Hamed Sharifi1 Kamal Asadi1

1, Max Planck Institute for Polymer Research, Mainz, , Germany

Thermal decomposition is a promising route for the synthesis of highly monodisperse magnetite nanoparticles. The simplicity of the synthesis however is counterbalanced by the complex chemistry of the system, e.g. the interplay of the reagents with the reaction variables that determine the final particle size and dispersity.
Control over nanoparticle size can be obtained by adjusting the reaction parameters, namely precursor concentration or heating rate. In this contribution, we show that in the size-controlled synthesis via the precursor concentrate, the size does not monotonically increase with increasing the precursor concentration but passes through a maximum with increasing precursor concentration. The observation of two different size regimes is closely related to the amount of surfactant. Next, we present a combined experimental and theoretical study on the influence of the heating rate on crystal growth, size, and monodispersity of iron-oxide nanoparticles. Monodisperse nanoparticles were synthesized with sizes varying from 6.3 nm to 27 nm simply by controlling the heating rate of the reaction. Using numerical calculations based on the classical nucleation theory and growth model, we identified the relative time scales associated with the heating rate and precursor to monomer (growth species) conversion rate as a decisive factor influencing the final size and dispersity of the nanoparticles. Furthermore, we show that the nanoparticle particles show size-dependent but superior superparamagnetic properties at room temperature.