  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.
