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 interpolyelectrolyte
neutralization in solution and at surfaces usually results in formation
of neutral and charged products, respectively.