Physics of Fluids - Publications

Competition between thermal and surfactant-induced Marangoni flow in evaporating sessile droplets

Open Access
Journal of Colloid and Interface Science 622, 892–903 (2022)

Authors

	R.T. van Gaalen
	Herman Wijshoff
	J.G.M. Kuerten
	Christian Diddens

BibTeΧ

@article{VANGAALEN2022892,
title = {Competition between thermal and surfactant-induced Marangoni flow in evaporating sessile droplets},
journal = {Journal of Colloid and Interface Science},
volume = {622},
pages = {892-903},
year = {2022},
issn = {0021-9797},
doi = {https://doi.org/10.1016/j.jcis.2022.04.146},
url = {https://www.sciencedirect.com/science/article/pii/S0021979722007214},
author = {R.T. {van Gaalen} and H.M.A. Wijshoff and J.G.M. Kuerten and C. Diddens},
keywords = {Droplets, Surfactants, Thermal Marangoni flow, Lubrication approximation, Quasi-stationary approach, Solutal Marangoni flow, Evaporation},
abstract = {Hypothesis
Thermal Marangoni flow in evaporating sessile water droplets is much weaker in experiments than predicted theoretically. Often this is attributed to surfactant contamination, but there have not been any in-depth analyses that consider the full fluid and surfactant dynamics. It is expected that more insight into this problem can be gained by using numerical models to analyze the interplay between thermal Marangoni flow and surfactant dynamics in terms of dimensionless parameters.
Simulations
Two numerical models are implemented: one dynamic model based on lubrication theory and one quasi-stationary model, that allows for arbitrary contact angles.
Findings
It is found that insoluble surfactants can suppress the thermal Marangoni flow if their concentration is sufficiently large and evaporation and diffusion are sufficiently slow. Soluble surfactants, however, either reduce or increase the interfacial velocity, depending on their sorption kinetics. Furthermore, insoluble surfactant concentrations that cause an order 0.1% surface tension reduction are sufficient to reduce the spatially averaged tangential flow velocity at the interface by a factor 100. For larger contact angles and smaller droplets this required concentration is larger (typically <1% surface tension reduction). The numerical models are mutually validated by comparing their results in cases where both are valid.}
}