Sedimentation of Polyelectrolyte Chains in Aqueous Solutions

Abstract

We have investigated the dynamics of poly(sodium styrenesulfonate) (PSSNa) in aqueous solutions with and without added salt (NaCl) by use of analytical ultracentrifuge (AUC) via sedimentation velocity (SV) as a function of NaCl concentration ( C s ) or PSSNa concentration ( C p ). As C s increases, the sedimentation coefficient monotonically increases, whereas the diffusion coefficient shows a minimum. On the other hand, as C p increases, the sedimentation coefficient decreases while the diffusion coefficient exhibits a minimum at C s < 1.0 × 10 −3 M. However, they linearly vary with C p at C s > 1.0 × 10 −3 M. The scaling relation between the molar mass and sedimentation coefficient or diffusion coefficient at infinite dilution indicates that PSSNa chain changes from an extended conformation to a random coil as NaCl concentration increases. Our experiments demonstrate that the dynamics of polyelectrolyte chains is mediated by interchain electrostatic repulsion, hydrodynamic interactions, and intrinsic excluded volume effect.