A Solid and A Liquid - Shaking the Foundations of Our Reality...

[M.D. Holloway]

'In a simple experiment on a mixture of water, surfactant (soap), and an organic salt, two researchers working in the Pritchard Fluid Mechanics Laboratory 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.




Image: 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.

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.

"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: Penn State

[Drago]

Glass...although it doesn't "heal" itself.

[mjohnson]

Rheology is pretty far from my area of expertise but how is this different than silly putty or the really thick corn starch-water solution they made on Mythbusters?

Just _really_ non-newtonian fluids?

I mean is the fluid under discussion behaving as a true solid under high stress or at high strain rates?

Maybe I'll have to find the paper...

mike
'78SC

[M.D. Holloway]

Internet magic - man I wish I had the internet in College!

[red-beard]

You've never played with corn starch? Go to the store and buy some corn starch. Put some in a glass bowl and add a little water. Mix it in. Keep adding water until it is like a dough, but a little liquid. Put you finger in slowly, and it will flow around your finger. Push your finger in fast, and it will solidify.

[M.D. Holloway]

Sure - In grad school I took a course in viscoelasticity. The math wasn't fun but the labs were cool. It is pretty amazing what sorts of things can be made. By increasing/decreasing temperature, aggitation, electric current some materials thicken up or thin out.

We made this slurry that was as thin as water until you passed a magnet near it then it solidified. It was a slurry of iron filings held in suspension. We also made all sorts or visco-polymers that just didn't behave like you would think they should have - things that got thinner the colder they got - not something that you would expect.

To understand how it worked was headey stuff though. Material science is pretty cool.

[legion]

I thought the cornstarch/water thing was a simple colloid.

[Porsche-O-Phile]

Originally posted by red-beard
You've never played with corn starch? Go to the store and buy some corn starch. Put some in a glass bowl and add a little water. Mix it in. Keep adding water until it is like a dough, but a little liquid. Put you finger in slowly, and it will flow around your finger. Push your finger in fast, and it will solidify.

Exactly what I was thinking - pretty wild stuff.

IIRC the new Corvette Z06s use some sort of variable-viscosity fluid in their suspensions - the liquid responds to a magnetic current (controlled by the vehicle computer) to increase or decrease dampening rate.

[masraum]

isn't the internet amazing??

this first one is super cool.

[LeRoux Strydom]

How is this different from thixotropic materials?

http://en.wikipedia.org/wiki/Thixotropy

[thrown_hammer]

Silly Putty did this years ago…Yawn.

[legion]

Originally posted by Porsche-O-Phile
Exactly what I was thinking - pretty wild stuff.

IIRC the new Corvette Z06s use some sort of variable-viscosity fluid in their suspensions - the liquid responds to a magnetic current (controlled by the vehicle computer) to increase or decrease dampening rate.

And they have licensed the technology to Ferrari.