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DY: Fachverband Dynamik und Statistische Physik

DY 12: Soft Matter I

DY 12.6: Vortrag

Dienstag, 23. März 2010, 15:45–16:00, H47

Molecular Weight Dependence of Polymer Dynamics: A Molecular Dynamics Simulation Study — Andre Bormuth and •Michael Vogel — Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstr. 6, 64289 Darmstadt

We perform molecular dynamics simulations for an all-atom model of poly(propylene oxide) to study the dependene of polymer melt dynamics on the molecular weight. The main focus is the regime of low molecular weights at the molecule-polymer crossover, i.e., chains comprised of N=2-100 monomers. Our studies include conformational transitions, structural relaxation, and Rouse dynamics. We find that the rates of conformational transitions, apart from weak chain end effects, do not depend on molecular weight and obey an Arrhenius law. However, upon cooling the heterogeneity of conformational dynamics increases and correlated forward-backward jumps, i.e., deviations from Markov behavior, become important. For the structural relaxation, a non-Arrhenius temperature dependence is accompanied by a more spatially heterogeneous nature of dynamics at lower temperatures. Mode-coupling theory captures some aspects of the glassy slowdown, but it does not enable a complete description. The structural relaxation time strongly increases with increasing molecular weight for short chains, while it is independent of chain length for sufficiently long chains N>30. The role of deviations from Gaussian chain statistics on the dynamical behavior is discussed.