• J.-U. Sommer, W. Chassé, J. L. Valentín, K. Saalwächter.
  Effect of excluded volume on segmental orientation correlations in polymer chains.
  Phys. Rev. E 78, 051803 (2008). DOI 10.1103/PhysRevE.78.051803.

  Abstract

  We study the impact of excluded volume interactions on the orientation statistics of chain segments in polymer gels, and show that 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 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 good solvent and for semi-dilute 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 crosslinked 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.

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