Featured Research

from universities, journals, and other organizations

Messy experiment cleans up cornstarch and water mystery

Date:
July 12, 2012
Source:
University of Chicago
Summary:
Most people buy cornstarch to make custard or gravy, but two scientists have used it to solve a longstanding physics problem with a substance known to generations of Dr. Seuss readers as “Oobleck,” and to scientists as a non-Newtonian liquid.

Cornstarch and water.
Credit: Image courtesy of University of Chicago

Most people buy cornstarch to make custard or gravy, but Scott Waitukaitis and Heinrich Jaeger have used it to solve a longstanding physics problem with a substance known to generations of Dr. Seuss readers as "Oobleck," and to scientists as a non-Newtonian liquid.

This substance, a liquid that can instantaneously turn into a solid under the force of a sudden impact, behaves in surprising ways. It consists of a simple mixture of cornstarch and water, and adults can actually run across a vat of this liquid, as has been done many times on television game shows and programs such as MythBusters.

The University of Chicago's Waitukaitis and Jaeger suspect that many similarly constituted suspensions -- liquids laden with micron-sized particles -- will behave exactly the same way. Scientists and engineers have attempted to explain the underlying physics of this phenomenon since the 1930s, but with incomplete success.

Current explanations predict a thickening of the suspension when it's subjected to the push-pull of shearing forces, but fall far short of accounting for the large forces needed to keep an adult high and dry while running across a pool of the stuff.

Now Waitukaitis and Jaeger report in the July 12 issue of the journal Nature how compressive forces can generate a rapidly growing, solid-like mass in the suspension. The study culminates a long struggle to understand a phenomenon that has elicited a wide range of explanations over the years.

Snowplow action

"We found that when you hit the suspension, a solid-like column grows below the impact site," said Waitukaitis, a graduate student in physics. "The way it grows is similar to how a snowplow works. If I push a shovel in loose snow, a big pile of compacted snow grows out in front of the shovel, which makes it harder and harder for me to push." With the suspension, the "snowplow" is caused by individual cornstarch grains piling up in front of the impacting object and becoming temporarily jammed after compression has halted all movement.

Jaeger's group has studied the physics phenomenon of "jamming" in numerous contexts, such as when the creation of a vacuum turns a fluid substance like coffee grounds into a solid.

Handling suspensions is important to a broad range of industries, from construction to biomedicine. Some engineers are even investigating these suspensions as the basis for a new type of body armor.

"It would be liquid, so it would conform to a particular shape, and when it gets hit hard it knows it needs to become hard," Waitukaitis said. It's a smart material, one that increases resistance with the amount of force applied against it.

Cornstarch and water individually behave strikingly differently to the application of force than they do when mixed. With water, a normal liquid, the resistance to intruding objects is hundreds of times smaller. A bucket of dry cornstarch grains, meanwhile, exists in a jammed state courtesy of gravity, and slamming a rod into the bucket unjams the grains. With mixtures of cornstarch and water, the material starts out unjammed and blunt force drives it to jam locally.

The UChicago experiment highlights how complex and often puzzling phenomena emerge from simple ingredients, and how established ways of looking at them need to be revisited with the benefit of modern technology. Historically, most experiments have looked at relatively small volumes of suspensions, and primarily under conditions of continuous shearing.

"To notice a transient phenomenon of the type that we describe, you need a large set up and you need to look very fast," said Jaeger, the William J. Friedman and Alicia Townsend Professor in Physics.

The UChicago experiment did just that with a combination of high- and low-tech instruments, including force sensors, laser sheets, X-rays, high-speed cameras taking images at 10,000 frames a second, and an industrial cement mixer.

Messy ingredients

"It's an incredibly messy experiment," Waitukaitis said. "I have a blue jumpsuit I wear all day. When I do these experiments, I'm totally covered in cornstarch."

The experiment was the first to investigate direct compression in these suspensions. The experiment shows that driving a rod into the cornstarch and water mixture easily generated stresses 100 times greater than the largest stresses encountered during shear.

The researchers found that their impacting rod initiated a shock-like, moving front that starts directly beneath the impacting object and then grows downward, transforming the initially liquid suspension into a temporarily jammed state. As the front of this jammed region moves forward, it transforms the liquid region directly ahead of it. "It essentially grows its own solid as it propagates," Jaeger said.

The UChicago scientists called this process "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 only temporarily.

Waitukaitis and Jaeger now are extending this work by collaborating with researchers at Leiden University in The Netherlands to model the propagating shock fronts in more detail. The are also working closely with UChicago colleagues Wendy Zhang, associate professor in physics, and Jake Ellowitz, graduate student in physics. Zhang and Ellowitz are developing simulations to test how altering the ingredients of various suspensions affect their behavior under impact.

"The feedback between the particle movements and the liquid flow makes this challenging. It's actually not at all easy to perform simulations on such a system," Jaeger said.

Video available: http://news.uchicago.edu/article/2012/07/12/messy-experiment-cleans-physics-mystery-cornstarch


Story Source:

The above story is based on materials provided by University of Chicago. The original article was written by Steve Koppes. Note: Materials may be edited for content and length.


Journal Reference:

  1. Scott R. Waitukaitis, Heinrich M. Jaeger. Impact-activated solidification of dense suspensions via dynamic jamming fronts. Nature, 2012; 487 (7406): 205 DOI: 10.1038/nature11187

Cite This Page:

University of Chicago. "Messy experiment cleans up cornstarch and water mystery." ScienceDaily. ScienceDaily, 12 July 2012. <www.sciencedaily.com/releases/2012/07/120712224549.htm>.
University of Chicago. (2012, July 12). Messy experiment cleans up cornstarch and water mystery. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2012/07/120712224549.htm
University of Chicago. "Messy experiment cleans up cornstarch and water mystery." ScienceDaily. www.sciencedaily.com/releases/2012/07/120712224549.htm (accessed October 22, 2014).

Share This



More Matter & Energy News

Wednesday, October 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Reuters - Innovations Video Online (Oct. 22, 2014) — Inspired by the way a chameleon changes its colour to disguise itself; scientists in Poland want to replace traditional camouflage paint with thousands of electrochromic plates that will continuously change colour to blend with its surroundings. The first PL-01 concept tank prototype will be tested within a few years, with scientists predicting that a similar technology could even be woven into the fabric of a soldiers' clothing making them virtually invisible to the naked eye. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Jet Sales Lift Boeing Profit 18 Pct.

Jet Sales Lift Boeing Profit 18 Pct.

Reuters - Business Video Online (Oct. 22, 2014) — Strong jet demand has pushed Boeing to raise its profit forecast for the third time, but analysts were disappointed by its small cash flow. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Internet of Things Aims to Smarten Your Life

Internet of Things Aims to Smarten Your Life

AP (Oct. 22, 2014) — As more and more Bluetooth-enabled devices are reaching consumers, developers are busy connecting them together as part of the Internet of Things. (Oct. 22) Video provided by AP
Powered by NewsLook.com
What Is Magic Leap, And Why Is It Worth $500M?

What Is Magic Leap, And Why Is It Worth $500M?

Newsy (Oct. 22, 2014) — Magic Leap isn't publicizing much more than a description of its product, but it’s been enough for Google and others to invest more than $500M. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins