Binding of electrolytes to poly(ethylene oxide) in methanol

Abstract

The binding of potassium and sodium salts (thiocyanate and iodide as anions) to polyethylene oxide) in methanol solutions has been studied. The study was performed by the use of fluorescence techniques and ultrafiltration experiments coupled with conductivity measurements. The results obtained conform to an adsorption model of fixed adsorption sites where the cations are the primary species adsorbed, thus creating a charged polymer able to concentrate the anions in the surroundings of the coil. For a given cation, the local concentration of the anions depends on the ionic strength of the media in a manner not accounted for byconsidering only electrostatic interaction, thus indicating that specific interactions such as ion-pair formation (or other factors such as differences in the activity coefficients of the counterions) must be considered in the adsorption process. The ultrafiltraton experiments are compatible with a simple model of “bound” and “free” counterions by showing that at least some of the anions are able to move freely in the solution, but the experiments also indicate that specific interactions of the counterions with the charged polymer are operative.