Base-acid equilibria in polyelectrolyte systems: From weak polvelectrolytes to interpolyelectrolyte complexes and multilayered polyelectrolyte shells

We have measured potentiometric titration curves of the weak polyelectrolytes, PAH(1) 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 approximate to 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 little higher than unity for the PAH-PAA system, indicating their much lower stability in comparison with the classical PAH-PSS system. The apparent pK values of PAH and PAA shift approximately 2-3 units to alkaline (PAH) or to the acidic (PAA) region both in multilayered microcapsules and in their stoichiometric complexes with oppositely charged polyelectrolytes. No essential difference was found between proton binding patterns of multilayered polyelectrolyte microcapsules and interpolyelectrolyte complexes.