INTERACTIONS OF CADMIUM DODECYL-SULFATE MICELLES WITH POLY(ETHYLENE OXIDE) OR POLY(VINYLPYRROLIDONE) - A POTENTIOMETRIC INVESTIGATION

A potentiometric method with a cadmium ion-selective electrode has been employed to study the interaction of cadmium dodecylsulfate with two hydrosoluble nonionic polymers, poly(ethylene oxide) (PEO) and poly(N-vinylpyrrolidone) (PVP). The critical micelle concentration and the degree of counterion condensation were evaluated for all types of surfactant aggregates. In the case of PEO, depending upon the surfactant concentration, monomer surfactant, micellar adsorbed aggregates, and free micelles are formed. At low polymer concentration the degree of counterion condensation of adsorbed aggregates is small and increases with increasing polymer concentration. These results imply an increase in aggregation number with increasing polymer concentration. The opposite behavior is observed with cupric or sodium dodecylsulfates. In the case of PVP in the same cadmium dodecylsulfate concentration range as PEO, only adsorbed aggregates could be detected. These findings are interpreted by assuming a specific solvation of cadmium ions by both hydrosoluble polymers. This phenomenon, which is stronger with PVP than with PEO, increases the stability of the adsorbed negatively charged aggregates. © 1992.