VISCOELASTIC RELAXATION IN SEMIDILUTE AND CONCENTRATED POLYMER-SOLUTIONS

This article deals with the viscoelastic modes experimentally observed in semidilute poor-solvent systems. Comparisons are made between experimental data and the predictions of a recent theoretical description. The latter pivots on a coupling parameter beta which is proportional to the difference in partial specific volumes of the polymer and solvent and which is postulated to give rise to the amplitude of the viscoelastic component in the spectrum. It is found here that the relative amplitude of the viscoelastic modes is unrelated to the density parameter, beta, and furthermore, a substantial amplitude of the viscoelastic modes is observed under conditions where beta = 0. A discrepancy of 3 orders of magnitude results for the predicted longitudinal modulus and the plateau modulus. For a highly concentrated polymer/solvent mixture (0.7 g/mL) under the condition beta = 0, the spectrum of the plasticized polymer does not correspond solely to the relaxation of the density fluctuations as was theoretically predicted.