Cooperative dynamics in polymer liquids

The dynamics of molecular liquids is driven by the complex interplay between intermolecular and intramolecular forces. While theoretical approaches to the dynamics of simple liquids use a detailed description of the intermolecular interactions, the dynamics of polymer fluids is assumed to be mainly intramolecular in nature, with the intermolecular forces traditionally approximated by a mean-field description. This theoretical approach reproduces the experimental data in the long-time regime, while it is in disagreement with the short-time polymer dynamics as measured in experiments and computer simulations. To overcome this problem we derived from the first-principle Liouville equation, by means of the Mori-Zwanzig projection operator technique, a new Generalized Langevin Equation that explicitly contains intramolecular and intermolecular contributions to the single chain dynamics. We argue that intermolecular contributions are responsible for the onset of anomalous dynamical behavior. The single polymer dynamics calculated with our approach is in good agreement with the observed dynamics over the full range of time scales investigated.