Science corner

22nd November 2002 at 00:00
A life of slime: Sophie Duncan describes a polymer experiment that can get sticky.

You can find these everywhere - in the clothes we wear and the cars we drive. We eat them and eat from them. We run in them, play games with them, cover our floors with them and wash our hair with them. We even use them to help us see. They are, of course, polymers. A polymer is a chain of molecules or atoms. The chain is made up of parts that are all the same - the more of these parts that are joined together the longer the chain.

This activity enables you to explore polymers by making your own slime, and if you use the right food colouring it can look rather disgusting.

To make slime you need borax, PVA glue, water and food colouring. Borax can be bought at most chemists. It can cause irritation to the skin, and therefore should not be handled without plastic gloves. Take a quarter of a teaspoon of borax, and dissolve it in half a cup of water. Keep stirring until all the borax is dissolved.

Take a quarter of a cup of glue and mix in a quarter of a cup of water. Add food colouring if you wish. Mix the two solutions in a plastic container with a secure lid. Shake the mixture for a few minutes. As you shake, it will become more and more solid.

Pour the slime into a zippable bag. Explore how it feels. Wearing plastic gloves, handle the slime and find out how stretchy it is. Experiment with different quantities of borax, water and glue. Test which combination makes the most realistic slime. (If you do handle the slime directly, make sure you wash your hands afterwards, and avoid getting it into your eyes.) The glue and water mixture is a polymer - the borax causes the long polymer chains to link together, and is called a cross-linking agent.

If you add too little borax the excess glue makes the slime feel sticky. You can add more borax solution to correct this. However, if the slime feels wet you have added too much borax. You can sometimes correct this by removing the slime from the container and kneading it.

Sophie Duncan is a physicist and programme manager with Planet Science (formerly Science Year). www.planet-science.com

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