Gels

[petrushka.googol]

Are gels solids, liquids or semi-solids ?

 

Please explain.

[studiot]

This question really belongs in the province of physical chemistry.

 

A gel is an example of a disperse system, the old name for which was a colloid.

 

A disperse system consists of two materials intimately mixed so they don't separate in normal conditions and act as if they were one substance.

 

The two materials are called

the disperse medium (which corresponds to the solvent in a solution)

and

the disperse phase (which corresponds to the solute in a solution)

 

The mention of phase brings up that the two substances may be in different states,

So smoke is a solid dispersed in a gas and foam is a gas dispersed in a liquid.

 

Gels are harder to characterize. They are a mixture of a liquid and a solid, but which is the disperse medium and which the phase is sometimes hard to tell, though their softness and flowability would suggest a solid in a liquid most of the time.

[John Cuthber]

A gel is a solid, but (like all solid materials) it's not perfectly rigid.

[Sensei]

That reminds me the longest going physical experiment in the world

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

[DrP]

The sol-gel reaction of something like TEOS goes from being a liquid with a suspension of growing solid particulates in it to being a solid gel at the 'gel point' of the reaction. This is the moment that the growing seed particles become large enough that they all interact and cross link and form a complete skeletal structure throughout the body of the medium. This yields a soft solid which gets firmer as the reaction proceeds.