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Updated: May 24, 2026

Microtensiometer for Confocal Microscopy Visualization of Dynamic Interfaces
Published on: September 9, 2022
Surfactant-induced Marangoni eddies alter the coffee-rings of evaporating colloidal drops
Tim Still1, Peter J Yunker, Arjun G Yodh
1Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States. timstill@seas.upenn.edu
Abstract:
The influence of the small ionic surfactant sodium dodecyl sulfate (SDS) on the evaporation of drying colloidal droplets is quantitatively investigated. The addition of SDS leads to a significantly more uniform deposition of colloidal particles after evaporation (i.e., the so-called "coffee-ring effect" is dramatically altered). We understand this phenomenon in the context of circulating radial Marangoni flows induced by the variation of SDS concentration along the air-water interface. Video microscopy permits the direct visualization of the colloidal particles involved in these flows, revealing a surprisingly stable "Marangoni eddy" that prevents particle deposition at the drop perimeter.
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