Superparamagnetic nanomagnetites forming oriented structures in elastomer composites

MIETTA, J. L; ANTONEL, P. S.; PEREZ, O. E.; JORGE, G. A.; NEGRI, R. M.

Buenos Aires

Congreso; At the Frontiers of Condensed Matter V; 2010

Comisión Nacional de Energía Atómica - Centro Atómico Constituyentes

Structured magnetoelastic composites are promising materials for its applications in field sensitive devices, such as field-modulated inductances and sensors of magnetic fields and pressure. The central aspect is that smart materials can be obtained by combining the magnetic properties of the fillers nanoparticles with the elastic characteristic of a hosting elastomeric polymer matrix, particularly when anisotropy is induced in the composite. In the present work, the preparation and characterization of structured composites is presented, using nanoparticles of magnetite as fillers and polydimethylsiloxane (PDMS) as the elastomer matrix. The strategy for obtaining structured magnetoelastomers was preparing the magnetite-PDMS mixture before casting and then curing the mixture in the presence of a uniform, and relatively intense, magnetic field. Magnetite nanoparticles were prepared by the coprecipitation method, dissolving stoichiometric amounts of the precursors (Fe(II) and Fe(III) chlorides), in acid media, which was added to a basic solution at controlled pH and temperature. The precipitation of dark brown nanoparticles occurred immediately. The obtained material was magnetic, with a superparamagnetic behaviour at room temperature (determined by Vibrating Sample Magnetometer, VSM). XRD pattern was compatible with magnetite structure, while SEM images have shown particles of 15 nm average size.Mixtures of magnetite-PDMS at defined proportions were placed for curing inside a cylindrical mould, which is part of a designed device that allows curing the samples at a given temperature in the presence of an applied magnetic field, while rotating the sample at constant speed. Formation of chains (needles) of magnetite aggregates, oriented in the direction of the applied field, appears after polymerization. Chains as long as 1.5 mm length and 40 microns diameters were observed, which are composed by aggregation of particles with individual sizes about 20 nm. Anisotropic effects are under quantification at present, both for the magnetic and elastic properties, by VSM, SQUID and texture analysis (1).It is remarkable that the anisotropic composite is obtained using superparamagnetic particles, while for the case of cobalt-iron oxides, structured composites were obtained when using ferromagnetic nanoparticles only.(1) R. M. Negri, S. D. Rodriguez, D. L. Bernik, F. V. Molina, A. Pilosof, O. Pérez. J. Applied Physics (2010) 107 113703.