A COMPARISON OF CONDITIONS OF CONSTANT SURFACE POTENTIAL AND CONSTANT SURFACE CHARGE IN DLVO THEORY OF COLLOID STABILITY

The usual flocculation criteria in the D.L.V.O. theory of colloid stability are compared under the conditions of constant plate potential and constant plate charge, for two parallel plates in a binary, z-z valency type, electrolyte in aqueous medium. A simple, approximate method of determining the double-layer interaction, which is an extension of the so-called linear superposition approximation (L.S.A.), is used. It is shown that the L.S.A. gives the same double-layer interaction between parallel plates at constant plate potential and constant plate charge. Differences in these two conditions are noticeable at small plate potentials. © 1997 Elsevier Science Ltd. All rights reserved.