Divalent metal‐ion distribution around linear polyelectrolyte chains by continuous diafiltration: comparison of counterion condensation cell models

Abstract

AbstractConcepts proposed in the two‐state model (Manning), two‐zone model (Deshkovski–Obukhov–Rubinstein) and extensions of these models based on Donnan equilibria around polyelectrolyte phases (Marinsky) were compared and discussed in terms of retention data obtained by continuous diafiltration of various linear polyelectrolyte solutions that were in contact with copper and cadmium salt solutions at pH = 6.0. Concentration and retention profiles were investigated and the metal‐ion retention values of the polymers (Rp) were compared with the respective values calculated using the theoretical assumptions of the models. An adequate connection was not observed between the two‐state model and diafiltration experiments when a null interaction between states 1 and 2 was assumed. If a Donnan equilibrium between states 1 and 2 was assumed, the metal‐ion fraction in state 1 was smaller than the Rp values obtained from the retention profiles for all systems. In contrast, a good correspondence between Rp values and the two‐zone model combined with Donnan's equilibrium was obtained by adding the weakly bound fraction of counterions around the polyelectrolyte chains. Copyright © 2010 Society of Chemical Industry