Dynamics of Na⁺-Polystyrene Sulfonate in Solution at Low Ionic Strength

Abstract

The dynamics of Na⁺-Polystyrene-Sulfonate (Na⁺-PSS) of molecular weight 10⁵ in water of low ionic strength was investigated by photon correlation spectroscopy. The cooperative diffusion coefficient obtained from the first cumulant was measured in a concentration range of five decades. Concentrations range from the dilute (c > c*) to the semi dilute (c* > c > c**)₃ to the concentrated regime. The overlap concentration is c*≈ 10–⁴ g/cm³ which corresponds to 3 x 10^–7 monomers/Å3 It is in good agreement with the overlap concentration calculated for fully extended rodlike molecules. In the dilute regime, the diffusion coefficient is smaller than the one of a gaussian coil. This may be explained by the assumption of a rodlike shape of the molecule. In the semi dilute regime the cooperative diffusion coefficient follows a power law D_eff ≈ c 0.52 ± 0.02 in good agreement with theoretical predictions for polyelectrolytes.