Ouzo Effect Examined at the Nanoscale via Direct Observation of Droplet Nucleation and Morphology

Abstract

Herein, we present the direct observation via liquidphase transmission electron microscopy (LPTEM) of the nucleation and growth pathways of structures formed by the so-called "ouzo effect", which is a classic example of surfactant-free, spontaneous emulsification. Such liquid−liquid phase separation occurs in ternary systems with an appropriate cosolvent such that the addition of the third component extracts the cosolvent and makes the other component insoluble. Such droplets are homogeneously sized, stable, and require minimal energy to disperse compared to conventional emulsification methods. Thus, ouzo precipitation processes are an attractive, straightforward, and energy-efficient technique for preparing dispersions, especially those made on an industrial scale. While this process and the resulting emulsions have been studied by numerous indirect techniques (e.g., X-ray and light scattering), direct observation of such structures and their formation at the nanoscale has remained elusive. Here, we employed the nascent technique of LPTEM to simultaneously evaluate droplet growth and nanostructure. Observation of such emulsification and its rate dependence is a promising indication that similar LPTEM methodologies may be used to investigate emulsion formation and kinetics.

Controlling Nano-to-Microscale Multilevel Architecture in Polymeric Microfibers through Polymerization-Induced Spontaneous Phase Separation

“…To achieve this task, we chose a system that consists of the polyamine trimethylolpropane tris[poly(propylene glycol), amine terminated] ether (Jeffamine T-403) and glutaraldehyde (GA) in water, taking advantage of the high reactivity of GA with amine groups. Figure 1a and Movie S1 demonstrate the self-emulsification process, also known as the "Ouzo Effect" [35,36], at the interface of a droplet of Jeffamine T-403 and a droplet of GA in water, taken using bright-field microscopy. Upon the formation of an interface, the Jeffamine T-403 phase penetrates the GA/water phase, and microdroplets are vigorously produced.…”

Research advances in Zein-based nano-delivery systems

“…The basic principle of this method is to prepare nanoparticles by changing the polarity of the solvent around Zein. In this process, the proportion of organic solvent is reduced, the solubility of Zein is reduced, and the nanoparticles are self-assembled (67,68). The unique solubility of Zein makes it to self-assemble into nucleus-like particles in the antisolvent and the nucleus can grow further by trapping non-aggregated solute molecules, but the particle growth will stop when the concentration of Zein in the solvent is too low (69)(70)(71).…”

Self-lubricating drops

“…Therefore, minor concentration fluctuations can induce component nucleation, resulting in the formation of liquid phase at a microscopic length scale. This thermodynamic process leads to the creation of numerous sub-micro or microdroplets that are homogeneously sized and stable, with minimal energy input required [55].…”