Magnetic silica:epoxy composites with a nano- and micro-scale control

Multiscale composites with magnetic properties were prepared by incorporating Cu–Ni nanoferrites filled silica microparticles in an epoxy matrix. The size of the nanoferrites was controlled both by the structure of the silica template and the annealing temperature (700 and 900 °C) used during the synthesis procedure. The ferrite:silica particles prepared at 700 °C showed a narrow size distribution close to 8.3 nm with a superparamagnetic behaviour. A less symmetric size distribution was obtained when annealing was performed at 900 °C, with diameters ranging from 15 to 80 nm. The reinforcement incorporation increased up to 7 °C the glass transition temperature and 30 °C the decomposition temperatures of the composites. The proposed strategy permits the nanoscale control, by the trapping effect of the silica on the magnetic nanoparticles, as well as the control of the micro-scale distribution through a simple protocol. These composites could have potential applicability as EMI shielding materials, owing to their magnetic nature, lightweight and enhanced thermal stability.