SAXS Study Ferrofluids Structure

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

Campinas, San Pablo

Otro; 22ª Reunião Anual de Usuários do LNLS; 2012

Laboratório Nacional de Luz Síncrotron

Stable ferrofluids were studied by Small Angle X Ray Scattering (SAXS) at Brazilian Synchrotron Light Laboratory (LNLS) / Brazilian Biosciences National Laboratory (LNBio) under proposal D11A - SAXS1 9293. These systems consist of CoFe2O3 nanoparticles (NP) with mean sizes in the range from 4 to 7 nm coated with 2 nm of oleic acid and resuspended in hexane. The core-shell type magnetic nanoparticles of different sizes were prepared by thermal decomposition of iron-acetylacetonate (acac)3 and cobalt-acetylacetonate (acac)2 as organic precursors and solvents having different boiling temperatures (538, 573, 593 and 638 K) in order to control the final particle size [1]. Nanoparticles self organized due to Van der Waals and dipole-dipole interactions between the magnetic cores. This effect is reflected in the SAXS pattern, and was taken into account modeling the SAXS pattern with a spherically symmetric form factor of the NP convoluted with a log-norm distribution and modulated whit a monodispersed structure factor [2]. Mean core radii, polydispersity, degree of aggregation and topology of size aggregates are determined. Polydispersity of aggregates was not introduced into the model, but the coexistence of clustered particles with unaggregated ones was considered thought a slight modification of the mentioned fitting function. The so determined aggregation degree range from 0 to 40 The results indicate that samples present low primary particle polydispersity, but in the tested size scale some of them self organized forming clusters displaying a chain like tendency and other more compact structures. NP size and polydispersity are in very good agreement with TEM results. [1] Goya, G.F., Lima, E., Arelaro, A.D., Torres, T., Rechenberg, H.R., Rossi, L., Marquina, C. Magnetic Hyperthermia with CoFe2O3 nanoparticles: the influence of particle size on energy absorption. IEEE Trans. on Magn, 44 (11) 2008. [2] Sorensem C.M., Wang, G.M. Size distribution effect on the power law regime of the structure factor of fractal aggregates. Phys. Rev. E. Vol. 60 (6) 1999.