INFLUENCE OF CHARGE-DENSITY AND CONCENTRATION ON THE DYNAMICS OF AQUEOUS POLYELECTROLYTE SOLUTIONS

We have investigated the dynamics of protonated poly(2-vinylpyridine) (M(W) = 135 000) in aqueous solution by dynamic light scattering over a wide concentration range (0.5 less than or equal to C-pe less than o r equal to 100 g/l). The charge density on the polymer chain (degree o f protonation a) was varied from 0.26 to 0.62 by hydrochloric acid. Th e reduced composition variable Lambda = a . c(pe)(m)/c(s) with c(pe)(m ) and c(s) the molar concentrations of the polymer repeat unit and sal t, respectively, was constant for a given charge density. We always ob served two well separated relaxation processes (a fast and a slow mode ). At low charge density the diffusion coefficient of the fast mode re veals an increase-maximum-decrease pattern with concentration while th e diffusion coefficient of the slow mode decreases with increasing con centration. The relaxation times of both modes as well as the ratio of their amplitudes were found to depend strongly on the degree of proto nation of the polymer chains. Temperature-dependent measurements at lo w polymer concentration (C-pe = 2g/l) exhibit that both modes follow t he Stokes-Einstein prediction, except that we observed a significant n on-zero intercept for the fast mode. A possible influence of hydrophob ic effects on the dynamics of protonated poly(2-vinyl-pyridine) in aqu eous solution is discussed.