INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Hydrophobic magnetic nanocomposites silica aerogel/maghemite
P. MENDOZA ZÉLIS, M. B. FERNÁNDEZ VAN RAAP, L. M. SOCOLOVSKY, A. G. LEYVA AND F. H. SÁNCHEZ
Workshop; Latin American Workshop on Magnetism and Magnetic Materials; 2010
Universidad Nacional de Colombia
Silica aerogels are the lightest solid materials that find applications in several areas. Here we discussed on the preparation and characterization of magnetic hydrophobic aerogels which may have novel applications. Silica aerogel/iron oxide nanocomposites were produced by sol-gel process followed by hypercritical drying. Samples were synthesized from tetraethylorthosilicate (TEOS) and methytrimethoxysilane (MTMS) with a molar ratio MTMS/TEOS= 0.5. The later was added to achieve the hydrophobic property by surface modification. Iron nitrate was used as Fe oxide precursor. Molar ratios alcohol/TEOS= 2.3, H2O/TEOS=1.8 were hold fixed while iron concentration was varied as mFe/mSi=0.083, 0.207 and 0.330. The structural and magnetic properties of Fe2O3−SiO2 nanocomposite porous aerogels were systematically investigated by XRD, Mössbauer Spectroscopy, TEM, SQUID magnetometry and with SAXS and XAF by using synchrotron radiation at LNLS. The aim of this work is to investigate the interrelation between porosity and magnetic nanostructure in these porous nanocomposites which exhibit an accessible internal porous structure, both in the meso and in the micro scale. Field cooled and zero field cooled magnetization data indicates that the composites behave as an assembly of non interacting superparamagnetic nanoparticles for the three compositions studied. The samples become blocked at a temperature TB between 27 to 40K. Porosity was studied by SAXS and displays the typical fractal power law behaviors with primary particle radius of 20 nm. Direct magnetic particle size determination is not an easy task because these materials exhibit low crystallinity and low constrast for TEM. Hydrophobicity allows the aerogel to be loaded with an organic liquid. Loaded aerogeles were also studied by SAXS in an attempt to lower the silica/porous constrast. Contrast studies and the feasibility of a direct determination of magnetic structure from the scattering data is discussed. The results provide new insights into innovative materials and on the relation between the compositional and microstructural features, and the properties of magnetic nanocomposite.