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Affinity interactions in counterion‐polyelectrolyte systems: Competition between different counterions
Author(s) -
Benegas Julio C.,
Paoletti Sergio,
van den Hoop Marc A. G. T.
Publication year - 1999
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/(sici)1521-3919(19990101)8:1<61::aid-mats61>3.0.co;2-a
Subject(s) - counterion , counterion condensation , polyelectrolyte , chemistry , divalent , valence (chemistry) , chemical physics , aqueous solution , computational chemistry , inorganic chemistry , ion , organic chemistry , polymer
Non‐bonding, specific interactions between linear polyelectrolytes and different species of counterions (of equal or different valence) are considered in the framework of the counterion condensation theory. It is assumed that these interactions are of short distance nature and that, within our theoretical approach, they apply only to the counterions territorially associated (condensed) to the polyion, which are free to move within the condensation volume V p around it. It is found that a simple additive term in the total free energy is sufficient to account for this interaction, resulting in a modulation of the polyelectrolytically determined population of territorially bound counterions. The distribution of free and condensed counterions as well as its variation with the physicochemical variables of the solution can be readily calculated. Analysis of literature data on titrations of poly(methacrylic acid) and dextran sulfate in aqueous solution with different species of monovalent and divalent counterions show that both polyanions appear to have a modest affinity free energy (of about RT ) for Ca ++ counterions when compared with Na + . On the other hand, polyion interactions with the Mg ++ /Na + pair are well described by bare polyelectrolytic interactions.