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    Formation of cobalt nanoparticle dispersions in the presence of polysiloxane block polymers

    Year: 2002

    Journal: Polymer 43 (2002) 2337-2348, 20111221

    Authors: , M.S. Thompson, L.A. Harris, K.E. Farmer, A.R. Esker, J.S. Riffle , T.G. St. Pierre

    Organizations: aDepartment of Chemistry, Virginia Polytechnic Institute and State University, Mail Code 0212, Blacksburg, VA 24061-5976, USA bDepartment of Physics, The University of Western Australia, Nedlands, Perth, WA 6907, Australia

    Stable suspensions of superparamagnetic cobalt nanoparticles have been prepared in poly(dimethysiloxane) (PDMS) carrier fluids in the presence of poly[dimethysiloxane-b-(3-cyanopropyl)methysiloxane-b-dimethylsiloxane] (PDMS-PCPMS-PDMS) triblock copolymers as steric stabilizers. A series of polysiloxane triblock copolymers with systematically varied molecular weights were prepared via anionic polymerization using LiOH as an initiator. These copolymers formed micelles in toluene and served as "nanoreactors" for thermal decomposition of the Co2(CO)8 precursor. The nitrile groups on the PCPMS central blocks are thought to adsorb onto the particle surface, while the PDMS endblocks protrude into the reaction medium to provide steric stability. The particle size can be controlled by adjusting the cobalt to copolymer ratio. TEM shows non-aggreated cobalt nanoparticles with narrow size distributions which are evenly surrounded with copolymer sheaths. However, some degree of surface oxidation was observed over time, resulting in a decrease in magnetic susceptibility.