The interactions between polyelectrolytes and AOT in an oil/water system

Abstract

The interactions between sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and polyelectrolytes were studied by measuring the mass transfer of polycations from an aqueous to a reverse micellar phase. The quarternized poly(vinylpyridine) derivatives reacted with AOT and formed an insoluble complex (in isooctane or water) whenever surfactant/cationic monomer concentration ratio was less than 1.4. Surplus AOT in the system led to quantitative transfer of the complex from the aqueous to the micellar phase, which indicates a strong role of electrostatic interactions and probably hydrophobic ones. The phase behaviour and ion balance suggest a mode of “solubilization” of the polyelectrolytes in the micellar solution that differs from the previously observed incorporation of solute molecules into the reverse micelle. In the case investigated, the reverse micelles and surfactant-polyelectrolyte complex co-exist. The results of sedimentation (ultracentrifuge) measurements indicated strong interactions between the polyelectrolyte-AOT complex and the reverse micelles. The mass balance of AOT and water also suggests a certain kind of aggregation between the reverse micelles and the polyelectrolyte-surfactant complex. When barium was used instead of sodium as the counterion to AOT, the stoichiometry of the interphase-micellar phase transition changed from an AOT/monomer ratio of 1.4:1 to 1.1:1. The yield of the mass transfer of the protonated polyvinylpyridine was much lower than that of the quaternized product in the same system. A saturation-like isotherm of extraction was obtained if the AOT surplus was at least 20-fold. At AOT/monomer concentration ratios below 20, a third phase was formed. The addition of co-surfactants (n-alkanols) strongly increased the efficiency of mass transfer, but the critical AOT/monomer concentration ratio at the transition point (the appearance of a third phase or a clear oil/water system) remained the same.