Heteromorphic polymer nanoparticles containing iron oxide particles were prepared to obtain a nanometer-sized magnetic stir bar that remotely responds to external magnetic fields.The polymer nanoparticles were prepared by the mini-emulsion polymerization of styrene with small amounts of a cross-linker,and the spherical nanoparticles obtained were incorporated into a poly(vinyl alcohol)(PVA)film.The PVA film was stretched and deformed atl60°C to make the nanoparticles heterogeneous.The dimensions of the polymer nanoparticles with a heterogeneous morphology and rugby ball-like shape were about 210 nm xlOO nm with an average aspect ratio greater than 2.0.The dispersion ability of the nanoparticles was sufficient to use in aqueous circumstances.When an external magnetic field was applied to an aqueous suspension of the nanoparticles,the particles aggregated quickly.Also,on the application of a rotational magnetic field,the polymer nanoparticles began rotating with a velocity proportional to the rate of the external magnetic field rotation.Therefore,it was concluded that the heteromorphic polymer nanoparticles have the potential to stir a micrometer-scale reaction vessel,such as living cells.
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