Light Scattering on Semidilute Polyelectrolyte Solutions:  Molar Mass and Polyelectrolyte Concentration Dependence

Abstract

Dynamic and static light scattering experiments on solutions of the flexible highly charged polyelectrolyte sodium poly(styrenesulfonate) have been performed in the semidilute concentration regime. Over a very wide polyelectrolyte concentration range double-exponential correlation functions were found. At the lowest polyelectrolyte concentrations the correlation functions became single exponential. Apparent fast and slow diffusion coefficients were determined for three molar masses at a fixed added salt concentration of 0.01 M. The fast diffusion coefficient is both molar mass and polyelectrolyte concentration dependent at the lowest concentrations and becomes molar mass independent at semidilute concentrations. At even higher polyelectrolyte concentration the apparent fast diffusion coefficient is independent of both the molar mass and polyelectrolyte concentration. In the semidilute regime the fast diffusion coefficient follows the power law Df ∝ c0.72, close to the theoretical prediction of Odijk's sca...