Oobleck, a non-Newtonian fluid made up of water and cornstarch, is a perennial Internet favorite for its ability to dance and the fact that one can run across a pool of it. It’s typically described as a shear-thickening fluid and only exhibits solid-like behavior under impact. Strictly speaking, oobleck is a suspension of solid grains of cornstarch in water. When struck, the initially compressible grains jam together, creating a region more like a solid than a liquid. From this point of impact, a solidification front expands through the suspension, jamming more grains together and enabling the fluid to absorb large amounts of momentum. The process is known as dynamic solidification. (Video credit: University of Chicago; research credit: S. Waitukaitis & H. Jaeger)
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.
Shear-thickeningnon-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)
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-thickeningnon-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.