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  • 11
    Electronic Resource
    Electronic Resource
    Convergence of multiple scattering series for two-body hydrodynamic effects on shear viscosity of suspensions of spheres (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4557-4567 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An efficient computational scheme has been developed that includes many-body hydrodynamics for viscosity in a suspension of spheres following the approach of Jones and Muthukumar [J. Chem. Phys. 89, 6406 (1988)] for friction coefficients. The method combines the hydrodynamic scattering formalism of Freed and Muthukumar [J. Chem. Phys. 76, 6186 (1982)] with angular momentum diagrammatic techniques from quantum mechanics. The concentration dependence of the viscosity is expressed as a series of finite integrals labeled by the equivalent of angular momentum quantum numbers. This series is smoothly convergent in contrast to the case of the alternate formalism of a series of terms of inverse powers of the sphere separation. A comparison between different methods and the slowness of convergence of the series are addressed in detail. At the two-body level, the virial expansion for the shear viscosity η of a suspension of hard spheres of volume fraction Φ is determined to be η/η0=1+2.5Φ+4.8292Φ2+O(Φ3), where η0 is the viscosity of the fluid and the correction for the Brownian motion [G. K. Batchelor, J. Fluid Mech. 83, 97 (1977)] has been ignored. Our value for the two-body coefficient differs in 3.4% from the extrapolated value 5.0019 obtained by Cichocki and Felderhof [J. Chem. Phys. 89, 1049 (1988)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460738
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  • 12
    Electronic Resource
    Electronic Resource
    Calculation of the rotational cooperative and self-friction coefficients in a dilute suspension of spheres: Two-body effects (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5127-5129 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By employing the computational methods of Jones and Muthukumar, and the hydrodynamic scattering formalism of Muthukumar and Freed, we have computed the rotational friction coefficients for a dilute suspension of spheres to first order in concentration. These results are compared with previous calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457610
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  • 13
    Electronic Resource
    Electronic Resource
    Localization of a polymeric manifold in quenched random media (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4594-4603 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a replica calculation and obtain analytically the size of a polymer chain with excluded volume interactions in quenched random media. We show that the size of the polymer is shrunk as the density of the impurities constituting the random medium is increased. We demonstrate that this is a general phenomenon. There are three regimes depending on the strength of the impurity density v. In the weak impurity density regime the polymer obeys the self-avoiding statistics with its gyration radius R depending on its typical length L according to R∼L(D+2)/(d+2), where D is the dimension of the polymer and d is the space dimension. In the intermediate regime the polymer is in the unperturbed state where R∼L(2−D)/2. In the third regime of localization occurring for sufficiently large v, R∼v−(2−D)/[4D−(2−D)d] in the absence of three-body interactions and R∼v−1/d LD/d in the presence of strong three-body effects. We examine the effect of long-range interactions of the type w||r||−α between the segments of the polymer separated by r on the localization and find that the polymer collapse is suppressed for realistic impurity densities [v〈wR(d−α)/2].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456619
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  • 14
    Electronic Resource
    Electronic Resource
    Self-entanglement in ring polymers (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2873-2881 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We represent ring polymers with the off-lattice rod-bead model. We produce perfect unbiased model instances that have between 32 and 2048 beads. These rings are produced at several different values of bead radius, to represent polymers in solvents of different quality. These instances are subject to a novel smoothing operation that facilitates the determination of their topological state, which is represented with the Alexander polynomial. We observe that the probability of observing a trivial knot (P) has a decreasing exponential dependence on the contour length (N) of the polymer, or that P=exp(−N/N0). The characteristic length (N0) varies by many orders of magnitude depending on chain flexibility and solvent quality. For Gaussian rings in a theta solvent, the characteristic length (N0) is 2.6×102. For a good solvent, N0∼8×105. We also explore the expectation value of the minimum number of crossings and suggest that it probably cannot be represented as a power law or exponential function of N. We also suggest that sufficiently large rings will always be composite, and not prime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460889
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  • 15
    Electronic Resource
    Electronic Resource
    Effects of surface roughness on adsorbed polymers (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4062-4070 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polymer chains adsorbed on rough impenetrable surfaces have been investigated analytically and by simulations. The cases of physical and chemical roughness of surfaces are identified and their distinctive effects on the adsorption characteristics are studied. For the chemically rough surface the adsorption temperature is depressed by an amount proportional to the concentration of the impurities. A polymer adsorbed on a physically rough surface can be interpreted using the analogy to a one-dimensional electron in a periodic potential. It is shown that at low temperatures the chain is "localized'' in one of the wells. Between the localized regime and the unbinding transition point, there exists a "diffusive'' regime, where the chain is diffusing by being shared by several potential wells. This regime is equivalent to the conduction band in the electron analogy. In contrast to the case of a flat surface, the unbinding transition of a chain from a periodically rough surface is markedly sharp due to an effective anchoring of the chain in the wells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460656
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  • 16
    Electronic Resource
    Electronic Resource
    Dynamics of phase separation in a binary polymer blend of critical composition (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6899-6909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report results of a detailed numerical study of the phase separation process in a three dimensional model of polymer blends. The model system considered by us is described by Flory–Huggins–de Gennes free-energy functional. For a critical quench, we numerically integrate the corresponding time evolution equation for the conserved order parameter based on the above free-energy functional. We study the time dependence of the characteristic domain size as well as the pair correlation function and the structure factor for several quench temperatures. The results indicate that the growth law for the characteristic domain size is given by a modified Lifshitz–Slyozov law and the growth law exponent is independent of the quench temperature. We also find that both the pair correlation function and the structure factors show dynamical scaling at late times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458277
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  • 17
    Electronic Resource
    Electronic Resource
    Critical wetting in two-component polymer blends (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5749-5755 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We derive the free energy of a bulk two-component polymer blend in the presence of a planar surface, and use these results to map out the region of critical wetting in parameter space. Unlike previous investigations of wetting, our free energy has terms containing gradients of the composition profile at the surface, and we find that these terms have important consequences for critical wetting. In particular, the single gradient term causes the region of parameter space in which it is possible to find critical wetting to be greatly reduced. Although, as discussed in our concluding remarks, we find that the random phase approximation fails for a polymer blend near a surface, our conclusions concerning critical wetting are valid for a free energy which includes gradient terms of the general type considered here.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456383
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  • 18
    Electronic Resource
    Electronic Resource
    The size of a polymer in random media (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2435-2441 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Stimulated by the recent numerical simulation results of Baumgartner and Muthukumar, an analytic derivation is given of the size of a polymer in random media. It is shown that, for long Gaussian chains in three dimensions, the mean square end-to-end distance 〈∼(R2)〉 is proportional to (uρ0)−2, where uρ0 is the measure of the scattering power of the medium. For example, ρ0 is the number density of the scatterers and u is the strength of the pseudopotential between the chain segments. A simple extrapolation formula has been obtained using the replica theory for 〈∼(R2)〉 at intermediate values of (uρ0)2L, 〈∼(R2)〉 =(Ll/z) [1−exp(−z)], where L is the chain length, l is the Kuhn step length, and z=εu2ρ20Ll5 with ε being a numerical coefficient. This theory agrees well with the simulation results. The effects of space dimensionality and the replica breaking symmetry are also addressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455038
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  • 19
    Electronic Resource
    Electronic Resource
    Calculation of the cooperative friction coefficient in a dilute suspension of spheres. I. Two-body effects (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6406-6419 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply diagrammatic techniques of quantum-mechanical angular momentum algebra to the efficient calculation of transport properties in a solution of spheres, based on the hydrodynamic scattering formalism of Muthukumar and Freed. The method is illustrated by computing the two-body correction to the cooperative friction coefficient in a dilute suspension.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455409
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  • 20
    Electronic Resource
    Electronic Resource
    The response of semiflexible liquid crystals to quenched random disorder (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 578-585 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the effect of quenched random impurities on the first-order nematic to isotropic transition of trimers using Monte Carlo simulation. We have shown that the introduction of quenched impurities to a liquid crystalline system will lower the transition temperature, round the specific heat peak, and change the order of the transition. This is in agreement with previous calculations that show that the introduction of quenched random impurities can decrease or eliminate the discontinuity of a first-order transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463553
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