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. #
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Shear-Thinning at Home
Shear-thinning isn’t just confined to canned whipped cream. It’s also a feature of such non-Newtonian fluids as ketchup, shampoo, latex paint, and blood. The NASA research on shear-thinning the video author refers to is here and comes from the Critical Viscosity of Xenon-2 (CVX-2) experiment flown on the final mission of Columbia. Surprisingly, almost all of the experimental data was recovered from the crash. #
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)
Mythbusters Walking on “Water”
The Mythbusters walk on “water” using non-Newtonian fluids. I think everyone wants to do this at least once in their life.
Pouring Paint
In this artwork by Holton Rower, paint (typically a non-Newtonian fluid) is poured down a rectangular prism; the result is a neat demonstration of shearing in laminar flows. Paint is usually shear-thinning, meaning that its viscosity decreases under shear; this is why the color stripes on the vertical panels expand more than those on the horizontal surfaces do. # (submitted by Stephan)
Cornstarch Monsters
The patterns formed when vibrating a liquid on a speaker cone are standing waves known as Faraday waves. With a large enough amplitude, this produces some very cool effects with a shear-thickening non-Newtonian fluid like oobleck. (It would actually be interesting to see what happens when you vibrate a shear-thinning liquid like shampoo…) This video also details how you can set up this demonstration yourself at home.
Plugging an Oil Leak
Recent research indicates that adding cornstarch to drilling mud increases the likelihood that a “top-kill” procedure will plug a leaking oil well. Adding cornstarch to water (or mud) turns it into a non-Newtonian fluid with viscoelastic properties that prevent the instabilities that lead to turbulent breakup. On the left, an underwater photo of the Deepwater Horizons leak; in the center, colored water breaks into turbulence when descending into oil; on the right, water with cornstarch maintains its coherence when pumped downward into the oil. # (PDF of research paper)
Waves on Cornstarch
A thin layer of the non-Newtonian fluid oobleck on a vibrating surface (in this case, a speaker) is a great way to show off nonlinear standing waves known as Faraday waves. The waves form because, under these circumstances, the flat surface of the air/oobleck interface has actually become unstable.
Reader Question: Oswald de Waele
fyeahhexagons-deactivated201103 asks:
Could you do a quick post explaining the Oswald de Waele relationship please? Thanks!
Sure! The Oswald-de Waele relationship (a.k.a. a power-law fluid) is an attempt to generalize the relationship between shear stress and shear rate in fluids. For a Newtonian fluid, that relationship is linear:
This relationship describes many fluids–like air or water–very well. But there are plenty of non-Newtonian fluids as well, both shear-thinning (paint, shampoo, ketchup) and shear-thickening (oobleck). The Oswald-de Waele relationship approximates the behavior of these fluids using:
Values of n less than one correspond to shear-thinning (or pseudoplastic) fluids; a value greater than one is a shear-thickening (or dilatant) fluid. And n = 1 corresponds to a regular Newtonian fluid. #
Vibrating Oobleck
[original media no longer available]
This video explores some of the non-Newtonian behaviors of oobleck when shaken. The pattern across the surface once the vibrations start is called Faraday waves, a type of nonlinear standing wave that forms once a critical vibrational frequency is passed and the flat surface of the fluid becomes unstable. Toward the end of the video, the frequency of the vibrations is increased until “finger-like protrusions” form. This is a behavior exhibited by shear-thickening non-Newtonian fluids.
