Shear-thickening non-Newtonian fluids like oobleck become more viscous as force is applied to them. This behavior causes them to form finger-like structures when vibrated, makes it good liquid armor, and even enables people to run across a pool of it without sinking. Now undergraduates at Case Western Reserve University have found a new use for such fluids: pothole filling. They have created a pothole patch that consists of a waterproof bag filled with a dry solution that, when mixed with water, creates a non-Newtonian fluid capable of flowing to take the shape of the pothole but resisting a car tire like a solid. They cover the patch with a layer of black fabric so that drivers don’t avoid the patch. See the video above for a demonstration and ScienceNOW for more. (submitted by aggieastronaut)
Search results for: “shear thickening”
Cornstarch Monsters
[original media no longer available]
Shaking a fluid surface often results in standing waves known as Faraday waves, but with a non-Newtonian fluid like oobleck, at some frequencies it’s possible to incite other behaviors. Oobleck is shear-thickening, meaning that its viscosity increases when force is applied. This is what allows it to develop finger-like protrusions under high frequency vibrations.
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.
Thixotropic and Rheopectic Fluids
There’s more to non-Newtonian fluids than shear-thickening and shear-thinning. The viscosity of some fluids can also change with time under constant shear. A fluid that becomes progressively less viscous when shaken or agitated is called thixotropic. The opposite (and less common) behavior is a fluid that becomes more viscous under constant agitation; this is known as a rheopectic fluid. This video demonstrates both types of fluids using a rotating rod as the agitator. The rheopectic fluid actually appears to climb the rod–similar to the Weissenberg effect–while the thixotropic fluid moves away from the rod.
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.
Protecting an Egg with Oobleck
Using non-Newtonian fluids as “liquid armor” is an active area of research and development. Here students demonstrate the efficacy of shear-thickening as a defense against sudden impact by dropping a bag of oobleck containing a raw egg from different heights.
Canon Sound Sculptures
In a new series of ads for Canon, colorful paints are placed on a speaker cone and filmed at high speed to create beautiful “sound sculptures”. Paint, like oobleck, is a non-Newtonian fluid but does not react the same when excited by sound because it is shear-thinning. (When painting, you want the paint to run off the brush easily but not drip when it’s on the wall; hence, shear-thinning.) Both the photos and videos are lovely examples of fluid mechanics as art. Watch how they did it. # (Via jshoer, @ftematt, @JetForMe)
Running on a Pool of Oobleck
What happens when you fill a pool with a non-Newtonian fluid? Well, for one, you can hold races across the surface! In this video, the pool is filled with a mixture of cornstarch and water, a shear-thickening fluid known as oobleck.
Cornstarch Monsters
In shear-thickening, non-Newtonian fluids, disturbances make the fluid more viscous (“thicker”, more resistant to motion). This is well-demonstrated by putting some on a speaker and turning it on! #