Evaporating droplets on oil-wetted surfaces: Suppression of the coffee-stain effect

Yaxing Li, Christian Diddens, Tim Segers, Herman Wijshoff, Michel Versluis, Detlef Lohse*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

12 Citations (Scopus)
1 Downloads (Pure)

Abstract

The evaporation of suspension droplets is the underlying mechanism in many surface-coating and surface-patterning applications. However, the uniformity of the final deposit suffers from the coffee-stain effect caused by contact line pinning. Here, we show that control over particle deposition can be achieved through droplet evaporation on oil-wetted hydrophilic surfaces. We demonstrate by flow visualization, theory, and numerics that the final deposit of the particles is governed by the coupling of the flow field in the evaporating droplet, the movement of its contact line, and the wetting state of the thin film surrounding the droplet. We show that the dynamics of the contact line can be tuned through the addition of a surfactant, thereby controlling the surface energies, which then leads to control over the final particle deposit. We also obtain an analytical expression for the radial velocity profile which reflects the hindering of the evaporation at the rim of the droplet by the nonvolatile oil meniscus, preventing flow toward the contact line, thus suppressing the coffee-stain effect. Finally, we confirm our physical interpretation by numerical simulations that are in qualitative agreement with the experiment.

Original languageEnglish
Pages (from-to)16756-16763
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number29
DOIs
Publication statusPublished - 21 Jul 2020

Keywords

  • coffee-stain effect
  • contact line dynamics
  • evaporation
  • oil-wetted surface

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