Polyelectrolyte complexes, 1. The effect of pH and ionic strength on the stoichiometry of model polycation—polyanion complexes

The interactions between model polycations and polyanions have been studied using the fluorescent dye acridine orange as a probe. The dye emission at 540 nm is quenched by the addition of polyanions, a process which is reversed by the addition of certain polycations. Techniques have been developed which enable a determination of the stoichiometry of polyelectrolyte complexes so formed between three polyanions {carboxymethylcellulose, κ‐carrageenan and poly(styrenesulfonate)} and two polycations {poly(L‐lysine hydrobromide) and poly(p‐xylylviologen dibromide)}. A one to one pairing of acidic sites with basic groups was observed over a wide range of temperature, pH and ionic strength. Deviations from unit stoichiometry in the presence of multi‐charged metal ions have been interpreted as due to conformational changes in the polyanion. Results from viscosity measurements are included which suggest the neutralisation of charged groups in the polyelectrolyte complex.