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A classic example is milk, (7) an emulsion with fat globules dispersed in an aqueous phase, which usually requires high stability of fat particles to ensure a long shelf life and increase consumer satisfaction. (6) Understanding emulsion stability is important for both materials processing and shelf life. (4) These w/o emulsions not only cause the corrosion of pipelines and equipment but also reduce the recovery rate of the oil significantly.Įmulsions are also frequently encountered in our daily life, such as in the food industry (5) and pharmaceuticals. Interfacially active asphaltenes from asphalt rocks are major components of crude oil (3) and have been proven to stabilize the w/o emulsion during the production of oils. (2) Another example is asphaltene-stabilized w/o emulsions found in oil recovery. Water entrained in fuel is detrimental to engine life because it causes rust and corrosion of various components of the system hence, coalescing filters are used to remove water from the diesel prior to injection into the engine. (1) Similarly, w/o emulsions are undesirable in automobile engines and heavy machinery operating on diesel fuel.
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According to International Maritime Organization regulations, bilgewater with more than 15 mg/L of oil poses an environmental hazard and cannot be discharged into the ocean prior to an onboard treatment step to separate the emulsion. This oily wastewater consists of micrometer-sized diesel fuel or oil droplets, typically from heavy machinery aboard the ship, stabilized by various detergents used aboard the ship. One such example of an o/w emulsion is bilgewater stored aboard ships.
![thessa neef thessa neef](https://pbs.twimg.com/media/Buwl-EaCQAErcu1.jpg)
Such chemically stabilized emulsions can be challenging to separate, particularly when formed by agitation or mixing. Both oil-in-water (o/w) and water-in-oil emulsions (w/o) are possible and usually require surface-active molecules or surfactants to chemically stabilize the interface. Finally, recent experiments using a hydrodynamic Stokes trap to investigate the impact of interfacial surfactant transport, or “mobility”, and the phase containing the surfactant on film drainage and droplet coalescence will be presented.Įmulsions, which are dispersions of one fluid phase in another, are ubiquitous in technological and environmental applications. Furthermore, recent studies are highlighted showing the different IFT decay rates and its long-time equilibrium value depending on the phase into which the surfactant is added, particularly on the microscale. Next, equilibrium isotherm models as well as dynamic diffusion and kinetic equations are discussed to characterize the surfactant and the time scale of the surfactant transport. In this feature article, the measurement techniques for dynamic IFT are first reviewed due to their importance in characterizing surfactant transport, with a specific focus on macroscale versus microscale techniques. Other key factors, such as the viscosity ratio between the dispersed and continuous phases and Marangoni stress, will also have an impact on surfactant transport and therefore the coalescence and emulsion stability. For example, the rate of IFT decay depends on the phase in which the surfactant is added (dispersed vs continuous) due in part to differences in the near-surface depletion depth. Many studies have investigated the surfactant transport behavior that leads to corresponding time-dependent lowering of the IFT. One important factor that stabilizes emulsions is the lowered interfacial tension (IFT) between the fluid phases due to surfactants, inhibiting the coalescence. Liquid–liquid emulsion systems are usually stabilized by additives, known as surfactants, which can be observed in various environments and applications such as oily bilgewater, water-entrained diesel fuel, oil production, food processing, cosmetics, and pharmaceuticals.