la8b03486_si_002.avi (6.07 MB)
Influence of Interfacial Gas Enrichment on Controlled Coalescence of Oil Droplets in Water in Microfluidics
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posted on 2019-02-12, 00:00 authored by Jianlong Wang, Adrian J. T. Teo, Say H. Tan, Geoffrey M. Evans, Nam-Trung Nguyen, Anh V. NguyenInterfacial gas enrichment
(IGE) of dissolved gases in water is
shown to govern the strong attraction between solid hydrophobic surfaces
of an atomic force microscopy (AFM) colloidal probe and solid substrate.
However, the role of IGE in controlling the attraction between fluid–fluid
interfaces of foam films and emulsion films is difficult to establish
by AFM techniques because of the extremely fast coalescence. Here,
we applied droplet-based microfluidics to capture the fast coalescence
event under the creeping flow condition and quantify the effect of
IGE on the drainage and stability of water films between coalescing
oil droplets. The amount of dissolved gases is controlled by partially
degassing the oil phase. When the amount of dissolved gases (oxygen)
in oil decreases (from 7.89 to 4.59 mg/L), the average drainage time
of coalescence significantly increases (from 19 to 50 ms). Our theoretical
quantification of the coalescence by incorporating IGE into the multilayer
van der Waals attraction theory confirms the acceleration of film
drainage dynamics by the van der Waals attractive force generated
by IGE. The thickness of the IGE layer decreases from 5.5 to 4.9 nm
when the amount of dissolved gas decreases from 7.89 to 4.59 mg/L.
All these results establish the universal role of dissolved gases
in governing the strong attraction between particulate hydrophobic
interfaces.
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50 msIGE layer decreasesMicrofluidics Interfacial gas enrichmentfilm drainage dynamicsoil phasecoalescing oil dropletsOil Dropletscoalescence eventInterfacial Gas Enrichmentflow conditionControlled Coalescencewater filmsoil decreases4.9 nmdroplet-based microfluidicsemulsion filmsfoam filmsvan der Waalsforce microscopyAFM techniquesdrainage timegas decreasesvan der Waals attraction theory
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