Investigation of particle size distribution and aggregate structure of various ferrofluids by small-angle scattering experiments

The size and the size dispersion of the composite particles of ferrofluids were determined assuming a lognormal distribution of core radii. Small-angl e X-ray scattering data were fitted by the theoretical scattering function of two-phase spheres. Reliable results were obtained, because the scatterin g share of the surface layer can be taken into account. The particles aggre gate at high as well as very low concentrations. After freezing of the carr ier liquid, the particles within the clusters come together tightly. The me asured minimal particle distance gives information about the effective surf ace-layer thickness. Two types of aggregates, namely compact clusters and e xtended net-like aggregates, were distinct in middle length scales.