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Self-wrapping of an ouzo drop induced by evaporation on a superamphiphobic surface

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Abstract

Evaporation of multi-component drops is crucial to various technologies and has numerous potential applications because of its ubiquity in nature. Superamphiphobic surfaces, which are both superhydrophobic and superoleophobic, can give a low wettability not only for water drops but also for oil drops. In this paper, we experimentally, numerically and theoretically investigate the evaporation process of millimetric sessile ouzo drops (a transparent mixture of water, ethanol, and trans-anethole) with low wettability on a superamphiphobic surface. The evaporation-triggered ouzo effect, i.e. the spontaneous emulsification of oil microdroplets below a specific ethanol concentration, preferentially occurs at the apex of the drop due to the evaporation flux distribution and volatility difference between water and ethanol. This observation is also reproduced by numerical simulations. The volume decrease of the ouzo drop is characterized by two distinct slopes. The initial steep slope is dominantly caused by the evaporation of ethanol, followed by the slower evaporation of water. At later stages, thanks to Marangoni forces the oil wraps around the drop and an oil shell forms. We propose an approximate diffusion model for the drying characteristics, which predicts the evaporation of the drops in agreement with experiment and numerical simulation results. This work provides an advanced understanding of the evaporation process of ouzo (multi-component) drops.

Graphical abstract: Self-wrapping of an ouzo drop induced by evaporation on a superamphiphobic surface

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Publication details

The article was received on 22 Dec 2016, accepted on 05 Mar 2017, published on 08 Mar 2017 and first published online on 08 Mar 2017


Article type: Paper
DOI: 10.1039/C6SM02860H
Citation: Soft Matter, 2017, Advance Article
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    Self-wrapping of an ouzo drop induced by evaporation on a superamphiphobic surface

    H. Tan, C. Diddens, M. Versluis, H. Butt, D. Lohse and X. Zhang, Soft Matter, 2017, Advance Article , DOI: 10.1039/C6SM02860H

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