In this chemistry project, we'll learn about polymers as a type of molecule. To do this, we'll make slime by combining glue with liquid starch and water.
Introduction to Experiment
To start, here are the basics to our experiment.
|| To create a polymer with glue and water but no borax
|| Middle school and up
|| 1 hour, plus as much time as you like to enjoy the slime
When you think about slime, you probably think of the toxic waste from comic books or movies, an electric green liquid oozing from barrels dumped somewhere. But what if you could make slime at home? Don't worry, we won't make a toxic version that might turn your pet turtle into a monster, but rather a fun version you can add glitter and food coloring to. And since we are scientists, we'll also learn about the chemical principles that allow us to turn two common household items - glue and liquid starch - into the fantastic compound that has both the properties of solids and liquids: slime.
Before you start, consider why adding starch to glue would create slime. What is going on between the molecules in the substances we start with?
All right, here are the materials that we're going to need for this project:
- 1 cup white craft glue, like Elmer's
- 1/2 cup room temperature water
- 1/2 cup liquid starch
- Bowl for mixing
- Measuring cup to measure the liquids
- Glitter or food coloring (which is of course optional, but fun)
Now let's cover our three main steps for our experiment:
- First, combine the glue and water in a bowl. Mix until they are homogeneous, meaning they're all essentially the same, single substance.
- Next, add any food coloring or glitter you'd like to your slime. Again, mix thoroughly.
- Then, add your liquid starch. Continue to mix with the spoon until it reaches a thick consistency you can hold.
Also make sure you conduct some troubleshooting. For example, if your slime is too runny, add some more liquid starch. If it's too thick, on the other hand, you can add more water to the glue to thin it out.
Then all you have to do is consider these discussion questions:
- What happened when you added the liquid starch?
- Why do you think the starch was the key ingredient to solidify the glue into slime? How did it change the glue molecules?
How It Works
Liquid glue is a polymer, or a long molecule made of repeating units of a single molecule called a monomer. There are both natural and synthetic polymers. For example, wool is a natural polymer while all plastics are synthetic polymers. The craft glue we use is called polyvinyl alcohol (PVA) and is made up of repeating molecules of vinyl alcohol. We can compare polymers to LEGO toys. Let's imagine you had 100 red LEGO bricks. The individual LEGO bricks are your monomers. If you link all the bricks together in a chain, you have a polymer.
Glue is a liquid polymer, meaning the long PVA chains aren't linked together. There are thousands of individual chains in the glue mixed with water molecules, but they don't stick together. The water allows the PVA chains to slide past each other, which makes the glue a sticky liquid.
Starch is also a polymer, made of repeating units of a sugar called glucose. When the starch chains interact with the PVA chains, they stick together, slowing down the movement of the PVA polymers. The starch chains weave in and out of the PVA chains, the way strands of wicker are woven together to make a basket. The basket still stretches when pulled, but it ultimately comes back to the same shape. This is how the starch and PVA chains come together to make slime.
The more starch you add, the more weaving will happen between the polymers, and the stiffer the slime will be. When you add less starch, there is less weaving and the slime will be more runny. You can experiment by adding more or less starch to see how it affects the consistency of your slime.
Borax is another agent used to create slime with glue. The borax, however, acts as a crosslinking agent. It binds to multiple PVA chains, holding them in place together. This creates the same effect as the starch but does so due to a different type of chemical reaction. The starch does not actually bind to the PVA chains, but rather winds around them, creating a similar effect.
All right, let's take a few moments to recap the important information we learned about this experiment involving making slime. The limitation we placed on ourselves was making slime without the aid of borax, which is a normal crosslinking agent which binds to multiple PVA chains, holding them in place together. The key was using liquid glue, which is a polymer, or a long molecule made of repeating units of a single molecule called a monomer, as well as starch, which is made of repeating units of a sugar called glucose. After getting all the materials together, we followed the necessary steps, which included the following:
- Combining the glue and water in a bowl and mixing until they're homogeneous, meaning they're all essentially the same, single substance.
- Adding any food coloring or glitter you'd like to your slime. Again, mixing thoroughly.
- And, finally, adding your liquid starch and continuing to mix with the spoon until it reaches a thick consistency you can hold.
So now you should be able to make slime without borax with very little trouble.