Aqueous solutions of acrylamide-acrylic acid copolymers: Stability in the presence of alkalinoearth cations

The interactions between acrylamide-acrylic acid copolymers and alkalinoearth cations were studied by many different techniques, as functions of various parameters: composition of the copolymer and distribution of the acrylic units along the chain; pH, temperature; ionic strength. In a first step, the phase diagrams were established and reveal ranges of polymer and salt concentrations where phase separation occurs. In a second series of experiments, the change in the chain conformation and the aggregation phenomena were investigated by viscosimetry and light scattering. It sorts out that at low enough polymer and salt concentrations (inside the solubility domain), it is possible to get a variation of the intrinsic viscosity of the polymer as a function of calcium concentration and charge parameter of the polymer consistent with previous literature results obtained in the presence of sodium if a binding term depending on the nature of the ion is taken into account. At higher polymer and calcium concentration, high Huggins constants and large increases of scattered intensity reveal the formation of aggregates, which are attributed to intermolecular bridges. The third series of experiments (conductimetry and densimetry) were carried out to characterize the ion-polyion interactions. Finally, the phase separation is discussed in light of the other results, using some simple association models. (C) 1997 Elsevier Science Ltd.