Cornstarch Unusual Properties & Extra Water Effects

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In summary, the conversation revolved around the properties of cornstarch in solution, specifically its ability to become hard when hit and soft when moved slowly. The person had added too much water to the solution and tried to heat it to get rid of the excess, resulting in globules forming and making it difficult to return to its normal state. This is due to the nonlinear effect of dilatancy in the solution, which is not fully understood. It is an open topic in the field of nonlinear dynamics in materials.
  • #1
WiFO215
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I was playing around with cornstarch solution as I saw on T.V. that it had some really funny properties. It becomes hard when you hit it, but its soft if you go slow on it.
I was preparing some at home in two containers. In one container however, I added too much water. Having finished the cornstarch, I couldn't add more. So to get rid of this extra water, I tried to heat the solution, but instead of returning to normal, globules formed in the solution as it became thicker. I'm finding it very difficult to make it normal.
Why does this happen? What does adding extra water and then heating do to the mix?
 
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  • #2
Anyone?
 
  • #3
Sounds to me like you simply cooked the cornstarch. If you want to remove water, just let the (uncooked) mixture sit, undisturbed, and the cornstarch will eventually settle, then just pour off some of the water.

Google "non-Newtonion fluids" for more information, recipes and experiments.
 
  • #4
anirudh215 said:
I was playing around with cornstarch solution as I saw on T.V. that it had some really funny properties. It becomes hard when you hit it, but its soft if you go slow on it.
I was preparing some at home in two containers. In one container however, I added too much water. Having finished the cornstarch, I couldn't add more. So to get rid of this extra water, I tried to heat the solution, but instead of returning to normal, globules formed in the solution as it became thicker. I'm finding it very difficult to make it normal.
Why does this happen? What does adding extra water and then heating do to the mix?

Cornstarch in solution is an example of a dilatant (shear thickening) fluid:

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

The phenomenon is partially understood at best- hand-waving arguments about tangled polymers are usually invoked. It's a nonlinear effect, and part of a more general phenomena:

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

Unfortunately, when you heated the solution, you most likely made some irreversible changes to the starch itself, causing the behavior you experienced. best to just start over- next time, mix the material much more slowly. It's a nonlinear effect, so there's a narrow range of concentration that will produce the dramatic effect:

http://en.wikipedia.org/wiki/Oobleck
 
  • #5
Andy Resnick said:
Cornstarch in solution is an example of a dilatant (shear thickening) fluid:

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

The phenomenon is partially understood at best- hand-waving arguments about tangled polymers are usually invoked. It's a nonlinear effect, and part of a more general phenomena:

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

Unfortunately, when you heated the solution, you most likely made some irreversible changes to the starch itself, causing the behavior you experienced. best to just start over- next time, mix the material much more slowly. It's a nonlinear effect, so there's a narrow range of concentration that will produce the dramatic effect:

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

I see. So not many people have done research on this stuff yet? Is it an open topic?
 
  • #6
In as much as the nonlinear dynamics of materials is an open topic, yes.
 

1. What are the unusual properties of cornstarch?

Cornstarch is a carbohydrate derived from corn and has unique properties that make it useful in various applications. Its most notable properties include its ability to thicken, bind, and stabilize food and non-food items. It also has a low freezing point, which makes it useful in preventing ice crystals from forming in frozen foods.

2. How does cornstarch behave when mixed with water?

Cornstarch has a unique behavior when mixed with water. It forms a non-Newtonian fluid, which means its viscosity changes depending on the force applied to it. When mixed with a small amount of water, cornstarch forms a solid-like substance, but when mixed with a larger amount of water, it becomes a liquid-like substance.

3. Why does cornstarch and water mixture become solid when pressure is applied?

When pressure is applied to a cornstarch and water mixture, the starch granules align and form a tighter structure, making it more solid-like. This is due to the increased intermolecular forces between the starch molecules, resulting in a more rigid structure.

4. How can cornstarch and water be used for non-food applications?

Cornstarch and water mixture has various non-food applications due to its unique properties. It can be used as a thickening agent in cosmetics, as a binder in paper, and as a biodegradable packaging material. It is also used in fire extinguishers as a non-toxic alternative to traditional chemicals.

5. What is the effect of adding extra water to a cornstarch mixture?

Adding extra water to a cornstarch mixture results in a decrease in its viscosity and thixotropic properties. This means that the mixture becomes less thick and takes longer to regain its original consistency when left at rest. It also results in a weaker structure, making it less suitable for certain applications.

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