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1135-CC02-08

Fabrication of Novel Magnetic Janus Microparticles Amro K. F. Dyab and Vesselin N. Paunov*, Department of Chemistry, University of Hull, Hull, HU6 7RX, United Kingdom.

ABSTRACT We have designed a novel technique for fabrication of magnetic Janus microparticles based on “trapping” the alignment of magnetite nanoparticles dispersed within the oil drops of polymerizable oil-in-water emulsion. We polymerized the oil drops after gelling the continuous aqueous phase in the presence of an external magnetic filed. This allowed us to produce magnetic Janus particles with optical and magnetic anisotropy which form unusual zigzag chains and structures when an external magnetic field is applied to a suspension of such particles. These novel microparticles retain high remanence magnetization and coercivity values indicative of ferromagnetic behavior, which indicates that the composite polymeric Janus microparticles posses a net magnetic dipole and behave like micro-magnets due to the “trapped” orientation of the magnetite nanoparticles in their polymeric matrix. INTRODUCTION Anisotropic microparticles have attracted substantial interest over the past few years.1 Anisotropy from non-spherical particle shape or non-uniform surface properties makes their physical properties different from those of isotropic microparticles, which puts them as potentially promising building blocks for assembling photonic crystals with novel symmetries, colloidal substitutes for liquid crystals and electrorheological fluids.1,2 In addition, anisotropic colloids can be used to control suspension rheology and optical properties,3 for stabilization of emulsions4 and foams,5 engineering of biomaterials6 and complex colloidal composites.7 A range of techniques for fabrication of anisotropic particles have been developed, including micro-contact printing,8 lithography-based micro-stamping,9 clusterization of microspheres10 or partial coating of particle monolayers,11 micro-fluidics,12 electrohydrodynamic jetting,13 and controlled nucleation and precipitation.14 “In bulk” preparation of anisotropic polymeric particles from emulsions was performed by deforming droplets in a stretched gel matrix during polymerization,15 by solvent attrition of elongated polymer solution droplets in shear flow,16 and by using liquid crystal droplets in surfactant director fields.17 Recently, we published a simple method for fabricating anisotropic non-spherical polymeric magnetic microparticles of various morphologies by a surface formation technique.18 In this paper, we report the fabrication of novel magnetic Janus microparticles which behave like micro-magnets and can be assembled and manipulated in solution by external stimuli such as magnetic field. The basics of the method are illustrated in Fig.1 and involve the following stages: (i) a magnetic o/w emulsion is prepared from a polymerizable oil, loaded with a known amount of hydrophobized magnetite nanoparticles, and stabilised by a polymerizable anionic surfactant; (ii) the resultant stable o/w emulsion is