ChemixaLEARN CHEMISTRY

Polymer slime lab

Objective: make slime by cross-linking PVA glue with borate ions from contact lens solution, and explain its stretchy behavior with polymer networks. You will mix, knead, test the texture, and adjust the recipe.

Safety:

Do not eat the slime or any ingredients; keep them away from young children who might taste them. Wash hands after playing. An adult must supervise the entire activity and handle the contact lens solution. Store slime in a sealed container and throw it away if it dries out or smells odd.

Materials

  • White school glue (PVA-based)
  • Baking soda
  • Contact lens solution containing sodium borate
  • Water
  • Bowl and spoon
  • Measuring spoons
  • Food coloring (optional)

Procedure

1

Dilute the glue

Pour half a cup of white school glue into a bowl and stir in half a cup of water until smooth.

2

Add baking soda

Mix in half a teaspoon of baking soda until fully dissolved.

3

Color it (optional)

Add food coloring now if you want colored slime, and stir well.

4

Add the cross-linker

Add one tablespoon of contact lens solution and stir; the mixture will start clumping.

5

Build the network

Keep adding solution one teaspoon at a time, stirring, until the slime pulls away from the bowl.

6

Knead to finish

Knead the slime with your hands for three minutes until it is smooth and stretchy.

What to observe

  • The mixture thickens and pulls away from the bowl as solution is added.

  • The slime stretches slowly but snaps when pulled fast.

  • Kneading for a few minutes reduces stickiness.

  • Too much solution makes the slime stiff and rubbery.

Why it happens

School glue contains polyvinyl alcohol (PVA), a polymer made of long chains of repeating units floating loosely in water. Contact lens solution contains sodium borate, which releases borate ions that act as bridges, each grabbing onto two PVA chains at once. These bridges are called cross-links, and they tie the loose chains into a single three-dimensional network that traps water inside. The network can stretch and flow but holds together, which is why slime is elastic yet pourable. More cross-linker makes a firmer, less sticky slime; less makes it runnier. This is the same cross-linking idea behind rubber, gels, and many plastics.

Try variations

  • Change the amount of contact solution and rank the firmness.

  • Stretch the slime slowly versus quickly and compare.

  • Leave a piece exposed to air overnight and describe what happens.