How to Rip a Fluid

Jun 01, 2007
   How to Rip a Fluid
Birefringent visualization of the micellar fluid layer around a diagonally oriented square "cutting tool." A white outline is superimposed on the outer edge of the square.

In a simple experiment on a mixture of water, surfactant (soap), and an organic salt, two researchers working in the Pritchard Laboratories at Penn State have shown that a rigid object like a knife passes through the mixture at slow speeds as if it were a liquid, but rips it up as if it were a rubbery solid when the knife moves rapidly.

The mixture they study shares properties of many everyday materials -- like toothpaste, saliva, blood, and cell cytoplasm -- which do not fall into the standard textbook cases of solid, liquid, or gas. Instead, these "viscoelastic" materials can have the viscous behavior of a fluid or the elastic behavior of a solid, depending on the situation. The results of these experiments, which are published in the current issue of the journal Physical Review Letters and are featured on its cover, provide new insights into how such materials switch over from being solid-like to being liquid-like.

   How to Rip a Fluid
Responses of a micellar fluid to a cylinder moving at three speeds: (a) 2.8 mm/s, d=3.1 mm; (b) 9.9 mm/s, d=1.8mm; (c) 16 mm/s, d=7.9 mm. The view shown is along the cylinder axis.

"As a child will swish its finger through an unknown liquid to find out what it is, we built an experiment to pull a cylinder through this viscoelastic material, to learn how it responds," explains Andrew Belmonte, associate professor of mathematics at Penn State and a member of the research team. Their study revealed experimentally, for the first time, the response of a viscoelastic material to increasingly extreme conditions of flow. "We found that flow happens at slow speeds, cutting happens at intermediate speeds, and tearing happens at the highest speeds," says Joseph R. Gladden, a co-author of the research paper, who collaborated on the study while he was a postdoctoral scholar at Penn State. The researchers also found that the viscoelastic material heals in the wake of the tear, as a torn solid would not, and recovers completely after several hours. "Surprisingly, the strength of the material when it acts like a solid is essentially the same as its surface tension as a liquid. This fact reconnects our understanding of these materials between the extremes of flow and fracture," said Belmonte.

Source: University of Minnesota

Explore further: Super Bowl athletes are scientists at work

add to favorites email to friend print save as pdf

Related Stories

Flexible, stretchable fire-ant rafts

Nov 26, 2013

What do Jell-O, toothpaste, and floating fire-ant rafts have in common? All are so-called "viscoelastic" materials, meaning that they can both resist flow under stress, like honey, and they can bounce back ...

Physicist develops new silicone rubber

Feb 28, 2013

(Phys.org)—If anything bothers University of Virginia physicist Lou Bloomfield, it's a wobbly table. So much so that he actually invented a material to eliminate the problem. The material, a type of silicone ...

Ultrafine processing technology continues its evolution

Nov 21, 2011

The performance of optical and electronic components such as lenses and semiconductors is strongly influenced by the precision of surface grinding, which involves shaping the surface, and polishing, and provides ...

Recommended for you

Super Bowl athletes are scientists at work

3 hours ago

Seattle Seahawks cornerback Richard Sherman gets called a lot of things. He calls himself the greatest cornerback in the NFL (and Seattle fans tend to agree). Sportswriters and some other players call him ...

Sundance doc examines real-life Close Encounter

20 hours ago

Earth authorities are completely unprepared for the arrival of alien visitors and worried humans should ready themselves by watching a groundbreaking documentary, the film's director boasts.

Toward a scientific process freed from systemic bias

Jan 26, 2015

Research on how science works - the science of science - can benefit from studying the digital traces generated during the research process, such as peer-reviewed publications. This type of research is crucial for the future ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.