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  • 1
    Electronic Resource
    Electronic Resource
    Fluids and fluid mixtures containing square-well diatomics: Equations of state and canonical molecular dynamics simulation (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 3930-3946 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present new perturbation theory equations of state for square-well dimer fluids, square-well dimer mixtures, square-well dimer/monomer mixtures and square-well heteronuclear dumbbell fluids. Our first- and second-order perturbation terms are based on Barker and Henderson's local compressibility approximation and Chang and Sandler's perturbation theory, respectively. The perturbation approach requires knowledge of the radial distribution functions of the reference hard-dimer fluid and hard dimer/monomer mixture, which are obtained from molecular dynamics simulation. For mixtures we use one fluid mixing rules to approximate the average mixture structure and perturbation parameters. The predictions of the perturbation theory are compared to the compressibility factors obtained from discontinuous canonical molecular dynamics simulation, an adaptation of Anderson's canonical ensemble molecular dynamics method to the case in which the potential is discontinuous. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474749
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  • 2
    Electronic Resource
    Electronic Resource
    Solid–liquid phase equilibrium for binary Lennard-Jones mixtures (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11433-11444 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Solid–liquid phase diagrams are calculated for binary mixtures of Lennard-Jones spheres using Monte Carlo simulation and the Gibbs–Duhem integration technique of Kofke. We calculate solid–liquid phase diagrams for the model Lennard-Jones mixtures: argon–methane, krypton–methane, and argon–krypton, and compare our simulation results with experimental data and with Cottin and Monson's recent cell theory predictions. The Lennard-Jones model simulation results and the cell theory predictions show qualitative agreement with the experimental phase diagrams. One of the mixtures, argon–krypton, has a different phase diagram than its hard-sphere counterpart, suggesting that attractive interactions are an important consideration in determining solid–liquid phase behavior. We then systematically explore Lennard-Jones parameter space to investigate how solid–liquid phase diagrams change as a function of the Lennard-Jones diameter ratio, σ11/σ22, and well-depth ratio, ε11/ε22. This culminates in an estimate of the boundaries separating the regions of solid solution, azeotrope, and eutectic solid–liquid phase behavior in the space spanned by σ11/σ22 and ε11/ε22 for the case σ11/σ22〈0.85. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479084
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  • 3
    Electronic Resource
    Electronic Resource
    Chemical potential gradient driven permeation of small molecules through polymeric media (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10714-10722 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Grand canonical molecular dynamics techniques are used to study small molecular penetrant permeation through polymeric media. Penetrants are modeled as hard spheres and square-well spheres. The polymer is modeled as a collection of hard chains and square-well chains. Glassy polymers are modeled using stationary chains while rubbery polymers are modeled using mobile chains. Facilitated transport polymers are also modeled by varying the square-well depth for specific sites along polymer chains. Penetrant partitioning, mutual diffusivity, solubility, and permeability (taken to be a product of diffusivity and solubility) are calculated as a function of reservoir chemical potential, barrier mobility, and, for the facilitating polymer case, the strength of the penetrant/facilitating site attraction. Penetrant diffusivity, solubility, and hence permeability are greater in a mobile barrier than in a stationary barrier. Diffusivity decreases and solubility increases upon the addition of facilitating sites to the barrier or upon increasing the strength of the penetrant/facilitating site attraction. Permeability decreases in these cases, contradicting our expectations concerning the phenomenon of facilitated transport. Comparisons are made between the permeation results presented here and experimental facilitated transport systems. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475221
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  • 4
    Electronic Resource
    Electronic Resource
    Generalized Flory equations of state for copolymers modeled as square-well chain fluids (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 7478-7492 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Generalized Flory–Dimer (GFD) equation of state has been extended to fluids containing copolymers modeled as heteronuclear chains of freely-jointed tangent spheres that interact via a site–site square-well potential. Compressibility factors are obtained for block, alternating and random copolymer fluids. The GFD theory for square-well copolymers requires expressions for the insertion factors of SW monomers in SW monomer mixtures, SW dimers in SW dimer mixtures, and SW heteronuclear dumbbells in SW heteronuclear dumbbell fluids. These insertion factors are obtained using recently-derived perturbation-theory-based equations of state. The effects of variations in composition, segment size ratios, and well-depth ratios on the compressibility factor are studied. The predictions of the Generalized Flory–Dimer theory are compared to compressibility factors obtained from discontinuous canonical molecular dynamics simulation. The Generalized Flory–Dimer theory accurately predicts the compressibility factors of square-well copolymer fluids for a variety of cases including those in which the size ratio and well-depth ratio of the two components are different. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476168
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  • 5
    Electronic Resource
    Electronic Resource
    Thermodynamic perturbation theory for fused hard-sphere and hard-disk chain fluids (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2688-2695 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We find that first-order thermodynamic perturbation theory (TPT1) which incorporates the reference monomer fluid used in the generalized Flory–AB (GF–AB) theory yields an equation of state for fused hard-sphere (FHS) chain fluids that has accuracy comparable to the GF–AB and GF–dimer–AC theories. The new TPT1 equation of state is significantly more accurate than other extensions of the TPT1 theory to FHS chain fluids. The TPT1 is also extended to two-dimensional fused hard-disk chain fluids. For the fused hard-disk dimer fluid, the extended TPT1 equation of state is found to be more accurate than the Boublík hard-disk dimer equation of state. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470528
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  • 6
    Electronic Resource
    Electronic Resource
    Phase instabilities in charged hard-sphere mixtures. II. Binary mixtures of salts (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8111-8123 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Charged hard-sphere mixtures consisting of two positively charged species and one negatively charged species (common anion mixtures) are used to represent binary mixtures of salts. Phase separation in the mixture is studied using the Gibbs free energy expression for common anion mixtures derived in paper I of this series. A detailed description of the dependence of the resulting phase diagrams on molecular size and charge of the species, and on the osmotic pressure of the mixture is presented. Binary mixtures of salts containing equal-sized ions exhibit type III phase behavior whereas binary mixtures of salts containing ions of unequal size exhibit either type II or type IV phase behavior. The type of phase behavior observed in binary mixtures of salts is characterized as a function of the critical pressures and critical volumes of the pure salts. Our results suggest that phase separation in mixtures of charged hard spheres is influenced by a competition between mixing effects (entropy), which encourage miscibility and ion-pairing effects (enthalpy), which encourage phase separation. Potential applications of the model to experimental systems are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470175
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  • 7
    Electronic Resource
    Electronic Resource
    Computer simulation study of the approximations associated with the generalized Flory theories (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9100-9110 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chain increment method and configurational bias Monte Carlo methods are used to test the approximations made in the derivation of the generalized Flory-Dimer (GF-D) theory for tangent hard sphere chains. Insertion probabilities and residual chemical potentials are calculated for hard chain fluids containing chains of length n=4, 8, 16, and 32 at monomer densities, ρM, up to 0.8. We find that the largest errors in the GF-D theory are those associated with assuming that the probability of inserting a monomer into a chain fluid is approximately equal to the probability of inserting a monomer into a monomer fluid, as predicted by the Carnahan–Starling equation of state. The errors in the incremental compressibility factor of the second segment associated with assuming that the conditional probability of inserting a second bead next to the first bead in a chain fluid is approximately equal to the probability of inserting a second bead next to the first bead in a dimer fluid as predicted by combining the Carnahan–Starling and Tildesley–Streett equations of state are relatively small. Consistent with the findings of Mooij and Frenkel, we find that these two approximations lead to an overprediction of the incremental contributions to the compressibility factor. Despite the overprediction of the incremental contributions to the compressibility factor of the first segment, the GF-D equation of state accurately predicts the compressibility of hard chains; this accuracy is traced to (1) the insensitivity of the compressibility factor to errors in the insertion probability and (2) cancellation of errors in the incremental compressibility factor of the first segment with small cumulative errors in the incremental compressibility factors of the third and subsequent segments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471617
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  • 8
    Electronic Resource
    Electronic Resource
    Monte-Carlo simulation of polymers confined between flat plates (1990)
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 1865-1872 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00208a052
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  • 9
    Electronic Resource
    Electronic Resource
    Monte Carlo calculation of the osmotic second virial coefficient of off-lattice athermal polymers (1992)
    s.l. : American Chemical Society
    Macromolecules 25 (1992), S. 3979-3983 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00041a021
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  • 10
    Electronic Resource
    Electronic Resource
    Equation of state for chain molecules: Continuous-space analog of Flory theory (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4108-4115 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: New, accurate equations of state for fluids of chain molecules are derived as generalizations of the well-known Flory and Flory–Huggins lattice theories to continuous space. Comparison with the results of new Monte Carlo simulations of athermal chains (freely jointed hard disks and spheres), extending over a wide range of densities, reveals that the generalized Flory–Huggins equation of state provides an accurate prediction for the pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450881
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