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  • 1
    Electronic Resource
    Electronic Resource
    Screening of hydrodynamic interactions in dense polymer solutions: a phenomenological theory and neutron-scattering investigations (1984)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 88 (1984), S. 6618-6633 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j150670a026
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  • 2
    Electronic Resource
    Electronic Resource
    Interdiffusion and self-diffusion in polymer mixtures: A Monte Carlo study (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2294-2304 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A lattice model for dense polymer solutions and polymer mixtures in three dimensions is presented, aiming to develop a model suitable for efficient computer simulation on vector processors, with a qualitatively realistic local dynamics. It is shown that the bond fluctuation algorithm for a suitable set of allowed bond vectors has the property that due to the excluded volume constraint no crossing of bonds by local motions can occur, and entanglement restrictions thus are fully taken into account. For athermal binary (AB) symmetrical polymer mixtures, the dependence of both self-diffusion coefficient and interdiffusion coefficient on polymer density is obtained, simulating a thin film geometry where a film of polymer A is coated with a film of polymer B. For one density, the dependence of the interdiffusion coefficient on an attractive energy between unlike monomers is also studied. For weak attraction an enhancement of interdiffusion proportional to this energy occurs. For strong attraction, however, a rather immobile tightly bound AB layer forms in the interface which hampers further unmixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459901
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  • 3
    Electronic Resource
    Electronic Resource
    Orientational order in lipid monolayers: A one-dimensional model (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6195-6209 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Lipid monolayers at low temperatures and large spreading pressure exhibit long-range translational order and the hydrophobic alkane chains of the lipid molecules are then stretched out in an all-trans configuration. The orientational order of the remaining rotational degree of freedom of these alkane chains is studied by means of Monte Carlo and molecular dynamics simulations as well as analytical calculations, but considering a one-dimensional rather than a two-dimensional model. Depending on the interactions among the chains, the ground state of the model is either a "uniformly tilted'' state (all chains are tilted by an average angle +θ¯ or −θ¯ relative to the direction perpendicular to the lattice direction) or a "no-tilt'' state (θ¯=0). At nonzero temperature, the uniform tilt state disorders by soliton-like kink–antikink excitations, in addition to phonon-like excitations, which exist also in the no-tilt state. In the continuum limit the treatment can be related to the Krumhansl–Schrieffer theory of the one-dimensional φ4 model. However, the quantitative predictions of the latter are in pronounced disagreement with the numerical results, in the temperature regime investigated. By our Monte Carlo techniques, we are able to study the orientational correlation function over the full temperature range, except extremely low temperatures. It is shown that for this model and temperature range the molecular dynamics technique requires much more computer time in order to obtain similarly reliable results than our discretized Monte Carlo approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458343
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  • 4
    Electronic Resource
    Electronic Resource
    Shift of first-order phase transitions in thin films due to boundary fields: A computer simulation (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3700-3706 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first-order phase transition of the ferromagnetic Ising model driven by the magnetic field at temperatures below criticality is studied by Monte Carlo methods for a two-dimensional thin film geometry, L×M with two free boundaries of length M(very-much-greater-than)L, at which boundary fields act. This model study is relevant, in particular, for phase transitions in monolayers adsorbed at stepped surfaces. While in the bulk geometry (L→∞) this transition occurs for zero field in the present model, with the system "jumping'' from a state with uniformly positive magnetization to a state with uniformly negative magnetization, in the thin film geometry the transition occurs at a critical field H*∼L−1, and the two states between which the transition occurs are characterized by strongly nonuniform magnetization profiles across the film. These findings are in agreement with the scaling theory of Fisher and Nakanishi.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456851
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  • 5
    Electronic Resource
    Electronic Resource
    Polymer chain dynamics derived from the Kramers potential: A treatment of the Rouse model with and without excluded volume interaction (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5194-5201 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We suggest that at least for single polymer chains relaxation times of typical dynamical processes can be obtained from biased sampling Monte Carlo computations on equilibrium data. We show this explicitly for the viscosity difference relaxation time τ in the Rouse or Zimm model (with any suitable, iterated or not, preaveraging of the Oseen–Burgers tensor) chain. We briefly discuss the corrections of such theory due to the excluded volume effect. We illustrate by performing the biased average of the equilibrium radius of gyration of Rouse chains of up to 150 monomer beads on a cubic lattice which yields directly τ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455609
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  • 6
    Electronic Resource
    Electronic Resource
    Finite size effects for the simulation of phase coexistence in the Gibbs ensemble near the critical point (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6989-6995 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the Gibbs ensemble gas–liquid phase coexistence can be studied by obtaining the density distribution function in a finite system from the study of two subsystems exchanging particles. The temperature dependence of the peak of this distribution function is studied near the critical point, and Monte Carlo simulations for the simple special case of the two-dimensional lattice gas model are presented. This case is a "restricted Gibbs ensemble'' where the particle numbers of the two systems fluctuate but their volume fluctuations are suppressed. From formal analysis and physical arguments, we predict that the density difference of the peak positions vanishes according to a classical power law [1−T/Tc(L)]1/2, where Tc(L) is a shifted critical temperature of the finite system of linear dimension L, for temperatures within a regime where fluctuations are significant (L does not exceed the correlation length ξ there). This behavior is verified by Monte Carlo simulations for L×L lattices with periodic boundary conditions and L in the range from 4≤L≤20. It is also shown that Tc(L) approaches the critical point of the infinite system from above, according to a law Tc(L)−Tc(∞)∼L−1/ν, ν being the correlation length exponent, as expected. Our discussion also applies to the standard grand canonical ensemble of the lattice gas or the equivalent canonical ensemble of an Ising magnet, respectively. Some Monte Carlo results for this ensemble are also presented. They are consistent with the theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462557
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  • 7
    Electronic Resource
    Electronic Resource
    Orientational ordering in lipid monolayers: A two-dimensional model of rigid rods grafted onto a lattice (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2269-2277 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple model for lipid monolayers on water surfaces at high spreading pressure is investigated in this work. In this model, the hydrophilic head group of the lipid molecules form a rigid regular triangular lattice, and the hydrophobic alkane chains (assumed to be in an all-trans state) are represented by rigid rods with two angular degrees of freedom (θ, cursive-phi). The rods consist of "effective monomers,'' and between the effective monomers on neighboring rods a Lennard-Jones interaction is assumed. The model is studied by exact ground-state calculations, mean-field theory, and Monte Carlo simulations. Basic parameters are rod length a and lattice constant b. The ground-state phase diagram shows the following phases: for small b, the rods are oriented perpendicularly to the monolayer plane (no-tilt phase, 〈θ〉=0); for somewhat larger b, a sixfold degenerate uniform-tilt state occurs with all rods tilted towards one of their next-nearest neighbors. For still larger b, the rods are tilted nonuniformly and form a "striped'' structure. These unexpected phases do not occur if we allow a rectangular distortion of the lattice. For T〉0, the simplest mean-field theory predicts a gradual disordering of the uniform-tilt state via a second-order phase transition. For the transition region, the Monte Carlo results disagree with this picture. Instead they show a strong asymmetric first-order phase transition with pronounced hysteresis. The transition temperature increases with increasing rod length a, qualitatively similar to experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462077
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  • 8
    Electronic Resource
    Electronic Resource
    Capillary condensation in the lattice gas model: A Monte Carlo study (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1444-1454 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A three-dimensional lattice gas model with nearest-neighbor attractive interaction confined to a slitlike adsorbing capillary of thickness D is studied by computer simulation, varying the chemical potential μ, temperature, T, as well as the strength of the short-range interaction between the walls of the capillary and the gas. We show that the chemical potential μc(D) at the condensation transition in the capillary is shifted relative to its bulk value μc(∞) according to the Kelvin equation, μc(D)−μc(∞)∝D−1, for large enough D. Deviations are found for small D, however (of the order of 10 lattice spacings), particularly under conditions where for μ=μc(∞) the surfaces of the capillary for D→∞ are wet. For D=16 lattice spacings we also locate a capillary condensation critical point, and study the distortion of the gas–fluid coexistence curve due to the attractive walls. Profiles of density and local energy across the capillary are studied, and data for the temperature dependence of the local density at the wall both in the gas and in the liquid phase are presented. It is shown that these quantities vary very smoothly near the wetting temperature TW of the bulk (D→∞) system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462180
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  • 9
    Electronic Resource
    Electronic Resource
    On the construction of coarse-grained models for linear flexible polymer chains: Distribution functions for groups of consecutive monomers (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6014-6025 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coarse-grained models for linear flexible polymers are constructed defining effective segments by taking together n successive chemical monomers of a polymer chain, for n=1,2,3,... . The distribution function Pn(l) for the length l of such effective segments is studied as well as the distribution function Pn(cursive-theta) of the angle between successive effective segments. If n is large enough, all these distribution functions tend towards universal limiting functions. For small n, information on chemical structure and effective potentials for the various degrees of freedom of the polymer chains is still preserved. Using polyethylene (PE) as one example, it is shown that these distribution functions for small n depend somewhat on the choice of the model for the effective potential (and the degrees of freedom included). Bisphenol-A-polycarbonate (BPA-PC) as a second example, serves to study to which extent these distribution functions Pn(l) and Pn(cursive-theta) differ for chemically different polymers, such as PE and BPA-PC. Consequences for the molecular modeling of polymeric materials are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461826
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  • 10
    Electronic Resource
    Electronic Resource
    The microphase separation transition in symmetric diblock copolymer melts: A Monte Carlo study (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8349-8366 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use Monte Carlo methods to study a lattice model of a dense melt of symmetric diblock copolymers. The calculations are performed in three dimensions using a slithering snake algorithm. In this work we present results for temperatures at and above the microphase separation transition (MST). The location of the MST is found through a study of the relaxation time associated with lamellar compositional fluctuations. A range of copolymer chain lengths are studied, and from our results, approximate scaling relationships are established. A collective length scale characterizing the compositional fluctuations is found which results from a nontrivial compositional mesostructure. At infinite temperature (athermal conditions), the copolymers exhibit the expected Gaussian conformational behavior. We find, however, that at finite temperatures, the copolymers exhibit non-Gaussian behavior indicative of a stretched or elongated state. The magnitude of this stretching, and hence of the deviation from Gaussian behavior, is found to increase as the temperature decreases towards the MST.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460067
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