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  • American Institute of Physics (AIP)  (21)
  • Periodicals Archive Online (PAO)  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Mean and Gaussian curvatures of randomly decorated Voronoi and cubic tesselations (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3246-3251 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is now generally accepted that some midrange microemulsions are bicontinuous, i.e., continuous in both oil and water simultaneously. The first model of the microstructure of microemulsion that could account for a progression from discrete to bicontinuous was the Talmon–Prager or "randomly decorated Voronoi'' model. Space is tessellated into Voronoi polyhedra and the polyhedra are randomly decorated with oil and water. In variations of the model DeGennes and Taupin and Widom decorate a cubic tesselation of space. At first glance it might appear that the decorated Voronoi and cubic tessellations are zero-mean-curvature models, since they are constructed from polyhedra with planar faces. However, the edges of the polyhedra are concentrations of mean curvature, and the vertices are concentrations of Gaussian curvature. The area-averaged mean and Gaussian curvatures of the oil–water interface in the randomly decorated Voronoi and cubic models are calculated. The area-averaged mean curvatures of the two models are linear functions of oil volume fraction, change sign at a volume fraction of 0.5, and are within 0.2% of one another in magnitude. The area-averaged Gaussian curvature of the Voronoi model varies quadratically with volume fraction, and is negative for oil volume fractions from 0.18 to 0.82 (oil and water are bicontinuous for volume fractions ranging from 0.135 to 0.865). The area-averaged Gaussian curvature of the randomly decorated cubic model is a sixth-order polynomial function of oil volume fraction and is negative for volume fractions ranging from 0.23 to 0.77 (oil and water are bicontinuous over the volume fraction range 0.25 to 0.75). As an additional application, the model results are used to interpret curvature aspects of the bilayer theory of the L3 phase of surfactant solutions presented recently by Cates et al. [Europhys. Lett. 5, 733 (1988)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456899
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  • 2
    Electronic Resource
    Electronic Resource
    Gradient theory of the electric double layer at hydrocarbon–water interfaces (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6120-6127 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gradient theory of inhomogeneous fluids is used to model the electric double layer at a hydrocarbon–aqueous electrolyte interface. It is applied to a four-component regular solution (two solvent components and two ionic species) in which the dielectric permittivity is also inhomogeneous. The permittivity is determined by a Clausius–Mossotti constitutive equation based on the local densities of the solvent species. The gradient equations are coupled to Poisson's equation and are solved using a Galerkin/finite element scheme. The results indicate that in dilute solution, the dependence of the interfacial tension on bulk electrolyte concentration is linear, and the sign and magnitude of the deviation of the tension from the pure solvent value depends strongly on the degree of ion partitioning between the two phases. In more concentrated solutions, the deviation becomes nonlinear and can change sign as the electrolyte concentration is increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453486
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular dynamics for discontinuous potential. IV. Lennard-Jonesium (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4307-4313 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Argon, represented as a Lennard-Jones fluid, is simulated using a discontinuous version of the potential. The effect of discretization is thoroughly investigated in terms of the number of discontinuities and the cutoff diameter. Radial distribution functions, pressure, energy, self-diffusion coefficients, and velocity autocorrelation functions are used in order to evaluate this effect. A reduction of five times on computing time can be achieved by varying the cutoff radius and the number of discontinuities without much departure from the physical representation of Lennard-Jonesium atoms. The results indicate that discontinuous molecular dynamics is a viable alternative method to Monte Carlo and continuous molecular dynamics in simulating the properties of simple fluids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456811
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  • 4
    Electronic Resource
    Electronic Resource
    Wetting transitions at a solid–fluid interface (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4479-4489 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonlocal density functional free energy theories are used to investigate the nature of the wetting transition of a Lennard-Jones fluid near a Lennard-Jones wall. In particular, the wetting behavior is investigated for argon films on a solid carbon dioxide substrate for which the Lennard-Jones parameters are known. In accordance with previous predictions of local density functional theories, the transition is found to be of first order. The locus of the prewetting line of the Ar–CO2 system is calculated. Density profiles obtained from the Tarazona and generalized hard rod models are both in qualitative agreement with Monte Carlo simulations of Finn and Monson, although Tarazona's model performs better quantitatively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460604
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  • 5
    Electronic Resource
    Electronic Resource
    Efficient molecular simulation of chemical potentials (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2370-2385 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper evaluates methods of estimating chemical potential—actually fugacity coefficient—from molecular simulations. These methods are based on formulas given by Widom, by Bennett, and by Shing and Gubbins. They are tested with molecular dynamics simulations of Lennard-Jones liquids along the isotherm kT/ε=1.2 for densities from 0.65σ−3 to 0.90σ−3. A new test molecule sampling method, excluded volume map sampling, is found to be as much as 2 orders of magnitude more efficient than uniform test molecule sampling; it is more efficient and reliable than restricted umbrella sampling proposed by Shing and Gubbins. Several difficulties of estimating the variance of the fugacity coefficient estimates are surmounted by novel application of standard statistical methods. The statistical analysis shows that Bennett's method yields estimates with the least variance and Widom's method yields estimates with the greatest variance although all methods are consistent to within statistical error. Pressure and fugacity coefficient estimates obey the Gibbs–Duhem equation along the chosen isotherm up to densities of 0.75σ−3 for 108-molecule, 0.8σ−3 for 200-molecule, and 0.9σ−3 for 500-molecule simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455979
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular theories of confined fluids (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2422-2436 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density profiles and normal pressures predicted by three different approximate density functional free energy theories and the Fischer–Methfessel approximation to the Yvon–Born–Green (YBG) equation are compared with computer simulation results for fluids confined between planar walls. All models require as input a homogeneous fluid equation of state. Comparisons are made using two mean-field equations of state, one based on a Clausius hard-sphere reference fluid and the other based on a Carnahan/Starling hard-sphere reference fluid. The simplest and oldest of the models, the generalized van der Waals model, becomes unphysical at high mean pore densities. The Carnahan/Starling version of Tarazona model agrees best overall with the simulations. This model represents a systematic improvement on the generalized van der Waals model and is computationally the most complicated of all models examined. The YBG and generalized hard-rod models are not as accurate as the Tarazona model, but they capture the qualitative trends observed in the simulations. Both of these models are intuitive extensions of the exact theory of one-dimensional hard rods, and are computationally much simpler than the Tarazona model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455985
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  • 7
    Electronic Resource
    Electronic Resource
    The generalized van der Waals theory applied to the electrical double layer (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2309-2318 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The generalized van der Waals theory expression for ion density distribution is used with Poisson's equation to solve the electrical double-layer problem for 1:1, 2:1, and 2:2 restricted primitive model electrolytes in contact with a diffusively charged, hard, planar surface. Electrical potential and ion density profiles are compared to Monte Carlo results and are shown to be more accurate at lower electrolyte concentration and surface charge density than at higher. In addition, values for the diffuse layer potential drop are shown to be less exact than those predicted by the hypernetted chain equation, modified Gouy–Chapman theory and modified Poisson–Boltzmann equation, but could be brought closer to Monte Carlo results by an appropriate choice of excluded volume parameter. Surface tension, ion adsorption, and differential capacitance are also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452129
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  • 8
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of model amphiphile-oil–water systems (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2411-2420 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A square-lattice model of amphiphile-oil–water systems is developed in which oil and water molecules occupy single sites and amphiphiles occupy chains of sites. Energies and free energies estimated by Monte Carlo sampling of configuration space show that when the head, or water-loving portion, of the amphiphile has no tendency to hydrate or surround itself with water, as opposed to surrounding itself with other heads, the capability of even long amphiphiles to solubilize repellant oil and water into a single phase is weak. Although the Monte Carlo free energies deviate markedly from those given by quasichemical theory, the deviation of the phase behavior is modest. Computer drawings of typical equilibrium configurations show highly irregular interfaces, apparently caused by capillary waves which are pronounced in two dimensions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449286
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of solvent exclusion on the force between charged surfaces in electrolyte solution (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4527-4530 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Effects of hard-core exclusions of solvent molecules on the force between charged surfaces immersed in electrolyte solution are investigated theoretically. A three-component model of electrolyte solution is used, in which the solvent is modeled as a fluid of neutral hard spheres. A free energy density functional theory, which has been applied previously to study the interaction between primitive electrical double layers, is extended to include ion–solvent and solvent–solvent interactions. Hard-core correlations are incorporated in a nonlocal free energy density functional, while electrostatic correlations are evaluated using the mean spherical approximation. The force between charged surfaces as a function of surface separation is found highly oscillatory, with a period approximately equal to the particle diameter. Because of the dominant role of the hard-core exclusions of the solvent fluid, the force does not depend strongly on either electrolyte concentration or surface charge density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466283
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  • 10
    Electronic Resource
    Electronic Resource
    Statistical mechanics of rigid particles in an external field (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6699-6704 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new density functional is employed which simplifies and unifies the generalized van der Waals (GVDW) theory and the exact one-dimensional theory of hard particles in the presence of an external potential or solid walls. Numerical solution of density profiles in planar systems is made easy by introduction of the density functional. Numerical results for one-and three-dimensional fluids reveal that the GVDW theory fails at high chemical potentials by admitting negative densities. We have some evidence that the cause of the failure is a negative eigenvalue of the weighting function defining the local mean density or excluded volume in the theory. Density profiles of the exact one-dimensional theory are compared to those of the GVDW theory, those of the former exhibiting similar but stronger oscillations and of course no regions of negative density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451400
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