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  • 1
    Electronic Resource
    Electronic Resource
    Ice under pressure: transition to symmetrical hydrogen bonds (1983)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 87 (1983), S. 4281-4288 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100244a058
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  • 2
    Electronic Resource
    Electronic Resource
    Crystallization of polyethylene and polytetrafluoroethylene by density-functional methods (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 9348-9366 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular density-functional theory is extended to address the crystallization of chemically realistic polymers. The polymer (RISM) reference interaction site model integral-equation approach is employed to calculate the liquid-state structural information required as "input'' into our density-functional theory. The single-chain structure is described by the rotational isomeric state model, and the accuracy of both the theoretically calculated single-chain and liquid structures have been verified by direct comparison with Monte Carlo simulation and x-ray scattering, respectively. The driving forces for the crystallization of polymers are found to be completely different from those in monatomic systems and can be understood in terms of an effective "chain-straightening force'' (which results from chain packing) combined with a background attractive potential. Remarkably, the predicted melting temperatures for polyethylene and polytetrafluoroethylene at atmospheric pressure are within a few degrees of the experimental values, and the density–temperature phase diagrams are also in good agreement with experiment. Chemically unrealistic, coarse-grained models of polymer structure appear to be inadequate for the crystallization phenomenon, which is found to be quantitatively sensitive to interchain attractive forces and melt compressibility. The aspect ratios in polyethylene and polytetrafluoroethylene melts at the phase transition are predicted to be virtually identical.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461163
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  • 3
    Electronic Resource
    Electronic Resource
    Integral equation theory of polymer blends: Numerical investigation of molecular closure approximations (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9080-9093 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermodynamics of symmetric polymer blends is investigated using the polymer reference interaction site model integral equation theory with the new molecular closures presented in the previous paper. In contrast to the atomic mean spherical approximation reported earlier by Schweizer and Curro [J. Chem. Phys. 91, 5059 (1989); Chem. Phys. 149, 105 (1990)] (in which the critical temperature is proportional to the square root of the degree of polymerization), the molecular closures predict a linear dependence of the critical temperature on the degree of polymerization, in agreement with classical mean field theory. Detailed numerical calculations using the reference molecular mean spherical approximation (R-MMSA) and the reference molecular Percus–Yevick (R-MPY) closures are presented for the intermolecular structure and effective chi parameter in symmetric blends of semiflexible chains. For the symmetric blend, the R-MMSA closure is almost an integral equation realization of mean field theory, consistent with the analytical results presented in the previous paper. With the R-MPY closure, at low densities, the effective chi parameter is significantly renormalized down from its mean field value and displays a strong composition dependence. As the density is increased, both the renormalization of the effective chi parameter and its composition dependence become weaker. These trends are consistent with recent computer simulations. The influence of chain aspect ratio and the precise choice of intermolecular potentials on blend thermodynamics and phase separation are also explored. With the exception of the composition dependence of the effective chi parameter in the R-MPY theory, the analytical thread calculations are shown to be in qualitative, and sometimes quantitative, agreement with all the numerical results for symmetric blends.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464466
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  • 4
    Electronic Resource
    Electronic Resource
    On the scaling of the critical temperature with the degree of polymerization in symmetric polymer blends (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5927-5930 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The scaling of the critical temperature (Tc) with the degree of polymerization (N) in symmetric polymer blends is investigated via a new molecular closure to the polymer reference interaction site model integral equation theory. The theory predicts Tc∼N, which is qualitatively consistent with classical mean field ideas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463755
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  • 5
    Electronic Resource
    Electronic Resource
    Reference interaction site model theory of polymeric liquids: Self-consistent formulation and nonideality effects in dense solutions and melts (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3211-3225 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reference interaction site model (RISM) integral-equation approach to polymeric liquids is generalized to allow a self-consistent determination of single-chain and intermolecular pair correlations. Nonlinear medium-induced effects on intrachain statistics are described at the level of self-consistent pair interactions. Tractable schemes to implement the self-consistency aspect are formulated for semiflexible and rotational isomeric state chain models, and applied numerically to concentrated solutions and melts of semiflexible polymers. Theoretical results are in good agreement with off-lattice molecular dynamics simulations, and a rich dependence of the renormalized persistence length on temperature, aspect ratio, density, and degree of polymerization is found. The general formalism for polymer alloys is sketched and the potentially important role of local density and concentration fluctuations as nonuniversal mechanisms for inducing conformational perturbations is emphasized. A detailed analysis is made of the connections between the polymer RISM integral-equation theory and the field theoretic psuedopotential formalism, and remarkable similarities in the predictions of the two distinct approaches for solutions of long thread-like polymers are demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461965
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  • 6
    Electronic Resource
    Electronic Resource
    Local structure of polyethylene melts (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4659-4662 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polymer-RISM (Reference-interaction-site-model) theory is used to examine the local structure of a dense polyethylene melt near the freezing point. Predictions for the static structure factor are found to be in near quantitative agreement with new x-ray diffraction data obtained at 430 K and 1 atm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460594
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  • 7
    Electronic Resource
    Electronic Resource
    Microscopic theory of the dynamics of polymeric liquids: General formulation of a mode–mode-coupling approach (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5802-5821 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A formally exact, nonlinear generalized Langevin equation (GLE) for a flexible probe polymer in a dense melt has been derived using molecular phase space kinetic theory and Mori–Zwanzig projection operator techniques. An approximate, linearized dynamic memory function is developed, and the resulting GLE is specialized to the problem of an overdamped liquid of uncrossable Rouse polymers. An analytically tractable, perturbative/short time evaluation of the projected force time correlation function matrix is proposed which accounts for uncorrelated intermolecular pair interaction effects in the polymer melt. The detailed predictions for transport coefficients and various time correlation functions are determined for linear chains, and compared with recent lattice Monte Carlo simulations. Significant slowing down of all dynamical processes relative to the Rouse behavior is found, but the molecular weight scaling is not correctly described. A nonperturbative approach based on a polymeric generalization of molecular-scale mode–mode coupling theory is formulated which does properly capture the strong caging and viscoelastic effects in dense melts.The phenomenological concepts of topological entanglements, a static tube, and primitive path are not employed, and simplified assumptions about liquid structure and mode of motion are not introduced a priori. The microscopic theory is based on an explicit nonlinear coupling of the collective fluid density fluctuations with the segmental density fields of a probe polymer. Equilibrium structural information is naturally incorporated, and the associated renormalized intermolecular potential, or vertex, is found to be spatially long range due to chain connectivity and correlation hole effects. The projected dynamics describing the time evolution of the mode-coupling part of the memory function matrix is evaluated using the short time/pair interaction theory. The polymeric mode-coupling theory can be employed as a rigorous and unified framework for qualitatively and quantitatively studying transport coefficients, material response functions, crossover phenomena, collective density fluctuation dynamical effects, nonlinear molecular architectures (e.g., ring polymers), tracer diffusion, semidilute solutions and blends.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457533
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  • 8
    Electronic Resource
    Electronic Resource
    Equation of state of polymer melts: Numerical results for athermal freely jointed chain fluids (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3350-3362 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Our microscopic RISM integral equation theory for the virial equation of state of polymer liquids developed in the preceding paper is numerically implemented for athermal melts composed of freely-jointed chains interacting via hard core site–site potentials. A modified ideal description of the single chain intramolecular correlations is employed which rigorously enforces the nonoverlapping core condition and leads to significant local coil expansion. Comparison of the theoretically computed virial pressure for tangent diatomics and short chains with available Monte Carlo simulation results over a wide range of packing fractions suggests the theory is quite accurate. Significant inconsistencies between the pressure computed via the virial and compressibility routes are found and discussed in light of the known limitations of the RISM method and the importance of self-consistency corrections for flexible chain molecule liquids. A detailed numerical study of the density and degree of polymerization dependences of the total virial pressure, and its individual two- and three-body components, is presented, along with the limiting infinite chain behavior. The integral equation results are also compared with the predictions of several simple mean field and/or lattice models for both short chains and high polymers. Significant, and in some cases massive, differences are found between the predictions of the various approaches and the integral equation calculations which are attributed to the neglect of polymeric connectivity, intermolecular correlations, and/or the use of a lattice model inherent to the simple theories. In particular, both the density dependence of the pressure and its sensitivity to degree of polymerization are found to be much stronger than the simple theories predict due to self-screening and correlation hole effects absent in the latter. Finally, model calculations of the intermolecular radial distribution function and static structure factor at fixed pressure are performed for several degrees of polymerization and are found to be very weakly dependent on chain length due to compensating effects associated with a molecular weight dependent packing fraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454944
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  • 9
    Electronic Resource
    Electronic Resource
    Self-consistent polymer integral equation theory: Comparisons with Monte Carlo simulations and alternative closure approximations (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1455-1464 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently, Schweizer, Honnell, and Curro reported a self-consistent formulation of the polymer reference interaction site model (PRISM) theory for polymer melts. The purpose of this paper is to compare the predictions of this theory to Monte Carlo simulations of hard chains thereby allowing an independent test of the various approximations in the PRISM theory. We find that the self-consistent PRISM theory with the Percus–Yevick (PY) closure is very accurate for both the intramolecular and intermolecular correlations in hard 20-mers for a wide range of densities. The accuracy of the theory for longer chains is somewhat diminished. We also compare the PRISM theory predictions using the PY, hypernetted chain (HNC), and Martynov–Sarkisov (MS) atomiclike closures. All the closures give equally good predictions at high densities, but the HNC and MS closures exhibit unphysical features, and ultimately fail to converge, at lower densities and/or large chain lengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463221
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  • 10
    Electronic Resource
    Electronic Resource
    Analytic reference interaction site model-mean spherical approximation theory of flexible polymer blends: Effects of spatial and fractal dimensions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3986-4000 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently developed methods for obtaining exact and approximate analytical solutions of the reference interaction site model-mean spherical approximation (RISM-MSA) integral equations for liquid mixtures composed of long, flexible polymers are applied to study the critical temperature Tc for phase separation of symmetric isotopic binary blends as a function of degree of polymerization N, spatial dimension D, and fractal dimension df of the individual macromolecules. For ideal random walk coils, the theory predicts a nonclassical behavior given by Tc∝N(D−2)/2 in two and three dimensions, and the classical Flory–Huggins mean field Tc∝N law is recovered in four and higher dimensions. For arbitrary interpenetrating polymeric fractals, the theory predicts Tc∝N(D−df)/df for spatial dimensions below 2df and Flory–Huggins behavior for D〉2df. These novel scaling laws for isotopic mixtures are a consequence of a consistent treatment of chain connectivity on all length scales, intermolecular excluded volume, and a short range unfavorable interaction between hydrogenated and deuterated polymers. A general, closure-independent physical argument based on a renormalization of the bare chi parameter by relatively long range correlated fluctuations in the blend is proposed which reproduces all the qualitative predictions of the RISM-MSA integral equation theory. Analogies with nonclassical critical fluctuation effects are established. Application of the analytical approach to purely athermal blends is also presented. The magnitude and composition dependence of the effective chi parameter is found to be a sensitive function of both spatial and fractal dimensions, and also local nonuniversal features. The various theoretical predictions are favorably compared with recent small angle neutron scattering measurements on binary polymer alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460704
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