Concentration Regimes in Polyelectrolyte Solutions

Abstract

A general description of the electrolytic conductivity behavior of highly charged strong polyelectrolytes in dilute and semidilute aqueous solutions is presented. For the first time this model considers the influences of the molar mass, charge density (for charge distances less than the Bjerrum length), polyelectrolyte concentration, and the ionic strength adjusted by both the polyelectrolyte concentration (c p in monomol L-1) and added simple salt concentration (c s in mol L-1). Above the overlap concentration (c*) the molar mass influence is weak. Below this overlap concentration the equivalent conductivity (Λ) increases strongly with decreasing c p, as long as c p > c s. Correlations could be established for the maximum of Λ, Λmax ∼ c s -1/5 and Λmax ∼ M -2/5. The conductivity behavior can be qualitatively explained in terms of Manning's theory with an additional change of the interaction parameter f c. On the basis of this fact an empirical dependence of f c on the ratio of the Debye length to the contour length (l D/L) has been found. Three concentration regimes differing in the polyion−counterion interaction could be identified. These are characterized by l D/L located below (4π)-1/2, between (4π)-1/2 and unity, and above unity, respectively. The model description includes polyelectrolyte solutions without added salt as well as solutions with any ratio of polyelectrolyte to salt concentration. This is the first model which is based on sufficient experimental data in the highly diluted concentration regime. Therefore, it should stimulate further theoretical studies.

Conformation of Polyelectrolyte Chains in Dilute Aqueous Solutions Investigated by Conductometry, 1. Influence of the Degree of Polymerization on the Conformation of Flexible Vinylic Polyanions and Rigid Native DNA

“…As it was mentioned above, this discrepancy could be due to the inadequacy of Manning's theory for the quantitative description of the behavior of rather short polyions. As it was shown by Wandrey, [22] in this case the conductivities of the solutions were higher than expected from Manning's theory.…”

“…At the same time, it was noted that the degree of polymerization of polyions could affect the conductivity of their solutions. [22] In the present work, we studied the influence of the chain length on the conformational behavior of typical flexible water-soluble polyelectrolytes -vinylic polyelectrolytes (PSS) and poly(sodium acrylate) (PA) -in salt-free aqueous solutions. For this purpose, we used different narrow fractions of PSS and PA. For comparison, the same experiments were done with samples of rather rigid native DNA polyanions that differed in the number of base pairs (bp) in the double helix.…”

Thickness of electrical double layer. Effect of ion size

“…It has already been suggested that a description of the electrical double layer by the Debye length is oversimplified in diluted solutions where solution behavior can be conveniently studied by the electrolytic conductivity [11].…”

On the nature of influence of polyelectrolyte molecular weight on aniline electropolymerization

“…Indeed, some authors [27][28][29][30] established enhanced counterion condensation by HMW polyelectrolyte. More efficient counterion condensation leads to lower effective charge of macromolecule chain, and as a result, the higher the molecular weight of polyelectrolyte, the more coiled conformation it has [27,31].…”