Concentration-dependent correlations in ferrofluids studied by small-angle scattering of synchrotron X-radiation

Small-angle X-ray scattering has been used to study correlations between the magnetic grains of ferrofluids : for dilute colloïids, the grains look isolated or associated in dimers, trimers, etc ... depending on the nature of the ferrofluids. At higher concentration, an order appears in the spatial distribution of the grains even without magnetic field. The application of a magnetic field can generate alongated fibers of grains. An average interfiber spacing has been put in evidence. Small-angle X-ray scattering reveals as a sensitive quality test of the grain agglomeration in ferrofluids.