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Lecture Kay Saalwaechter

Rooster

WanneerWaar
25 september 2009 FWN-Building 5115.0015, Nijenborgh 4, 9747 AG, Groningen
Speaker: Prof. Dr. Kay Saalwaechter
Affiliation: M.L.-University of Halle-Wittenberg, Germany
Title: Optical and NMR probes of diffusion mechanisms in polymer networks and melts
Date: Fri Sep 25, 2009
Start: 13.15
Location: FWN-Building 5115.0015
Host: A. Herrmann
Telephone: +31 50 363 6318

Abstract

Transport phenomena in polymeric systems are still a field with many unknowns. This presentation will deal with diffusion of small probe molecules in polymer melts, solutions, and in particular networks, and with the reptative motion of polymer chains in entangled melts. Theunderstanding of probe diffusion in polymers is relevant for thefunction of dialysis membranes and or drug-release systems, and despite the importance of such applications, there is no consensus yet on how to theoretically describe the effect of permanent cross-links on diffusion. We demonstrate that new insights can be gained by combining pulsed-gradient diffusion NMR and fluorescence correlation spectroscopy, with one important finding being that the inhomogeneity of the systems appears to play a major role. Second, the motion of linear chains in a melt is fundamental for the understanding of the mechanical properties of polymer melts, yet despite almost 40 years of research following the publication of de Gennes famous reptation theory, prominent deviations from this theory have not yet been explained consistently. We demonstrate that simple low-field NMR techniques can be used to gain unprecedented molecular information on the specific timescales of polymer motion, providing direct evidence for the effect of constraint release, i.e., the finite lifetime of the `reptation tube' as governed by surrounding chains.

Laatst gewijzigd:22 oktober 2012 14:30