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

• Published in: Polymer (Guilford) 2002-04, Vol.43 (8), p.2337-2348
• Main Authors: RUTNAKORNPITUK, M, THOMPSON, M. S, HARRIS, L. A, FARMER, K. E, ESKER, A. R, RIFFLE, J. S, CONNOLLY, J, PIERRE, T. G. St
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Diamagnetism and paramagnetism; Diamagnetism, paramagnetism and superparamagnetism; Exact sciences and technology; Inorganic and organomineral polymers; Magnetic properties and materials; Physicochemistry of polymers; Physics; Properties and characterization; Small particles and nanoscale materials; Studies of specific magnetic materials
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(02)00015-0

Stable suspensions of superparamagnetic cobalt nanoparticles have been prepared in poly(dimethysiloxane) (PDMS) carrier fluids in the presence of poly[dimethylsiloxane-b-(3-cyanopropyl)methylsiloxane-b-dimethylsi l oxane] (PDMS--PCPMS--PDMS) triblock copolymers as steric stabilizers. A series of the 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 Co sub 2 (CO) sub 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-aggregated 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.