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  • American Institute of Physics (AIP)  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics in concentrated polymer solutions by polarized Rayleigh–Brillouin scattering and dynamic light scattering (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8568-8577 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Solutions of polystyrene in toluene in the concentration range 0.1–1.0 g/ml have been examined using polarized Rayleigh–Brillouin scattering and dynamic light scattering. The purpose was to extend measurements to the hitherto little studied interval between semidilute solutions and the bulk polymer. The Brillouin shift increases monotonically with polymer volume fraction (Φp) and a linewidth maximum is observed at about Φp=0.6. Up to Φp=0.56, a single cooperative diffusion mode is found, which passes through a broad maximum at Φp=0.5. For the sample with Φp=0.78, the nature of the main component depends sensitively on temperature. At 17 °C it is purely relaxational (q independent), while at 40 and 50 °C, it is diffusive. At intermediate temperatures, mixed behavior is noted where the dynamic processes overlap because the slower relaxational mode has a stronger temperature dependence. At Φp=0.89, the correlation functions are highly nonexponential and strongly temperature dependent. The bimodal correlation function contains contributions from both concentration fluctuations due to cooperative diffusion and density fluctuations arising from segmental motions in the polymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461235
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamic properties of concentrated solutions above the glass transition temperature (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6274-6280 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Concentrated solutions of polybutylacrylate (PBA) in dioxane and polybutadiene (PBD) in cyclohexane and carbon tetrachloride have been studied at 50 °C in the concentration range 0.1–0.9 g/ml using Rayleigh–Brillouin scattering (RBS) and static and dynamic light scattering. The purpose was to extend measurements to concentrated solutions of "soft'' polymers in a temperature range well above the glass transition temperature. The high frequency modulus from RBS is much larger than the low frequency osmotic modulus, but they have identical power law behavior. Contrary to the pronounced maximum in Dc observed as a function of Φp in concentrated polystyrene/toluene solutions [Brown et al., J. Chem. Phys. 95, 8568 (1991); Macromolecules 24, 5484 (1991)], the concentration dependence of Dc increases strongly above Φp≈0.56 in the PBA/dioxane system. This change is attributed to a reduction in the effective solvent viscosity caused by the presence of the polymer and analogous to the effect noted by Lodge and co-workers in polybutadiene solutions using oscillatory electric birefringence and pulsed-field-gradient nuclear magnetic resonance (NMR) measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462618
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  • 3
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    Electronic Resource
    Coupling of density to concentration fluctuations in concentrated solutions of polystyrene in toluene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9014-9017 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In concentrated polystyrene (PS) solutions in toluene, close to the glass transition temperature (Tg), both concentration (q2 dependent) and density fluctuations (q independent) are simultaneously observable in the time window of the polarized (VV) dynamic light scattering experiment. At Φp=0.89, both modes (Γc and Γd) are well separated on the time scale. Close to Tg, the diffusion relaxation is "frozen-in,'' a phenomenon anticipated from free-volume theory but not previously observed in polymer solutions. At Φp=0.78, a q2-dependent mode is found above about 40 °C, whereas it is q independent at 17 °C. At intermediate temperatures, the two modes are coupled when Γc≈Γd. The coupling of density to concentration fluctuations is analyzed here in terms of a recent theory of Jäckle and Frisch [J. Polym. Sci. Polym. Phys. Ed. 23, 675 (1985)]. The latter is found to provide a good semiquantitative description of the complex dynamic behavior in this system close to the glass transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464460
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