Self-Diffusion in Polymer Solutions: A Test for Scaling and Reptation

Abstract

We present preliminary results on the self-diffusion coefficient $D_{\mathrm{self}}$ of polystyrene chains (molecular weight $M_n=245\mathrm{}000 \mathrm{and} 123000$) in benzene, obtained by forced Rayleigh scattering. In the semidilute regime where the chains overlap, $D_{\mathrm{self}}$ decreases with the polymer concentration $c$ as $c^{-1.7\mathrm{}\pm 0.1}$. This behavior is compatible with scaling-law predictions and is the first experimental evidence for the existence of reptation in this regime.