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IRTG / Soft Matter Science
Freiburger Materialforschungszentrum
Stefan-Meier-Str. 21
79104 Freiburg, Germany

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You are here: Home Events Prof. Thomas Thurn-Albrecht "The Underestimated Effect of Molecular Dynamics on the Morphology of Semicrystalline Polymers"

Prof. Thomas Thurn-Albrecht "The Underestimated Effect of Molecular Dynamics on the Morphology of Semicrystalline Polymers"

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Faculty of Chemistry and Physics, Martin-Luther-University Halle-Wittenberg, Germany

What
  • Seminar
When Jul 22, 2019
from 02:15 PM to 03:00 PM
Where Seminarraum B, FMF, Stefan-Meier-Str. 21, Freiburg
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A large fraction of today’s polymers are used in the crystalline state. On the one hand crystallization and melting is decisive for their processing. The fact that polymers crystallize only incompletely and possess a semicrystalline morphology on the other hand is important for their mechanical or electrical properties. Although under investigation for a long time, the process of crystallization and the formation of the semicrystalline morphology is still only partially understood. In my talk I will focus on the effect of molecular dynamics on polymer crystallization and morphology. A special property of polymers crystals as opposed to low molecular weight materials is that many of them display a relaxation process related to intracrystalline chain dynamics, enabling material transport between crystalline and amorphous regions and crystal reorganization. Accordingly, semicrystalline polymers have been classified into crystal-mobile and crystal-fixed polymers, depending on the existence or absence of such intracrystalline chain dynamics. Although it was claimed early on that crystal-mobile polymers generally have a higher crystallinity, the underlying causes were not investigated in detail. Using a new approach for the quantitative analysis of small angle X-ray scattering data in combination with NMR experiments, which allow to characterize the intracrystalline dynamics, we compare the structural characteristics for model polymers with and without chain motion in the crystallites and find fundamental differences. Whereas for crystal-fixed polymers the semicrystalline morphology is characterized by lamellar crystals of well-defined thickness and marginal thermal stability, the intra-crystalline dynamics in crystal-mobile polymers leads to additional stabilization of the crystals during growth and a minimization of the amorphous layers characterized by a well-defined thickness. Concerning the thickness of amorphous regions on the other hand, entanglements and other topological constraints which are frozen in by crystallization play an important role and cause a molecular weight dependence of the crystallinity, which we investigated in a series of model polymers over an unprecedented large range of molecular weights. In general, all our observations emphasize the non-equilibrium character of the semicrystalline state.

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