  Multicomponent liquid drops in a host liquid are very relevant in various
technological applications. Their dissolution or growth dynamics is complex.
Differences in solubility between the drop components combined with the solutal
Marangoni effect and natural convections contribute to this complexity, which
can be even further increased in combination with the ouzo effect, i.e., the
spontaneous nucleation of microdroplets due to composition-dependent
miscibilities in a ternary system. The quantitive understanding of this
combined process is important for applications in industry, particularly for
modern liquid-liquid microextraction processes. In this work, as a model
system, we experimentally and theoretically explore water/ethanol drops
dissolving in anethole oil. During the dissolution, we observed two types of
microdroplets nucleation, namely water microdroplet nucleation in the
surrounding oil at drop midheight and oil microdroplet nucleation in the
aqueous drop, again at midheight. The nucleated oil microdroplets are driven by
Marangoni flows inside the aqueous drop and evolve into microdroplets rings. A
one-dimensional multiphase and multicomponent diffusion model in combination
with thermodynamical equilibrium theory is proposed to predict the behavior of
spontaneous emulsification, i.e. the microdroplet nucleation, that is triggered
by diffusion. A scale analysis together with experimental investigations of the
fluid dynamics of the system reveals that both the solutal Marangoni flow
inside the drop and the buoyancy-driven flow in the host liquid influence the
diffusion-triggered emulsification process. Our work provides a physical
understanding of the microdroplet nucleation by dissolution of a multicomponent
drop in a host liquid.
