Regensburg 2000 – scientific programme

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DY: Dynamik und Statistische Physik

DY 12: Polymere und Membranen

DY 12.3: Talk

Monday, March 27, 2000, 11:30–11:45, H2

Rheological evidence for a dynamical crossover in polymer melts via nonequilibrium molecular dynamics — •Martin Kröger and Siegfried Hess — Institut für Theoretische Physik, Technische Universität Berlin

We show, that a certain ‘critical’ molecular weight characterizes the rheological properties of the multibead finitely extensible nonlinear elastic (FENE) chain model polymer melt. The rheological crossover manifests in a change of power law behavior for the viscous properties at a critical number of beads per chain N_c=100± 10. From equilibrium simulations, a characteristic slow-down of the diffusivity had been observed beyond an entanglement molecular weight which turns out to be a factor of 2.9 smaller than the critical weight reported here. Thus a prediction of Bueche, already stated in 1952, is confirmed. Consequently, the (many chain) FENE model is capable in predicting static, dynamic and flow behaviors for arbitrary molecular weights in view of its success in modelling the diverse rheological properties of real polymers at low and intermediate polymer weights. Large scale molecular dynamics simulation is conducted to cover the range of relevant molecular weig! hts. The correspondence of dimensionless simulation parameters with experimentally accessible quantities is made.