Base−Acid Equilibria in Polyelectrolyte Systems: From Weak Polyelectrolytes to Interpolyelectrolyte Complexes and Multilayered Polyelectrolyte Shells

We have measured potentiometric titration curves of the weak polyelectrolytes, PAH1 and PAA, interpolyelectrolyte complexes PAH−PAA, PDADMAC−PAA, and PAH−PAA, prepared by mixing of the polyelectrolyte solutions, and multilayered microcapsules made by layer-by-layer adsorption of the same pairs of oppositely charged polyelectrolytes onto CaCO3 microspheres(PAH/PAA)5, (PDADMAC/PAA)5, and (PAH/PSS)5. The data were analyzed within the frame of an Ising model taking into account the nearest-neighbor interaction between proton binding sites. The anticooperative character of proton binding with PAH (cooperativity parameter q = 0.13) was shown to become a highly cooperative process in the interpolyelectrolyte complex PAH−PSS and multilayered microcapsules (PAH/PSS)5, q ≈ 2−3. The cooperativity of the process is increased also for complexes PDADMAC−PAA and PAH−PAA and for multilayered shells (PDADMAC/PAA)5 and (PAH/PAA)5; however, the cooperativity parameter q remains below unity for the PDADMAC−PAA system or a li...