(475a) pH and Salt-Dependent Charging and Coacervation of Weak Polyelectrolytes: Hydrophobic Effects

By treating deprotonation and cation binding in polyacids as reversible reactions and using a random phase approximation (RPA) that captures the chain connectivity, the pH-dependent ionization of acid groups along a polyacid chain is predicted and compared with results of experiments for titration of rodlike and Gaussian coil polyacids. We find that the former is followed by hydrophilic poly(acrylic acid) (PAA), while the latter is followed more closely by hydrophobic poly(2-acrylamido-2-methyl-1-propanesulfonic acid). Large deviations from Henderson-Hasselbalch behavior are both observed and successfully predicted by the theory. We also investigate PAA hydrophobicity through its phase separation from solutions of water and polyelectrolyte, which we model by a Flory chi parameters. Finally, we measure and model the phase behavior of mixtures of poly(acrylic acid) (PAA) and poly(diallyldimethylammonium), PDADMA in both NaCl and KCl salts at pH values ranging from 4.9 to 7.0, where the PAA ranges from partially to fully charged. We find significant and unexpected changes in phase behavior as a function of salt concentration and pH, showing strong effects of hydrophobicity of PAA in both the charge regulation and phase behavior. The phase behavior can be qualitatively predicted by theory, with parameters in part predicted by molecular dynamics simulations.