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Bulk Synthesis of Metal–Organic Hybrid Dimers and Their Propulsion under Electric Fields
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posted on 2014-03-26, 00:00 authored by Sijia Wang, Fuduo Ma, Hui Zhao, Ning WuMetal–organic hybrid particles
have great potential in applications
such as colloidal assembly, autonomous microrobots, targeted drug
delivery, and colloidal emulsifiers. Existing fabrication methods,
however, typically suffer from low throughput, high operation cost,
and imprecise property control. Here, we report a facile and bulk
synthesis platform that makes a wide range of metal–organic
colloidal dimers. Both geometric and interfacial anisotropy on the
particles can be tuned independently and conveniently, which represents
a key advantage of this method. We further investigate the self-propulsion
of platinum-polystyrene dimers under perpendicularly applied electric
fields. In 1 × 10–4 M KCl solution, the dimers
exhibit both linear and circular motion with the polystyrene lobes
facing toward the moving direction, due to the induced-charge electroosmotic
flow surrounding the metal-coated lobes. Surprisingly, in deionized
water, the same dimers move in an opposite direction, i.e., the metallic
lobes face the forward direction. This is because of the impact of
another type of electrokinetic flow: the electrohydrodynamic flow
arising from the induced charges on the conducting substrate. The
competition between the electrohydrodynamic flow along the substrate
and the induced-charge electroosmotic flow along the metallic lobe
dictates the propulsion direction of hybrid dimers under electric
fields. Our synthetic approach will provide potential opportunities
to study the combined impacts of the geometric and interfacial anisotropy
on the propulsion, assembly, and other applications of anisotropic
particles.