Characterization of aggregate state of polydisperse ferrofluids: Some aspects of anisotropy analysis of 2D SAXS in magnetic field

2D small-angle X-ray scattering (SAXS) patterns for dilute ferrofluids with different degree of particle interaction under external magnetic field are analyzed to obtain structural characteristics of aggregates formed by polydisperse particles. Classical ferrofluids based on organic low-polarity solvents (toluene, decalin) with dispersed nanoparticles of magnetite and cobalt coated with oleic acid and water-based ferrofluid with dispersed magnetite nanoparticles coated with double layer of sodium oleate, are studied. All systems show the Langevin type behavior regarding the orientation of the anisotropic aggregates in them with the saturation at a relatively weak magnetic field strength. The field-induced anisotropy in the SAXS patterns is considered in the frame of a simple approximation.