Aggregation mechanisms of latex of different particle sizes in a controlled shear environment

Latex particles with diameters of 60, 380, and 810 nm, respectively, were sheared in a controlled shear environment of circular couette flow after being destabilized by the addition of MgCl2. The evolution of aggregate size and structure, as well as a measure of aggregate mass, was monitored with use of a particle size analyzer (Coulter LS230) operating on the principle of small-angle light scattering. The aggregates of different primary particle sizes displayed distinct behavior in attaining steady state under similar shear conditions, notably at low to moderate shear rates (G less than or equal to 100 s(-1)). Restructuring of aggregate structure was favored over fragmentation for aggregates composed of 60- and 380-nm particles, whereas fragmentation and reaggregation were the main mechanism in governing the final floe size and structure for aggregates made up from 810-nm particles. Also presented in this study is a dimensional analysis that yields a correlation between a floe factor (consisting of floc size and structure) and an aggregation factor, which encompasses the fluid properties, applied shear, number concentration and size of primary particles, as well as the estimated bonding force between particles. This relationship provides a better appreciation of other significant aggregation parameters. apart from the shear level and aggregate size, which are often ignored in the more conventional manners of presenting data from flocculation processes.