Crossover from Rouse to Reptation Dynamics: A Molecular-Dynamics Simulation

We present the results of an extensive molecular-dynamics simulation of a dense polymer system. We show for the first time that simulations are able to cover the whole regime from pure Rouse dynamics to reptation dynamics and give strong evidence of the latter. The mean square displacements clearly exhibit a t1/4 power law. A mode analysis shows that the high-frequency modes follow the Rouse relaxation while those at lower frequency display reptation relaxation. Both quantities give the same entanglement length.