Encapsulation of Magnetic Nickel Nanoparticles Via Inverse Miniemulsion Polymerization Ana Paula Romio, 1 Heloı ´sa H. Rodrigues, 1 Augusto Peres, 2 Alexandre Da Cas Viegas, 3 Elena Kobitskaya, 4 Ulrich Ziener, 4 Katharina Landfester, 5 Claudia Sayer, 1 Pedro H. H. Ara ujo 1 1 Department of Chemical Engineering and Food Engineering, Federal University of Santa Catarina, Florian opolis, SC, Brazil 2 Petrochemical Technology, CENPES/PETROBRAS, Rio de Janeiro, Brazil 3 Department of Physics, Federal University of Santa Catarina, Florian opolis, SC, Brazil 4 Institute of Organic Chemistry III – Macromolecular Chemistry and Organic Materials, University of Ulm, Ulm, Germany 5 Max Planck Institute for Polymer Research – MPI-P, Mainz, Germany Correspondence to: P. H. H. Ara ujo (E-mail: pedro@enq.ufsc.br) ABSTRACT: In this work, the encapsulation of magnetic nickel nanoparticles in polyacrylamide particles was performed via inverse miniemulsion polymerization. The dispersion of nickel nanoparticles was characterized in polar solvents including water, ethanol, and dimethyl sulfoxide using different stabilizers. The best results were obtained when the nonionic stabilizer poly(ethylene glycol) octadecyl ether (Brij 76) was used to stabilize the nickel nanoparticles in dimethyl sulfoxide. In addition, the block copolymer poly(ethylene-co-butylene)-b-poly(ethylene oxide) was used as a surfactant to create inverse miniemulsions while minimizing the coalescence of the miniemulsion droplets. Different types of salts such as zinc, nickel, and sodium nitrates were tested as lipo- phobes to retard Ostwald ripening. Transmission electron microscopy images of polyacrylamide/nickel particles synthesized with zinc and nickel salts as lipophobes indicate that nickel nanoparticles are embedded in the polyacrylamide matrix. Magnetization curves show that the saturation magnetization of polyacrylamide/nickel particles is only slightly below that of the pure nickel nanoparticles. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000–000, 2012 KEYWORDS: nanoparticles; nanowires and nanocrystals; emulsion polymerization; composites Received 28 September 2012; accepted 9 November 2012; published online DOI: 10.1002/app.38840 INTRODUCTION Organic–inorganic magnetic nanoparticles synthesized by minie- mulsion polymerization combine the advantages of polymer latexes, such as high solid content, low viscosity, good process control of polymer composition and functionality with the properties of inorganic magnetic nanoparticles. 1 Among those metallic nanoparticles, the ones formed by Co, Fe, and Ni had received considerable attention due to their unique magnetic properties. 2–6 Nickel nanoparticles, in particular, present great potential in many fields of application, including electromag- netic interference shielding, 4,7 catalysis 8 and electro-conductive materials. 9 Nevertheless, nickel nanoparticles have a strong tend- ency to aggregate and form large clusters, thus losing their spe- cific magnetic properties and limiting their practical use. 10 This problem can be overcome by the encapsulation of the nickel nanoparticles with a polymer shell that could not only prevent aggregation but also provide nanoparticles with specific functionalities. The encapsulation of hydrophilic inorganic nanoparticles by direct (oil in water) miniemulsion polymerization requires the modification of the nanoparticle surface to change its hydro- philic–hydrophobic character 11 as it is extremely difficult for hydrophilic inorganic nanoparticles to diffuse into nonpolar monomer droplets. 12 Transferring the encapsulation process to inverse miniemulsion polymerization, where the dispersed phase is a polar (water-soluble) monomer, could avoid the necessity of surface modification of the hydrophilic inorganic nanoparticles. In the inverse miniemulsion, the polymerization occurs in sub- micrometric aqueous (polar) droplets containing a water-soluble monomer, such as hydroxyethyl methacrylate, 13 acrylamide 14 or acrylic acid, 15 and lipophobic osmotic pressure agents, usually a highly hydrophilic salt or low-molecular weight electrolyte, for instance, NaCl 13 and MgSO 4 , 14 to minimize diffusional droplet degradation. The droplets are dispersed in a continuous organic media (nonpolar) with an oil-soluble non-ionic surfactant producing stable colloidal particles. 16,17 The polymerization can V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2012, DOI: 10.1002/APP.38840 1