FYFD

Tag: rheology

  • Inside Fondue

    Inside Fondue

    Cheese fondue is a complex – and delicious – Swiss delicacy. The perfect fondue requires the right mix of ingredients and preparation to get the rheology – the flow character – just right. Fondue is a colloid, a fluid containing a mixture of suspended insoluble particles.

    The major components, rheologically speaking, are fat globules and casein proteins from the cheese, ethanol from the wine, and some added starch. Left on their own, the fat and casein tend to separate, something that’s sure to ruin the fondue. Adding the right amount of starch prevents that separation and keeps the fondue together. The viscosity of fondue is very important as well. If it’s too runny or too gummy, the mouthfeel will be wrong and it may not stick to the bread when dipped. Adding wine decreases the viscosity.

    All in all, the quality and perception of a good fondue relies heavily on its rheological character. Without the right proportion of ingredients to set the perfect viscous and chemical character, the dish literally comes apart. (Image credit: Pixabay; research credit and submission: P. Bertsch et al.)

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    Bioinspiration, Underwater Sniffing, and Mixing Toothpaste

    In this month’s FYFD/JFM video, we explore some intersections between the animal kingdom and our own lives. Learn about designing better buildings with inspiration from termites; see the fascinating superpower of the star-nosed mole; and learn what goes into products like the toothpaste you (hopefully) use daily. All this and more in the latest video! Missed one of our previous ones? Good news: we’ve got you covered. (Image and video credit: N. Sharp and T. Crawford)

  • Replacing Kalliroscope

    Replacing Kalliroscope

    Although you may not recognize the name, you’ve probably seen Kalliroscope (top image), a pearlescent fluid that creates beautiful flow patterns when swirled. This rheoscopic fluid was invented in the mid-1960s by artist Paul Matisse and, over the following decades, became a staple of flow visualization techniques. Kalliroscope contained a suspension of crystalline guanine. Since the crystals were asymmetric, they would orient themselves depending on the flow and, from there, scatter light, creating the beautiful pearlescent effect seen above.

    Unfortunately for researchers, the production of guanine crystals was expensive and difficult. The cosmetics industry was their main consumer and over time, they moved toward mica and other cheaper mineral alternatives. The company that produced Kalliroscope gave up production in 2014, leaving researchers scrambling for a suitable alternative.

    One contender for a new standard rheoscopic fluid is based on shaving cream. By diluting shaving cream 20:1 with water, researchers are able to extract stearic acid crystals, which form an admirable alternative to Kalliroscope (middle collage). Like Kalliroscope, the resulting fluid is pearlescent and reveals flow features well (bottom two images). Stearic acid crystals are also closer in density to water than guanine, so the fluid remains in suspension far better than Kalliroscope. Plus, the best shaving cream is cheap and widely available, meaning that this is a DIY project just about anyone can do! (Image credits: Kalliroscope – P. Matisse; other images – D. Borrero-Echeverry et al.; research credit: D. Borrero-Echeverry et al.)

  • Wild Extrusions

    Wild Extrusions

    In their continuing quest to squish all the things, the Hydraulic Press channel recently debuted a tool with a series of small holes they can extrude various substances through. The video features several great extrusions, including oobleck, temperature-sensitive putty, cheese, and crayons (above). Most of these substances are non-Newtonian fluids of some kind, and the extreme forces the hydraulic press causes makes for some wild effects.

    Many of the substances, including the crayons above, display signs of the sharkskin instability in their rough edges. When non-Newtonian fluids (like the paraffin wax in crayons) get extruded quickly, the material at the edges experiences a lot of friction and shear when trying to flow along the wall of the hole. When the fluid finally breaks free, the region along the outside accelerates to match the speed of fluid at the center of the extrusion. Parts of the mixture may resist that acceleration, resulting in the uneven edges seen above. (Video credit: Hydraulic Press Channel; GIF via Colossal)

  • Bioluminescent Plankton

    Bioluminescent Plankton

    In nutrient-rich marine waters, dinoflagellates, a type of plankton, can flourish. At night, these tiny organisms are responsible for incredible blue light displays in the water. The dinoflagellates produce two chemicals – luciferase and luciferin – that, when combined, produce a distinctive blue glow. The plankton use this as a defense against predators, creating a flash of blue light when triggered by the shear stress of something swimming nearby. The dinoflagellates respond to any sudden application of shear stress this way, so they glow not only for predators, but for any disturbance – mobula rays (above), sea lions, boats, or even just a hand splashing in the water. In person, the experience feels downright magical. I had the opportunity to experience bioluminescence in the Galapagos last year. The light from the dinoflagellates is incredibly difficult to film because it can be so dim, but as the BBC demonstrates, it’s well worth the effort it takes to capture. (Image credit: BBC from Blue Planet II and Attenborough’s Life That Glows; video credit: BBC Earth)

  • Hagfish Crash

    Hagfish Crash

    Last week a flatbed truck in Oregon overturned and released 3400 kilograms of live hagfish on the highway and nearby cars. Hagfish are eel-like fish known for their impressive slime production. When threatened, the hagfish produce mucins that, when combined with water, form an extremely viscoelastic mucus. As it’s stretched, the mucus thickens and becomes more viscous. Normally, hagfish use this property to clog the gills of fish trying to eat them. The slime is weak, however, to shearing; hagfish actually tie themselves in knots to slide the slime off when there’s too much of it. The Oregon Department of Transportation managed to clear the road of mucus (and hagfish) using bulldozers and fire hoses, but it did take them several hours. For more photos and videos from the incident, check out Gizmodo and the Oregon State Police Twitter feed. (Image credit: Oregon State Police; via Gizmodo)

  • Are Cats a Fluid?

    Are Cats a Fluid?

    Are cats a fluid? It’s a question that has inspired many a meme. There are a few common definitions as to what makes a fluid. One is that a fluid changes its shape to that of its container. Another more technical definition is that a fluid deforms continuously under shear forces. But the real picture is messier than these seemingly simple definitions allow for. On the Improbable Research podcast, I tackle the question of whether cats are a solid or a fluid and what fluid dynamics–specifically, the subject of rheology–has to teach us about the topic. Give it a listen! (Original image credits: Huffington Post; imgur; research credit: M. A. Fardin, pdf – article begins on page 16)

    Post-Thanksgiving bonus: Today is the traditional Science Friday broadcast of this year’s (abridged) Ig Nobel Prize ceremony. Check your local NPR station for broadcast times or listen to it on their website. You’ll hear me deliver a 24/7 lecture on the subject of “Fluid Dynamics” (and you may find me cropping up elsewhere, too). Alternatively, you can check out the full ceremony video on YouTube.

  • Hagfish Escape Mechanisms

    Hagfish Escape Mechanisms

    The hagfish is an eel-like creature that has not changed much in the past 300 million years in part because the hagfish is very good at escaping would-be predators. When attacked, the hagfish excretes mucins that combine with seawater to form slime. This gel-like viscoelastic fluid forms quickly and has some handy properties. For example, when stretched, the slime becomes extremely viscous. Many fish feed using a suction method, in which they thrust their jaws forward and enlarge their mouths to suck water and prey inside. This strong unidirectional flow stretches the slime, which thickens it and clogs the fish’s gills. Suddenly, the fish is much more concerned with being unable to breathe, allowing the hagfish to flee.

    Being surrounded by all that slime could smother the hagfish, too, if it were not for another clever feature of the slime. When sheared, hagfish slime collapses, losing its viscosity. The hagfish actually ties itself in a knot to create this shear and slide the slime right off. (Image credit: V. Zintzen et al.; L. Böni et al., source)

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    Fluids Round-Up

    Time for another fluids round-up! Here are some of the best fluids-related links I’ve seen around:

    – Above The Brain Scoop tells us about beetles that spend their whole lives underwater. They carry a little bubble of air with them in order to breathe!

    – Microfluidics are helping reveal how cancer cells metastasize and spread through the bloodstream.

    – It’s official! NASA’s going to build X-planes again.

    – See how snake venom kills by changing the fluid properties of a victim’s blood. (via Gizmodo)

    – Metallic foams can stop bullets and radiation, spawning many potential future uses here on Earth or in space.

    – Why nature prefers hexagons, especially in honeycomb, bubbles, and foam.

    – Earth has beautiful auroras, but if you could look at Jupiter with x-ray vision, you’d see something even more spectacular – a non-stop aurora that brightens on a regular schedule.

    – SciShow asks where the water goes in Minnesota’s Devil’s Kettle Falls. Conservation of mass says it has to go somewhere!

    And, in case you missed it, you can check out the latest FYFD video and learn more about the Brazil Nut effect over at Gizmodo.

    (Video credit: The Brain Scoop)

  • Bonbon Coatings

    Bonbon Coatings

    If you’ve ever bitten into a chocolate-covered bonbon, you may have noticed that the candy’s chocolate coating is remarkably uniform. Inspired by this observation, a group of engineers have investigated how viscous fluids poured over a curved surface flow and solidify; their findings were published this week.

    Rather than heated chocolate, the group used polymer-filled fluids that cure and harden over time. Interestingly, they found that the final shell is quite uniform and that its thickness does not depend on the pouring technique. Instead, they can predict the final shell thickness based on the radius of the mold and the rheological properties of the fluid–specifically its density, viscosity, and curing time. The reason for this is that the time it takes for the fluid to drain and coat the mold is much shorter than the time it takes for the polymer to cure. As a result, the amount of fluid that sticks to the mold depends on geometry and fluid properties – not how the fluid was poured.

    Amateur confectioners rejoice: pouring uniform chocolate coatings may be easier than you thought!  (Image credit: MIT News, video; research credit: A. Lee et al.)