Self organization of magnetic nanoparticles in Ferrofluids

P. MENDOZA ZÉLIS; M. B. FERNÁNDEZ VAN RAAP; D. CORAL; T. TORRES; G. F. GOYA; S. STEWART; F. H. SÁNCHEZ

Activity Report 2010: LNLS ISNN1518-0204

Ministry of Science and Technology / Brazilian Association for Synchrotron Light Technology

Año: 2011; p. 100 - 102

A very important effort is being made nowadays to improve properties of magnetic nanoparticles (MNP) for biomedical applications.For Magnetic Fluid Hyperthermia (MFH), a therapy to treat cancer tumors, low MNP polydispersity and no aggregation is crucial to achieve large specific loss power (SLP). The degree of aggregation must be determined in the fluid state, making Small Angle X-ray Scattering (SAXS) the most adequate technique to conduct this kind of studies. Nanoparticles aggregate due to Van der Waals and dipole-dipole interactions between the magnetic cores giving rise to an assembly of hierarchies, demanding observation in a wide q-range. Here, SAXS is applied to the study of core-shell type CoFe2O4 redispersed in hexane [2, 3]. To take into account the MNP aggregation, SAXS patterns analysis was performed using an analytic form of the structure function S(q, ξ) derived for an exponential cut-off h(r, ξ) = exp[-r/ξ] [4] which modulates the spherically symmetric form factor of the NP convoluted with a log-norm distribution. A slight modification was introduced to take into account the aggregation degree. MNP mean core radii, polydispersity, degree of aggregation and topology of ξ-size aggregates are determined.