Non Newtonian Fluids: Why & How Do They Respond to Stress?

[hy23]

Why do non Newtonian fluids such as the cornstarch and water mixture respond to stress the way they do? What prompts the atoms to come together to resist the force?

 

[Spinnor]

See:

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

A dilatant (also termed shear thickening) material is one in which viscosity increases with the rate of shear. Such a shear thickening fluid, also known by the acronym STF, is an example of a non-Newtonian fluid.

The dilatant effect occurs when closely packed particles are combined with enough liquid to fill the gaps between them. At low velocities, the liquid acts as a lubricant, and the dilatant flows easily. At higher velocities, the liquid is unable to fill the gaps created between particles, and friction greatly increases, causing an increase in viscosity.[1] This can readily be seen with a mixture of cornstarch and water[2] (sometimes called oobleck), which acts in counterintuitive ways when struck or thrown against a surface. Sand that is completely soaked with water also behaves as a dilatant material. This is the reason why when walking down the beach, a dry area always appears underneath your foot. ...

found above link in:

http://en.wikipedia.org/wiki/Non-Newtonian_fluid