DETECTION OF THE HETEROCOAGULATION-STABILITY TRANSITION IN BINARY COLLOIDAL SYSTEMS BY ELECTROPHORETIC LIGHT-SCATTERING SILICA-SILICA AMINOPROPYL SYSTEM/

Electrophoretic light scattering is shown to detect the heterocoagulat ion-stability transition, induced by a variation of pH, in a model bin ary colloidal (silica-silica/aminopropyl) system. For stable mixtures of silica, bimodal zeta-potential distributions have been obtained wit h peak positions corresponding to those of monomodal zeta-potential di stributions due to the separate silicas, while for heterocoagulated mi xtures, only monomodal distributions appeared with peak positions betw een those of separate silicas. The isoelectric point was found at pH 3 .7 and 6.25 for silica and silica/aminopropyl respectively, and the he terocoagulation-stability transition was predicted at pH 6.6. This is in accordance with the DLVO theory.