Self knotting of polystyrene chains in a Theta solvent

For many reasons, it is instructive to examine situations in which topological 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 adopts random walk configurations which favour self entanglements. However, because of differences in space filling, effects of topological constraints are noticeably different in poor solvents and in the melt state. We present the results of a neutron quasielastic scattering experiment by a semi-dilute solution of polystyrene in cyclohexane at the Flory temperature. Both solvent and solute contain labeled molecules in proportions satisfying the zero average contrast condition. The outcome of the experiment is the dynamical, time dependent autocorrelation function of the polystyrene chain in a semi-dilute solution. Comparing the results obtained on the same sample at and above the Theta temperature, we display the observed differences and interpret them as the result of self entanglements.