Influence of Charge Density and Concentration on the Dynamics of Aqueous Polyelectrolyte Solutions

Abstract

AbstractWe have investigated the dynamics of protonated poly(2‐vinylpyridine) (Mw = 135000) in aqueous solution by dynamic light scattering over a wide concentration range (0.5 ≤ cpe ≤ 100 g/l). The charge density on the polymer chain (degree of protonation α) was varied from 0.26 to 0.62 by hydrochloric acid. The reduced composition variable Λ = αcmpe/ with cmpe and cs the molar concentrations of the polymer repeat unit and salt, respectively, was constant for a given charge density.We always observed two well separated relaxation processes (a fast and a slow mode). At low charge density the diffusion coefficient of the fast mode reveals an increase‐maximum‐decrease pattern with concentration while the diffusion coefficient of the slow mode decreases with increasing concentration. The relaxation times of both modes as well as the ratio of their amplitudes were found to depend strongly on the degree of protonation of the polymer chains. Temperature‐dependent measurements at low polymer concentration (cpe = 2g/l) exhibit that both modes follow the Stokes‐Einstein prediction, except that we observed a significant non‐zero intercept for the fast mode. A possible influence of hydrophobic effects on the dynamics of protonated poly(2‐vinylpyridine) in aqueous solution is discussed.