Magnetic properties study of iron-oxide nanoparticles/PVA ferrogels with potential biomedical applications

P. MENDOZA ZELIS, D. MURACA, J. S. GONZALEZ, G. A. PASQUEVICH, V. A. ALVAREZ, K. R. PIROTA, F. H. SÁNCHEZ

JOURNAL OF NANOPARTICLE RESEARCH

SPRINGER

Lugar: Berlin; Año: 2013

1388-0764

A study of the magnetic behavior of maghemite nanoparticles inpolyvinyl alcohol polymer matrices prepared by physical cross-linking is reported.The magnetic nanocomposites (ferrogels) were obtained by the in situco-precipitation of iron salts in the presence of polyvinyl alcohol polymer, andsubsequently subjected to freezing-thawing cycles. The magnetic behavior ofthese ferrogels was compared with that of similar systems synthesized usingthe glutaraldehyde. This type of chemical cross-linking agents presents severaldisadvantages due to the presence of residual toxic molecules in the gel,which are undesirable for biological applications. Characteristic particle sizedetermined by several techniques are in the range 7.9-9.3 nm.The iron oxidation state in the nanoparticles was studied by X-ray absorptionspectroscopy. M¨ossbauer measurements showed that the nanoparticlemagnetic moments present collective magnetic excitations and superparamagneticrelaxations. The blocking and irreversibility temperatures of the nanoparticlesin the ferrogels, and the magnetic anisotropy constant, were obtainedfrom magnetic measurements. An empirical model including two magneticcontributions (large nanoparticles slightly departed from thermodynamic equilibrium bellow 200 K, and small nanoparticles at thermodynamic equilibrium)was used to fit the experimental magnetization curves. A deviation from thesuperparamagnetic regime was observed. This deviation was explained on thebasis of an interacting superparamagnetic model. From this model, relevantmagnetic and structural properties were obtained, such as the magnitude orderof the dipolar interaction energy, the nanoparticles magnetic moment, andthe number of nanoparticles per ferrogel mass unit. This study contributes tothe understanding of the basic physics of a new class of materials that couldemerge from the PVA-based magnetic ferrogels.