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

Abstract

We 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.

A Simple Method To Estimate Chain Conformations of Polyelectrolytes in the Semidilute Regime

“…However, although the Manning's limiting law has proven very successful in the experimentally accessible dilute ragime, 31 it may underestimate the number of condensed counterions in the semidilute regime as suggested by Kuhn et al 32 On the other hand, as for the chain overlapping in the semidilute regime, researchers often reported that the polyelectolyte chains turn to aggregate to form a multichain cluster in the salt-free aqueous solution as observed by dynamic light scattering experiments. [33][34][35][36][37] We have also investigated the chain aggregation phenomenon of NaPSS in the salt-free aqueous solution by dialysis. 23 According to Stevens and Kremer, 8 when the concentration of polyelectrolyte solution is increased, the monomer-monomer repulsion is more strongly screened by forcing the counterion clouds closer to the monomers.…”

Effect of Charge Density on the Dynamic Behavior of Polyelectrolytes in Aqueous Solution

“…10 There are reports in the literature that the same is true for solutions of weakly charged polyelectrolytes with no added salt (poly(methylacrylic acid) partially neutralized with NaOH and P2VP partially protonated with HCl). 8,9 (c) For Λ g 1 and 0.09 e R e e 0.15 the distribution is trimodal (fast mode, τ f ; "intermediate mode", τ int ; slow 5394 Topp et al Macromolecules, Vol. 29, No.…”

Influence of Aggregation and Dialysis on Conductivity of Salt-Free Polyelectrolyte Solution in the Dilute/Semidilute Region

“…Odijk has pointed out that the theoretical predication on the solution behavior of polyelectrolytes with added salt was straightforward, whereas no satisfactory theory in the absence of salt was available. The polyelectrolyte solutions with no or low added salt have been often regarded as a heterogeneous solution in which the polyions formed a multichain cluster (or domain). − For example, Ise et al observed a single broad peak in the small-angle X-ray scattering of polyelectrolyte dilute solution and suggested the presence of quasi-lattice-like ordering domains. In the dynamic light scattering of polyelectrolyte solutions with no or low added salt, a double-exponential correlation function interpreted as consisting of fast and slow modes was frequently reported. − The fast mode was interpreted as a coupled diffusion of polyions and counterions.…”

“…The polyelectrolyte solutions with no or low added salt have been often regarded as a heterogeneous solution in which the polyions formed a multichain cluster (or domain). − For example, Ise et al observed a single broad peak in the small-angle X-ray scattering of polyelectrolyte dilute solution and suggested the presence of quasi-lattice-like ordering domains. In the dynamic light scattering of polyelectrolyte solutions with no or low added salt, a double-exponential correlation function interpreted as consisting of fast and slow modes was frequently reported. − The fast mode was interpreted as a coupled diffusion of polyions and counterions. The slow mode was interpreted as the diffusion of multichain domains and regarded as evidence of the existence of polyions' aggregation .…”

“…In the dynamic light scattering of polyelectrolyte solutions with no or low added salt, a double-exponential correlation function interpreted as consisting of fast and slow modes was frequently reported. − The fast mode was interpreted as a coupled diffusion of polyions and counterions. The slow mode was interpreted as the diffusion of multichain domains and regarded as evidence of the existence of polyions' aggregation . It was also demonstrated that the slow mode appeared along with a slight increase of apparent equivalent conductivity of poly( l -lysine−HBr) when the external NaBr salt concentration is decreased below a certain critical value …”