Émulsion

Résumé

thumb|A. Deux liquides non-miscibles. B. Émulsion instable. C. Les deux liquides se séparent progressivement. D. Un tensioactif (ou agent de surface) entoure les gouttelettes d'un des liquides, stabilisant l'émulsion. Une émulsion est un mélange hétérogène de deux substances liquides non miscibles, l'une étant dispersée sous forme de petites gouttelettes dans l'autre. Ce sont toujours deux liquides qui ne se mélangent pas spontanément (non miscibles), comme l’eau et l’huile, mais qui vont grâce à des opérations spécifiques (agitation, mélange, ajout de quelques principes actifs) adopter un aspect macroscopiquement homogène, mais microscopiquement hétérogène. L'une des substances sera dispersée dans la seconde substance sous forme de gouttelettes. Le mélange reste stable grâce à un troisième ingrédient appelé « émulsifiant » (vitesse ou cinétique d'évolution du mélange quasi nulle). Une mousse ressemble à une émulsion mais la seconde substance est un gaz (au lieu d'un liqui

Source officielle

https://fr.wikipedia.org/wiki/%C3%89mulsion

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Miniaturization has been a driving force in many areas of science and technology, most notably in the electronics industry. Droplet-based microfluidics, a methode to produce emulsion drops in a controlled way and at high-throughputs, enables the miniaturization and automation of biological and chemical experiments. Each emulsion drop is used as a closed reaction vessel, enabling the performance of thousands of experiments per second, at throughputs traditional technologies cannot meet. Droplet-based microfluidics is a driving technology in the advances of genomics, proteomics, single-cell analysis, high-throughput screening, and diagnostics. Crucial for using emulsion drops as reaction vessels is that they do not break and that they are tight, not allowing material to be exchanged between drops. To prevent emulsion drops from coalescing, they can be stabilized with surfactants. They adsorb at the liquid-liquid interface, lower the interfacial tension, and add steric stability. For most drop-based biological assays, aqueous drops are dispersed in fluorinated oils. These drops are stabilized with fluorinated surfactants, composed of two perfluoropolyether blocks linked to a polyethylene glycol (PEG) block. These surfactants impart good stability to emulsion drops but can contribute to an exchange of reagents between them. In this thesis, we studied how the composition of fluorinated surfactants influences the prop- erties of emulsion drops. Therefore we synthesized different fluorinated surfactants and varied the length of the hydrophilic block and the number of hydrophobic blocks a surfactant contains. We show that the mechanical and thermal stability of single emulsion drops strongly depends on the composition of the surfactants. The stability of drops stabilized with triblock copolymers inversely scales with the interfacial tension, where as the stability of drops coated with diblock copolymers scales with the surfactant packing density. To investigate the transport of reagents across oil phases, we employ water-oil-water double emulsions as templates. We show that the leakage, resulting in cross-contamination, is mainly caused by emulsion drops with sizes around 100 nm that spontaneously form at the water-oil interface. These drops result in leakage of larger objects such as plasmids with 11â000 base pairs or 100 nm polystyrene beads. We show that the leakage can be reduced by an order of magnitude if surfactants that only moderately lower the interfacial tension are used to stabilize double emulsions or if the shell thickness of double emul- sions is reduced to values similar to the diameter of the spontaneously forming drops. Lastly, we developed novel types of surfactants containing a catechol group in the hydrophilic block, that can be ionically cross-linked at the interface of a drop, creating a viscoelastic shell. We demon- strate that by cross-linking the surfactant at the drop interface, we create capsules that show high mechanical stability, and are impermeable to encapsulants. Leveraging their stickiness, we demonstrate that these capsules, if densely packed, can be printed into 3D structures.

EPFL2019

Chargement

Assessment of solar panel efficiency under realistic conditions

Raluca Anisie

2014

Chargement

Emulsion drops with defined sizes are frequently used to conduct chemical reactions on picoliter scales or as templates to form microparticles. Despite tremendous progress that has been achieved in the production of emulsions, the high throughput formation of drops with well-defined diameters of a few micrometers remains challenging. Drops of this size, however, are in high demand, for example, for many pharmaceutical, food, and materials science applications. Here, we introduce a scalable method to produce water-in-oil emulsion drops possessing controlled diameters of just a few micrometers: We fabricate calibrated aerosol drops and transfer them into an oil bath to form stable emulsions at rates up to 480 mu L min(-1) of the dispersed phase. We demonstrate that the emulsification is thermodynamically driven such that design principles to successfully form emulsions can easily be deduced. We employ these emulsion drops as templates to form well-defined micrometer-sized hydrogel spheres and capsules.

AMER CHEMICAL SOC2022

Chargement

EPFL2019