Stoichiometry and coacervation of complexes formed between polyelectrolytes and mixed micelles

Abstract

Turbidimetry was used to investigate the association of mixed anionic—nonionic micelles with a strong polyelectrolyte in dilute aqueous solutions of high ionic strength. The state of aggregation was found to depend primarily on the ionic strength, I, and the mole fraction of anionic surfactant (basis total surfactant), Y. At critical conditions for I and Y, a pseudo phase transition to soluble polyion—micelle aggregates takes place. The size and number of these aggregates appears to vary reversibly with change in Y. Farther from this phase boundary (e.g., at larger Y), macroscopic phase transitions are observed. One of these involves the formation of a second liquid phase rich in polymer and surfactant; this coacervation takes place only when the ratio of polymer:surfactant concentrations lies within certain bounds. Regardless of stoichiometry, a continued increase in Y ultimately leads to irreversible precipitation of an amorphous solid. The observed phase transitions are discussed in terms of strong attractive intermacromolecular coulombic forces.