What is Rheopecty and How Does it Explain the Strange Behavior of Blue Clay?

[SAZAR]

A while ago I've been watching some TV program (some Italian so I didn't understand a word they were saying) - it was a scientific show, a man was sitting on a stone explaining something about geology obviously, and then the strangest thing - in his hand he was holding some sky-blue plasticin-like amorph mass (more like a bubblegum or clay) - he was shaping it with ease - with one hand, it was almost flowing between his fingers (and I think it was a bit colder weather there so it was even stranger); then he put it on that stone he was sitting on, he took a hammer and hit that blue clay - it broke into pieces like it was ceramic vase; then he picked up fragments and put it all together - it was just like it was before(!) - he was passing it thorough his fingers and shaping it like it was flowing!

So it acts both extremely breakable and extremely melleable - at the same time! Strange!

My question here: what is that blue clay - what's the deal about it - how come it acts so strange?

 

[mrjeffy321]

From your description, it sounds like the substance was a mixture of Corn Starch and water (colored blue with food coloring).

If you mix water and Corn Starch to make a very thick paste, it will have many similar properties to what you described. If you let it sit, it will "melt" and behave much like a liquid, but if you strike it suddenly, the substances hardens up and becomes much more regid.

 

[NoTime]

No idea what the blue goo is.

The response has to do with how shear stress is transmited in the substance.

Many things have similar properties.
You can easily push your finger to the bottom of a cornstarch/water mixture.
If you hit the same mixture with a hammer it will just stop or perhaps even bounce.

 

[satan]

Yeah it has to be cornstarch,
I saw an English prog which incidental had the cornstarch dyed blue as well.

 

[SAZAR]

Interesting... But I thought it was an inorganic stuff...
(Heh... I must try this with corn starch.)

 

[DaveC426913]

No, it's called D30.

I mentioned it https://www.physicsforums.com/showthread.php?t=129315&highlight=armour".

http://www.youtube.com/watch?v=Grq2NzI9nNI&search=d3o"

 

[SAZAR]

...But I haven't seen this D30 break apart - it resists, this blue one I saw is fragile (I guess that's why they choosed it to demonstrate geology (like: stone masses moving (flowing) below surface of the Earth etc... seem rigid, but great masses show more elasticity... or something like that))

 

[Viterbo]

Its definitely not corn starch. Have a friend at uni that worked for a lab last summer that manufactures the stuff but i can't remeber what its called off hand, will ask him tomorrow and post the details for ya.

 

[dichotomy]

Dow Corning 3179 Dilatant Compound?

http://csc2.sunbelt-software.com/putty/

 

[ChemGuy]

The material is termed Rheopectic and is not all that strange. It is fairly common. There is a whole field called...Rheology that studies non Newtonian fluids.

See the link http://en.wikipedia.org/wiki/Rheopecty"