At Home with the Mad Scientist: 3-6 for September 2008

Slime and Polymers

Remember: Always have an adult help you with any experiment.

Materials

1. Elmer's White Glue (be sure and use Elmer's only; not the 'Washable' type)
2. Borax (sodium tetraborate, available from your local supermarket. Look for Borax™ in the laundry detergent section.)
3. Water
4. Ziploc or other sealable plastic bags
5. Spoon or craft sticks
6. A jar or large cup
7. A bowl to mix all the ingredients

Procedure

1. In the bowl, mix an equal quantity of the Elmer's glue and water. Mix well with a spoon or popsicle sticks.
2. In the jar or water cup, we'll make a saturated solution of borax. Combine a tablespoon of borax powder with a cup or so of water and stir. It's easier if you use a jar with a lid as you can then screw on the lid and shake the mixture well. If all of the borax powder dissolves, then you need to add a bit more. When you get to the point where no more borax will dissolve, then the solution is saturated.
3. Now, add about two tablespoons of the borax solution to the bowl with the glue and water mixture and stir quickly. The resulting mixture should be slimy or gooey. You can save your slime for a long time by putting the 'stuff' into sealable plastic bags. If your slime dries out, you can add a bit of water back into it. If it gets too dry, you'll have to start over.

What's Going On?

When you mix Elmer's glue with a bit of water, you make a substance that is known as a polymer (polyvinyl acetate) and that the borax solution (sodium tetraborate) is a 'cross-linking' substance that binds the polymer chains together to make the glue solution thicker. So, as the polymer chains get more 'bound-together', it gets harder for them to move around, and your slime starts to be more like Silly-putty™. Experiment with adding more borax solution to see if this indeed makes the slime thicker or thinner.

Knowing just how much Borax solution to add is the trick to this experiment. If you add too little, your slime will contain excess glue (the polymer part) and it will be sticky. If you add too much, your slime will be very wet (too much 'cross-linking'). Touch your slime with your hands when it doesn't look like a liquid anymore. If your slime feels sticky, try adding a little Borax solution. If your slime feels very wet and slippery (but is not still runny), remove it from the container and kneed it in your hands. In a few minutes, any extra Borax solution will evaporate or be absorbed.

The substance known as 'Gak™' is really a specialized form of a polymer known as Poly-vinyl Alcohol, but is not too far off what we made with Elmer's glue.

From: Discovery Kids