Hierarchical Structure of Magnetic Nanoparticles -Fe 3 O 4 - Ferrofluids Revealed by Small Angle X-Ray Scattering

Small-angle X-ray scattering (SAXS) experiments were set up to investigate the form and structure of Fe 3 O 4 magnetic nanoparticles (MNPs) using BL1.3:SAXS at the Synchrotron Light Research Institute (SLRI) of Thailand in the range of scattering vector q, 0.7 < q (nm –1 ) < 4. The scattering data from samples, background, and empty cells were collected and then subtracted using small-angle X-ray scattering image tool (SAXSIT) software. The analysis of the corrected scattering patterns for four different pH, i.e., 2, 3, 4, and 5, has been revealed by applying log-normal spherical and mass fractal models calculation. The results showed that the SAXS measurement could investigate the hierarchical structures of MNPs Fe 3 O 4 containing primary and secondary particles. The two-dimensional fractal (D f ) aggregates as secondary particles (in volume) have various sizes ranging from 21 to 103 nm in diameter, confirming the correlation to their pH. Those structures consist of primary particles with a mean length of 2 nm in radius and the particle size distribution (σ) of 0.5.