Magneto-dielectric properties of polymer–Fe3O4Fe3O4 nanocomposites

The aim of this research is to elucidate the size effect of magnetic nanoparticles on the resultant magneto-dielectric properties of polymer nanocomposites at radio frequencies. The block copolymer of [styrene-b-ethylene/butylene-b-styrene] (SEBS) was utilized as a matrix for the templating of magnetic nanoparticles. Surfactant-modified iron oxide (Fe3O4Fe3O4) nanoparticles of various sizes were successfully synthesized by a seed-mediated growth method. The surfactant prevented Fe3O4Fe3O4 aggregation and provided compatibility with the polymer matrix. The nucleation and growth of Fe3O4Fe3O4 nanoparticles was controlled by changing the concentration ratio of surfactant to iron-precursor. The free iron ions present during synthesis are the major factor contributing to the growth of larger particles. The Fe3O4Fe3O4 nanoparticle critical size for superparamagnetic to ferrimagnetic transition was determined to be near 30 nm at room temperature. The dielectric permittivity (ɛr)(ɛr) of the polymer composite increased with increasing amount of Fe3O4Fe3O4 doping, and was not influenced by nanoparticle size. However, the magnetic permeability (μrμr) of the composites was significantly influenced by the size of Fe3O4Fe3O4 nanoparticles templated within the block copolymer matrix due to thermal energy fluctuations from the nanoparticle surroundings.