Depolarized Rayleigh scattering and backbone motion of polypropylene glycol

Jones, Dane R.; Wang, C. H.

doi:10.1063/1.433275

Cited by 27 publications

(7 citation statements)

References 17 publications

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“…In VH scattering, the low a, is probably due to the Rayleigh wing and some fast segmental mode, which are in fact observed by the Fabry-Perot interferometer. 7 Finally, it should be pointed out that the fast segmental mode as probed by the interferometer depends on the macroscopic shear viscosity7 as well as temperature, in contrast to the relaxation modes, which depend only on the temperature, as studied in the present work. It is our intent to carry out in future work a detailed interferometric concentration-dependence study of PPG to elucidate the nature of the fast component.…”

Section: Resultsmentioning

confidence: 54%

Laser light beating spectroscopic studies of dynamics in bulk polymers: poly(propylene glycol)

Wang¹,

Fytas²,

Lilge³

et al. 1981

Macromolecules

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105

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Section: Resultsmentioning

confidence: 54%

Laser light beating spectroscopic studies of dynamics in bulk polymers: poly(propylene glycol)

Wang¹,

Fytas²,

Lilge³

et al. 1981

Macromolecules

Self Cite

105

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“…The correlation time sensitive to the short-range cooperative motions in the PPO chains, τ cor (PPO), remains around ∼1 ns in the whole temperature range (see Figure ). Relaxation times for backbone motions in PPO were also found in the same range …”

Section: Discussionmentioning

confidence: 68%

“…These values are close to the activation energies found in bulk PPO for segmental motions. Indeed, NMR measurements give E s = 27, 28.5, and 23 kJ/mol, while the reported value from Rayleigh scattering gives E s = 25 kJ/mol . The activation energy of η/ T for the solvent D 2 O obtained from ref is 19.5 ± 0.2 kJ/mol.…”

Section: Discussionmentioning

confidence: 84%

H NMR Relaxation Studies of the Micellization of a Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Triblock Copolymer in Aqueous Solution

1996

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1H nuclear magnetic resonance (NMR) relaxation studies of the temperature-induced micellization of a poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide), PEO−PPO−PEO, block copolymer in aqueous solution were performed in the range 280−345 K. 1H NMR spectra of the block copolymer were well resolved, thus allowing us to probe specifically the methyl and methylene relaxation processes in the PPO and PEO blocks, respectively. Interpretation of the relaxation data in terms of the Hall−Helfand correlation function leads to four distinct correlation times for the PPO and PEO blocks. The slower correlation time in the PPO block was identified as the Zimm−Rouse first normal mode of the copolymer and served to determine the hydrodynamic radius, R H, of the unimers and the micelles. On a more local scale, the behavior of the correlation time for segmental motions in the PPO block indicates an extension of the PPO chains in micelles relative to the unimers. This conformational change is related to the formation of a water insoluble liquid-like core created by the PPO chains in the micelle where the trans isomers are favored. The rotational isomeric states model used to interpret the faster correlation time in the PEO chains yields an activation energy of 14.6 kJ/mol for the correlated transitions in the PEO blocks, in agreement with previous theoretical calculations. The slower correlation time in the PEO blocks shows a marked increase upon micellization attributed in part to the polymer−polymer interactions between the different PEO blocks constituting the hydrophilic moiety of the micelles. A power law relating this relaxation time to the micelle hydrodynamic radius is predicted and observed experimentally. The concentration dependence of the critical micellization temperature, inferred from the methyl spin−lattice relaxation time in the PPO block, was found to be adequately described by a closed association model. The standard free energy, enthalpy, and entropy of micellization obtained by NMR are in close agreement with the recent experimental thermodynamic studies of P. Alexandridis et al. (Macromolecules 1994, 27, 2414).

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“…The Rayleigh relaxation time is obtained from using eq 2. For small molecules is related to the single particle orientational relaxation time rs by9 T = giTs (5) where rs for an ellipsoidal molecule in a uniform fluid with shear viscosity is given by the modified Stokes-Debye-Einstein (SDE) relation:…”

Section: Discussionmentioning

confidence: 99%