Birefringence of Polymers in the Softening Zone

Mott, P. H.; Roland, C. M.

doi:10.1021/ma980174p

Cited by 18 publications

(29 citation statements)

References 25 publications

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“…However, since segmental relaxation is manifested over a substantial length scale, [40][41][42][43][44] cross-link junctions constrain the motion of even topologically remote chain segments. Consequently, segmental relaxation times, as well as the shape of the relaxation function itself, are affected by cross-link density.…”

Section: Discussionmentioning

confidence: 99%

Mechanical Behavior of Polystyrene Microgels

Roland¹,

Santangelo²,

Antonietti³

et al. 1999

Macromolecules

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Polystyrene microgels are nanometer-sized particles produced by polymerization and crosslinking in microemulsion. As a result of their internal network structure, microgels have negligible intermolecular entanglement interactions. This can have a profound effect on their rheology; it also leads to glassy fracture resembling the behavior of low molecular weight, linear polystyrene. At higher frequencies, the mechanical response of microgels is quite similar to that of linear polystyrene. Breakdown of time-temperature superpositioning occurs in the softening zone of the viscoelastic spectrum. In the glass transition region, the segmental relaxation function is broadened and exhibits an enhanced dependence on temperature. The latter two effects, due to the cross-linking of the microgels, are also seen in conventional, macroscopic networks.

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Section: Discussionmentioning

confidence: 99%

Mechanical Behavior of Polystyrene Microgels

Roland¹,

Santangelo²,

Antonietti³

et al. 1999

Macromolecules

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“…This assumption is at odds with various experimental facts, as detailed elsewhere. 9,10 The present work is motivated by a recent publication by Urakawa et al, 11 in which relaxation and transport properties of unentangled polystyrene (PS2K, molecular weight ) 2 kg/mol) were reported. In their analysis, Urakawa et al 11 identified the terminal viscosity with the G-component of Inoue et al 8 and reported that η 0 /T had the same T dependence as the segmental dynamics.…”

Section: Introductionmentioning

confidence: 99%

Modes of Molecular Motion in Low Molecular Weight Polystyrene

2004

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The variations with temperature of the viscosity, η, and the relaxation times for various low molecular weight, unentangled polystyrenes (PS) are analyzed. We find that the temperature dependence of η does not directly reflect the behavior of the global chain modes. Depending on molecular weight and temperature, η can exhibit a stronger temperature dependence than even the local segmental modes. However, this is only a consequence of the strong temperature dependence of the recoverable compliance J s. The Rouse relaxation time, τ1, deduced from the product of the viscosity and the recoverable compliance, has the expected behavior. For example, this Rouse time for a PS of molecular weight equal to 2 kg/mol has the same temperature dependence as that for self-diffusion; hence, there is no enhancement of translational diffusion in the polymer. The same conclusion was reached by Urakawa et al. [Urakawa, O.; Swallen, S. F.; Ediger, M. D.; von Meerwall, E. D . Macromolecules 2004, 37, 1558], although the analysis leading to it was different. The conclusion is consistent with two extant explanations of the enhancement of translational diffusion in small molecular glass-formers, one which invokes spatially heterogeneous dynamics and the other ascribing the effect to the different coupling parameters for the translational and rotational correlation functions.

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“…At frequencies close to the segmental relaxation time, local processes such as segmental relaxation, or even sub‐Rouse modes,30 start to dominate the mechanical relaxation. Therefore, the validity of both, decomposition of the modulus at high frequencies into a rubbery and glassy contribution and the extrapolation of the entropic behavior to the high frequency limit is questionable 31 The estimate of E R (∞) depends strongly on the accuracy of the technique and subtraction of E G .…”

Section: Introductionmentioning

confidence: 99%

Comment on the dynamic bead size and Kuhn segment length in polymers: Example of polystyrene

Ding

Sokolov

2004

J Polym Sci B Polym Phys

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Discrepancies between the length of a traditionally defined Kuhn segment length (l k ) and a bead size estimated from experimental data have been reported in a number of articles. In this work we emphasize that the traditional definition of the Kuhn segment is an oversimplification and the characteristic ratio, C ϱ , is not the only parameter that defines a bead size. We show that the dynamic bead size in polystyrene (PS) might be as large as ϳ50 monomers, whereas the traditionally defined Kuhn segment is ϳ8 -10 monomers. It is shown that with 50 monomers (M ϳ 5000) as a size of the dynamic bead, one can explain many inconsistencies in the interpretation of compliance and mechanical relaxation data known for low-molecular weight PS. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: [3505][3506][3507][3508][3509][3510][3511] 2004

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Birefringence of Polymers in the Softening Zone

Cited by 18 publications

References 25 publications

Mechanical Behavior of Polystyrene Microgels

Mechanical Behavior of Polystyrene Microgels

Modes of Molecular Motion in Low Molecular Weight Polystyrene

Comment on the dynamic bead size and Kuhn segment length in polymers: Example of polystyrene

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