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

Abstract

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