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Afshin Eskandari Nasrabad - One of the best experts on this subject based on the ideXlab platform.
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Self-Diffusion Coefficient of two-center Lennard-Jones fluids: Molecular simulations and free volume theory
Journal of Chemical Physics, 2009Co-Authors: Afshin Eskandari NasrabadAbstract:A comprehensive investigation is conducted to study the thermodynamics, structure, and mean free volume of rigid two-center Lennard-Jones fluids through Monte Carlo simulations. For a large number of states, the Self-Diffusion Coefficient is computed using the following two different approaches: the equilibrium molecular dynamics simulation method and the modified Cohen–Turnbull theory. The effects of the bond elongation on different thermophysical properties are studied. The generic van der Waals theory, which has recently been extended to rigid polyatomic fluids [A. Eskandari Nasrabad and R. Laghaei, J. Chem. Phys.125, 154505 (2006)], is used to compute the mean free volume needed in the modified Cohen–Turnbull theory. The effective site diameter is computed using the virial minimization method and the results are applied within the generic van der Waals theory. The Gibbs ensemble Monte Carlo simulation technique is applied to determine the location of the fluid phase envelope. The N V T Monte Carlo simulation method is then utilized to compute the equation of state and the correlation functions appearing in the generic van der Waals theory. It appears that the logarithm of the mean free volume versus density is almost linear at ρ > ρ c independent of the bond length, which suggests a universal behavior. The self diffusion Coefficient results of the modified Cohen–Turnbull theory are analyzed in detail.
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excluded volume in the generic van der waals equation of state and the self diffusion Coefficient of the lennard jones fluid
Journal of Chemical Physics, 2006Co-Authors: Rozita Laghaei, Afshin Eskandari Nasrabad, Byung Chan EuAbstract:In the previous papers applying the generic van der Waals equation of state the mean excluded volume was defined with the contact diameter of particles at which the potential energy is equal to zero—the size parameter in the case of the Lennard-Jones potential. This parameter appears as the upper limit of the integral for the generic van der Waals parameter B (mean excluded volume divided by the density) in the generic van der Waals equation of state. Since the choice is not unique, in this paper we reexamine the manner of defining the upper limit and propose another choice for the upper limit. We also propose an interpretation of the free volume overlap factor α appearing in the free volume theory of diffusion and a method of estimating it in terms of the intermolecular potential energy only. It is shown that with the so-estimated free volume overlap factor and the new choice of the upper limit of the integral for B the Self-Diffusion Coefficient in the modified free volume theory of diffusion not only a...
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pair correlation functions and the self diffusion Coefficient of lennard jones liquid in the modified free volume theory of diffusion
Journal of Physical Chemistry B, 2005Co-Authors: Rozita Laghaei, Afshin Eskandari NasrabadAbstract:In this paper, we apply the Matteoli−Mansoori empirical formula for the pair correlation function of simple fluids obeying the Lennard-Jones potential to calculate reduced Self-Diffusion Coefficients on the basis of the modified free volume theory. The Self-Diffusion Coefficient thus computed as functions of temperature and density is compared with the molecular dynamics simulation data and the Self-Diffusion Coefficient obtained by the modified free volume theory implemented with the Monte Carlo simulation method for the pair correlation function. We show that the Matteoli−Mansoori empirical formula yields sufficiently accurate Self-Diffusion Coefficients in the supercritical regime, provided that the minimum free volume activating diffusion is estimated with the classical turning point of binary collision at the mean relative kinetic energy 3kBT/2, where kB is the Boltzmann constant and T is the temperature. In the subcritical regime, the empirical formula yields qualitatively correct, but lower values ...
Joan F Brennecke - One of the best experts on this subject based on the ideXlab platform.
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effect of structure on transport properties viscosity ionic conductivity and self diffusion Coefficient of aprotic heterocyclic anion aha room temperature ionic liquids 1 variation of anionic species
Journal of Physical Chemistry B, 2015Co-Authors: Oscar Moralescollazo, Joan F BrenneckeAbstract:A series of room temperature ionic liquids (RTILs) based on 1-ethyl-3-methylimidazolium ([emim]+) with different aprotic heterocyclic anions (AHAs) were synthesized and characterized as potential electrolyte candidates for lithium ion batteries. The density and transport properties of these ILs were measured over the temperature range between 283.15 and 343.15 K at ambient pressure. The temperature dependence of the transport properties (viscosity, ionic conductivity, Self-Diffusion Coefficient, and molar conductivity) is fit well by the Vogel–Fulcher–Tamman (VFT) equation. The best-fit VFT parameters, as well as linear fits to the density, are reported. The ionicity of these ILs was quantified by the ratio of the molar conductivity obtained from the ionic conductivity and molar concentration to that calculated from the Self-Diffusion Coefficients using the Nernst–Einstein equation. The results of this study, which is based on ILs composed of both a planar cation and planar anions, show that many of the [...
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effect of structure on transport properties viscosity ionic conductivity and self diffusion Coefficient of aprotic heterocyclic anion aha room temperature ionic liquids 1 variation of anionic species
Journal of Physical Chemistry B, 2015Co-Authors: Liyuan Sun, Oscar Moralescollazo, Han Xia, Joan F BrenneckeAbstract:A series of room temperature ionic liquids (RTILs) based on 1-ethyl-3-methylimidazolium ([emim](+)) with different aprotic heterocyclic anions (AHAs) were synthesized and characterized as potential electrolyte candidates for lithium ion batteries. The density and transport properties of these ILs were measured over the temperature range between 283.15 and 343.15 K at ambient pressure. The temperature dependence of the transport properties (viscosity, ionic conductivity, Self-Diffusion Coefficient, and molar conductivity) is fit well by the Vogel-Fulcher-Tamman (VFT) equation. The best-fit VFT parameters, as well as linear fits to the density, are reported. The ionicity of these ILs was quantified by the ratio of the molar conductivity obtained from the ionic conductivity and molar concentration to that calculated from the Self-Diffusion Coefficients using the Nernst-Einstein equation. The results of this study, which is based on ILs composed of both a planar cation and planar anions, show that many of the [emim][AHA] ILs exhibit very good conductivity for their viscosities and provide insight into the design of ILs with enhanced dynamics that may be suitable for electrolyte applications.
Taku Ohara - One of the best experts on this subject based on the ideXlab platform.
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self diffusion Coefficient and structure of binary n alkane mixtures at the liquid vapor interfaces
Journal of Physical Chemistry B, 2015Co-Authors: Hari Krishna Chilukoti, Gota Kikugawa, Taku OharaAbstract:The Self-Diffusion Coefficient and molecular-scale structure of several binary n-alkane liquid mixtures in the liquid–vapor interface regions have been examined using molecular dynamics simulations. It was observed that in hexane–tetracosane mixture hexane molecules are accumulated in the liquid–vapor interface region and the accumulation intensity decreases with increase in a molar fraction of hexane in the examined range. Molecular alignment and configuration in the interface region of the liquid mixture change with a molar fraction of hexane. The Self-Diffusion Coefficient in the direction parallel to the interface of both tetracosane and hexane in their binary mixture increases in the interface region. It was found that the Self-Diffusion Coefficient of both tetracosane and hexane in their binary mixture is considerably higher in the vapor side of the interface region as the molar fraction of hexane goes lower, which is mostly due to the increase in local free volume caused by the local structure of t...
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hydrodynamic consideration of the finite size effect on the self diffusion Coefficient in a periodic rectangular parallelepiped system
Journal of Chemical Physics, 2015Co-Authors: Gota Kikugawa, Takeo Nakano, Taku OharaAbstract:In the present study, we use molecular dynamics (MD) simulations to provide an insight into the system size effect on the Self-Diffusion Coefficient of liquids in the periodic rectangular parallelepiped system, from the hydrodynamic perspective. We have previously shown that in the rectangular box system, the diffusivity exhibits anomalous behaviors, i.e., the diffusion tensor appears to be anisotropic despite the bulk liquid simulation and the diffusion component in the direction along the short side of rectangular box with a high aspect ratio exceeding the diffusivity in the infinite system [Kikugawa et al., J.Chem. Phys. 142, 024503 (2015)]. So far, the size effect on the diffusivity has been intensively studied in the cubic system and has been interpreted quite well by the theoretical considerations employing the hydrodynamic interaction. Here, we have extended the hydrodynamic theory to be applied to periodic rectangular box systems and compared the theoretical predictions with MD simulation results....
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hydrodynamic consideration of the finite size effect on the self diffusion Coefficient in a periodic rectangular parallelepiped system
Journal of Chemical Physics, 2015Co-Authors: Gota Kikugawa, Takeo Nakano, Taku OharaAbstract:In the present study, we use molecular dynamics (MD) simulations to provide an insight into the system size effect on the Self-Diffusion Coefficient of liquids in the periodic rectangular parallelepiped system, from the hydrodynamic perspective. We have previously shown that in the rectangular box system, the diffusivity exhibits anomalous behaviors, i.e., the diffusion tensor appears to be anisotropic despite the bulk liquid simulation and the diffusion component in the direction along the short side of rectangular box with a high aspect ratio exceeding the diffusivity in the infinite system [Kikugawa et al., J.Chem. Phys. 142, 024503 (2015)]. So far, the size effect on the diffusivity has been intensively studied in the cubic system and has been interpreted quite well by the theoretical considerations employing the hydrodynamic interaction. Here, we have extended the hydrodynamic theory to be applied to periodic rectangular box systems and compared the theoretical predictions with MD simulation results. As a result, the diffusivity predicted by the hydrodynamic theory shows good agreement with the MD results. In addition, the system size effect was examined in a rod-shaped rectangular box in which the two shorter side lengths were equivalent and a film-type rectangular box in which the two longer side lengths were equivalent. It is of interest that we found that the aspect ratio, at which the diffusivity coincides with that in the infinite system, is a universal constant independent of the cross-sectional area for the rod system or the thickness for the film system. By extracting the universal structure in the hydrodynamic description, we also suggested a simplified approximate model to accurately predict the size effect on the diffusivity over a practical range of aspect ratios.
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effect of the computational domain size and shape on the self diffusion Coefficient in a lennard jones liquid
Journal of Chemical Physics, 2015Co-Authors: Gota Kikugawa, Shotaro Ando, Jo Suzuki, Yoichi Naruke, Takeo Nakano, Taku OharaAbstract:In the present study, molecular dynamics (MD) simulations on the monatomic Lennard-Jones liquid in a periodic boundary system were performed in order to elucidate the effect of the computational domain size and shape on the Self-Diffusion Coefficient measured by the system. So far, the system size dependence in cubic computational domains has been intensively investigated and these studies showed that the diffusion Coefficient depends linearly on the inverse of the system size, which is theoretically predicted based on the hydrodynamic interaction. We examined the system size effect not only in the cubic cell systems but also in rectangular cell systems which were created by changing one side length of the cubic cell with the system density kept constant. As a result, the diffusion Coefficient in the direction perpendicular to the long side of the rectangular cell significantly increases more or less linearly with the side length. On the other hand, the diffusion Coefficient in the direction along the lon...
Byung Chan Eu - One of the best experts on this subject based on the ideXlab platform.
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generic van der waals equation of state for polymers modified free volume theory and the self diffusion Coefficient of polymeric liquids
Physica A-statistical Mechanics and Its Applications, 2010Co-Authors: Haidar Sabbagh, Byung Chan EuAbstract:In this paper, a molecular theory of Self-Diffusion Coefficient is developed for polymeric liquids (melts) on the basis of the integral equation theory for site–site pair correlation functions, the generic van der Waals equation of state, and the modified free volume theory of diffusion. The integral equations supply the pair correlation functions necessary for the generic van der Waals equation of state, which in turn makes it possible to calculate the Self-Diffusion Coefficient on the basis of the modified free volume theory of diffusion. A random distribution is assumed for minimum free volumes for monomers along the chain in the melt. More specifically, a stretched exponential is taken for the distribution function. If the exponents of the distribution function for minimum free volumes for monomers are chosen suitably for linear polymer melts of N monomers, the N dependence of the Self-Diffusion Coefficient is N−1 for the small values of N, an exponent predicted by the Rouse theory, whereas in the range of 2.3≲lnN≲4.5 the N dependence smoothly crosses over to N−2, which is reminiscent of the exponent by the reptation theory. However, for lnN≳4.5 the N dependence of the Self-Diffusion Coefficient differs from N−2, but gives an N dependence, N−2−δ(0<δ<1), consistent with experiment on polymer melts in the range. For polyethylene δ≈0.48 for the parameters chosen for the stretched exponential. Because the stretched exponential function contains undetermined parameters, the N dependence of diffusion becomes semiempirical, but once the parameters are chosen such that the N dependence of D can be successfully given for a polymer melt, the temperature dependence of the Self-Diffusion Coefficient can be well predicted in comparison with experiment. The theory is satisfactorily tested against experimental and simulation data on the temperature dependence of D for polyethylene and polystyrene melts.
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excluded volume in the generic van der waals equation of state and the self diffusion Coefficient of the lennard jones fluid
Journal of Chemical Physics, 2006Co-Authors: Rozita Laghaei, Afshin Eskandari Nasrabad, Byung Chan EuAbstract:In the previous papers applying the generic van der Waals equation of state the mean excluded volume was defined with the contact diameter of particles at which the potential energy is equal to zero—the size parameter in the case of the Lennard-Jones potential. This parameter appears as the upper limit of the integral for the generic van der Waals parameter B (mean excluded volume divided by the density) in the generic van der Waals equation of state. Since the choice is not unique, in this paper we reexamine the manner of defining the upper limit and propose another choice for the upper limit. We also propose an interpretation of the free volume overlap factor α appearing in the free volume theory of diffusion and a method of estimating it in terms of the intermolecular potential energy only. It is shown that with the so-estimated free volume overlap factor and the new choice of the upper limit of the integral for B the Self-Diffusion Coefficient in the modified free volume theory of diffusion not only a...
Rozita Laghaei - One of the best experts on this subject based on the ideXlab platform.
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excluded volume in the generic van der waals equation of state and the self diffusion Coefficient of the lennard jones fluid
Journal of Chemical Physics, 2006Co-Authors: Rozita Laghaei, Afshin Eskandari Nasrabad, Byung Chan EuAbstract:In the previous papers applying the generic van der Waals equation of state the mean excluded volume was defined with the contact diameter of particles at which the potential energy is equal to zero—the size parameter in the case of the Lennard-Jones potential. This parameter appears as the upper limit of the integral for the generic van der Waals parameter B (mean excluded volume divided by the density) in the generic van der Waals equation of state. Since the choice is not unique, in this paper we reexamine the manner of defining the upper limit and propose another choice for the upper limit. We also propose an interpretation of the free volume overlap factor α appearing in the free volume theory of diffusion and a method of estimating it in terms of the intermolecular potential energy only. It is shown that with the so-estimated free volume overlap factor and the new choice of the upper limit of the integral for B the Self-Diffusion Coefficient in the modified free volume theory of diffusion not only a...
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pair correlation functions and the self diffusion Coefficient of lennard jones liquid in the modified free volume theory of diffusion
Journal of Physical Chemistry B, 2005Co-Authors: Rozita Laghaei, Afshin Eskandari NasrabadAbstract:In this paper, we apply the Matteoli−Mansoori empirical formula for the pair correlation function of simple fluids obeying the Lennard-Jones potential to calculate reduced Self-Diffusion Coefficients on the basis of the modified free volume theory. The Self-Diffusion Coefficient thus computed as functions of temperature and density is compared with the molecular dynamics simulation data and the Self-Diffusion Coefficient obtained by the modified free volume theory implemented with the Monte Carlo simulation method for the pair correlation function. We show that the Matteoli−Mansoori empirical formula yields sufficiently accurate Self-Diffusion Coefficients in the supercritical regime, provided that the minimum free volume activating diffusion is estimated with the classical turning point of binary collision at the mean relative kinetic energy 3kBT/2, where kB is the Boltzmann constant and T is the temperature. In the subcritical regime, the empirical formula yields qualitatively correct, but lower values ...