The Polyelectrolyte Complex/Coacervate Continuum

Stoichiometric polyelectrolyte complexes (PECs) of the strong polyelectrolytes poly(styrenesulfonate) (PSS) and poly(diallyldimethylammonium) (PDADMA) were dissociated and dissolved in aqueous KBr. Water was added to dilute the salt, allowing polyelectrolytes to reassociate. After appropriate equilibration, these mixtures yielded compositions spanning complexes (solid) to coacervates (elastic liquid) to dissolved solutions with increasing [KBr]. These compositions were defined by a ternary polymer/water/salt phase diagram. For coacervates, transient microphase separation could be induced by a small departure from equilibration temperature. A boundary between complex and coacervate states was defined by the crossover point between loss and storage modulus. Salt ions within the complex/coacervate were identified as either ion paired with polyelectrolytes (“doping”) or unassociated. The fraction of ion pair cross-links between polyelectrolytes as a function of KBr concentration was used to account for viscosity using a model of “sticky” reptation.