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Dissolved atmospheric gases are typically assumed to have negligible influence on liquid behaviour because their solubility is considered too low to affect macroscopic properties. However, long‑standing observations contradict this view: for example, it is well known that dissolved gases can accumulate at solid hydrophobic surfaces immersed in water;[1] the emergence of long-range hydrophobic interactions has been ascribed to nanobubble cavitation between two hydrophobic surfaces; [2] as the concentration of dissolved gases in an oil-in-water emulsion decreases, the average time of droplet coalescence significantly increases.[3,4]
In this work, we developed a precise droplet rise experiment that explores the effect of gas enrichment at oil microdroplets as a function of the gas content.[5] By using high speed video microscopy, we measure a faster rise velocity for microdroplets of gassed oil (silicone oil and hexadecane) released in ultrapure quiescent gassed water, than expected based on a no-slip boundary condition. We fit the rise velocity with a slip length that increases from a few m for partially gassed liquids, to several hundred m for fully gassed oils and water. Interfacial gas enrichment governs these effects, demonstrating that dissolved gases actively shape liquid–liquid interfacial transport beyond classical predictions. Negligible or negative slip was measured for fully degassed systems, and for contaminated systems, confirming that the liquid-liquid interface is immobilised when impurities are present.
[1] Lohse, D. & Zhang, X. Surface nanobubbles and nanodroplets. Rev. Mod. Phys. 87, 981-1035 (2015). https://doi.org/10.1103/RevModPhys.87.981
[2] Christenson, H. K. & Claesson, P. M. Direct measurements of the force between hydrophobic surfaces in water. Adv. Colloid Interface Sci. 91, 391-436 (2001).
[3] Eastoe, J. & Ellis, C. De-gassed water and surfactant-free emulsions: History, controversy, and possible applications. Adv. Colloid Interface Sci. 134-135, 89-95 (2007). https://doi.org/https://doi.org/10.1016/j.cis.2007.04.017
[4] Wang, J. et al. Influence of Interfacial Gas Enrichment on Controlled Coalescence of Oil Droplets in Water in Microfluidics. Langmuir 35, 3615-3623 (2019). https://doi.org/10.1021/acs.langmuir.8b03486
[5] Azadi, R. & Neto, C. Interfacial gas enrichment at rising oil droplets. in preparation (2026).