Dynamics of Na+-polystyrene sulphonate in solution at low ionic strength

Abstract

The dynamics of Na⁺-polystyrene sulphonate (Na⁺PSS) (MW=10⁵) in water of low ionic strength was investigated by photon correlation spectroscopy. The cooperative diffusion coefficient D_eff obtained from the first cumulant was measured in a concentration range of five decades. The lowest concentrations are in the dilute regime. In the semidilute regime, that is for concentrations greater than the overlap concentration c* approximately=3*10^-7 monomers AA^-3, the cooperative diffusion coefficient follows a power law D_eff approximately c^0.52+or-0.02 which is in good agreement with theoretical predictions for polyelectrolytes. At very high concentrations, c>c** approximately=10^-5 monomers AA^-3, a new regime, which is called the concentrated regime, is observed which shows a constant D_eff. This behaviour may be explained by a scaling law, which takes the electrostatic persistence length as the fundamental parameter.