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.
Charging of interfaces between water and hydrophobic media is a mysterious feature whose nature and origin have been under debate. Here, we investigate the fundamentals of the interfacial behaviors of water by employing opto-thermophoretic tweezers to study temperature-gradient-induced perturbation of dipole arrangement at water/oil interfaces. With surfactant-free perfluoropentane-in-water emulsions as a model interface, additional polar organic solvents are introduced to systematically modify the structural aspects of the interface. Through our experimental measurements on the thermophoretic behaviors of oil droplets under a light-generated temperature gradient, in combination with theoretical analysis, we propose that water molecules and mobile negative charges are present at the water/oil interfaces with specific dipole arrangement to hydrate oil droplets, and that this arrangement is highly susceptible to the thermal perturbation due to the mobility of the negative charges. These findings suggest a potential of opto-thermophoresis in probing aqueous interfaces and could enrich understanding of the interfacial behaviors of water.
more » « less- Award ID(s):
- 2001650
- NSF-PAR ID:
- 10368485
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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