Evidence for reptational motion and the entanglement tube in semidilute polymer solutions

The internal dynamics of high molar mass polystyrene in semidilute solution have been examined using pulsed gradient spin echo NMR. We find evidence for reputationlike motion characterized by mean-square displacement {φ}(t){~}t1/4, t1/2 and t regimes. We observe clear transitions between {φ}(t){~}t1/2 and {φ}(t){~}t regimes and the date are broadly consistent with the quantitative predictions of Doi-Edwards theory. In an experiment akin to dynamic neutron scattering, we obtain a structure factor from which some information about entanglement tube dimensions can be deduced.