(332b) Partitioning of Charged Colloidal Particles in Coacervating Systems of Strong and Weak Polyelectrolytes.

Complex coacervation is the liquid-liquid phase separation of oppositely charged species into a concentrated coacervate phase and a dilute phase. This spontaneous phase separation occurs in the presence of salt and is driven by attractive electrostatic interactions between charged groups and the displacement of polyelectrolyte counterions. Progress has been made in understanding coacervation between two polyelectrolytes, but much less is known about coacervation in multicomponent systems. Emerging applications involve formulating coacervating systems to suspend colloids, both to deliver active ingredients to a surface or remove pollutants from wastewater. Designing these systems demands a deeper understanding of how charged colloids interact with coacervate phases. We have experimentally measured the partitioning of negatively charged polystyrene colloids in mixtures of sodium poly(styrene sulfonate) and poly(diallyldimethylammonium chloride), two strong polyelectrolytes undergoing coacervation. We found no change in the coacervation phase boundary with the addition of dilute colloidal particles, consistent with the low amount of charge contributed by the colloids relative to the polyelectrolytes. We demonstrate a clear salt dependence, with the colloids preferential partitioning and uniformly distributing into the coacervate phase at lower salt concentrations, then approaching an equal partitioning between both phases with increasing salt concentration. This trend is consistent with the partitioning of the polyelectrolyte species with increasing salt. Now we consider the impact of switching to pairs of weak polyelectrolytes. We hypothesize that the local microenvironment of the colloidal particles will neutralize the charged backbone of the oppositely charged polyelectrolytes. Turbidimetric measurements are used to measure changes in the phase diagram and fluorescence spectroscopy is used to measure colloidal partitioning between the coacervate and dilute phases.