Monodispersed, hydrophilic, superparamagnetic magnetic nanospheres with a high fraction of magnetite were synthesized by combining modified miniemulsion/emulsion polymerization and sol-gel technique for the first time. The surface of the nanospheres was coated by a silica layer with controlled thickness. Transmission electron microscopy experimental results showed well-proportioned, equal-sized, magnetite/polystyrene (Fe3O4/PS) nanospheres with a thin silica shell. Based on the TGA data, the fraction of magnetite in the Fe3O4/PS nanospheres core was estimated to be 80 wt %. Magnetization measurements indicated that the superparamagnetic nature of the nanospheres had high saturation magnetization of 40 emu/g at 300 K. The procedures of the novel synthesis are described in detail. Also discussed are the mechanisms of the novel combined miniemulsion/emulsion polymerization processes.

A hybrid emulsion polymerization was formulated for synthesizing Fe 3 O 4 / polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)-droplets with a diameter of 100-200 nm and styrene (St)-droplets with a diameter of 3-4 lm, was obtained by mixing Mag-miniemulsion and St-macroemulsion. With extremely low surfactants concentration ((critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag-droplets, as the result of smaller droplet size and larger surface ratio. Both water-soluble potassium persulfate (KPS) and oil-soluble 2,2 0 -azobis(2-isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60-200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe 3 O 4/ polystyrene latices assembled into well-ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as-synthesized Fe 3 O 4 /polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag-miniemulsion and St-macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285-5295, 2007

No abstract

No abstract