INTERACTION OF TWO PARALLEL PLATES IN A BINARY ASYMMETRICAL ELECTROLYTE I. UNIVALENT COAGULATING ION

Abstract

The interaction of two charged plate-like parallel colloidal particles immersed in a binary asymmetrical electrolyte of valency type 1−m, where the coagulating ion is univalent, is considered. Applying the Derjaguin–Verwey–Overbeek theory of colloid stability, it is assumed that the plate surface potential is independent of the plate separation. The Stern modification in the absence of specific adsorption of the coagulating ion is also considered. It is demonstrated that as the valency m of the non-coagulating ion increases, the concentration of the coagulating ion at flocculation increases somewhat, but not to the extent predicted by Ostwald's activity coefficient rule. Application of the Stern theory reduces this trend and may even produce a decrease, with increasing m, in the coagulating ion concentration, particularly for a 1–2 electrolyte.