.
    Journal of Physical Chemistry B, 2014
    Co-Authors: Xavier Paredes, Josefa Fernández, Agílio A. H. Pádua, Patrice Malfreyt, Friedrich Malberg, Barbara Kirchner, Alfonso S. Pensado
    Abstract:

    Using molecular dynamics simulations, we have studied the structure of three 1-butyl-1-methylpyrrolidinium ionic liquids whose anions are triflate, bis(trifluoromethanesulfonyl)imide, and tris(pentafluoroethyl)trifluorophosphate. The structure of the bulk phase of the three ionic liquids has been interpreted using radial and spatial distribution functions and structure factors that allows us to characterize the morphology of the polar and nonpolar domains present in this family of liquids. The size of the polar regions depends on the anion size, whereas the morphology of the nonpolar domains is anion-independent. Furthermore, the surface ordering properties of the ionic liquids and charge and density profiles were also studied using molecular simulations. The surface tension of the Liquid-Vapor Interfaces of these ionic liquids was also predicted from our molecular simulations. In addition, microscopic structural analysis of orientational ordering at the interface and density profiles along the direction normal to the interface suggest that the alkyl chains of the cation tend to protrude toward the vacuum, and the presence of the interface leads to a strong organization of the liquid phase in the region close to the interface. In the interfacial area, the polar regions of the ionic liquids are more structured than those in the bulk phase, whereas the opposite behavior is observed for the nonpolar regions.

Aziz Ghoufi - One of the best experts on this subject based on the ideXlab platform.

  • Test-area surface tension calculation of the graphene-methane interface: Fluctuations and commensurability
    Journal of Chemical Physics, 2017
    Co-Authors: H. D. D'oliveira, Patrice Malfreyt, X. Davoy, E. Arche, Aziz Ghoufi
    Abstract:

    The surface tension (gamma) of methane on a graphene monolayer is calculated by using the test-area approach. By using a united atom model to describe methane molecules, strong fluctuations of surface tension as a function of the surface area of the graphene are evidenced. In contrast with the Liquid-Vapor Interfaces, the use of a larger cutoff does not fully erase the fluctuations in the surface tension. Counterintuitively, the description of methane and graphene from the Optimized Potentials for Liquid Simulations all-atom model and a flexible model, respectively, led to a lessening in the surface tension fluctuations. This result suggests that the origin of fluctuations in gamma is due to a model-effect rather than size-effects. We show that the molecular origin of these fluctuations is the result of a commensurable organization between both graphene and methane. This commensurable structure can be avoided by describing methane and graphene from a flexible force field. Although differences in gamma with respect to the model have been often reported, it is the first time that the model drastically affects the physics of a system. Published by AIP Publishing.

  • Recent advances in Many Body Dissipative Particles Dynamics simulations of Liquid-Vapor Interfaces
    The European Physical Journal E, 2013
    Co-Authors: Aziz Ghoufi, Janine Emile, Patrice Malfreyt
    Abstract:

    Many Body Dissipative Particles Dynamics (MDPD) simulation is a novel promising mesoscopic method to model the Liquid-Vapor Interfaces. Based upon works of Paganobarraga and Frenkel (J. Chem. Phys. 15, 5015 (2001)) and Trofimov (J. Chem. Phys. 117, 9383 (2002)) and of Warren (Phys. Rev. E 68, 066702 (2003)) this method has been critically reviewed during this last decade. We propose here to give an overview of the Many Body Dissipative Particles Dynamic simulation within the framework of the Liquid-Vapor Interfaces. We recall the theoretical background of MDPD and we present some recent results of systems of interest such as water Liquid-Vapor Interfaces and salt effect on water surface tension. Additionally we discuss the ability of MDPD to capture the mechanisms at the mesoscopic scale through the formation of micelles and the coalescence of a nanodroplet water on water surface.

  • calculation of the surface tension and pressure components from a non exponential perturbation method of the thermodynamic route
    Journal of Chemical Physics, 2012
    Co-Authors: Aziz Ghoufi, Patrice Malfreyt
    Abstract:

    Surface tension is probably the most important interfacial property and a large number of techniques have been devoted to its calculation. Usually, this calculation is carried out using mechanical or thermodynamic definitions. The mechanical route uses an arbitrary choice to affect the contribution of the pairwise force. To overcome this arbitrariness, a thermodynamic route based on the area perturbation (test-area (TA) method) has been developed for the calculation of surface tension. The volume perturbation (VP) method provides an original route to compute the components of the pressure tensor. These two routes are developed from the perturbation theory leading to working expressions using exponential averages of energy. The use of exponential averages makes the calculation strongly dependent on the occurrence of low values of ΔU. Additionally, the decomposition of the energy to obtain local surface tension is nontrivial. From the explicit derivation of the partition function the exponential average is avoided providing an interesting alternative to TA, VP, and mechanical methods. To make a consistent comparison, we study the profiles of the surface tension along the direction normal to the surface for the different definitions and techniques in the cases of Liquid-Vapor Interfaces of acids gases, binary, and apolar systems.

  • Calculation of the surface tension from multibody dissipative particle dynamics and Monte Carlo methods.
    Physical Review E : Statistical Nonlinear and Soft Matter Physics, 2010
    Co-Authors: Aziz Ghoufi, Patrice Malfreyt
    Abstract:

    We report the calculation of the coexisting densities and surface tensions of the Liquid-Vapor equilibrium using the multibody dissipative particle dynamics and Monte Carlo (MMC) methods. We focus on the calculation of the surface tension by using the thermodynamic and mechanical routes. It is the first time that the test-area method is applied on the many-body conservative potential. We discuss the mechanical equilibrium of these two-phase systems by analyzing the profiles of the normal and tangential components of the pressure tensor using the Irving-Kirkwood and Kirkwood-Buff approaches. The profile of the configurational temperature is shown to establish the thermal equilibrium of these two-phase simulations carried out with large time steps. We complete this study to show the impact of the range of the many-body repulsive term of the conservative force on the surface tension. We conclude that the MMC method is an efficient sampling scheme to compute the interfacial properties of Liquid-Vapor Interfaces using the multibody soft potential.

Bjorn Kvamme - One of the best experts on this subject based on the ideXlab platform.

  • measurements and modelling of interfacial tension for water carbon dioxide systems at elevated pressures
    ICCMSE-2004 : International Conference on Computational Methods in Sciences and Engineering 2004, 2007
    Co-Authors: Bjorn Kvamme, Tatyana Kuznetsova, Andreas Hebach, Alexander Oberhof, Eivind Lunde
    Abstract:

    A novel apparatus, PeDro, was used to measure interfacial tension in a two-component system made of water and compressed carbon dioxide at temperatures ranging 278-335 K and pressures 0.1-20 MPa. Our optimized experimental setup utilized the quasi-static pendant drop method and ensured experimental errors below 2%. The interfacial tension showed a pronounced dependence on pressure and temperature. A regression function was derived that allows to interpolate between the experimental data with high precision. Molecular dynamics simulations were performed for liquid-liquid and Liquid-Vapor Interfaces between water and carbon dioxide at elevated pressures. The interfacial tension was obtained from long constant-volume production runs as the difference between normal and tangential pressure components. The results showed a good agreement with experimental data, with our model system reproducing faithfully the pressure-temperature dependence of the interfacial tension.

  • thermodynamic properties and interfacial tension of a model water carbon dioxide system
    Physical Chemistry Chemical Physics, 2002
    Co-Authors: Tatyana Kuznetsova, Bjorn Kvamme
    Abstract:

    We performed molecular dynamics (MD) simulations of liquid–liquid and liquid–vapor Interfaces between bulk water and carbon dioxide. Interfacial systems, constructed from periodically replicated slabs, were studied at different pressures and temperatures by means of npT and nVT MD. Constant-pressure runs of 3, 1.2, and 0.3 nanoseconds were used to estimate the water–CO2 interfacial tension at 284.5 K and 298 K for a liquid–liquid system comprising 108 SPC water molecules and 108 three-site CO2 molecules. The liquid–vapor interface was studied under nVT conditions using 108 water molecules and 32 CO2 molecules. Interfacial tension was obtained from the difference between pressure components normal and tangential to the interface. The results showed a surprisingly (CO2 potential used has been never optimized for water–CO2 interaction) good agreement with experimental data; our model system also reproduced the pressure–temperature relationship of the interfacial tension. A second liquid–liquid system of 256 SPC water and 108 CO2 molecules was tested for temperature persistence of the interface at higher pressures (100 atm and 300 atm). The results of the simulation prove the feasibility of using the model system to predict the key properties of liquid–liquid water–carbon dioxide interface under widely varying conditions, including those relevant for deep-sea disposal of carbon dioxide.