Contour-length fluctuation of polymers: NMR experiments and statistical physics

Abstract

A series of NMR experiments concerning chain fluctuations in concentrated polymer systems is briefly viewed. There is growing evidence for the influence of longitudinal displacements and contour-length fluctuation as fundamental mechanisms. On this basis a segment orientation correlation function has been established which describes and explains a broad variety of dependences and phenomena. This concept involves a new interpretation of the Doi-Edwards tube. The crucial element is the existence of fluctuating chain folds. It is argued that these folds should thermodynamically be stable. The primitive path of a chain is considered to be quasi-static in the time scale of fold fluctuations. The dynamic and conformational degrees of freedom of the fluctuating folds therefore dominate the partition function. This function has been calculated by the aid of a simplified model merely retaining the features essential for principal statements and conclusions. In order to discuss microscopic irreversibility, i.e., globally all degrees of freedom other than longitudinal displacements, nonlinear Schrodinger equations have been used for the derivation of the dynamic part of the partition functions. The time-scale effect inherent to the present treatment should generally be relevant if dynamic degrees of freedom are partly suppressed by topological restraints.