Ph- and Salt-Dependent Phase Composition Measurements of Two-Phase Mixtures of Oppositely Charged Polyelectrolytes Using C-NMR

A general protocol for quantifying the compositions of both supernatant and coacervate phases formed by oppositely charged polyelectrolytes in salt solutions, using a combination of proton and carbon quantitative nuclear magnetic resonance spectroscopy, thermogravimetric analysis and silver chloride titration techniques. With these methods, phase diagram of polyacrylic acid / poly (diallydimethylammonium chloride) in potassium chloride system at different pH values are generated experimentally. We find that with the increasing of salt concentration in the system, the coacervate phase volume initially increases and then quickly drops to zero at the critical salt concentration, and we quantify the concentrations of both polyelectrolytes in both phases for some compositions. At low pH value, we also find a novel phase separation re-entry at high salt concentration, probably related to the solubility of PAA as a function of pH and salt, implying strong non-electrostatic driving forces for coacervation at low pH value.