Use of a cooperative-motion domain model to analyze brillouin light scattering measurements of the dynamic modulus in triblock copolymers

Lehman, Susan; McNeil, L. E.; Albalak, Ramon J.

doi:10.1002/1099-0488(20000815)38:16<2170::aid-polb100>3.0.co;2-s

Cited by 8 publications

(12 citation statements)

References 35 publications

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“…The addition of small amounts of water shifts the relaxation frequency toward lower temperatures. A very similar result has been observed for mixtures of PEG600 in different organic solvents 7,8 as well as in many other moderately viscous polymers or polymeric solutions. − …”

Section: Viscoelastic Behaviorsupporting

confidence: 79%

“…A very similar result has been observed for mixtures of PEG600 in different organic solvents 7,8 as well as in many other moderately viscous polymers or polymeric solutions. [13][14][15][16] For pure water, the well-known anomalous behavior of the velocity, with a maximum at 345 K, is observed which is related with the collapse, on heating, of the open 3D structure of the H-bonded network. Such a structural rearrangement results in increasing of density with a simultaneous decrease in compressibility.…”

Section: Viscoelastic Behaviormentioning

confidence: 95%

See 1 more Smart Citation

Structuring Effects and Hydration Phenomena in Poly(Ethylene Glycol)/Water Mixtures Investigated by Brillouin Scattering

et al. 2006

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Aqueous solutions of poly(ethylene glycol) (PEG) of mean molecular mass of 600 g/mol (PEG600) are investigated by Brillouin scattering technique. At high PEG content, a relaxation phenomenon is observed, which is related to a local rearrangement of the polymer structure where the interaction, via hydrogen bonding, with the solvent molecules plays a role. The obtained values of the relaxation times match the literature data very well for a fast relaxation time revealed by dielectric relaxation measurements in very similar mixtures. The calculated concentration behaviors of the excess adiabatic compressibility turns out in good agreement with the previous findings from ultrasonic measurements at 3 MHz. The observed minimum in the adiabatic compressibility is interpreted as the result of the interaction between water and the EO units of the PEG chain, which results in a structure tighter then that typical of bulk water and of pure PEG600. Such a hypothesis is supported by the observation that volume fraction value of about 0.3 coincides with the concentration value at which full hydration of EO units takes place. The observation that at the same concentration, the polymer coils start to overlap each other further supports the idea that the adiabatic compressibility behavior is monitoring the structural evolution of the mixture. However, similar results are obtained for largely different binary mixture which suggests caution in taking this conclusion too literally. In particular, the hypothesis that the occurrence of an extreme in the excess adiabatic compressibility could be simply originated by statistical effects and that further work is required for disentangling entropic contribution from effects of hetero-association and self-aggregation of one or both the components.

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Section: Viscoelastic Behaviorsupporting

confidence: 79%

Section: Viscoelastic Behaviormentioning

confidence: 95%

Structuring Effects and Hydration Phenomena in Poly(Ethylene Glycol)/Water Mixtures Investigated by Brillouin Scattering

et al. 2006

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“…In particular, the maximum in the normalized absorption of the pure PEG600, occurring at the same temperature where v B exhibits an inflection point, is a common result for many moderately viscous polymers or for polymeric solutions. − It is usually assigned to conformational rearrangements of the polymeric chains, triggered by reorientation of the side groups. On dilution, the same relaxation process shifts toward lower temperatures (i.e., toward higher frequencies).…”

Section: Discussionmentioning

confidence: 99%

“…A very similar behavior has been recently observed in PEG600/CCl 4 15 mixtures and has been analyzed with different theoretical models. 12, [38][39][40][41] In particular, we have assumed as is the case for many viscous liquids that the relaxation process can be suitably described in terms of a single relaxation time and accordingly we adopted the following expressions for the hypersonic sound velocity and normalized absorption where V 0 and V ∞ are the low-and high-frequency limit values of the sound velocity, τ is the structural relaxation time, and C is a constant term accounting for all the nonrelaxing highfrequency contributions. Following the same procedure outlined in ref 15, we have fitted our experimental data with two different models for the temperature behavior of the relaxation time, namely, simple Arrhenius, eq 7, or Vogel-Fulcher-Tamman (VFT), eq 8 In the first case, E represents the activation energy of the relevant relaxation process and R g is the universal gas constant.…”

Section: Discussionmentioning

confidence: 99%

Evidences of Nonideal Mixing in Poly(ethylene Glycol)/Organic Solvent Mixtures by Brillouin Scattering

et al. 2005

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The concentration dependence of the hypersonic properties of solutions of poly(ethylene glycol) of mean molecular mass 600 g/mol (PEG600) in benzene and toluene has been investigated by Brillouin scattering. The two solvents are very similar in structure and chemical properties, but while benzene is nonpolar, toluene possess a modest dipole. In both solvents a high-frequency relaxation process has been observed at high concentrations which has been assigned to conformational rearrangements of the polymeric chains, triggered by reorientation of the side groups. In both cases, the concentration dependence of the adiabatic compressibility deviates significantly from linearity, indicating the existence of nonideal mixing phenomena driven by aggregation processes taking place in the systems. However, there is no temperature dependence for solutions of PEG600 in benzene; on the contrary, the results obtained for solutions of PEG600 in toluene are noticeably dependent on the temperature. The comparison of the experimental data with the results of previous experiments on similar systems allows a general picture for weakly interacting mixtures of hydrogen-bonded systems and organic solvents to be developed. In particular, in the presence of a nonpolar solvent molecule the local structure of the mixture is dominated by solute self-association processes and any resulting solute-solvent correlation is barely induced by excluded volume effects. At high enough dilution the self-aggregation of solute molecules produces a variety of new local topologies that cannot be observed in bulk solute, and as a consequence, the concentration evolution of the system is too rich to be described in terms of a linear combination of a few components over the whole concentration range. The situation seems to be simpler for the polar toluene solvent molecules, where a three-component model seems able to fit the experimental concentration dependence of the hypersonic velocity. This result is interpreted to imply that the interaction between the solvent dipoles and the active sites of the solute produces a relatively stable heterocoordination, while the relevance of self-association is partially reduced.

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“…Polymer processing requires a complete understanding of the complex rheological behavior of polymers in a temperature range from subvitreous temperature to the terminal flow zone. However, because of the long‐chain character of polymer molecules, polymers are viscoelastic materials with rheological behaviors characterized by nonexponential relaxation processes exhibited in numerous experiments, such as dynamic mechanical analysis (DMA),1–4 dielectric spectroscopy,1, 5–7 quasielastic light scattering,8, 9 and specific heat measurements 1, 3, 7, 10. Relaxation processes are associated with molecular motions that lead to a new structural equilibrium with a low energy content.…”

Section: Introductionmentioning

confidence: 99%

Application of fractional calculus to the modeling of the complex rheological behavior of polymers: From the glass transition to flow behavior. I. The theoretical model

Melo

González-González

Guerrero-Salazar

et al. 2008

J of Applied Polymer Sci

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ABSTRACT:A model based on the concept of fractional calculus is proposed for the description of the dynamic elastic modulus (E* 5 E 0 1 iE 00 , where E* is the complex modulus, E 0 is the storage modulus, or real part of the complex modulus, and E 00 is the loss modulus, or imaginary part of the complex modulus) under isothermal and isochronal conditions for amorphous polymers, including both the glass transition process and the flow behavior. The differential equations obtained for this model, which we call the extended fractional Zener model (EFZM), have differential and/or integral operators of fractional order between 0 and 1. The application of the Fourier transform to the fractional equation of the EFZM, the association of their parameters to the relaxation times of the cooperative or noncooperative molecular movements of polymer chains, and the isothermal and isochronal diagrams of E 0 and tan d 5 E 00 /E 0 were evaluated. These theoretical diagrams were typical curves that clearly showed the glass-transition (a-relaxation) and flow behavior. The EFZM will enable us to analyze the complex rheological behavior of amorphous polymers.

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Use of a cooperative-motion domain model to analyze brillouin light scattering measurements of the dynamic modulus in triblock copolymers

Cited by 8 publications

References 35 publications

Structuring Effects and Hydration Phenomena in Poly(Ethylene Glycol)/Water Mixtures Investigated by Brillouin Scattering

Structuring Effects and Hydration Phenomena in Poly(Ethylene Glycol)/Water Mixtures Investigated by Brillouin Scattering

Evidences of Nonideal Mixing in Poly(ethylene Glycol)/Organic Solvent Mixtures by Brillouin Scattering

Application of fractional calculus to the modeling of the complex rheological behavior of polymers: From the glass transition to flow behavior. I. The theoretical model

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