The Kaye effect is particular to shear-thinning non-Newtonian fluids – that is, fluids with a viscosity that decreases under deformation. The video above includes high-speed footage of the phenomenon using shampoo. When drizzled, the viscous liquid forms a heap. The incoming jet causes a dimple in the heap, and the local viscosity in this dimple drops due to the shear caused by the incoming jet. Instead of merging with the heap, the jet slips off, creating a streamer that redirects the fluid. This streamer can rise as the dimple deepens, but, in this configuration, it is unstable. Eventually, it will strike the incoming jet and collapse. It’s possible to create a stable version of the Kaye effect by directing the streamer down an incline. (Video credit: S. Lee)
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The Kaye Effect
When a viscous fluid falls onto a surface, it will form a heap, like honey coiling. But for shear-thinning liquids like soap or shampoo something a little wild can happen as the heap grows. A dimple can form and, when the incoming jet of fluid hits that dimple, it slips against it and is ejected outward. If you wonder why you don’t see this every day in the shower, it’s because the outgoing jet usually hits the incoming jet, causing the whole system to collapse in less than 300 ms. By dropping the fluid on an inclined surface, one can keep the two jets from colliding, thereby creating a stable Kaye effect. (Photo credit: E. Eichelberger)
The Kaye Effect
The Kaye effect is an instability particular to a falling stream of non-Newtonian fluids with shear-thinning properties. When these fluids are deformed, their viscosity decreases; this, for example, is why ketchup flows out of a bottle more easily once it’s moving. Like most fluids, the falling shampoo creates a heap on the surface. The Kaye effect is kicked off when the incoming jet creates enough shear on part of the heap that the local viscosity decreases, causing the streamer–or outgoing jet–to slip off the side of the heap. As the incoming jet continues, a dimple forms in the heap where the streamer originates. As the dimple deepens, the streamer will rise until it strikes the incoming jet. This perturbation to the system collapses the streamer and ends the Kaye effect. This video also has a good explanation of the physics, along with demonstrations of a stable form of the Kaye effect in which the streamer cascades down an incline. (Video credit: Minute Laboratory; inspired by infplusplus)
When Fluids Behave Like Solids
Many common fluids–like air and water–are Newtonian fluids, meaning that stress in the fluid is linearly proportional to the rate at which the fluid is deformed. Viscosity is the constant that relates the stress and rate of strain, or deformation. The term non-Newtonian is used to describe any fluid whose properties do not follow this relationship; instead their viscosity is dependent on the rate of strain, viscoelasticity, or even changes with time. A neat common example of a non-Newtonian fluid is oobleck, a mixture of cornstarch and water that is shear-thickening, meaning that it is resistant to fast deformations. Like the cornstarch-based custard in the video above, these fluids react similarly to a solid when struck, resisting changing their shape, but if deformed slowly, they will flow in the manner of any liquid.
Getting Ketchup to Flow
Most everyone is familiar with the difficulty of getting ketchup out of its bottle. Part of the trouble is that ketchup is a shear-thinning fluid, meaning that its viscosity decreases with an increasing rate of shear. Thus, a shear-thinning fluid flows better once it starts moving. This is why the ketchup moves much faster once it is initially disturbed. LiquiGlide, a new coating material demonstrated above, has gained a lot of popular attention in the press recently for solving the difficulty of the stuck condiments. It appears that the coating reduces the static coefficient of friction between the food and the bottle, meaning that the ketchup starts sliding down the wall even before an increase in shear stress starts the flow. (submitted by @szescstopni)
Sound Sculptures
This is another fun and artistic use of non-Newtonian fluids (paint) vibrating on a speaker cone for advertising purposes. The shear-thinning viscous properties of the paint vie with surface tension to create lovely instantaneous sculptures of color. Check out Canon’s Pixma ads for similar artwork.
Leaping Shampoo
The Kaye effect is a neat phenomenon associated with falling shear-thinning non-Newtonian fluids like shampoo or hand soap. As the falling liquid piles up after hitting a solid surface, it ejects streams of fluid upwards. The effect usually only lasts for a few hundred milliseconds, but it is possible to see it at home without a high-speed camera if you pay close attention. More detailed physics of the effect are discussed in this previously featured video.
Paint Vibrations
Paint vibrated on a loud speaker explodes in multi-colored jets and droplets. Most paints are shear-thinning non-Newtonian fluids (like ketchup, shampoo, or whipped cream), meaning that their viscosity decreases as they are sheared. This allows them to flow more readily once they are perturbed. #
Venom Properties
Most venomous snakes deliver venom to their prey via grooves in their fangs, rather than through a pressurized bolus through hollow fangs. New research shows that these venoms are shear-thinning non-Newtonian fluids. The surface tension of the venom is such that a drop of venom will tend to flow into and down the groove. Once moving, the shear-thinning properties of the venom decrease the venom’s viscosity, increasing its flow rate down the fang and into the snake’s prey. (via Scientific American; Photo: green mamba, banded snake fang)
Hawaiian Fissures
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New fissures opened on Mount Kilauea in Hawaii earlier this month, resulting in some fountain-like eruptions of lava. This molten rock is a non-Newtonian fluid with shear-thinning and thixotropic properties. This is what allows the lava to flow long distances before it cools and solidifies. (via jpshoer)
