Self-Assembly of Magnetic Nanoparticles

Nanoparticle Shape Effect on Self-Assembled Nanostructures 

As the structure of a nanoparticle assembly depends mostly on interparticle interactions, the shape of a particle will alter such interactions and affect the position of the nanoparticles in a superlattice structure. HRTEM analysis on all nm Co nanoparticle assembly shows that the particles in the assembly have three different types of shapes square-like, hexagon-like and square [45]. Evaporation of the hexane solvent from the dispersion results in an assembly that is different from the spherical ones. These different shapes break the normal six-fold symmetry in a typical hep superlattice assembly, resulting in two popular defects, twins and stacking faults. 

On the other hand, if the shape of the particles can be controlled, self-assembly of these shaped particles can lead to crystal orientation of each particle in a self-assembled superlattice. For example, MnFe204 nanoparticles have been made in cube-like and polyhedron shapes, as shown in Fig. 6 [46]. Controlled evaporation of the carrier solvent from the hexane dispersion (about 2 mg/mL) of the particles led to MnFe204 nanoparticle superlattices. 

Interparticle Spacing Control in a Self-Assembled Structure 

This control is the key to form exchange-coupled nanocomposites (see Section 5.3). 

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Xia H, Cheng D, Xiao C, Chan HS (2006). Controlled synthesis of Y-junction polyaniline nanorods and nanotubes using in situ self-assembly of magnetic nanoparticles. J. Nanosci. Nanotechnol. 6 3950-3954. 

Sun SH, Anders S, Hamann HF, Thiele JU, Baglin JEE, Thomson T, Fullerton EE, Murray CB, Terris BD. Polymer mediated self-assembly of magnetic nanoparticles. J Am Chem Soc 2002 124 2884-2885. 

Perez, J.M., Simeone, F.J., Saeki, Y., Josephson, L., and Weissleder, R. (2003) Viral-induced self-assembly of magnetic nanoparticles allows the detection of viral particles in biological media, J. Am. Chem. Soc. 125, 10192. Description of a viral nanosensor using iron oxide nanoparticles. This group is at Harvard Medical School. 

Figure 6.5 (a) The formation of ferritin-mediated self-assembly of FePt nanoparticles via electrostatic interactions, (b) magnetic dipole-dipole interaction of ferritins assembled with FePt nanoparticles, and (c) zero field cooling and field cooling results for the ferritin-FePt nanoparticle composite film and individual components. Reprinted with permission from Srivastava, Samanta, Jordan, et al. (2007). Copyright 2007 American Chemical Society. 

Song T, Zhang Y, Zhou T, Lim CT, Ramakrishna S, Liu B (2005) Encapsulation of self-assembled FePt magnetic nanoparticles in PCL nanofibers by coaxial electrospinning. Chem Phys Letts 415 317-322... 

The self-assembly of ordered nanostructures consisting of nanoparticles with sizes between 1 and 1000 nm has attracted a lot of attention owing to their unique optical, electronic, magnetic, catalytic, and other physical properties.1 The ability to attach nanoparticles onto planar surfaces in a well-defined, controllable, and reliable... 

This chapter illustrates how self-assembled nanomagnets can be fabricated using solution phase chemical approaches. Section 2 outlines the general concepts of self-assembly Section 3 describes several common chemical procedures leading to monodisperse magnetic nanoparticles Section 4 gives a few self-assembly examples of magnetic nanoparticles, and Section 5 discusses potential applications. 

M. Chen and D. E. Nddes. Synthesis, self-assembly, and magnetic properties of FexCoyPtlOO-x-y nanoparticles. Nano Lett, 2 211-214, 2002... 

Core-shell particles have attracted much research attention in recent years because of their great potential in the protection, modification, and functionalization of the core with suitable shell materials to achieve specific physical or chemical performances. For instance, the optical, electrical, thermal, mechanical, magnetic, and catalytic properties of core particles can be finely tuned by coating them with a thin mineral shell [73, 74]. Silica shells are produced by a variety of methods that can be divided into two groups (1) the layer-by-layer self-assembly of preformed silica nanoparticles on oppositely charged templates, and (2) seeded polycondensation techniques involving sol-gel precursors. The former method is outside the scope of this article and only the second method will be discussed. 

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