Immiscible surfactant droplets on thin liquid films: Spreading dynamics, subphase expulsion and oscillatory instabilities

[Display omitted] ► Immiscible surfactant droplets on thin liquid (‘subphase’) films are studied. ► The ‘near-field’ two-phase flow dynamics are characterized experimentally. ► The ‘far-field’ fingering instability is preceded by subphase trapping and release. ► Subphase expulsion is accompanied by...

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Bibliographic Details
Published in:Journal of colloid and interface science 2011-12, Vol.364 (2), p.519-529
Main Authors: Sinz, David K.N., Hanyak, Myroslava, Darhuber, Anton A.
Format: Article
Language:English
Subjects:
Chemistry
Deposition
Droplets
Exact sciences and technology
General and physical chemistry
Immiscible liquids
Instability
Liquid films
Liquids
Marangoni stresses
Mathematical analysis
Microscopy, Fluorescence
Oscillatory instability
Solubility
Spreading
Surface physical chemistry
Surface-Active Agents - chemistry
Surfactant spreading
Surfactants
Thin liquid films
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Summary:[Display omitted] ► Immiscible surfactant droplets on thin liquid (‘subphase’) films are studied. ► The ‘near-field’ two-phase flow dynamics are characterized experimentally. ► The ‘far-field’ fingering instability is preceded by subphase trapping and release. ► Subphase expulsion is accompanied by an oscillatory contact line instability. After deposition of immiscible, surface-active liquids on thin liquid films of higher surface tension, Marangoni stresses thin the liquid film around the surfactant droplet and induce a radially outward flow. We observed an oscillatory instability, caused by temporary trapping and subsequent release of subphase liquid from underneath the surfactant droplet. Height profiles of the thin liquid films were monitored using optical interferometry and fluorescence microscopy, both in the vicinity of the deposited surfactant droplet and at larger distances. Numerical calculations based on the lubrication approximation are compared to the experimental results. Good agreement between the experimental and calculated far-field dynamics and values of the spreading exponents was found.
ISSN:0021-9797
1095-7103
DOI:10.1016/j.jcis.2011.08.055