Spontaneous gas film expansion at an oil-water interface.

In a water-submerged micropillar array, introducing a bubble enables spontaneous gas-film expansion at an oil–water interface via confinement-driven capillary pressure and dissolved-air uptake.

• Why it matters: Oil–water separation by inserting a gas film is thermodynamically unfavorable in bulk, so the work addresses how confinement can make this interfacial transformation proceed.
• What they did: The authors combine experiments on spontaneous oil imbibition and contact-line pinning with a coupled transport–capillarity framework that predicts a characteristic timescale from geometry, capillarity, and gas-phase transport.
• The result: Confinement-induced pressure deficits lower bubble air partial pressure, promoting dissolved-air uptake and lateral invasion through adjacent oil-filled cells, with spatially varying microstructure controlling the gas-film pathway and morphology.

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