Sedimentation of polyelectrolyte chains in solutions: From dilute to semidilute

Sedimentation of poly(sodium styrenesulfonate) (PSSNa) in aqueous solutions with or without added salt (NaCl) has been investigated by use of analytical ultracentrifuge (AUC) via sedimentation velocity (SV). In a solution without added salt or a low salt solution, as PSSNa concentration (Cp) increases, the sedimentation coefficient (s) decreases and exhibits two transitions corresponding to the overlap concentration (C*) and entanglement concentration (Ce). On the other hand, either C∗ or Ce increases with salt concentration (Cs). When the salt concentration is high enough, the interchain electrostatic interactions are screened, and s slightly varies with Cp at Cp < C∗. However, s decreases with Cp at Cp > C∗ with s ∼ Cp-α, where the scaling index α has dependence on the salt concentration but not on PSSNa molar mass.