Perikinetic and Orthokinetic Aggregation/Fragmentation of Hairy Colloids

Abstract

The aggregation of spherical colloids partially stabilized by a thin hairy surface layer was investigated under peri- and orthokinetic conditions. The weight and number average sizes of the aggregates were derived from the aggregate size distribution which was provided by particle counting. Perikinetic aggregation conditions were obtained in batches where polystyrene latex particles were suspended in a deuterium oxide/water mixture in order to prevent sedimentation. Periodically, small samples were taken from the medium and immediately analyzed. Orthokinetic aggregation conditions were established by flowing the suspension through a 1.25-m-length capillary of various internal diameter. Samples were collected at the outlet of the tube and immediately analyzed. At any time the aggregate size was found to decrease with the colloid concentration. Aggregate aging over periods of the order of the average time elapsed between two successive collisions was found to exert a major effect on the aggregate sizes in peri- and orthokinetic processes. This effect was increased by the particle concentration showing typical threshold effects such as a fast aggregation in dilute suspensions, a reduced influence of the concentration in the intermediate domain and a strong inhibition of the aggregate growth in more concentrated systems. Orthokinetic aggregation of hairy colloids was found to produce a narrower aggregate size distribution than perikinetic aggregation.