Sorting Self-assembled Single-crystalline Gold Microplates by Eddy Current
Ed Chen1*, Jer-Shing Huang1
1Chemistry, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:Ed Chen,
Time-variant magnetic flux can induce eddy current in metallic objects and thereby create induced magnetic dipoles that oppose the change of external magnetic field. Eddy current has been applied in centimeter- to meter-scale sorting of metallic objects. The magnitude of eddy current is in general proportional to the area intersecting the varying magnetic field. Therefore, eddy current is usually weak in metallic nanoparticles. Recently, we have chemically synthesized self-assembled gold microplates (AuMPs) with very large aspect ratio (surface area >103 μm2; thickness > 1 μm). In such kind of thin AuMPs, we have successfully induced significantly large eddy current using rotating permanent magnets (1400 rpm, 7000 Gauss) and the effect of eddy current on the motion of plates is observable. We found that the AuMPs are sorted in the moving direction of the magnets and the positions of the AuMPs is correlated to the distribution of the surface area. Such surface area dependent spatial distribution is because more eddy currents and thus stronger magnetic force are induced in larger AuMPs compared to smaller ones. Therefore, larger flakes are brought farther by the external magnetic field than smaller ones.
Our observation demonstrate that eddy current can be used to sort microplates in terms of their size, shape and material. In principle, other applications of eddy current, such as heating and alignment, can be push down to micro- to nano-meter scale. The induced eddy current and corresponding magnetic dipole offers unique opportunity for particle sorting and alignment as well as nanoscale heating.

Keywords: Nanoscacle Sorting , Nanoscacle Heating, Nanoscacle Alignment , Eddy Current , Gold nanoplate