Fabrication of novel anisotropic magnetic microparticles

Abstract

We report a novel technique for fabrication of magnetically anisotropic microparticles based on “arresting” of the alignment of oleic acid coated magnetite nanoparticles (OCMNs) dispersed within the oil drops of a polymerisable oil-in-water emulsion. This was achieved by polymerising the oil drops after gelling the continuous aqueous phase in the presence of an external magnetic field. This approach allowed us to produce magnetic Janus particles with anisotropic optical and magnetic properties which form unusual zig-zag chains and structures when exposed to an external magnetic field. We studied the magnetic properties of these novel microparticles and showed that they retained remanence magnetisation with high coercivity values indicative of ferromagnetic behaviour. This indicates that the composite polymeric Janus microparticles posses a net magnetic dipole and behave like micromagnets due to the “arrested” orientation of the OCMNs in their polymeric matrix. Utilizing the same technique, magnetic Janus microparticles have been prepared based on emulsions stabilised only by OCMNs without the use of surfactants, and the effect of pH of continuous aqueous phase on the morphology of these microparticles has been investigated.