We investigate the dynamics of metallodielectric Janus particles moving via contact charge electrophoresis (CCEP) between two parallel electrodes. CCEP uses a constant voltage to repeatedly charge and actuate conductive particles within a dielectric fluid, resulting in rapid oscillatory motion between the electrodes. In addition to particle oscillations, we find that micrometer-scale Janus particles move perpendicular to the field at high speeds (up to 600 μm/s) and over large distances. We characterize particle motions and propose a mechanism based on the rotation-induced translation of the particle following charge transfer at the electrode surface. The propulsion mechanism is supported both by experiments with fluorescent particles that reveal their rotational motions and by simulations of CCEP dynamics that capture the relevant electrostatics and hydrodynamics. We also show that interactions among multiple particles can lead to repulsion, attraction, and/or cooperative motions depending on the position and phase of the respective particle oscillators. Our results demonstrate how particle asymmetries can be used to direct the motions of active colloids powered by CCEP.
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Reversible Aggregation and Dispersion of Particles at a Liquid–Liquid Interface Using Space Charge Injection
Colloids at water–oil interfaces can form ordered monolayers when surface charge–induced repulsion overcomes capillary attraction. Such particle monolayers play an important role in the stabilization of emulsions and also can serve as an exquisite model system to study fundamental physical phenomena. However, it is challenging to dynamically control the relative magnitudes of repulsion and attraction between the particles, especially with reversibility, to induce reversible aggregation and dispersion because forces that are relevant tend to be much greater than those induced by thermal fluctuation. Here, the authors show that reversible assembly, that is reversible aggregation and dispersion, can be induced by space charge injection from corona discharge. The authors find that space charge injection modulates the strength of charge‐induced repulsion. By injecting charges, it is possible to either induce aggregation of repulsion‐dominated colloids or dispersion of aggregated particles. Interfacial electrophoretic experiments show that the alteration of the repulsion is caused by the variation of the particle surface charge that results from charge injection. The authors also demonstrate that even particles that initially form aggregated clusters due to low surface charge can be induced to organize into a hexagonally ordered structure. This method can be a powerful tool for studying phenomena involving interface‐trapped particles.
more » « less- Award ID(s):
- 1705891
- NSF-PAR ID:
- 10462405
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 6
- Issue:
- 5
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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