Identification of aggregates of magnetic nanoparticles in ferrofluids at low concentrations
- Different very dilute suspensions of magnetic nanoparticles (magnetite surrounded by an organic shell) in water (ferrofluids) were investigated using small-angle X-ray scattering. It is shown that the scattering originates not only from noncorrelated coreshell nanoparticles, but also from larger structures. By modelling, these structures can be identified as close-packed clusters consisting of coreshell particles (core diameter ~10 nm). The analysis of the radial distance distribution function, obtained by Fourier transformation of the scattered intensity, reveals a lower bound of the mean cluster size of about 40 nm. The formation of clusters is persistent, even in very dilute suspensions.