title: Self-wrapping of an ouzo drop induced by evaporation on a superamphiphobic surface.
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.
authors.affiliation: Physics of Fluids Group, Department of Science and Technology, Mesa+ Institute, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands. h.tan@utwente.nl d.lohse@utwente.nl.
authors.forename: Huanshu
authors.identifier: http://orcid.org/0000-0002-2474-4843
authors.initials: H
authors.lastname: Tan
authors.affiliation: Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Christian
authors.initials: C
authors.lastname: Diddens
authors.affiliation: Physics of Fluids Group, Department of Science and Technology, Mesa+ Institute, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands. h.tan@utwente.nl d.lohse@utwente.nl.
authors.forename: Michel
authors.identifier: http://orcid.org/0000-0002-2296-1860
authors.initials: M
authors.lastname: Versluis
authors.affiliation: Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Butt
authors.affiliation: Physics of Fluids Group, Department of Science and Technology, Mesa+ Institute, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands. h.tan@utwente.nl d.lohse@utwente.nl and Max Planck Institute for Dynamics and Self-Organization, 37077 Gottingen, Germany.
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse
authors.affiliation: Physics of Fluids Group, Department of Science and Technology, Mesa+ Institute, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands. h.tan@utwente.nl d.lohse@utwente.nl and Soft Matter & Interfaces Group, School of Engineering, RMIT University, Melbourne, VIC 3001, Australia. xuehua.zhang@rmit.edu.au.
authors.forename: Xuehua
authors.identifier: http://orcid.org/0000-0001-6093-5324
authors.initials: X
authors.lastname: Zhang