(468i) Modeling of Doping and Overcharging of Polyelectrolyte Complex Coacervates

Polyelectrolyte complex coacervates (PECs) are dense polymeric materials formed spontaneously when solutions of oppositely charged polymers are mixed. PECs are either neutral with equimolar ratios of polyanion and polycation, or overcharged, where one type of polyelectrolyte is present in excess in PECs. Here, using a polyelectrolyte solution theory which accounts for the specifity of salt ions and polyelectrolyte monomers and chain connectivity, we model “doping” of PECs, in which ion-pairs between polyelectrolytes in the PEC are gradually broken up by and replaced with salt ions upon increase of the salt concentration in the solution in contact with the PEC. The predictions of our model agree well with the experimental data for doping of stoichiometric PECs, made of poly(diallyldimethylammonium) PDADMA and poly(styrene-sulfonate) PSS, with KBr as well as for salt partitioning between the PEC and the co-existing solution. Further, we model overcharging of PECs by putting a stoichiometric PEC in contact with a solution, containing an excess of polycation. We rationalize the adsorption of the excess polycation by the stoichiometric PEC in terms of two entropic forces: counterion release and combinatorial binding entropy. Using the same parameters used to model doping of PDADMA/PSS PECs with KBr, we find semi-quantitative agreement between our predictions and the equilibrium overcompensation experiments of multilayer films of the Schlenoff group. Given the diverse library of salt-polyelectrolyte candidates for PECs, development of such theories is crucial in rational design of applications of PECs.