Shedding light on the formation and stability of mesostructures in ternary “Ouzo” mixtures

Iglicki, Déborah; Goubault, Clément; Mahamoud, Mouktar Nour; Chevance, Soizic; Gauffre, Fabienne

doi:10.1016/j.jcis.2022.11.060

Cited by 6 publications

(20 citation statements)

References 42 publications

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“…4 Several mechanisms of formation and growth for ouzo emulsions have been hypothesized, and these follow the destabilization methods of classical emulsions: diffusion-driven processes (ripening), or combination events (coalescence). 9,12 Here, no coalescence events were observed under any conditions, despite previously establishing that such events are visible by this technique at comparable time and length scales 71 However, droplet growth was consistently logistic in time, which is contrary to classical ripening mechanisms, wherein r 3 is linear in time. 73 Thus, our findings strongly suggest that the predominant mechanism here is the diffusion-driven growth of initial nuclei, but not Ostwald ripening.…”

Section: ■ Results and Discussionmentioning

confidence: 62%

“…72 It is notable that coalescence was not observed for this system of emulsions, as it lends credence to hypotheses that ripening-type behaviors dominate the evolution of such emulsions in time. 72,76 Further, as is the nature of microscopy, quantitative evaluation can be made from direct observations as compared to the suite of parallel techniques which must otherwise be employed to glean similar information. 76…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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

et al. 2023

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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.

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Section: ■ Results and Discussionmentioning

confidence: 62%

Section: ■ Results and Discussionmentioning

confidence: 99%

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

et al. 2023

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“…The whitening of the ouzo or pastis drinks when water is added may be just a solubility limit when the ethanol content goes below 30%. These systems are often referred to as surfactantless microemulsions, − although this can be misleading because they differ significantly from traditional microemulsions formation, thus adding even more confusion to the terminology.…”

Section: Emulsions and Microemulsions Have Quite Different Microstruc...mentioning

confidence: 99%

Review on Some Confusion Produced by the Bicontinuous Microemulsion Terminology and Its Domains Microcurvature: A Simple Spatiotemporal Model at Optimum Formulation of Surfactant-Oil-Water Systems

et al. 2023

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Fundamental studies have improved understanding of molecular-level properties and behavior in surfactant-oil-water (SOW) systems at equilibrium and under nonequilibrium conditions. However, confusion persists regarding the terms “microemulsion” and “curvature” in these systems. Microemulsion refers to a single-phase system that does not contain distinct oil or water droplets but at least four different structures with globular domains of nanometer size and sometimes arbitrary shape. The significance of “curvature” in such systems is unclear. At high surfactant concentrations (typically 30 wt % or more), a single phase zone has been identified in which complex molecular arrangements may result in light scattering. As surfactant concentration decreases, the single phase is referred to as a bicontinuous microemulsion, known as the middle phase in a Winsor III triphasic system. Its structure has been described as involving simple or multiple surfactant films surrounding more or less elongated excess oil and water phase globules. In cases where the system separates into two or three phases, known as Winsor I or II systems, one of the phases, containing most of the surfactant, is also confusedly referred to as the microemulsion. In this surfactant-rich phase, the only curved objects are micellar size structures that are soluble in the system and have no real interface but rather exchange surfactant molecules with the external liquid phase at an ultrafast pace. The use of the term “curvature” in the context of these complex microemulsion systems is confusing, particularly when applied to merged nanometer-size globular or percolating domains. In this work, we discuss the terms “microemulsion” and “curvature”, and the most simple four-dimensional spatiotemporal model is proposed concerning SOW equilibrated systems near the optimum formulation. This model explains the motion of surfactant molecules due to Brownian movement, which is a quick and arbitrary thermal fluctuation, and limited to a short distance. The resulting observation and behavior will be an average in time and in space, leading to a permanent change in the local microcurvature of the aggregate, thus changing the average from micelle-like to inverse micelle-like order over an extremely short time. The term “microcurvature” is used to explain the small variations of globule size and indicates a close-to-zero mean curvature of the surfactant-containing film surface shape.

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“…Among different methods of producing nanocapsules, nanoprecipitation has recently emerged as a versatile technique to fabricate nanocapsules made of various components. − At the core of nanoprecipitation lies a hydrophobic solute dissolved in a polar organic solvent which is mixed with a nonsolvent of the solute (typically water). The related ternary phase diagram consists of a one-phase region where the existence of surfactant-free thermodynamically stable microemulsions has been reported, , a two-phase region where rapid precipitation and demixing of the hydrophobic species occurs by spinodal decomposition, and a metastable nanoprecipitation region known as the Ouzo domain. , Mixing of the solute solution with the non-solvent while maintaining concentrations bounded by the Ouzo domain induces nucleation of the solute into nanometric droplets that are aggregated. These droplets coarsen with time and can settle into a metastable emulsion state having diameters of ∼1 μm or less depending on the preparation details. , …”

Section: Introductionmentioning

confidence: 99%

“…While microfluidic-based nanoprecipitation to produce nanoparticles of various molecular architectures has been dealt with, − few studies have reported on microfluidic co-precipitation of core and shell materials for the continuous production of nanocapsules. Those that do take an empirical approach to nanoparticle/nanocapsule fabrication in terms of precursor concentrations, rather than quantitatively relying on ternary phase diagrams eliminating the guesswork in approaching the Ouzo phenomenon. , Additionally, often polymers soluble in organic solvents are precipitated , so that use of water-soluble polymers would expand the palate and enhance the stability of nanocapsules in water-based dispersions.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Oil/Polymer Nanocapsule Size via Phase Diagram-Guided Microfluidic Coprecipitation

2023

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Flow-based nanoprecipitation of different solutes via rapid mixing of two miscible liquids is a scalable strategy for manufacturing nanoparticles with various shapes and morphologies. Controlling the size of nanoparticles in flow-based nanoprecipitation, however, is often left to empirical variations in the flow rate ratios or the total flow rate of the two streams. In this work, we investigate the coprecipitations of oil and polymer to form nanocapsules via the Ouzo effect using glass capillary microfluidics across a range of mixing conditions. In the range of flow rates studied, the two streams mix convectively in microvortices formed at the junction of the two stream inlets. Using computational fluid dynamics simulations and glass capillary microfluidic nanoprecipitation, we establish a relationship between the precipitation conditions occurring experimentally in situ and the location on the ternary Ouzo phase diagram where precipitation is taking place. We find that a key variable in the resulting average diameter of the fabricated capsules is the degree of supersaturation experienced by both the oil and the polymer in the vortex zone of the device, showing a strong correlation between the two values. The control over the nanocapsule size by varying the extent of supersaturation of both precipitants is demonstrated by using two oils having distinct phase diagrams. This work provides a systematic approach to controlling the size of nanoparticles fabricated via continuous nanoprecipitation by linking the in situ flow conditions to ternary phase diagram behavior, enabling accurate control over nanocapsule size.

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Shedding light on the formation and stability of mesostructures in ternary “Ouzo” mixtures

Cited by 6 publications

References 42 publications

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

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

Review on Some Confusion Produced by the Bicontinuous Microemulsion Terminology and Its Domains Microcurvature: A Simple Spatiotemporal Model at Optimum Formulation of Surfactant-Oil-Water Systems

Modulation of Oil/Polymer Nanocapsule Size via Phase Diagram-Guided Microfluidic Coprecipitation

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