Dependency of polyelectrolyte complex stoichiometry on the order of addition: 2. Aluminum chloride and poly-vinylsulfate

In the first part of this series it was shown that the stoichiometry of complexation between oppositely charged polyelectrolytes became increasingly dependent on the order of addition as the concentrations of monovalent and divalent ions were increased. This study considers the effect of aluminum ions on titrations between solutions of a strong poly-acid and a strong poly-base. In addition, the titratable charge of aluminum ion itself was also investigated. It was found that aluminum ions can interfere with the results of charge titrations, in the sense that the titration results became unpredictable. Stoichiometric relationships between the amount of aluminum present and the amount of titrant required to achieve streaming current values of zero were obtained only at pH values associated with a maximum in the amount of titrant needed to neutralize a given concentration of dissolved aluminum. The results are consistent with complexation between the anionic titrant and polynuclear species of aluminum, where the relative proportion of such species depends strongly on the molar ratio of OH to Al.