Local reorientation dynamics of semiflexible polymers in the melt

The reorientation dynamics of local tangent vectors of chains in isotropic amorphous melts containing semiflexible model polymers was studied by molec ular dynamics simulations. The reorientation is strongly influenced both by the local chain stiffness and by the overall chain length. It takes place by two different subsequent processes: a short-time nonexponential decay an d a long-time exponential reorientation arising from the relaxation of medi um-size chain segments. Both processes depend on stiffness and chain length . The strong influence of the chain length on the chain dynamics is in mark ed contrast to its negligible effect on the static structure of the melt. T he local structure shows only a small dependence on the stiffness and is in dependent of chain length. Calculated correlation functions related to doub le-quantum NMR experiments are in qualitative agreement with experiments on entangled melts. A plateau is observed in the dependence of segment reorie ntation on the mean-squared displacement of the corresponding chain segment s. This plateau confirms, on one hand, the existence of reptation dynamics. On the other hand, it shows how the reptation picture has to be adapted if , instead of fully flexible chains, semirigid chains are considered.