“Internal pKa's” in Polyelectrolyte Multilayers: Coupling Protons and Salt

In situ UV−vis absorption spectroscopy is used to probe the extent of dissociation of a weak polycarboxylic acid incorporated within a polyelectrolyte multilayer. The effective acid dissociation constant is shown to depend on the nature of the multilayer. Salt counterion and proton populations within the multilayer are shown to be coupled, leading to a quantitative relationship between polyelectrolyte acidity and salt within these reluctant exchangers.