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Tag: emulsion

  • Cooking Perfect Cacio e Pepe

    Cooking Perfect Cacio e Pepe

    In cooking, sometimes the simplest recipes are the toughest to master. Cacio e pepe — a classic three-ingredient Italian pasta — is an excellent example. Made properly, the sauce of cheese and black pepper combines with starchy water to coat the pasta in a uniform, cheesy sauce. Or, if you’re me, you wind up with a pasta sauce flecked with stringy clumps of melted cheese. Fortunately for those of us who have yet to master this one, a new research paper has us covered with tips to make the perfect cacio e pepe.

    The key to that elusive silky sauce, they found, is the starch – water – cheese combination. Your water needs just the right amount of starch — they found that between 1 – 4% starch by (cheese) mass worked. If the starch concentration is too low (which can easily happen in pasta water), you’ll get the clumpy cheese mess that so frequently happens in my kitchen. Temperature is also critical; if the water is too hot when it’s added, then it can destabilize the sauce. Check out the pre-print’s Section V for the scientific, supposedly foolproof, recipe. I know I’ll be trying it! (Image credit: O. Kadaksoo; research credit: G. Bartolucci et al. pre-print; via APS News)

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    Toying With Density and Miscibility

    Steve Mould opens this video with a classic physics toy that uses materials of different densities as a brainteaser. Two transparent, immiscible liquids fill the container, along with beads of a couple different densities. When you shake the toy, the liquids emulsify, creating a layer with an intermediate density. As the two liquids separate, the emulsified middle layer disappears, causing the beads (which have densities between that of the two original liquids) to come together.

    The rest of the video describes the challenges of expanding this set-up into three immiscible liquids and four sets of beads. Along the way, Steve had to contend with issues of miscibility, refractive index, and even chemical solvents. It’s amazing, sometimes, what it takes to make a seemingly simple idea into reality. (Video and image credit: S. Mould)

  • Liquid-in-Liquid Printing

    Liquid-in-Liquid Printing

    With 3D printing and other recent technologies, manufacturing options are always in flux. Here, researchers explore a method for printing a liquid inside of a liquid. Their materials are specially chosen such that the injected liquid forms an emulsion at its interface with the surrounding fluid. Once injection ends, the interface forms a wrinkly, viscoelastic skin that acts like a tube. As shown below, the tube is robust enough that it can be pumped full of yellow-dyed water without any loss of structure. (Image and research credit: P. Bazazi et al.)

  • Swapping Emulsions

    Swapping Emulsions

    Chemically speaking, oil and water don’t mix. But with a little fluid mechanical effort, it’s possible to make them an emulsion — a mixture of oil droplets in water or water droplets in oil. Researchers in the Netherlands discovered that the viscosity of these emulsions depends critically on which of those mixtures you have.

    To create their emulsions, the team used a tank consisting of two concentric cylinders. When the inner cylinder spins, it creates a well-understood flow field between the inner and outer cylinder. By varying the ratio of oil to water in the tank, they could explore a wide range of emulsions. They found that the emulsion’s viscosity changed dramatically when the emulsion shifted from oil droplets in water to water droplets in oil, something known as a catastrophic phase inversion. During this switch the viscosity dropped from 3 times higher than pure water to 2 times lower! (Image credit: A_Different_Perspective; research credit: D. Bakhuis et al.; via APS Physics; submitted by Kam-Yung Soh)

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    Ultrasonic Vibrations

    Ultrafast vibrations can break up droplets, mix fluids, and even tear voids in a liquid. Here, the Slow Mo Guys demonstrate each of these using an ultrasonic homogenizer, a piece of lab equipment capable of vibrating 30,000 times a second. At that speed generating cavitation bubbles is trivial, and the flow induced by that cavitation is well-suited to emulsifying otherwise immiscible liquids like oil and water. They also show how a lone droplet gets torn into many microdroplets, a process formally known as atomization. (Image and video credit: The Slow Mo Guys)

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    “Float”

    In “Float” artist Susi Sie uses water and oil to create a whimsical landscape of bubbles and droplets. Coalescence is a major player in the action, though Sie uses some clever time manipulations to make her bubbles and droplets multiply as well. Watching coalescence in reverse feels like seeing mitosis happen before your eyes. (Video and image credit: S. Sie)

  • Emulsions By Condensation

    Emulsions By Condensation

    Oil and water are hard to mix, as any salad dressing aficionado will attest. Technically, the two fluids are immiscible – they won’t mix with one another – but one way around this is to emulsify them by distributing droplets of one in the other. This is usually accomplished by shaking or using sound waves to vibrate the mixture, but the results are typically short-lived. The larger a droplet is, the more gravity affects it, causing the buoyant oil to rise and separate from the water.

    The key to making an emulsion last is creating tiny droplets, which a new study accomplishes energy efficiently through condensation. Instead of mixing the oil and water immediately, the researchers used a surface covered in a mixture of oil and surfactant and cooled it in a humid chamber. As the temperature dropped, water condensed onto the oil and became encapsulated, creating nanoscale emulsion droplets. At such a tiny scale, buoyant forces are unable to overcome surface tension, so the emulsion remains stable for months. (Image credit: MIT, source; research credit: I. Guha et al.; via MIT News)

  • Equatorial Streaming

    Equatorial Streaming

    Here you see a millimeter-sized droplet suspended in a fluid that is more electrically conductive than it. When exposed to a high DC electric field, the suspended drop begins to flatten. A thin rim of fluid extends from the drop’s midplane in an instability called “equatorial streaming”. As seen in the close-up animation, the rim breaks off the droplet into rings, which are themselves broken into micrometer-sized droplets thanks to surface tension. The result is that the original droplet is torn into a cloud of droplets a factor of a thousand smaller. This technique could be great for generating emulsions of immiscible liquids–think vinaigrette dressing but with less shaking! (Image credit: Q. Brosseau and P. Vlahovska, source)

  • Emulsion Impact

    Emulsion Impact

    Emulsions – mixtures of two immiscible fluids – are quite common; the oil and vinegar combination used in many salad dressings is one. The image sequence above shows the first 800 microseconds of the impact of a similarly emulsified droplet. The outer drop, seen on the left, consists of a water/glycerin mixture, and inside the drop are 20 smaller perfluorohexane droplets. These smaller droplets are denser and tend to settle toward the bottom of the outer drop. When the compound droplet hits a solid surface, it spreads in a spectacular starburst pattern that depends on the number and location of interior droplets. You can see a similar impact in motion here. (Image credit: J. Zhang and E. Li; source: C. Josserand and S. Thoroddsen)

  • Plume Stratification

    Plume Stratification

    Clean-up of accidents like the 2010 Deepwater Horizon oil spill can be complicated by what goes on beneath the ocean surface. Variations in temperature and salinity in seawater create stratification, stacked layers of water with differing densities. When less dense layers are on top, the fluid is said to be stably stratified. Since oil is less dense than water, one might assume that buoyancy should make an oil plume should rise straight to the ocean surface. But the presence of additives or surfactants in the oil mixture plume can prevent that. With surfactants present, an oil mixture tends to emulsify, breaking into tiny droplets like a well-mixed salad dressing. Even if the density of the emulsion is smaller than the surrounding fluids, such a plume can get trapped at a density boundary, as seen in the photo above. Researchers report a critical escape height, which depending on the plume’s characteristics and stratification boundary, determines whether a plume escapes or becomes trapped.  (Image credit: R. Camassa et al.)