In-situ Gold Coating of Superparamagnetic Nanoparticles by Microemulsion Method
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In-situ gold coating of superparamagnetic nanoparticles by microemulsion method. D. K. Kim1, M. Mikhailova1, M. Toprak1, Y. Zhang1, B. Bjelke2, J. Kehr3, M. Muhammed1. 1
Materials Chemistry Division, Royal Institute of Technology, SE-100 44 Stockholm, Sweden MRI-Center, Experimental Unit, Karolinska Institutet, SE-171 76 Stockholm, Sweden 3 Division of Cellular and Molecular Neurochemistry, Karolinska Institutet, SE-171 77 Stockholm, Sweden 2
ABSTRACT Monodispersed gold coated Superparamagnetic Iron Oxide Nanoparticles (SPION) were prepared in water-in-oil reverse microemulsion ( µE ) of CTAB (cetyltrimethyl -ammonium bromide)/octane/butanol/water and Brij@97/cyclohexane/water. Gold coated SPION were obtained in the µE system by coprecipitation of magnetite and subsequent reduction of Au on the surface of the magnetite using NaBH4. The SPION were characterized by TEM with EDX, AFM, TGA, ESA, UV-Vis spectroscopy, and SQUID at intermediate and final stages. INTRODUCTION A colloid is a suspension in which the dispersed phase is so small(~1-1000nm) that gravitational forces are negligible and interactions are dominated by short-range forces, such as van der Waals’ attraction and surface charges. The inertia of the dispersed phase is small enough that it exhibits Brownian motion, a random walk driven by momentum transferred through collisions with molecules of the suspending medium.[1] Colloidal processing of magnetic nanoparticles has been extensively studied, emphasizing on the characteristics of a dispersion of SPION as a ferrofluid. Suspensions of SPION have van der Waals’ forces and magnetic dipoledipole interactions generated from residual magnetic forces that tend to agglomerate the particles. Dispersion forces due to thermal motion, repulsion, etc. in the ferrofluid must be stronger than attraction forces in order to stabilize the ferrofluid. Many inorganic colloids consisting of particles of different chemical composition, shape, and size have been prepared by precipitation in homogeneous solution. There are many reports on the use of µE as nanoreactors for the synthesis of a variety of nanoparticles, including magnetic materials [2]. Reverse µE consist of nanometer sized water droplets dispersed in a continuous oil phase and stabilized by surfactant/cosurfactant molecules accumulated at the oil-water interface[3]. Homogeneously dispersed water droplets work as nanoreactors for the formation of nanoparticles. Water droplets are related to the water to surfactant ratio (W0) and the molar ratio between co-surfactant and surfactant (P0). So, µE systems are widely used to control the size and shape of the reaction products, which are relatively difficult to form by normal chemical and mechanical methods. In this study, a sequential µE based synthesis is introduced to fabricate nanoparticles with a core-shell structure. The reverse micelle microreactor was prepared contains CTAB, octane, and varying the water to surfactant ratio (W0) and molar ratio between cosurfactant and surfactant (P0). After preparing three µE
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