Abstract
A catalytic Janus particle is capable of gaining energy from the surrounding fuel solution to drive itself to move continuously, which has an important impact in different fields, especially the field of micro-systems. However, the randomness of self-propulsion at the microscale restricts its use in practice. Achieving a directed self-propelled movement would greatly promote the application of the Janus particle. We proved experimentally that an AC electric field was an effective way to suppress Brownian motion and control the direction of self-propelled movement. The self-propulsion and dielectrophoretic response of a 2μm Janus particle were observed and the related basic data were collected. Interdigital electrodes, 20 μm in width, were energized in pulsed style to modulate the self-propulsion, which resulted in a shuttle-style motion in which a single Janus particle moved to and fro inside the strip electrode. The change of direction depends on its unique position: the catalyst side is always pointed outward and the orientation angle relative to the electrode is about 60°. Numerical simulation also proved that this position is reasonable. The present study could be beneficial with regard to self-propulsion and AC electrokinetics of the Janus particle.
Highlights
The Janus particle, proposed by de Gennes in 1991, has a non-homogeneous structure on its two hemispheres, which enables some novel physical and chemical properties to be induced.[1]
A high frequency AC electric field generated by indium tin oxide (ITO) interdigital electrodes (IDEs) was applied
It was found that the randomness of self-propulsion is significant due to the appearance of Brownian-like motion, at short time scales, directional movement is still approached
Summary
The Janus particle, proposed by de Gennes in 1991, has a non-homogeneous structure on its two hemispheres, which enables some novel physical and chemical properties to be induced.[1] At present, the Janus particle has been fabricated by different methods including microfluidics, self-assembly, sputtering, and so on.[2,3] Among all applications, a very interesting example is self-propulsion (Fig. 1(a)), where one hemisphere of the Janus particle covered with a thin layer of catalyst (e.g. platinum (Pt)) serves to decompose the fuel reactants (e.g. 2H2 O2 → 2H2 O + O2) surrounding the particle.[4] Because the catalytic reaction generates asymmetry of the molecule number at the two sides of the Janus particle, the concentration gradient of molecules will force the Janus particle to move autonomously,[5] with the direction opposite to the catalyst side.
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