Flocculation of cationic amylopectin starch and colloidal silicic acid. The effect of various kinds of salt

The kinetics of the flocculation of nanosized silica particles (5 nm) with cationic amylopectin has been investigated with stopped-flow technique. The flocculation process has been followed with turbidity. A kinetic mechanism is suggested where the initial process is a bridging flocculation. In this process the large amylopectin,molecules gather a number of the small silica particles forming a polyelectrolyte complex. This process is followed by a collapse of the formed flocs. These processes have time constants of less than 1 s. In a subsequent process the polyelectrolyte complex may also flocculate on a larger time scale, several seconds. The effect of mono- and divalent ions on the flocculation processes has been investigated. A large effect was found when a monovalent cation was replaced by a divalent cation indicating that the electrostatic screening of the silica particles is the most important factor. (C) 1998 Elsevier Science B.V. All rights reserved.