Aggregation and Disruption Mechanisms of Nanoparticulate Aggregates. 2. Dispersion of Aggregates Using a Motionless Mixer

Abstract

A novel motionless mixer named Ramond supermixer (RSM) was used to disperse nanoparticle suspensions under the various process conditions. Commercially available nanoparticles, fumed silica (SiO2) of primary particle diameter (d0) ranging from 7 to 30 nm, zirconia (ZrO2) of d0 = 12 nm, and titanium oxide (TiO2) of d0 = 21 nm, were dispersed either in an ion-exchanged water or in aqueous ethylene glycol solutions. The smaller the d0, the harder it is to disperse the aggregates. Zeta potential was largely dependent on d0 and became independent of process variables and, hence, of aggregate diameter. By evaluation of energy barrier values, the aggregation during disruption was found to be negligible. Aggregate disruption was predominant at the viscous subrange. By balancing mechanical energy with turbulent disruptive energy, a mechanistic model was developed for aggregate disruption. The analysis of fractal dimension showed that nanoaggregates are made up by orthokinetic cluster−cluster collision. Fractal dimensions are invariant throughout the disruption process. The rheological measurements further confirmed the evaluated fractal dimensionality.