Anisotropic magnetic microparticles from ferrofluid emulsion

Abstract

A simple synthetic approach for the preparation of anisotropic Janus-like sub-micrometre sized hybrid magnetic particles consisting of inorganic superparamagnetic iron oxide nanoparticles and an organic polymer is demonstrated here. Two-step controlled processes, (a) the swelling of preformed magnetic oil in water ferrofluid droplets with styrene and (b) a seed emulsion polymerization of styrene in the presence of monomer swollen ferrofluid as seed, were accomplished. The swelling of ferrofluid droplets with styrene was investigated by gas chromatography (GC) to point out the partition of styrene in the continuous aqueous phase and in the droplets’ organic phase. A series of seed emulsion polymerizations initiated by AIBN and KPS in different concentrations of styrene was carried out in order to turn the monomer swollen ferrofluid droplets into the magnetic polymer particles having two different phases. This approach allows us to investigate the effect of the seed to monomer ratio and especially the initiator type on the anisotropic morphology of the prepared particles. Most importantly, we demonstrated that the used experimental method enables one to produce magnetic Janus hybrid particles. The independent phase of the anisotropic Janus particle morphology was evidenced by transmission electron microscopy (TEM). The complete characterization of particles was performed using light scattering measurement, thermogravimetric analysis (TGA) and size-exclusion chromatography to explain the properties of such “biphasic” microparticles. An interpretation based on thermodynamics and a proposed tentative polymerization mechanism is also discussed. This procedure can be adopted to produce large quantities of magnetic anisotropic submicron colloidal particles for biotechnological applications.