Self-assembly of colloidal particles at fluid-fluid interfaces is exploited for emulsion stabilization, tunable nanomaterials, and nanocomposites with complex morphologies. Disassembly of interfacial particle monolayers is equally important, for instance for green catalytic processes. Current methods require physico-chemical modification of the system, for instance by tuning the pH or electrolyte concentration. We demonstrate controlled disassembly from the interface of particle-laden microbubbles. We use ultrasound waves as remote trigger to drive the bubbles into oscillations, which cause violent interface deformations accompanied by particle ejection. We visualize ejection events at the single particle level using high-speed video microscopy. Measurements of the area density of particles and of the acceleration of the bubble interface reveal that the interplay of two mechanisms is responsible for particle expulsion: tangential stresses in the interface upon compression, and the body force acting on the particles due to the large radial acceleration of the interface. Non-linear bubble dynamics can also be exploited to design complex particle expulsion scenarios, such as non-spherical oscillations and jetting, with relevance to directed particle delivery in microreactors.

Remotely triggered colloidal disassembly from particle-laden microbubble

249th National Meeting (2015)

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