What allows colloids to have the properties of both a solid and a liquid?

CurioCity
13 October 2014

Above: Image © Nevit, Wikimedia Commons

Question

What allows colloids to have the properties of both a solid and a liquid?

Answer

The easiest colloid I can think of is cornstarch in water. You can do this at home: add 1 cup of cornstarch and 1/2 cup water and the result will be a thick mixture where closely packed solid particles are suspended in the liquid. As you mix it slowly or tilt the container it will flow like a liquid; this is because water minimizes friction (acts as a lubricant) and enables the solid particles to slide slowly past each other. However, if you try to grab a spoonful of this mixture or poke it quickly with your finger, it will behave like a solid and the surface will become resistant. This is because the water is squeezed out (viscosity increases) by the force applied, friction increases and the solid particles can no longer easily flow past each other and out of the way of your spoon/finger. The speed and the force of your action increase the viscosity of this mixture. Another example of a colloid is quicksand. So how would you get out of quicksand?

Answered By: Stefana Egli

CurioCity

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