CHAINS DYNAMICS IN ENTANGLED POLYMER-SOLUTIONS

Abstract The dynamic properties of entangled polymer solutions can be described in terms of collective or individual chain motions. Collective motions are detected by quasi elastic Rayleigh scattering or by sedimentation experiments and are well described by the scaling hypothesis. The problem of individual chains motions is more delicate to approach experimentally: it corresponds to very slow diffusion processes and the use of conventional tracer techniques becomes difficult. We have developped a Forced Rayleigh Scattering method which allows to reduce the diffusion length down to a few microns and scales down the duration of the experiment to reasonable values. The concentration and molecular weight dependences of the self diffusion coefficient of polystyrene chains in benzene solutions will be presented and compared with predictions from scaling and reptation models. They provide a sharp determination of the cross over concentration between dilute and entangled concentration regimes. Additional experim...