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  • 1
    Electronic Resource
    Electronic Resource
    On the simulation of thermodynamic and structural properties of simple liquids (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2717-2726 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This work, which is purely methodological, demonstrates new applications of perturbation methods in computer simulations of simple liquids. Most applications are based on the calculation of bulk and local excess chemical potentials of one or several inserted test particles, using a Widom technique in the canonical ensemble. This gives a powerful tool for obtaining distribution functions, some of which are virtually impossible to determine with other techniques. Results are also presented for single-ion activity coefficients and Donnan potentials. A perturbation approach is used to calculate thermodynamic response functions with respect to particle number, temperature, and volume changes. The applicability is exemplified by studies of hard-sphere fluids, uniform and nonuniform electrolyte solutions within the primitive model, and screened Coulomb systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460923
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  • 2
    Electronic Resource
    Electronic Resource
    The ionic correlation contribution to the free energy of spherical double layers (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5145-5152 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An estimate of the ion fluctuation contribution to the free energy for a dispersion of spherical macroions, without additional salt, is made using the cell model. The Poisson–Boltzmann approximation is used to estimate the linear response in a given cell, which together with second order perturbation theory allow us to calculate the free energy of interaction between a pair of cells. As well, an infinite order theory is developed. We find excellent agreement with simulations for monovalent counterions, the comparison becoming poorer for more strongly coupled systems. A cubic lattice of cells is studied, modeling a macroionic dispersion. The fluctuation contribution is shown to be several orders of magnitude larger than the usual quantum dispersion forces. However, it plays a minor role in the thermodynamics of the lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455632
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  • 3
    Electronic Resource
    Electronic Resource
    Electric double layer forces in the presence of polyelectrolytes (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2461-2469 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An electric double layer is studied by means of Monte Carlo simulations and mean-field theory. The counterions of the uniformly charged surfaces are modeled as flexible polyelectrolytes. For this particular model system it turns out that the traditional double layer repulsion becomes attractive for a wide range of systems. The main reason for this attraction is an entropically driven bridging mechanism, and its magnitude is significant compared to ordinary double layer or van der Waals forces. The polyelectrolyte Poisson–Boltzmann theory developed here behaves in a qualitatively correct manner, also predicting an attractive interaction extending over several nanometers. These results may have some relevance to technical and biological systems, where sometimes puzzling force behavior is seen in the presence of polyelectrolytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457006
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  • 4
    Electronic Resource
    Electronic Resource
    Simple approach to polyampholytes based on chain polarizabilities (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 3917-3924 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The polarizabilities of polyampholytes have been calculated in Monte Carlo simulations. For chains with random charge topologies, the polarizability increases with the chain length and the chain flexibility. For block copolymers, the polarizability initially increases with the block size to a maximum and then decreases. The polarizability is used to characterize the interaction between polyampholytes and external electric fields. As long as the field is not too strong, the polyampholyte response will be linear. This observation is used to describe the chain behavior near charged walls, and for low to moderately charged walls the results agree well with Monte Carlo simulations. At high field strengths the chain properties are dependent on the chain topology and several cases are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448288
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  • 5
    Electronic Resource
    Electronic Resource
    Depletion and bridging forces in polymer systems: Monte Carlo simulations at constant chemical potential (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5493-5501 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new Monte Carlo simulation method designed for polymer solutions confined to planar slits is presented. The slit is in equilibrium with a surrounding bulk solution and the method allows a variation of the slit width while maintaining the polymer chemical potential constant. This is achieved by changing the tangential pressure as a function of slit width. An analysis of chain parameters and monomer distribution within the slit has been carried out. The model system used is supposed to mimick a macromolecular solution whose stability is manipulated by addition of adsorbing and/or nonadsorbing polymers. Generally, for the nonadsorbing polymer an attractive depletion force is found. At high volume fractions the attraction is reduced and a repulsive force appears at short separations. The depletion force can also be extinguished in the case of an adsorption potential of intermediate strength, while strong adsorption gives rise to a significant attraction due to polymer bridges. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289821
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  • 6
    Electronic Resource
    Electronic Resource
    Forces between polyelectrolyte coated surfaces in the presence of electrolyte (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2569-2576 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interaction between charged surfaces bearing terminally attached polyelectrolyte chains is investigated using Monte Carlo computer simulations and a mean-field theory. In particular we focus on the role played by the addition of a simple electrolyte component. It is found that the force between the surfaces increases with increasing electrolyte concentration because of a repulsive osmotic pressure contribution due to the small ions, while the attractive bridging component is insensitive to added salt. Considering the approximate nature of the mean-field (polyelectrolyte Poisson–Boltzmann) theory it compares well with the computer simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467630
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  • 7
    Electronic Resource
    Electronic Resource
    A new algorithm for Reverse Monte Carlo simulations (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 2624-2629 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new algorithm for Reverse Monte Carlo (RMC) simulations of liquids. During the simulations, we calculate energy, excess chemical potentials, bond-angle distributions and three-body correlations. This allows us to test the quality and physical meaning of RMC-generated results and its limitations. It also indicates the possibility to explore orientational correlations from simple scattering experiments. The new technique has been applied to bulk hard-sphere and Lennard-Jones systems and compared to standard Metropolis Monte Carlo results. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476861
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  • 8
    Electronic Resource
    Electronic Resource
    Interaction and conformation of polyelectrolyte chains adsorbed on neutral surfaces (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4739-4747 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulations are used to study the conformation of surface bound polyelectrolytes and how two such surfaces interact. The linear polyelectrolyte chains consist of charged monomers connected via simple harmonic bonds, and all electrostatic interactions are treated within a dielectric continuum model. The interaction between the polyelectrolyte covered surfaces is found to be strongly repulsive, significantly stronger than the usual double layer force. The increased repulsion is due to an expansion of the chains perpendicular to the surfaces, which in turn is driven by the counterion entropy. Simple scaling laws are derived, showing the expansion to increase linearly with the number of monomers. The osmotic pressure in a polyelectrolyte double layer can be shown to be related to the pressure in a simple double layer via a relation of corresponding states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466045
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  • 9
    Electronic Resource
    Electronic Resource
    Double layer interactions in mono- and divalent electrolytes: A comparison of the anisotropic HNC theory and Monte Carlo simulations (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1424-1431 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interaction between charged surfaces in 1:1, 1:2, and 2:2 electrolyte solutions at various concentrations have been calculated using the anisotropic hypernetted chain (HNC) theory and Monte Carlo (MC) simulations. For divalent counterions, the surface interaction has an attractive minimum at short separations. This minimum turns more attractive at increasing electrolyte concentration, while the interaction at somewhat larger separations becomes oscillatory. The agreement between the HNC and the MC results is excellent for the 1:2 and 2:2 electrolyte systems. For 1:1 electrolytes the surface interaction is repulsive except at high concentrations at which it shows a weak attractive minimum. The HNC and the MC results agree quantitatively except in a few angstroms wide region at short separations, where the agreement is only qualitative due to a slight difference in the contributions from the hard core interactions. This is a consequence of the neglect of the short-range bridge function in the HNC approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463218
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  • 10
    Electronic Resource
    Electronic Resource
    Colloidal interactions mediated via polyelectrolytes (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9423-9434 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using Monte Carlo simulation, scaling, variational and mean-field arguments we investigate forces between charged spherical aggregates conferred by oppositely charged polymeric chains. Two types of polymer mediated attraction are found in this system, both of a bridging type but differing markedly in terms of the range. The entropic bridging force is of a range comparable to the average monomer–monomer separation in the chain. It is present whenever many chains have to compensate the charge on two macroions. The energetic bridging force has a range of the order of the length of the polymer chain and pertains to situations when a single chain has to compensate the charge on more than one macroion. In what follows we shall give a detailed analysis of both bridging interactions with a special regard for polycounterion versus simple counterion effects. The two types of bridging are in a certain sense complementary and should be present in polymer– surfactant systems at different regimes of the polymer–macroion concentration ratios. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468810
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