ESTIMATIONS OF THE AGGREGATION TIME OF VARIOUS COLLOIDAL SYSTEMS

Scaling approximations for the time after which macroscopic aggregatio n becomes visible are derived for various colloidal systems. It is sho wn that the aggregation rate, which is generally used as a measure of stability, is not the only factor determining the aggregation time. Th e total number of bonds that have to be formed before aggregation beco mes visible is at least as important. The aggregation rate increases a bruptly when orthokinetic aggregation or sedimentation becomes dominan t or just before gelation occurs. This enables the estimation of an ag gregation time without the use of an arbitrary or operational definiti on of visibility. This aggregation time refers to macroscopic aggregat ion, e.g. visible sedimentation or gelation. Complications that hinder an accurate determination of the aggregation time are listed, and the ir effects on the aggregation time are predicted. The obtained scaling relations provide useful insights into the progress and results of co lloidal aggregation phenomena.