Controlling the magnetic filaments length by tuning the particle interactions

Initially stable samples of monodisperse superparamagnetic particles were aggregated in the presence of an external magnetic field and different amounts of electrolyte. The aggregation process was monitored using dynamic light scattering (DLS). When the magnetic field was turned off, a significant change of the effective diffusion coefficient was observed at all electrolyte concentrations. This jump was interpreted in terms of filament break-up and additional rotational diffusive modes. Therefore, the length of the magnetic filaments (MF) was determined from the measured average diffusion coefficients applying an adequate theoretical approach. The results prove that the MFs disassemble completely at low electrolyte concentrations. At intermediate amounts of electrolyte added, a partial cluster break-up is observed. Only at high salt concentrations, the chains withstand the absence of the magnetic field. The results show that average filament size can be predicted and controlled by tuning the relative strength of the magnetic and electric interactions.