Formation of Magnetite Clusters Using a Confined Impinging Jet Mixer

Superparamagnetic nanoparticles (SPM NP) are commonly employed as magnetic resonance imaging contrast agents. Magnetite (Fe₃O₄) is of increasing interest because of its high magnetic susceptibility in an applied magnetic field. It has been shown in the literature that an increase in size of transverse NMR relaxivity agents leads to a significant decrease in T2 relaxation times and thus higher contrast in an MRI. It is therefore important to develop methods and conditions for controlling the size of polymer-stabilized magnetite clusters. Our strategy is to elucidate critical coagulation concentrations of water for magnetite particles that have been coated with an amphiphilic poly(propylene oxide-b-ethylene oxide)-OH (PPO-b-PEO) copolymer to control clustering size through the use of a confined impinging jet (CIJ) mixer. Using the critical coagulation concentrations, operating conditions for the CIJ mixer have been found where micellization of the copolymer occurs simultaneously with magnetite clustering. Preliminary results have shown that control over the size distribution may be possible by changing the concentration of water in the mixing chamber.