Aggregation and disruption mechanisms of nanoparticulate aggregates. 1. Kinetics of simultaneous aggregation and disruption

Aggregation and disruption of nanoparticle suspensions under the various process conditions were studied in a stirred vessel with a Ramond stirrer. Commercially available nanoparticles, fumed silica(SiO2) of primary particle diameter (d(0)) ranging from 7 to 30 nm, zirconia (ZrO2) of d(0) = 12 nm, and titanium oxide (TiO2) Of do = 21 nm, were dispersed either in an ion-exchanged water or in aqueous ethylene glycol solutions. A kinetic model for simultaneous aggregation and disruption was developed theoretically for both inertia and viscous subranges and was fitted to the experimental data. At the initial stage, aggregation becomes predominant, and as the time proceeds, disruption becomes evident. The energy barrier was evaluated by taking van der Waals attractive forces, electrostatic repulsive forces, and dispersive forces into consideration, and also the aggregation rates were measured. Fractal dimensions were obtained experimentally by ultra-small-angle X-ray scattering. Correlations were obtained for aggregate diameter at equilibrium stage, with process variables. The initial aggregation rate was modeled with process variables.