Magnetic Nanocomposite Particles and Hollow Spheres Constructed by a Sequential Layering Approach

Abstract

The fabrication of magnetic composite core-shell particles and hollow spheres with tailored dimensions and compositions has been accomplished by a multistep (layer-by-layer) strategy. Composite particles were prepared by coating submicrometer-sized anionic polystyrene (PS) latices with magnetite (Fe 3 O 4 ) nanoparticle layers alternately adsorbed with polyelectrolyte from aqueous solution. The thickness of the deposited multilayers could be finely tuned with nanoscale precision, either by selection of the number of adsorption cycles performed or by the number of polyelectrolyte layers deposited between each nanoparticle layer (i.e., interlayer). As demonstrated by transmission electron microscopy, a marked improvement in the growth, uniformity, and regularity of the composite multilayers was achieved when the number of polyelectrolyte interlayers was increased from one [(poly(diallyldimethylammonium chloride) (PDADMAC)] to three [(PDADMAC/poly(styrenesulfonate) (PSS)/PDAD-MAC)]. Hollow, intact magnetic spheres were obtained by calcination of the core-shell particles at elevated temperature. Furthermore, composite hollow spheres were prepared by calcination of PS latices coated with multilayers of silica and Fe 3 O 4 nanoparticles. These nanoengineered colloidal particles may potentially find applications as delivery systems, or in diagnostics, where the particles can be directed by application of an external magnetic field.

Superparamagnetic Iron Oxide Nanoparticle Probes for Molecular Imaging

“…Although the large size of the particles may remain a limitation, Caruso et al have developed protocols for dense and hollow SPIO sub-micron particles with interesting properties. 21,22 …”

Wave Propagation in Nanodoped Films

“…The amplitudes of the TE field must satisfy boundary conditions at z = 0 and z = d. Then, noting first that the Descartes-Snell relation n 1 sin i = n 0 sin † transforms (14) into † (x) = exp(i n 1 x sin i ) (17) we have at z = 0…”

“…that is their resistance to becoming demagnetized. The non existence of magnetic monopoles prevents to imagine the doping of these films as made of nano dots and, we have instead to consider magnetic hollow nano spheres [12][13][14][15][16][17]. Then, the permeability (z) in 0 z d may be represented by the expansion…”

Preparation and properties of nanostructured magnetic hollow microspheres: experiment and simulation

“…Driven by electrostatic forces, the nanometre sized particles assemble in an aqueous suspension on the spherical surface of micrometer sized beads. The preparation of these particles and magnetic characterisation has been described elsewhere [12,19,20]. We used polystyrene (PS) beads with diameters of 590 nm and 640 nm and nanoparticles of Fe 3 O 4 (Ø = 12 ± 3 nm) and Mn 0.5 Fe 2.5 O 4 (Ø = 10 ± 3 nm).…”

“…The fabrication of hollow spheres was previously realized by other groups via calcination, a time consuming process of many hours [12][13][14][15]. On the other hand, organic components surrounding core-shell nanoparticles can be removed in a matter of minutes by exposure to suitable plasmas [16].…”