Cation Polyelectrolyte Interactions in Aqueous Sodium Poly(vinyl sulfonate) as Seen by Ce3+ to Tb3+ Energy Transfer

Abstract

The interaction between trivalent lanthanide ions and the polyelectrolyte poly(vinyl sulfonate) (PVS) has been studied in aqueous solutions by monitoring lanthanide luminescence. The existence of specific binding of cations by PVS is indicated by blue-shifts in the maximum of the emission of cerium(III), effects on the decay of terbium(III) luminescence, and a slight broadening of the gadolinium(III) electron paramagnetic resonance (EPR). From the isotope effect observed on the decay of luminescence of Tb(III) bound to PVS in H2O and D2O solutions, it is suggested that complexation leads to a decrease in the number of bound water molecules from nine to three. In mixed PVS systems containing Ce(III) and Tb(III), energy transfer is observed. The efficiency of this is found to fit a multiple equilibrium model. The slope of the corresponding plot is shown to provide an effective measure of the extent of lanthanide binding to the polyelectrolyte. This is found to increase with temperature but to decrease upon addition of alcohols. The effect of alcohols is found to depend on their chain length, suggesting the importance of hydrophobic interactions. Increasing ionic strength by adding NaCl increases ion binding, while complex behavior, due to competing effects and precipitation, is observed upon addition of tetraalkylammonium bromide surfactants. Finally, from the energy-transfer data, it is possible to estimate the distance between lanthanide ions on the polyelectrolyte chain. Lanthanide luminescence promises to be an excellent technique for studying the interaction between metal ions and polyelectrolytes in aqueous solutions.