GAK
Have you ever played with Silly Putty? Is it a liquid or a solid?
What is a cross-linked polymer? What is a dilatant? What is liquid armor?
To answer these questions & observe characteristics of solids & liquids, let’s make Gak
MATERIALS: 1 tablespoon Borax (20 MULE TEAM® borax can be bought at a grocery store in the
laundry detergent aisle)
1 1/4 cups warm water
2 plastic cups
1⁄ 4 cup white glue (Elmer’s Glue works the best)
food coloring
2 ziplock plastic bags
tablespoon
A measuring cup
paper towels & newspaper
PREP: remove jewelry, wear old clothes, cover table with newspaper. Have extra paper
towels available for clean up of hands & table.
Warning: Food coloring will stain clothes. Gak will stick to clothes & carpeting.
1. Add 1 Tbsp. of borax to 1 cup of warm water in a plastic cup. Stir until completely
dissolved.(some may not dissolve)
2. Make a 50% water : 50% white glue solution. Take 1/4 cup of each (water & glue)
and mix thoroughly in a plastic cup. Add a couple drops of food coloring and stir.
Note: mixing can be done using either step 3
3a. -In a ziploc bag, add equal parts of the borax solution (leaving the crystals that did
not dissolve in the cup) to equal parts of the glue solution. 1/2 cup of each will make
a cup of gak.
- Seal the bag and squeeze (knead) gently for ~ 3 minutes to mix. The glue will
thicken in the bag forming a wet, slippery slime.
-Open the bag and hold it over the sink to let any remaining liquid drain off.
- The Fun Gross Part: use your hands to scoop out your wet Gak. Knead the gak
until the excess liquid is absorbed. This will take a couple minutes.
3b. Slowly add the borax solution to the glue solution (while stirring the glue). The
glue will begin to “thicken”. Continue adding borax solution until most of the glue
is thickened & Gak is wet and slippery (don’t add too much borax or glue will harden)
-The Fun Gross Part: use your hands to scoop out your wet Gak. Knead the gak
until the excess liquid is absorbed. This will take a couple minutes.
4. now play with the gak.
Questions: Is Gak more like a liquid or more like a solid?
Try the following activities with your Gak to determine what properties (liquid or solid)
the Gak exhibits. Record your observations and list the properties exhibited.
1. Shape the Gak into a ball. Does it bounce?
2. Let the ball sit on the table. Describe what happens during the next five minutes.
3. Quickly poke your finger into the Gak on the table. What happens?
4. Try pulling some of the Gak slowly between your hands. Does it stretch?
Let go and see if it will snap back.
5. Hold the Gak between your fingers & allow gravity to do its thing. What happens?
6. What happens when you pull it hard and fast?
7. Is it more like a liquid or more like a solid?
Explanation:
The borax (sodium tetraborate: Na2B4O7-10H2O) is acting as the crosslinking agent or
"connector" for the glue (polyvinyl acetate) molecules. Once the glue molecules (long
strands called monomers) join together to form even larger molecules called polymers,
you get a thickened gel. The borax and glue form a highly-flexible, cross-linked
polymer. Two glue molecules (the monomer) become cross-linked by a borax
molecule via reaction of alcohol end groups. Acetic acid is generated as the
byproduct - two molecules per cross-link. Many borax cross-links occur, thus
"glomming" together many polymer molecules to form a pliable putty material.
If the long molecules slide past each other easily, then the substance acts like a liquid
because the molecules flow. If the molecules stick together at a few places along the
strand, then the substance behaves like a rubbery solid called an elastomer. Borax is
the compound that is responsible for hooking the glue's molecules together to form the
putty-like material. When the borax solution is added to the glue, the molecules of the
borax bind up the glue “strands” so that the glue no longer flows freely. A cross-linked
polymer is formed.
If you have access to a chemical supply house, try a 4% solution of polyvinyl alcohol
instead of the glue for a less rubbery polymer and one that is transparent showing off
the color better.
Gak behaves as a "dilatant" , which means it reacts differently to hard, fast pressure
than it does to slow, even pressure.
The polymers in silly putty and gak have covalent bonds within the molecules, but
hydrogen bonds between the molecules. The hydrogen bonds are easily broken. When
small amounts of stress are slowly applied to the putty, only a few bonds are broken
and the putty "flows". When larger amounts of stress are applied quickly, there are
many hydrogen bonds that break, causing the putty to break or tear.
Other Things to Try:
1. Does cooling improve the "bounceability"? If cooled too much, in a freezer for
example, will the putty shatter when bounced?
2. How does your putty deform with time? (Suggestion: Take a blob, roll it in a ball and
stick it to the side of a metal cabinet or refrigerator. See how far it flows as days go
by.) Does temperature affect the deformation?
3. What happens if you hit a ball of putty with a heavy object, such as a hard-cover
book?
This recipe is based on using a brand new 8 ounce bottle of Elmer's Glue.
1. Empty the entire bottle of glue into a mixing bowl. Fill the empty bottle with warm
water and shake (okay, put the lid on first and then shake). Pour the glue-water
mixture into the mixing bowl and use the spoon to mix well. Add the glue-water
mixture to the glue in the mixing bowl. Go ahead... add a drop or two of food coloring.
2. Measure 1/2 cup of warm water into the plastic cup and add a teaspoon of Borax
powder to the water. Stir the solution - don't worry if all of the powder dissolves. This
Borax solution is the secret linking agent that causes the Elmer's Glue molecules to turn
into slime.
3. While stirring the glue in the mixing bowl, slowly add a little of the Borax solution.
Immediately you'll feel the long strands of molecules starting to connect. It's time to
abandoned the spoon and use your hands to do the serious mixing. Keep adding the
Borax solution to the glue mixture (don't stop mixing) until you get a perfect batch of
Elmer's slime. You might like your slime more stringy while others like firm slime. Hey,
you're the head slime mixologist - do it your way!
4. When you're finished playing with your Elmer's slime, seal it up in a zipper-lock bag
for safe keeping. Place in a refrigerator to prolong life of slime.
The history of silly putty is quite amusing. In 1943 James Wright, an engineer, was
attempting to create a synthetic rubber. He was unable to achieve the properties he
was looking for and put his creation (later to be called silly putty) on the shelf as a
failure. A few years later, a salesman for the Dow Corning Corporation was using the
putty to entertain some customers. One of his customers became intrigued with the
putty and saw that it had potential as a new toy. In 1957, after being endorsed on the
"Howdy Doody Show", silly putty became a toy fad. Recently new uses such as a grip
strengthener and as an art medium have been developed. Silly putt even went into
space on the Apollo 8 mission to secure tools in zero gravity space.