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  • 1
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics calculation of self-diffusion in a non-Newtonian fluid subject to a Couette strain field (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2149-2158 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations have been performed on a simple fluid in the non-Newtonian regime in order to study the nature of diffusion in the presence of shear stress. The nonequilibrium molecular dynamics (NEMD) sllod algorithm is used to generate a homogeneous boundary driven Couette flow. The elements of the tensor of diffusion coefficients have been evaluated by three different routes: through Einstein relations with the corresponding elements of the tensor of molecule displacements, through Green–Kubo expressions involving tensor of momentum autocorrelation functions and cross-correlation functions, and by utilizing an NEMD color field method. All three routes to the tensor of diffusion coefficients are shown to yield consistent results. A simple spherically symmetric Lennard-Jones fluid at its triple point was used in the simulation study. We find that in a Couette strain field of sufficiently large strain rate, diffusion in all directions is enhanced substantially. We propose and verify a new asymptotic relationship between the diagonal elements of the tensor of diffusion coefficients and the strain rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459886
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  • 2
    Electronic Resource
    Electronic Resource
    A general solution of the molecular Ornstein–Zernike equation for spheres with anisotropic adhesion and electric multipoles (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3741-3747 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the analytic solution of the molecular Ornstein–Zernike equation for a very general closure in which the direct correlation function is of the form suggested by the mean-spherical approximation for arbitrary multipolar interactions and the total correlation function contains terms that arise in the Percus–Yevick approximation for spheres with anisotropic surface adhesion. In addition to generalizing several earlier analyses of special cases of this closure, the solution presented here contains new simplifying insights that reduce the complexity of the resulting algebraic equations. A special case of the analysis is described to illustrate the method of solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457832
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  • 3
    Electronic Resource
    Electronic Resource
    Comment on: Molecular simulation of water along the liquid–vapor coexistence curve from 25 °C to the critical point (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 864-865 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In an earlier paper [J. Chem. Phys. 93, 7355 (1990)], de Pablo et al. reported Gibbs ensemble Monte Carlo (GEMC) simulations of SPC water with long-range intermolecular interactions computed using the Ewald summation method. The coexistence curve of SPC water was obtained from 25 to 300 °C. We report new simulations with a slight modification of the SPC potential to reflect the lower effective dipole moment in the vapor phase. The vapor–liquid coexistence curve is found to agree better with experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462421
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  • 4
    Electronic Resource
    Electronic Resource
    Simulation of supercritical water and of supercritical aqueous solutions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5606-5621 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics (MD) calculations have been performed to determine equilibrium structure and properties of systems modeling supercritical (SC) water and SC aqueous solutions at two states near the critical point using the simple point charge (SPC) potential model of Berendsen et al. for water. Both thermodynamic and dielectric properties from the simulations for pure water are accurate in comparison with experimental results even though the SPC model parameters were fitted to properties of ambient water. Details of the near-critical clustering in SC water have been predicted which have not been measured to date. MD studies have also been undertaken of systems that model sodium and chloride ions and neutral argon in SC water at the same states. The first solvation shell in SC water is observed to be similar to that in ambient water, and long-range solvation structures in SC water are similar to those observed for simple SC solvents. An excess of water molecules is observed clustering around ionic solutes which behave attractively and a deficit is observed around neutral atomic solutes which behave repulsively. These results should be helpful in developing a qualitative understanding of important processes that occur in SC water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460497
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  • 5
    Electronic Resource
    Electronic Resource
    Vapor-Liquid Equilibria and Salt Apparent Molar Volumes of the Water + 2-Propanol + Tetrabutylammonium Bromide System (1994)
    s.l. : American Chemical Society
    Journal of chemical & engineering data 39 (1994), S. 506-509 
    Details
    ISSN: 1520-5134
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/je00015a024
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  • 6
    Electronic Resource
    Electronic Resource
    The contribution of internal degrees of freedom to the non-Newtonian rheology of model polymer fluids (1991)
    Springer
    Rheologica acta 30 (1991), S. 33-43 
    Details
    ISSN: 1435-1528
    Keywords: non-Newtonian rheoloy ; kinetic theory ; FENE dumbbells ; non-equilibrium ; molecular dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract We report non-equilibrium molecular dynamics simulations of rigid and non-rigid dumbbell fluids to determine the contribution of internal degrees of freedom to strain-rate-dependent shear viscosity. The model adopted for non-rigid molecules is a modification of the finitely extensible nonlinear elastic (FENE) dumbbell commonly used in kinetic theories of polymer solutions. We consider model polymer melts — that is, fluids composed of rigid dumbbells and of FENE dumbbells. We report the steady-state stress tensor and the transient stress response to an applied Couerte strain field for several strain rates. We find that the rheological properties of the rigid and FENE dumbbells are qualitatively and quantitatively similar. (The only exception to this is the zero strain rate shear viscosity.) Except at high strain rates, the average conformation of the FENE dumbbells in a Couette strain field is found to be very similar to that of FENE dumbbells in the absence of strain. The theological properties of the two dumbbell fluids are compared to those of a corresponding fluid of spheres which is shown to be the most non-Newtonian of the three fluids considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366792
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of bead-and-spring chain models for semidilute polymer solutions in shear flow (1994)
    Springer
    International journal of thermophysics 15 (1994), S. 1085-1091 
    Details
    ISSN: 1572-9567
    Keywords: Brownian dynamics ; rheology ; semidilute polymer solutions ; viscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report preliminary results of simulations of the steady-state rheological behavior for semidilute polymer solutions of head-and-spring chain models in planar Couette now. The simulations include examination of the effects of excluded volume. hydrodynamic interactions and density. Hydrodynamic interactions are modeled by the Rotne -Prager Yamakawa tensor. The simulations are based on the nonequilibrium Brownian dynamics algorithm of Ermak and McCammon. In addition to the spring potential between neighboring beads in the chain. the interaction between any two beads in the solution is modeled using a shifted, repulsive Leonard-Jones potential. Lees Edward sliding brick boundary conditions are used for consistency with the Couette flow field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01458817
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  • 8
    Electronic Resource
    Electronic Resource
    A new method for the numerical solution of integral equation approximations (1990)
    Springer
    International journal of thermophysics 11 (1990), S. 97-107 
    Details
    ISSN: 1572-9567
    Keywords: critical phenomena ; integral equation approximations ; numerical methods ; Ornstein-Zernike equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new numerical technique for solving the Ornstein-Zernike equation is described. It is particularly useful in solving the Ornstein-Zernike equation for approximations and pair potentials (such as the Percus-Yevick and mean spherical approximations for finite ranged potentials) which imply a finiteranged direct correlation function since for such approximations the numerical technique is essentially exact. The only approximation involved in such cases is the discretization of direct and total correlation functions over the finite range on which the direct correlation function is nonzero. Thus, the new method avoids truncation of the total correlation function and should permit the critical point and spinodal curve to be mapped out with greater accuracy than is permitted by existing methods. Preliminary explorations on the stability and accuracy of the method are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00503862
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  • 9
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics of liquid crystals (1994)
    Springer
    International journal of thermophysics 15 (1994), S. 1125-1134 
    Details
    ISSN: 1572-9567
    Keywords: liquid crystals ; nematic phase ; noneyuilibrium molecular dynamics ; planar Couette flows ; rheology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract During the last 15 years, noneyuilibrium molecular dynamics (NEMD) has been successfully applied to study transport phenomena in fluids that are isotropic at equilibrium. A natural extension is therefore to study liquid crystals, which are anisotropic al equilibrium. The lower symmetry of these systems means that the linear transport coefficients are considerably more complicated than in an isotropic system. Part of the reason for this is that there are crosscouplings between tensors of different rank and parity. Such couplings arc symmetry-forbidden in isotropic phases. In this paper. we review some of fundamental theoretical results we have derived concerning the rheology of liquid crystals. report NEMD simulations of thermal conductivity and shear viscosity of liquid crystals, and present NEMD simulations of shear cessation phenomena. All of the NEMD results are presented for a model liquid crystal fluid which is a modification of the Gay-Borne fluid. The results obtained are in qualitative agreement with experimental measurements on liquid crystal systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01458821
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