Physics of Fluids - Publications

The evaporation of surfactant-laden droplets: A comparison between contact line models

Open Access
Journal of Colloid and Interface Science 579, 888 – 897 (2020)

Authors

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

BibTeΧ

@article{VANGAALEN2020888,
title = "The evaporation of surfactant-laden droplets: A comparison between contact line models",
journal = "Journal of Colloid and Interface Science",
volume = "579",
pages = "888 - 897",
year = "2020",
issn = "0021-9797",
doi = "https://doi.org/10.1016/j.jcis.2020.06.099",
url = "http://www.sciencedirect.com/science/article/pii/S0021979720308444",
author = "R.T. {van Gaalen} and C. Diddens and H.M.A. Wijshoff and J.G.M. Kuerten",
keywords = "Droplets, Insoluble surfactants, Evaporation, Lubrication approximation, Moving contact lines",
abstract = "Hypothesis
There are two different sharp-interface models for moving contact lines: slip models and precursor film models. While both models predict a mostly constant contact angle during the evaporation of pure droplets, it is expected that they behave differently when surfactants are present, because of the inherent dissimilarities in their respective interface definitions.
Simulations
Both contact line models are numerically implemented using lubrication theory to analyze evaporating droplets. A convection-diffusion equation is implemented for insoluble surfactants. For pure droplets the models are compared with experiments performed by Nguyen et al. (2012).
Findings
The two contact line models show results comparable to the experiments with pure droplets. If insoluble surfactants are present, the slip model increasingly shows pinning-like behavior as the initial surfactant concentration is increased. This ‘quasi-pinning’ is found to be consistent with experimental results in literature. The precursor film model, in contrast, shows no significant change when surfactants are added. This lack of change is a result of surfactant flowing from the droplet into the precursor film and vice versa. While suggesting potential solutions to this unphysical behavior, it is concluded that in the context of surfactants, slip models are preferable over precursor film models given the current state of the art."
}