Berlin 2005 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 29: POSTER: Polymer physics
CPP 29.67: Poster
Dienstag, 8. März 2005, 16:30–18:30, Poster TU D
The influence of constraint release on the reptation process: NSE study and comparison to simulation — •M. Zamponi1, A. Wischnewski1, M. Monkenbusch1, L. Willner1, D. Richter1, A. Likhtman2, B. Farago3, and G. Kali3 — 1Forschungszentrum Juelich, 52425 Juelich — 2University of Leeds, Leeds LS2 9JT, GB — 3Institut Laue-Langevin, 38042 Grenoble, France
The dynamics of long entangled polymer melts is well described by the reptation model, where the topological confinement is modeled by a virtual tube confining a given chain. However, with decreasing molecular weight reptation limiting processes such as contour length fluctuations and constraint release have to be taken into account. The latter process describes the loss of confinement due to the relaxation of the chains building the tube. To explore the role of the surrounding chains on the confinement a systematic study with neutron spin echo (NSE) spectroscopy has been performed on polyethylene melts. A few labeled long chains of fixed length have been put into successively shorter matrix chains to follow the onset of constraint release. Whereas long chains in a matrix of the same molecular weight display the constrained motion in the tube, with decreasing length of the matrix chains a gradual loss of confinement and transition to Rouse dynamics has been observed. In the limit of the lowest molecular weight matrix the long labeled chains show free Rouse motion. So far there is no full theoretical description of the dynamic structure factor including the effect of constraint release, but a new simulation concept based on the slip-links model gives a good description of the NSE data over the full range of matrix molecular weights.