Complexation between poly(allylammonium) cation and poly(styrenesulfonate) anion was investigated in aqueous solutions of binary 1:1 sodium electrolytes (NaX, X = F, Cl, Br, I, NO3, ClO4) by means of microcalorimetry, dynamic light scattering, electrokinetics and spectrophotometry. The obtained results revealed that at lower molar ratios of monomers charged polyelectrolyte complexes were formed. At molar ratios close to equivalence and at lower salt concentrations (c(NAX) / mol dm-3 ≤ 0.1) flocculation occurred. The obtained precipitates contained approximately equimolar amounts of oppositely charged monomers. At c(NAX) / mol dm-3 ≥ 0.5 (X = NO3, ClO4) and in the case when the polycation was present in excess, the amount of positively charged monomers in the precipitate was higher than that of negatively charged monomers. In addition, the aggregation of positively charged complexes in concentrated solutions of all investigated electrolytes was noticed. The onset of aggregation was strongly anion specific. However, the aggregation of negatively charged complexes did not occur even at NaX concentration as high as 3 mol dm-3. At 25 °C and c(NaClO4) = 1 mol dm-3 equilibrium was not reached after two months. By contrast, the supernatants showed no traces of free polyanion chains after being heated for a week at 60 °C. The interpolyelectrolyte neutralization was found to be predominantly entropically driven, irrespectively of the type of reaction products formed (polyelectrolyte complexes, precipitates), electrolyte type and concentration. Nevertheless, a correlation between obtained reaction enthalpies for complex and precipitate formation with anion hydration enthalpies was observed. The product formation was the least enthalpically favourable in electrolyte solutions containing weakly hydrated NO3- and ClO4- anions.
davor.kovacevic@chem.pmf.hr
