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

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Non-Newtonian fluids, like the cornstarch and water mixture, exhibit unique stress responses due to their shear thickening properties. When subjected to low shear rates, these fluids flow easily as the liquid fills the gaps between closely packed particles. However, at higher shear rates, the liquid cannot adequately occupy these spaces, leading to increased friction and viscosity. This behavior is evident in mixtures like oobleck, which become rigid upon impact. Understanding these mechanisms is crucial for applications involving non-Newtonian fluids in various industries.
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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?
 
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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
 

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