Jean-Claude Morawski

Study of Ca2+-induced silica coagulation by small angle scattering

Abstract The intefacial behavior of monodisperse (radius ≌ 15 nm) silica sols has been characterized by the evolution of their surface charge as a function of pH and salt concentration. The Ca2+ coagulation critical concentration, ccc, has been determined by turbidity between pH 7.5 and 9. The pH dependence of the calcium ccc shows that one adsorbed Ca2+ releases one H+ from the surface. Small angle neutron scattering gives a power law profile over one decade of Q for the silica aggregates. Their fractal dimension ranges from 1.7 to 2.1 depending on pH and [Ca2+; the faster the coagulation the greater the compacity. Small angle X-ray scattering (1.7 × 10−2