Coagulation of amphoteric latex colloids: reversibility and specific ion effects

Abstract

Coagulation studies of amphoteric latex sols of various i.e.p. values in LiNO₃, KNO₃ and CsNO₃ solutions are reported for a wide range of salt concentrations and pH. Three different techniques for the study of coagulation phenomena all indicate reversibility, in that sols coagulated by pH or salt are able to be redispersed. K⁺ and Li⁺ counter ions are able to stabilize these sols in the high salt concentration region. With NO₃^– and Cs⁺, the expected narrow zone of coagulation at low salt (i.e.p. coagulation) expands into the usual broad coagulation zone at high salt, where coagulation is observed at all pH values. The stabilizing effect of Li⁺ and K⁺ counter ions is attributed to a hydration barrier at the interface.