Dresden 2006 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 15: Dynamics and Diffusion
CPP 15.1: Talk
Wednesday, March 29, 2006, 14:00–14:15, ZEU 114
Anomalous diffusion in short chain polymer melts — •M. Zamponi1, A. Wischnewski1, M. Monkenbusch1, L. Willner1, B. Farago2, and D. Richter1 — 1Forschungszentrum Juelich, 52425 Juelich, Germany — 2Institut Laue-Langevin, 38042 Grenoble, France
The dynamics of linear polymer chains in the melt depends strongly on the chain length: Short unentangled chains perform free Rouse motion, long chains are confined by mutual entanglements. In the reptation model these topological constraints are described by a virtual tube which follows the primitive path of the observed test chain. However, this definition means that a test chain with a length in the order of one entanglement distance can not be captured in a tube, even if the matrix chains are much longer than the test chain.
We report on a systematic neutron spin echo study of different binary polyethylene blends. The measured dynamic structure factor of short test chains of various lengths (below or about the entanglement length) in a long chain matrix shows significant deviations from the expected Rouse behavior pointing to the fact that the short labelled chains are subject to topological constraints. Also anomalous behavior in the time dependence of the center of mass mean squared displacement was found showing a clear subdiffusive regime. Blends of short unentangled chains in a matrix of the same length still show discrepancies: Although the segmental diffusion shows Rouse behavior, again anomalous behaviour of the c.o.m. diffusion is found. These deviations may be explained by taking intermolecular interactions as discussed by Guenza [M.Guenza, Macromolecules 35, 2714 (2002)] into account.