Large-scale synthesis of defined cobalt nanoparticles and magnetic metal-polymer composites.

We present a method where epsilon-cobalt nanoparticles with an average diameter of 4.5 nm can be synthesized in a controlled process and in significantly larger quantities than previously reported in the literature, based on the thermal decomposition of dicobaltoctacarbonyl in the presence of oleic acid and trioctylphosphine oxide (TOPO). Moreover, since the resulting particles are coated with an oleate layer, as shown by infrared (IR) spectroscopy, the colloids can be re-dispersed in organic solvents. These dispersions are suitable for the preparation of nanocomposites by a simple procedure, i.e. mixing of the cobalt dispersion with a polymer solution followed by casting and solvent evaporation. Magnetization measurements confirm the expected superparamagnetic behavior for both the cobalt nanoparticles and the metal-polymer nanocomposites.