SAXS Study Ferrofluids Structure

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

Campinas

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

Laboratorio Nacional de Luz de Sincrotron

Stable ferrofluids were studied by Small Angle X Ray Scattering (SAXS) at Brazilian Synchrotron Light Laboratory (LNLS) / Brazilian Biosciences National Lab-oratory (LNBio) under proposal D11A - SAXS1 9293. These systems consist of CoFe2O3 nanoparticles (NP) with mean sizes in the range from 4 to 7 nm coatedwith 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) inorder to control the final particle size [1]. Nanoparticles self organized due to Van der Waals and dipole-dipole interactions between the magnetic cores. This effectis 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 aggregatesare determined. Polydispersity of aggregates was not introduced into the model, but the coexistence of clustered particles with unaggregated ones was consideredthought a slight modification of the mentioned fitting function. The so determined aggregation degree range from 0 to 40 The results indicate that samples presentlow primary particle polydispersity, but in the tested size scale some of them self organized forming clusters displaying a chain like tendency and other more com-pact 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 CoF e2 O3 nanoparticles: the influenceof 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.