How to Rip a Fluid

June 1, 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: Researchers show materials strengthen on their own when impacted at very high speed

Related Stories

How cytoplasm 'feels' to a cell's components

August 22, 2017

Under a microscope, a cell's cytoplasm can resemble a tiny underwater version of New York's Times Square: Thousands of proteins swarm through a cytoplasm's watery environment, coming together and breaking apart like a cytoskeletal ...

Soft solids and the science of cake

February 24, 2016

Researchers hope that working out the behaviours of soft solids, which can act like either solids or liquids, may make for tastier cakes – and safer oil wells.

Ants: Both solid-like and liquid-like

October 26, 2015

Collections of ants have a remarkable ability to change shapes and tasks based on the demands of their environment. When floodwaters hit, they self-assemble and form rafts to stay alive. They can also use their bodies to ...

Recommended for you

Fatty bird gland preserved over 48 million years

October 18, 2017

(Phys.org)—A team of researchers from the U.S., Ireland, Germany and the U.K. has found evidence of preservation of a fatty oil gland from a 48-million-year-old fossilized bird. In their paper published in Proceedings of ...

Waiting periods reduce deaths from guns, study suggests

October 17, 2017

(Phys.org)—A trio of researchers with Harvard Business School has found evidence that they claim shows gun deaths decline when states enact waiting period laws. In their paper published in Proceedings of the National Academy ...

Roman theater uncovered at base of Jerusalem's Western Wall

October 16, 2017

Israeli archaeologists on Monday announced the discovery of the first known Roman-era theater in Jerusalem's Old City, a unique structure around 1,800 years old that abuts the Western Wall and may have been built during Roman ...

0 comments

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.