Journal
JOURNAL OF NON-CRYSTALLINE SOLIDS
Volume 353, Issue 41-43, Pages 3838-3844Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jnoncrysol.2007.02.063
Keywords
glass transition; polymers and organics; fragility; rheology
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We studied chain and segmental relaxation in polyisoprene using broadband dielectric and light scattering spectroscopy. Our results demonstrate different temperature dependence of these processes (i.e. failure of the time-temperature superposition) in the entire temperature range studied. Segmental relaxation varies with temperature faster than chain relaxation at low temperatures while reverse is observed at high T. The transition between two regimes seems to occur around the dynamic crossover temperature. It appears that non-entangled and slightly entangled polymers exhibit the same behavior. The results are compared to predictions of the coupling model. We emphasize that current models cannot describe the data consistently. (C) 2007 Elsevier B.V. All rights reserved.
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