Glow in the Dark Gak

Gak, more commonly known as slime, is something almost everyone has made, but here are some instructions on how to make glow-in-the-dark gak.  At the end of this entry, explore some of the science behind gak and glow-in-the-dark toys.

For this experiment, you will need:  

• white glue
• borax
• water
• spoons
• plastic containers for mixing
• Green phosphorescent  pigment (available for purchase at www.douglasandsturgess.com)

Add 1/4 water and 1 tsp. of borax to one container.

Add 1/4 cup water and 1/4 cup white glue to a second container.

Make sure that both mixtures are fully combined and dissolved.

Add 1/2 tsp. green phosphorescent pigment to the glue and water mixture.  Stir well.

Add the water and borax mixture to the white glue, pigment, and water mixture.

Stir quickly to combine the two.  Strands should begin to form as the mixture thickens.

Stop stirring once all the water is dissolved.

The resulting mixture is gak.  This elastic, putty-like goo is fun to squish around and play with.

This gak is special because it glows bright green in the dark.  Charge it by holding it under a bright light.  Store in a plastic bag or airtight container so it does not dry out.  The pigment tends to "settle" out of the gak, so knead it every once in a while to keep it all combined.

It is likely that this gak isn’t the first glow-in-the-dark item you’ve seen.  Glow-in-the-dark toys such as plastic stars, key chains, and yoyos are everywhere.  How do all of these items glow in the dark?  Glow-in-the-dark items all include chemicals called phosphors.  There are many different types of phosphors, but they all work in the same way.  Recall that atoms have a center made up of neutrons and protons.  Flying around this center are quickly moving electrons.  Electrons are sometimes farther away or closer to the center, depending on the amount of energy they have.  You may have noticed that glow-in-the-dark items will glow less brightly over time, but “charging” them under a light makes them glow again.  When you hold the item under the light, the light gives the electrons energy, allowing them to move farther away from the pull of the center of the atom.  With time the electrons eventually relax and move closer to the center again, releasing the extra energy as light.

When atoms combine together, a molecule is formed.  Molecules can be many different shapes and sizes.  A familiar molecule is H20 or water.  Water is a small molecule made of two hydrogen atoms and one oxygen atom.  Sometimes small molecules combine to form one long chain.  This long chain is called a polymer.  Just like a chain, a polymer is made of the same repeating unit.

When water is added to the glue, the polymers in the glue slide around and allow the glue to flow. The borax mixture links the glue polymers creating a cross-link or net-like structure with the glue polymers as they get tangled up.  This cross-link allows the glue polymers to stick to each other and not to your hand. You can stretch it, and bounce it. The polymer chains can be easily broken and remade.  The polymers are held together by weak hydrogen bonds; it does not take much effort, or energy, to break apart and rebuild these bonds.