Conditions Leading to Polyelectrolyte Complex Overcharging in Solution: Complexation of Poly(acrylate) Anion with Poly(allylammonium) Cation

Complexation between poly(acrylate) (PA) and poly(allylammonium) (PAH) macroions at pH = 7.0 was studied by means of electrokinetics, microcalorimetry, and DLS. At low polyelectrolyte concentrations and no electrolyte present strong overcharging of primary nanocomplexes occurred. In contrast, the increase in polyelectrolyte concentration led to flocculation taking place near the equivalence. The nanocomplex charge reversal was also achieved in the high polymer concentration regime by the abrupt instead of stepwise titrant addition. The procedure was successfully used in the case of several other polyion pairs. The presence of electrolyte affected the PAH–PA interpolyelectrolyte neutralization considerably, leading to ion-specific aggregation and extrinsic charge compensation. The complexation energetics was weakly influenced by ionic conditions. To the best of our knowledge, the reported results are the first direct evidence for primary complex overcharging. Their rationalization explains why interpolyele...