Eur. Phys. J. E 1, 75-86
Solubility of highly charged anionic polyelectrolytes
in presence of multivalent cations:
Specific interaction effect
I. Sabbagh - M. Delsanti
CEA-Service de Chimie Moléculaire, CE-Saclay, 91191 Gif-sur-Yvette Cedex,
Received 3 March 1999 and Received in final form 2 September 1999
Studies performed on strong polyelectrolytes and on a weak polyelectrolyte, sodium poly(acrylate), show that their stability in presence of multivalent cations depends on the chemical nature of the charged side groups of the polymer. For sulfonate groups (SO3-) or sulfate groups (OSO3-) phase separation generally occurs in presence of inorganic cations of valency 3 (as La3+) or larger and a resolubilization takes place at high salt concentration. The interactions of the polyelectrolyte with multivalent cations are of electrostatic origin and the phase diagrams are weakly dependent on the chemical nature of the polymer backbone and on the specificity of the counterions. For acrylate groups, (COO-), the phase separation was observed with inorganic cations of valency 2 (as Ca2+) or larger without resolubilization at high salt concentration. The phase separation is due to a chemical association between cations and acrylate groups of two neighboring monomers of the same chain. This chemical association creates a hydrophobic complex by dehydrating both monomer and cation. With organic trivalent cation, as spermidine +H3N(CH2)4NH2+(CH2)3NH3+, where no chemical association occurs with the charged side groups COO- or SO3- of the polyelectrolyte, similar phase diagrams were observed whatever was the polyelectrolyte with a resolubilization at high trivalent cation concentration.
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc. - 83.70.Hq Heterogeneous liquids: suspensions, dispersions, emulsions, pastes, slurries, foams, block copolymers, etc.
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag