Aggregation of magnetic polystyrene particles: A light scattering study

The aggregation behavior of dilute dispersions of magnetic polystyrene particles was studied experimentally by means of light scattering techniques. In absence of external magnetic fields, the particles are stable against flocculation due to charged carboxylic surface groups. Aggregation was induced applying an external magnetic field. Static light scattering (SLS) was used to study the geometry of the fractally shaped aggregates. Fractal dimensions close to 1.2 were found for the aggregates. Transmission electron microscopy micrographs show that the formed aggregates are chain-like, as predicted by the SLS results. Dynamic light scattering (DLS) was employed to monitor the time evolution of cluster size and to study the underlying growth kinetics. The observed results could be explained qualitatively in the framework of the classical DLVO theory when magnetic dipole-dipole interactions are taken into account.