Aggregation of colloidal particles and breakup of aggregates

Aggregation of colloidal particles and breakup of aggregates are important processes in both engineered and natural systems. The objective of this work is to examine aggregation and breakup processes from the view of interparticle forces. An external magnetic force and a colloidal superparamagnetic particle suspension comprise the model system of the study. The external magnetic force is used as a tool to easily manipulate the interparticle forces and study their effects on both aggregation and breakup. The potential energy between two particles is calculated based on extended DLVO theory, which includes electrostatic, van der Waals, and magnetic dipole forces. Breakup mechanisms of magnetic chains formed at different magnetic-field strengths and solution conditions are identified. With increasing magnetic-field strength, secondary-minimum aggregation becomes primary-minimum aggregation. The transitional magnetic-field strength at which this change takes place is determined both experimentally and theoretically.