Coagulation of amphoteric latex colloids: reversibility and specific ion effects

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.