Regensburg 2010 – wissenschaftliches Programm

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SYMR: Symposium Nuclear Magnetic Resonance: from Applications in Condensed-Matter Physics to New Frontiers

SYMR 6: Polymer Dynamics

SYMR 6.3: Vortrag

Mittwoch, 24. März 2010, 10:30–10:45, H48

Bond-correlation functions determined in MD simulations of entangled polymer melts — •Hendrik Meyer — Institut Charles Sadron, CNRS UPR22, 67034 Strasbourg, France

The polymer dynamics of entangled bead-spring chains is analysed based on large scale molecular dynamics simulations. As found in previous studies, the predicted power law regimes of mean-square displacements attributed to Rouse-motion in the tube (cross-over from t^0.5 to t^0.25) are only well developed beyond Z≥ 10 entanglements per chain. Similar power law regimes are present for bond time-autocorrelation functions (P₁ ∝ t^−0.5 and t^−0.25). NMR experiments measure a correlation function proportional to the second Legendre polynomial P₂ of the bond correlations, which is found to be proportional to the square of P₁ only for flexible chains, whereas a slower time decrease is found for chains with a small angular potential. Clear evidence is found that the terminal relaxation time increases stronger than predicted by reptation theory for Z>5. We critically compare this finding with theories of contour length fluctuations, often invoked as the main explanation of this slowing down.