Structure and stability of aggregates formed by electrical double-layered magnetic particles

The aggregation of electrical double-layered magnetic particles has been induced by either adding a 1:1 electrolyte or by applying an external magnetic field. The spatial structure of clusters and the irreversibility of the processes were studied. Two different initially stable samples were used for the study: magnetite and magnetic polystyrene particles. The fractal dimension of the formed aggregates was measured by means of static light scattering. For the particles aggregated in the presence of a magnetic field, a fractal dimension close to 1.1 was obtained for both samples. Transmission electron microscopy micrographs confirmed the presence of chain-like aggregates predicted by the static light scattering measurements. The irreversibility of the aggregates could be explained qualitatively in the framework of the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory when the interplay between electrostatic and magnetic dipole–dipole interactions is considered. A “selective” aggregation was observed and qualitatively explained using the current “charge heterogeneity” concept.