Polyelectrolyte complex coacervation in solvent mixtures

A lower critical solution temperature (LCST) behavior was recently observed in the polyelectrolyte complex coacervation of stoichiometric mixtures in potassium poly(styrene sulfonate) (KPSS) and poly(diallyldimethylammonium bromide) (PDADMAB) in water with added KBr salt. Many features are explained by an interplay of entropy of mixing, electrostatic correlations, and solvent quality arguments. While the electrostatic correlations are quantified by magnitude of the Bjerrum length, the temperature dependence of the dielectric constant of water must be considered. However, alternate solvents should also independently tune the Bjerrum length (via the dielectric constant) beyond that achieved with water. We will show experimental measurements of the effects of solvent mixtures on the coacervation behavior of KPSS/PDADMAB through a combination of static and dynamic light scattering, turbidity, and measurements of the static dielectric constant. We identify regimes where solvent quality (hydrophobicity) become a predominant factor in coacervation.