Have you heard of hydrogels? Would you like to try a hydrogel experiment? Hydrogels are polymer chains (lots of atoms linked together) that are ‘hydrophillic’ which means they love water! This makes them super absorbent. Some hydrogels are saturated which means they have already soaked up water – hair gel is an example of this. Other hydrogels are unsaturated which means they haven’t soaked up water but they can if they need to. An example of this is the material inside a baby’s nappy! In this simple hydrogel experiment we are going to be removing the water from a saturated hydrogel – hair gel!

To do this hydrogel experiment – you will need:

• Hair gel – any brand will do.
• Salt
• Little pot or cup

The method:

1) Put some hair gel into a little pot. Just a little squirt will work fine.

2) Sprinkle some salt on top of the hair gel

You should see the hydrogel start to turn from a gel into a liquid – this is the water coming out of the hydrogel structure.   Why not try testing different hair gel brands or research some other household hydrogels and give them a try! Do you think the experiment would work with sugar instead of salt? Write a prediction and then give it a try.

The science:

So how did this hydrogel experiment work? Hair gel is a saturated hydrogel so it contains lots of water, held inside lots of chains of atoms stuck together. Water bonds to salt so when you put salt on top of your hair gel, the water came out of the hydrogel to try and stick to the salt. This made the hydrogel structure collapse. This is why when you have salty food, you feel thirsty – salt sucks water out of your cells in the same way that it sucked the water out of the hair gel. If you have too much salt, you get dehydrated.