Steric stabilization and the Hofmeister series

TLDR: In this paper, the Hofmeister series was applied to the flocculation of poly (vinyl acetate) hydrosols, stabilized solely by poly(ethylene oxide) chains, and the results were interpreted in terms of the influence which the positively hydrated ions exert on the structure of the water in their immediate neighborhood.

Abstract: The relevance of ion hydration and the Hofmeister series to the flocculation of poly (vinyl acetate) hydrosols, stabilized solely by poly(ethylene oxide) chains, has been examined. For these enthalpically stabilized dispersions, the flocculation potency of an electrolyte is determined by its ability to convert water into a theta-solvent for the stabilizing moieties. The order of decreasing flocculation effectiveness for the anions studied (SO4= > Cl− > NO3− > CNS− > Br− > I−) parallels that of the Hofmeister series. The order for cations (Rb+ = K+ = Na+ = Cs+ > NH4+ = Sr++ > Li+ = Ca++ = Ba++ = Mg++) is in direct conflict with the postulate that the more highly hydrated ions are the more effective flocculants. In general, monatomic anions and cations are less potent flocculants if their effective primary hydration radius (region A) is large. The results have been interpreted in terms of the influence which the positively hydrated ions exert on the structure of the water in their immediate neighborhood (region B), rather than simply in terms of dehydration of the stabilizing species. Preliminary measurements of the entropy and enthalpy of dilution parameters for poly (ethylene oxide) in electrolyte solutions support this interpretation.