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A capillary raft and its destabilization into armored droplets produced by the uniform sprinkling of dense particles
on a few mm thick oil layer (dyed in red for visualization) sitting on water. At the bottom of the container, a pile of armored droplets after several sinking events.
We sprinkle dense small particles into an oil layer, where the particles sediment until they straddle the oil-water interface as a consequence of surface tension forces. Due to the weight of a single particle there is a long-range attraction that gathers nearby particles into capillary rafts while simultaneously bending the interface downwards on a much larger scale than the particle radius. When the number of particles in the raft is large enough, the raft is unstable and sinks (see figure), thus encapsulating the upper oil phase in water. The sinking raft breaks into stable centimeter-size droplets. We thus form a new object called «armored droplets» which encapsulate and retain the oil. This could be a chemistry-free solution to the threat of oil spills on practical time scales necessary to mitigate spilling catastrophes.
Reporters may freely use this image. Credit: Protiere, Abkarian, Aristoff and Stone (2010).