Absorption of surfactant-laden droplets into porous media: A numerical study

R. T. van Gaalen, C. Diddens, D. P. Siregar, H. M.A. Wijshoff, J. G.M. Kuerten*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

Hypothesis: Droplets can absorb into permeable substrates due to capillarity. It is hypothesized that the contact line dynamics influence this process and that an unpinned contact line results in slower absorption than a pinned contact line, since the contact area between the droplet and the substrate will decrease over time for the former. Furthermore, it is expected that surfactants can be used to accelerate the absorption. Simulations: Lubrication theory is employed to model the droplet and Darcy's law is combined with the conservation law of mass to describe the absorption dynamics. For the surfactant transport, several convection-diffusion-adsorption equations are solved. Findings: It is found that moving contact lines result in a parabola-shaped wetted area and a slower absorption and a deeper penetration depth than pinned contact lines. The evolution of the penetration depth was quantitatively validated by comparison with two experimental studies from literature. Surfactants were shown to accelerate the absorption process, but only if their adsorption kinetics are slow compared to the absorption. Otherwise, all surfactant adsorbs onto the pore walls before reaching the wetting front, resulting in the same absorption rate as without surfactants. This behavior agrees with both experimental and analytical literature.

Original languageEnglish
Pages (from-to)149-159
Number of pages11
JournalJournal of colloid and interface science
Volume597
DOIs
Publication statusPublished - Sep 2021

Keywords

  • UT-Hybrid-D
  • Darcy's law
  • Droplets
  • Lubrication approximation
  • Porous media
  • Soluble surfactants
  • Absorption

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