Quasielastic scattering by dilute polymer solutions A summary of this work was presented at the IUPAP International Conference on Statistical Physics, August 25—29, 1975

Abstract

The scattering law S(k, w) for dilute polymer solutions is obtained from Kirkwood's diffusion equation via the projection operator technique. The width Ώ(Κ) of S(k, w) is obtained for all k without replacing the Oseen tensor by its average (as is done in the Rouse-Zimm model) using the “spring-bead” model ignoring memory effects. For small documentclass{article}pagestyle{empty}begin{document}$ left( {kasqrt N ll 1} right) $end{document} and large ( ka >> 1) values of k we find OHacgr; = 0.195 Κ 2 /Β aŋo, documentclass{article}pagestyle{empty}begin{document}$ sqrt N $end{document} and OHacgr; = Κ 2 /ΒΞ respectively, indicating that the width is governed mainly by the viscosity ŋo for small Κ values and by the friction coefficient Ξ for large Κ values. For intermediate Κ values which are of importance in neutron scattering we find that in the Rouse limit Ώ = Κ 4 a 2 /12ΒΞ. When the hydrodynamic effects are included, Ώ( Κ ) becomes 0.055 Κ 3 /Βeng;o. Using the Rouse-Zimm model, it is seen that the effect of pre-averaging the Oseen tensor is to underestimate the half-width Ώ( Κ ). The implications of the theoretical predictions for scattering experiments are discussed.