Tuesday, November 20, 2012

Glow in the Dark Gak

Gak 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'll need:  white glue, borax, water, spoons, containers for mixing, and 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.  Keep it charged up by holding it under a bright light.  Keep the gak stored in a plastic bag so it doesn't 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 calls phophors.  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, release 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.

Gak is formed when polymers are created.  When you stir the gak up, you should notice that it appears stringy like melted cheese.  Those are the polymers forming!  The white glue provides a type of monomer called a hydrocarbon; sodium borate in borax causes these monomers to link together into a polymer.  However, gak is very squishy and flexible.  This is because 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.


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