SELF KNOTTING OF POLYSTYRENE CHAINS IN A THETA-SOLVENT

For many reasons, it is instructive to examine situations in which top ological restrictions have conspicuous effects on polymer dynamics. A polymer solution, in a poor solvent at the Flory or Theta temperature, is one of them. Here, as in the case of polymer melts, the chain adop ts random walk configurations which favour self entanglements. However , because of differences in space filling, effects of topological cons traints are noticeably different in poor solvents and in the melt stat e. We present the results of a neutron quasielastic scattering experim ent by a semi-dilute solution of polystyrene in cyclohexane at the Flo ry temperature. Both solvent and solute contain labeled molecules in p roportions satisfying the zero average contrast condition. The outcome of the experiment is the dynamical, time dependent autocorrelation fu nction of the polystyrene chain in a semi-dilute solution. Comparing t he results obtained on the same sample at and above the Theta temperat ure, we display the observed differences and interpret them as the res ult of self entanglements.