Scientists Reveal Mystery of Cornstarch

The scientists from the University of Chicago are using cornstarch to solve the mystery of liquid that can instantaneously turn solid under the force of sudden impact known as the non Newtonian liquid.

The corn flour and water mixture is just one example of what are known as non-Newtonian fluids, who's viscosities or resistance to flow behave differently from the more familiar, "Newtonian" fluids from everyday life. 

Scott Waitukaitis and Heinrich Jaeger suspect that many similarly constituted suspensions- liquid laden with micron sized particles will behave exactly the same way. Since the 1930s scientists and engineers have been trying to explain the phenomena of this underlying physics.

The two of them have used an aluminium rod with an accelerometer and have used "tracer particles" within the solution to take slow motion X ray images in the middle of the bowl. They also used a laser line across the surface of the bowl. The moment the rod comes in contact with the surface of the mixture with a great intensity, the sensors measured where the forces were distributed at the bottom of the bowl.

"The corn starch grains are like tiny little rocks bobbing around in the water, very densely packed but not so densely that they're touching each other," said study author Scott Waitukaitis. "We found that when you hit the suspension, a solid like column grows below the impact site. The way it grows is similar to how a snowplow rock works. If I push a shovel in loosed now, a big pile of compacted snow grows out in front of the shovel, which makes it harder and harder for me to push"

What the scientists observe from these two studies is that, the appearance of striking object sinking slightly into the fluid as the particles coalesce around the contact surface. The fluid's contact surface develops an intense resistance to the striking object.

This process is being termed as "impact-activated solidification." Impacts typically are destructive processes but in the suspension they actually lead to the creation of a solid from a liquid, although temporarily.

The study has been published in the journal Nature. The two Chicogo scientists are extending this new finding by collaborating their work with researchers at Leiden University in the Netherlands to model the propagating shock fronts in depth.