title: Effect of excluded volume on segmental orientation correlations in polymer chains.
abstract: We study the impact of excluded volume interactions on the orientation statistics of chain segments in polymer gels, and show that nuclear magnetic resonance (NMR) experiments provide a direct and unique measure of excluded-volume effects on the chain statistics. In particular we consider the tensor order parameter, which can be expressed as the second Legendre polynomial of the segment orientation with respect to a fixed end-to-end distance vector and which is directly related to the residual coupling constant obtained in NMR experiments. We provide analytical results for the case of single chains in a good solvent and for semidilute solutions. Computer simulations using the bond fluctuation model are applied to compare with the analytical predictions. Considering polymer gels at the equilibrium state of swelling we predict a unique relation between the tensor order parameter and the correlation length (blob size) of the gel. Experiments applying multiple-quantum NMR methods to both end-linked and randomly cross-linked polymer networks are in excellent agreement with this prediction. The initial decay of the tensor order parameter as observed in experiments at low and intermediate degrees of swelling can be explained as a solvent effect without making additional assumptions about constraint release processes during swelling.
authors.affiliation: Leibniz-Institut für Polymerforschung Dresden e. V., Hohe Strasse 6, D-01069 Dresden, Germany. sommer@ipfdd.de
authors.forename: Jens-Uwe
authors.initials: JU
authors.lastname: Sommer
authors.forename: Walter
authors.initials: W
authors.lastname: Chassé
authors.forename: Juan López
authors.initials: JL
authors.lastname: Valentín
authors.forename: Kay
authors.initials: K
authors.lastname: Saalwächter