Effects of particle concentration and dispersion rheology on the breakup of nanoparticle clusters through ultrasonication

A key step in the manufacture of numerous high-performance products with nanoparticles in their formulation requires process intensification to achieve the deagglomeration of particle clusters and generate a fine dispersion. Concentrated dispersions as master batches offer several advantages and at the same time challenges due to the resulting complex rheology. This study, performed using an ultrasonicator as the energy intensive device, aimed at addressing the challenges relating to dispersion rheology resulting from increased powder concentration and continuous phase viscosity with the objective of obtaining process relevant recommendations based on the kinetics and mechanisms of deagglomeration. Findings obtained with representative test systems, dispersions of hydrophilic silica particles in water and aqueous solutions, allowed recommendations to be obtained beyond the specifics of the study. Mechanism of break up was consistent with that observed using other process devices and hence can be used as guidance for equipment selection at large scale. The complex, non-Newtonian rheology of the pre-dispersions with increases in concentration and continuous phase viscosity slowed down deagglomeration kinetics, evolved during the course of deagglomeration and pointed out the need for careful design to achieve homogeneity within the dispersion in order to achieve the desired outcome from an energy intensive process.