Interactions of anionic surfactants with nonionic polymers. Comparison of guanidinium, tetraalkylammonium, and alkali metal ions as counterions

Abstract

Abstract The interactions of anionic surfactants with nonionic polymers such as polyvinyl pyrrolidone (PVP), polyvinyl alcohol-acetate copolymers (PVA-Ac), and polyvinyl alcohol (PVA) in aqueous solution were studied with respect to guanidinium, four tetraalkylammoniums, sodium, and potassium as the counterions by means of electrical conductivity, dye solubilization, viscosity, and cloud point measurements. With sodium salts as the reference, guanidinium, a strongly water structure-breaking cation, lowers the critical micelle concentration (emc) of the long-chain alkylsulfates, and in the presence of PVP and PVA-Ac it promotes the binding of the anions to them and enforces the attraction between the bound anions by ion-pairing, exhibiting such phenomena as shrinking of the polymer chains or depression of the cloud points. Similar phenomena have been observed and discussed previously in the interactions of these polymers and long-chain alkylammonium or symmetrical tetraalkylammonium ions with thiocyanate or iodide as counterions, both also strongly water structure-breaking anions. Sodium and potassium dodecylsulfates interact with PVP and polyvinyl acetate to a similar extent because both counterions are of weak effect on water. On the other hand, for the quaternary ions, which promote the water structure, as the counterions to dodecylsulfate, the cmc lowers with increase in size of the quaternaries but the polymer interactions weaken, and tetrabutylammonium dodecylsulfate in particular barely interacts with PVP and PVA in the presence of the micelles, and only weakly with PVA-Ac. Thus, in comparison with the sodium salts, only the strongly water structure-breaking counterions enhance the binding of the long-chain anions to the polymers. The role of the quaternary counterions has been discussed in terms of the effect on the equilibria between micelle formation and complex formation with the polymer.