Microrheological Approach for Probing the Entanglement Properties of Polyelectrolyte Solutions

The entanglement dynamics and viscoelasticity of polyelectrolyte solutions remain active research topics. Previous studies have reported conflicting experimental results when compared to Dobrynin's scaling predictions derived from the by combining classical bulk shear rheometry with diffusing wave spectroscopy (DWS) microrheometry, we investigate how the key viscoelastic parameters (the specific viscosity tsp, the plateau modulus Ge, and the ratio of the reptation time to the Rouse time of an entanglement strand zrep/ze) depend on the polymer concentration for semidilute entangled (SE) solutions containing poly(sodium styrenesulfonate) with high molecular weight. Our experimental measurements yield Ge proportional to c1.51 +/- 0.04, in good agreement with the scaling of Ge proportional to c1.5 predicted by Dobrynin's model for salt-free polyelectrolyte SE solutions, suggesting that the electrostatic interaction influences the viscoelastic properties of polyelectrolyte SE solutions. On the other hand, the deviation in the scaling exponent for tsp proportional to c2.56 +/- 0.04 and zrep/ze proportional to c1.82 +/- 0.28 is observed between our DWS experiments and Dobrynin's model prediction (proportional to c1.5), likely due to the fact that Dobrynin's scaling model does not account for mechanisms such as the contour length fluctuation, the constraint release, and the retardation of solvent dynamics, which are known to occur for SE solutions of neutral polymers. Our results demonstrate that DWS serves as a powerful rheological tool to study the entanglement dynamics of polyelectrolyte solutions. The scaling relationships obtained in this study provide new insights to the long-standing debate on the entanglement dynamics of polyelectrolyte solutions.

Automated summary

The entanglement dynamics and viscoelasticity of polyelectrolyte solutions were studied, showing discrepancies between experimental measurements and Dobrynin's model predictions, indicating the influence of electrostatic interactions on the viscoelastic properties of polyelectrolyte solutions.