Diffusion and viscosity of non-entangled polyelectrolytes

TL;DR

This study investigates the diffusion and viscosity of sodium polystyrene sulfonate in salt-free aqueous solutions, confirming the Rouse-Zimm scaling model and linking microscopic friction to macroscopic properties.

Contribution

It provides experimental data on NaPSS diffusion and viscosity, validating the Rouse-Zimm model and connecting chain dimensions with scattering measurements.

Findings

Diffusion and viscosity follow Rouse-Zimm scaling.

Monomeric friction coefficient exceeds free-volume model predictions.

Calculated chain dimensions agree with SANS data.

Abstract

We report chain self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed field gradient NMR and rotational rheometry respectively. The observed concentration dependence of $\eta$ and $D$ are consistent with the Rouse-Zimm scaling model with a concentration dependent monomeric friction coefficient. The concentration dependence of the monomeric friction coefficient exceeds that expected from free-volume models of diffusion, and its origin remains unclear. Correlation blobs and dilute chains with equivalent end-to-end distances exhibit nearly equal friction coefficients, in agreement with scaling. The viscosity and diffusion data are combined using the Rouse model to calculate the chain dimensions of NaPSS in salt-free solution, these agree quantitatively with SANS measurements.