Electrostatic interactions between particles play important roles in the stability and function of colloids, emulsions, and food products. However, such interactions are not fully understood yet. One of the mysteries is the existence of an attraction between like-charged particles, as observed in bulk solution as well as at interfaces. The existence of particle attraction at fluid interfaces such as air-water and oil-water interface has been observed in a number of studies, but the mechanism of the attraction remains highly controversial. Most of the uncertainties arise from the ambiguity of those experiments, which is due to intrinsic complication akin to surface phenomena, including the possibility of surface contamination, roughness of particle surface, and the possible existence of external source of perturbation. Surface contamination has been observed to induce surface aggregation of particles in various cases, while the surface roughness of particles may lead to contact line fluctuation that was argued to incur quadrupole attraction between particles. The external source of perturbation, as proposed recently by Oettel et al., however, remains to be confirmed. Here, we present clear experimental evidence that external perturbation does induce attraction between like-charged particles at the oil-water interface. The external perturbation in this study is due to another charged interface at proximity. We further demonstrate that the particle attraction can be managed by adjusting the separation distance between the two interfaces.

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