Toward nanoscale multiferroic devices: Magnetic field-directed self-assembly and chaining in Janus nanofibers

Abstract

Optical microscopy is used to observe magnetic field driven chaining of Janus nanofibers electrospun from CoFe2O4 and BaTiO3 sol-gel precursors. Chaining as a function of applied field strength follows the expected power law for diffusion limited chaining at low concentrations. At higher concentrations chain length increases rapidly at low fields but more slowly at higher fields, with a transition at 100 Oe. This change in dynamics means field-dependent scaling exponents, suggesting mass-dependent chaining for low fields and diffusion limited chaining for higher fields. The angular dispersion of the chains relative to the external field direction also shows a transition near 100 Oe, decreasing monotonically at higher fields. These results suggest that assembly models developed for nanoparticles need to be modified to properly describe assembly in nanorods and nanofibers.

Low-Gradient Magnetophoresis of Nanospheres and Nanorods through a Single Layer of Paper

“…These particles clusters were formed during the droplet transferring process, and they were entrapped very close to the starting point without migration due to their large size. As moving further into the cellulosic matrix (to the right of the image) and getting closer to the magnet, under the influence of the magnetic field, the nanorod clusters formed a stringlike morphology (see Figure e) with an extremely high aspect ratio due to particle chaining . This particle chaining effect, leading to the formation of elongated nanorod clusters, is one of the major causes for the fast separation kinetics of the PSS-70k-coated nanorods (see Figure ) and allowed them to penetrate deep into the cellulosic matrix forming a more extended stain (see Figure ).…”

“…As moving further into the cellulosic matrix (to the right of the image) and getting closer to the magnet, under the influence of the magnetic field, the nanorod clusters formed a stringlike morphology (see Figure 6e) with an extremely high aspect ratio due to particle chaining. 40 This particle chaining effect, leading to the formation of elongated nanorod clusters, is one of the major causes for the fast separation kinetics of the PSS-70k-coated nanorods (see Figure 4) and allowed them to penetrate deep into the cellulosic matrix forming a more extended stain (see Figure 3). At a higher magnification of 20×, as shown in Figure 6l, the stringlike clusters were actually adsorbed onto the cellulose fiber, rather than physically entrapped between the pores.…”

Magnetic properties of aligned multiferroic Janus nanofiber agglomerates measured with the scattered magneto-optical Kerr effect

“…Fibers are mechanically separated from each other using tip sonication, and the resulting loose fibers are mixed into a viscous and transparent polyvinyl alcohol solution (PVA). The air-curable PVA and fiber solution is then allowed to cure on a glass substrate in a uniform external magnetic field [19]. The external field, which can be adjusted between 0 and 2kOe, causes fibers to aggregate.…”

Directed Assembly of Nanomaterials for Making Nanoscale Devices and Structures: Mechanisms and Applications

“…For example, in the presence of an electric field, nanoparticles become polarized because their permittivity is mismatched to their surrounding medium, inducing dipoles across the nanoparticles. − The adjacent dipoles tend to attract one another head-to-tail, which results in enhanced interaction between nanoparticles and thus long-range ordering for assembled nanostructures. Similarly, a magnetic field enhances the interelement interactions through induced magnetic dipole–dipole interactions. − Utilizing directing templates with chemically or physically (static charges, etc.) functionalized pattern areas provides a powerful means to accomplish selective self-assembly. , The pattern areas are typically designed to interact with nanoelements to enable their site-specific deposition.…”

“…Similarly, a magnetic field enhances the interelement interactions through induced magnetic dipole–dipole interactions. 71 − 74 Utilizing directing templates with chemically or physically (static charges, etc.) functionalized pattern areas provides a powerful means to accomplish selective self-assembly.…”