Polymers and Hydrogels

Hydrogels are polymers which can absorb large quantities of water.  They are alsol known as “smart” polymers, because they can change shape quickly in response to changes in their environment.  Examples include hair gel, water-retaining gel, eg in disposable nappies or plant pots, and soft contact lenses. Alison demonstrated hair gel’s excellent qualities on Tiny.  One source explains:  

“Hydrogels are networks of long polymer chains that attract and store large volumes of water. It is not uncommon for 90% of a hydrogel to be water. As water molecules are attracted and stick to the polymer chain network, this causes it to swell forming a gel.”

Hair Gel Collapse Experiment

We added salt to hair gel and found that the gel shrank and just a little liquid was left.

Salt replaces water in the polymer structure of the gel, because it’s more strongly attracted to the polymer than water is.  This is why you should choose your styling products carefully if you want to look cool in the sea.

RSC : Experiments with hydrogels 

University of Warwick : Hair Gel collapse experiment

Polymers : Disposable Nappies

We looked at a type of hydrogel, found in disposable nappies, and tested which of several brands of nappy was best value for money in terms of absorbency.

Method: We had Boots own brand, which cost 18.5p per nappy, Pampers, which cost 26p each, and Naty “natural” nappies, which were 28.2p.  We pulled the nappies apart and extracted the polymer granules, then added distilled water and measured how much water each collection of granules could absorb.

Results: Boots own brand absorbed 650ml ( so the cost of nappy divided by the liquid absorbed gives us 0.028p per ml), Pampers absorbed 800ml (0.0325p per ml) and Naty absorbed 680ml (0.041p per ml), although one group had an unexpected result of 900ml.

Conclusion: If all you’re concerned about is absorbency, the Boots own-brand nappies were best value for money.  However, there might be other factors which would influence your decision, such as whether the nappy fitted well, or environmental factors.

  http://lavenderpondnotes.tumblr.com/post/118965025616/polymers-disposable-nappies

Things to look at:

Catalyst -a magazine for teenage chemistry students - has a nice article about hydrogels which discusses medical applications.

 RSC experiment on hydrogels - discusses the chemistry behind the hydrogel.