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  • American Institute of Physics (AIP)  (12)
  • 1
    Electronic Resource
    Electronic Resource
    Temporal scaling analysis: Viscoelastic properties of star polymers (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 8144-8150 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A generalized temporal scaling ansatz for the frequency dependence of the loss and storage moduli and for the shear dependence of the viscosity is tested against studies on entangled solutions of star polymers in good and theta solvents. At lower frequencies or shear rates, the ansatz calls for an exponential or stretched-exponential form [e.g., G0 exp(−αων)] for G″(ω)/ω and G′(ω)/ω2, and correspondingly in κ for η(κ). At higher frequencies, the ansatz indicates that each of these quantities has a power-law dependence on its primary variable. The predicted forms are in excellent agreement with literature data on solutions of poly-α-methylstyrene, polybutadiene, polystyrene, and polyisoprene stars. A power-law correlation α∼G02/3 is observed between the zero-frequency, zero-shear modulus G0 and the low-frequency or low-shear decay constant α of the stretched exponential, the same power-law line describing both star and linear polymers in good solvents. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480149
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  • 2
    Electronic Resource
    Electronic Resource
    Polymer solution viscoelasticity from two-parameter temporal scaling (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5989-5992 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A novel approach for computing aspects of the loss modulus G″(ω) of a polymer solution is proposed. The path predicts the functional dependence of G″ on ω over a wide range of ω, independent of assumptions as to the nature of the dominant forces acting between polymer chains in solution. Comparison with representative results from the published literature finds excellent agreement with the predicted functional form for G″(ω). The approach is based on extension of the renormalization-group derivation [G. Phillies, Macromolecules 31, 2317 (1998)] of the hydrodynamic scaling model of polymer solution dynamics [G. Phillies, J. Phys. Chem. 93, 5029 (1989)] to the zero-shear viscosity, considering the fixed-point structure of η(c) as inferred from experiment, and analytic extrapolation of the fixed-point structure to a two-variable η(c,ω). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478500
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  • 3
    Electronic Resource
    Electronic Resource
    Translational diffusion of small and large mesoscopic probes in hydroxypropylcellulose-water in the solutionlike regime (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2975-2988 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quasi-elastic light scattering spectroscopy was used to study the translational diffusion of monodisperse spheres in aqueous 1 MDa hydroxypropylcellulose (HPC) at 25 °C. Probe diameters d spanned 14–455 nm; HPC concentrations were 0≤c≤7g/L. Light scattering spectroscopy consistently found spectra having the form g(1)(t)=(1−Af)exp(−θtβ)+Af exp(−θftβf). Here θf and βf refer to the "fast" mode; θ and β describe the "slow" mode. We examine the dependence of θ, β, θf, βf, and Af on d, c, scattering vector q, and viscosity η. β=1 for large probes; elsewise, β and βf are ∈(0,1). The slow mode, with short-lived memory function, is diffusive; for large probes θ(approximate)(dη)−1. The fast mode, with long-lived memory function, appears coupled to polymer chain internal dynamics. Probe behavior differs between "small" and "large" probes. Small probes have diameters d〈Rh, Rh being the chain hydrodynamic radius. Large probes have d≥Rg, Rg being the polymer radius of gyration. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475685
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  • 4
    Electronic Resource
    Electronic Resource
    Charged dielectric spheres in electrolyte solutions: Induced dipole and counterion exclusion effects (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4600-4612 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electrostatic interaction between two charged spheres in the presence of a screening electrolyte is calculated at the level of the linearized Debye–Hückel theory. The calculation was performed analytically as a multipole expansion by applying two-center spherical harmonic expansions and computer symbolic manipulation methods. We focus on charge–charge and charge–induced dipole interactions, calculated here for two spheres of possibly unequal size. The former interaction is given to good approximation by the familiar Debye–Hückel form ∼q1q2 exp[−κ(R−2a)]/[εr(1+κa)2]. The new results are the charge-induced dipole interactions. Physically, these terms arise from two sources, namely (i) surface polarization charge at the surface of each sphere, and (ii) exclusion of the counterion cloud of each sphere from the volume occupied by the other sphere. With parameters appropriate for micelles, at small separations the charge-induced dipole interactions dominate the charge–charge interaction. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470647
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  • 5
    Electronic Resource
    Electronic Resource
    Comment on "Remarks on the mutual diffusion coefficient of Brownian particles'' (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 5972-5973 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450786
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  • 6
    Electronic Resource
    Electronic Resource
    Phenomenological scaling laws for "semidilute'' macromolecule solutions from light scattering by optical probe particles (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5242-5246 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polymer solution dynamics may be inferred from light scattering spectra of dissolved optical probe particles. We compare a variety of probes in solutions of several polymers. In the "overlapping'' concentration/molecular weight regime, the Stokes–Einstein equation fails by up to a factor of 2, while the probe diffusion coefficient D follows a scaling law D/D0=exp(−aMγcνRδ) (c, M, and R are the polymer concentration, molecular weight, and the probe radius, respectively). Experimentally, γ=0.8±0.1, ν=0.6–1.0, and δ=−0.1 to 0, contrary to the theoretical predictions γ=0 and δ=1. With very high molecular-weight polymers, we observe a further "entangled'' regime, characterized by huge (104) failures of the Stokes–Einstein equation and the appearance of "fast'' modes in the scattering spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448969
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  • 7
    Electronic Resource
    Electronic Resource
    A novel representation of the dense-fluid pressure equation (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4711-4712 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new nonanalytic representation for the pressure of the nonideal gas is proposed, namely PV/NKBT=exp[a(N/V)v], where PV=NKBT is the ideal gas law and v and a are scaling coefficients. The form agrees well (often to within reported sampling errors) with Monte Carlo calculations on hard disks, hard spheres, and soft spheres. For hard-core bodies, v=3d/4 to good accuracy, d being the system's dimensionality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452688
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  • 8
    Electronic Resource
    Electronic Resource
    Low-shear viscosity of nondilute polymer solutions from a generalized Kirkwood–Riseman model (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5857-5866 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low shear viscosity η of a nondilute polymer solution is calculated from an extended Kirkwood–Riseman model that includes hydrodynamic interactions between chains. Hydrodynamic interaction tensors for chains in a weak shear field are obtained for interacting pairs and trios of chains. The model proposed here gives a general expansion for η(c) to arbitrary order in polymer concentration c. Divergent integrals encountered in some prior calculations using Stokes-level hydrodynamics are avoided. The model confirms empirical demonstrations that the intrinsic viscosity [η] is a good reducing variable for η(c). © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1456033
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  • 9
    Electronic Resource
    Electronic Resource
    On the temporal resolution of multitau digital correlators (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3423-3427 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article treats a class of systematic errors in determining the intensity–intensity correlation function S(t) with a digital correlator. Errors in determining S(t) will lead to incorrect computations of apparent diffusion coefficients and size distributions for micelles, vesicles, and other supramolecular assemblies. Systematic errors in interpreting the spectrum Sd(tm) measured by real correlators, in terms of the true spectrum S(t), are minimized by optimum interpretations of the delay time tm of each correlator channel. This identification is more complex for multitau correlators than for simple linear correlators. For a multitau correlator with current and delayed sampling times T and θ, and a delay channel beginning τ after the beginning of the zero-time sampling channel, the optimum choice is tm=τ−T/2+θ/2. The so-called "half-channel'' correction tm=τ+θ/2 is erroneous. For the "zero delay channel'' seen on some correlators, the most appropriate identification is tm=T/3. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147154
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  • 10
    Electronic Resource
    Electronic Resource
    Upon the application of cumulant analysis to the interpretation of quasielastic light scattering spectra (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 91-99 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulations were used to study how noise limits the interpretation of quasielastic light scattering spectra with cumulant analysis. The effects of signal-to-noise ratios, channel spacing, line shape, and the truncation order of the cumulant series were all examined. The underlying spectra included narrow and broad unimodal and bimodal forms, as expected for ternary polymer:polymer:solvent mixtures. The upper bound on the usable number of cumulants is determined by the signal-to-noise ratio, the spectral nonexponentiality, and the number and spacing of the spectrometer channels. Upper limits on the acceptable degree of spectral nonexponentiality—below which the cumulant expansion is useful—can be stated in terms of the measured second cumulant. Use of logarithmically rather than linearly spaced correlator channels greatly increases the region over which cumulant fits are useful.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455465
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