Universal nanodroplet branches from confining the Ouzo effect

Abstract

We report the self-organization of universal branching patterns of oil nanodroplets under the Ouzo effect [Vitale S, Katz J (2003) 19:4105-4110]-a phenomenon in which spontaneous droplet formation occurs upon dilution of an organic solution of oil with water. The mixing of the organic and aqueous phases is confined under a quasi-2D geometry. In a manner analogous to the ramification of ground stream networks [Devauchelle O, Petroff AP, Seybold HF, Rothman DH (2012) 109: 20832-20836 and Cohen Y, et al. (2015) 112:14132-14137] but on a scale 10 orders of magnitude smaller, the angles between the droplet branches are seen to exhibit remarkable universality, with a value around 74° ± 2°, independent of the various control parameters of the process. Numerical simulations reveal that these nanodroplet branching patterns are governed by the interplay between the local concentration gradient, diffusion, and collective interactions. We further demonstrate the ability of the local concentration gradient to drive autonomous motion of colloidal particles in the highly confined space, and the possibility of using the nucleated nanodroplets for nanoextraction of a hydrophobic solute. The understanding obtained from this work provides a basis for quantitatively understanding the complex dynamical aspects associated with the Ouzo effect. We expect that this will facilitate improved control in nanodroplet formation for many applications, spanning from the preparation of pharmaceutical polymeric carriers, to the formulation of cosmetics and insecticides, to the fabrication of nanostructured materials, to the concentration and separation of trace analytes in liquid-liquid microextraction.

Functional Femtoliter Droplets for Ultrafast Nanoextraction and Supersensitive Online Microanalysis

“…These droplets exhibit huge surface‐to‐volume ratio and excellent stability with time even in contact with a flow, thanks to the pinning effect on the three‐phase boundary . We refer to liquid–liquid extraction based on femtoliter surface droplets as nanoextraction, by which the solute can be enriched into droplets directly from the flow of an aqueous solution. The stability of these droplets on the substrate is a unique feature that can be explored to impart multipurpose functionalities in a single droplet platform through reactions with a reactive component in droplets.…”

Sequential Evaporation–Induced Formation of Polymeric Surface Microdents via Ouzo Effect

“…Recently, “Ouzo effect” was applied to fabricate micro/nanostructures, such as micro/nanodroplets, micro/nanoparticles, and micro/nanolenses 14b,18. “Ouzo effect” is referred to the nucleation of tiny oil droplets after water is added into a Greek drink of Ouzo .…”

“…Instead of adding water into ethanol–oil mixture, evaporation of ethanol in an Ouzo drop can also trigger Ouzo effect . The Ouzo effect provides an efficient approach to produce microdroplets that in turn serve as templates for the formation of micro/nanostructures . Compared with the existed methods, micro/nanostructure fabrication via Ouzo effect can be conducted without any special setups and complex operations.…”

Compositional ripening of particle-stabilized drops in a three-liquid system

“…Nucleation and growth of oil droplets follows; this phenomena and associated self assembly are currently the subject of intense research. [26][27][28] The late stage coarsening of the oil droplets is driven by Ostwald ripening which might be expected to lead to macroscopic phase separation. The 'Ouzo effect' occurs in a narrow region in between the binodal and spinodal lines in which metastability is possible.…”