Simply Slime: An Introduction to Polymer Chemistry
Whether you want to introduce students to polymers, engage them with a fun science demo, or simply have the most popular station at your school’s science night, making slime is always a great idea. This non-toxic slime is easy to make and keeps the mess to a minimum. Turn the demo into a lesson with the extension ideas at the end of this article.
Safety and teacher tips
- Even though PVA slime is non-toxic, have students wash their hands after handling slime.
- Do not eat slime.
- Over-aggressive mixing of slime in the plastic bags can lead to rupture, resulting in a slimy mess. Double-bag the slime formulations or use thicker freezer bags to prevent tears.
- Slime residue can be removed using warm water, but it may be difficult to remove from carpet.
- If slime is allowed to dry, water will evaporate from it, leaving behind a thin polymer film. In some cases, it may be easier to remove the dried polymer film than to wash with warm water.
Slime is a type of polymer, which is a large molecule formed by many repeating units of smaller molecules. There are naturally occurring polymers, including cellulose (found in wood and paper) and starch (found in plants), as well as human made polymers, such as polyester (used in fabrics) and polystyrene (used in foam cups). Polymers are also known as plastics.
Slime has properties of both solids and liquids. Like a solid, slime can be formed into a ball and keep its shape. However, slime contains over 90% water and can flow like a liquid.
Poly(vinyl alcohol), or PVA, is a polymer used to make many plastics. The term polymer comes from the Greek poly, meaning “many” and meros meaning “part.” A polymer is a large molecule made up of many smaller molecules, called monomers. In Greek, mono means “one.” As the name suggests, poly(vinyl alcohol) is made of many units of the monomer vinyl alcohol.
Borax is the common name for sodium tetraborate decahydrate, Na2B4O7 · 10H2O. When added to water, borax forms the borate ion.
When PVA and borax are mixed, the borax connects chains of PVA so that a 3-dimensional network of chains is formed.
The PVA/borate cross-linked polymer, or slime, has many interesting properties:
- Slime contains water integrated into a solid network of cross-linked polymer chains, forming a gel. It’s sticky, slippery, and wet.
- Slime is self-healing, meaning if you break a piece of slime into pieces and squish the pieces back together, they will bond to each other and form one piece again.
- Slime is a high-viscosity, non-Newtonian fluid. This means that slime flows differently than liquids like water or oil.
Materials (per individual or group)
- 4% Sodium Borate Decahydrate, 5 mL (item #888580)
- 4% Polyvinyl Alcohol (PVA), 40 mL (item #882371)
- Graduated Cylinder, 10 mL (item #721610)
- Graduated Cylinder, 50 mL (item #721612)
- Small Resealable Plastic Bag
- Food Coloring (optional, any color)
- With the 10 mL graduated cylinder, measure 5 mL of 4% sodium borate decahydrate (borax) into the plastic bag.
- With the 50 mL graduated cylinder, measure 40 mL of 4% polyvinyl alcohol (PVA) into the same plastic bag.
- Add 2 to 3 drops of food coloring to the plastic bag (optional).
- The PVA/borax mixture will quickly gel and form a slime. Seal the plastic bag and mix the gelled slime for 3 minutes by kneading it with your finger from the outside of the bag.
- The slime can be handled, but should be stored in the plastic bag. It will last up to a week before beginning to mold, at which time it should be disposed of in a waste container.
- Examine the properties of slime:
- Pull it apart quickly into pieces and squish it back together.
- Pull it apart slowly to observe it stretch into a thin film.
- Throw or hit the slime on a tabletop—it doesn’t splash or splatter.
- Compare the properties of PVA slime to other non-Newtonian fluids, such as pudding, cornstarch slime (oobleck), and ketchup.
- Add water (0 mL, 5 mL, and 10 mL) to the basic slime formulation to compare how increasing water affects slime’s properties, including cohesion, adhesion, and viscosity.
- Use a water soluble marker to draw or write on a piece of paper. Press a ball of slime onto the paper and quickly pick it up. The ink will transfer to the slime.
- Place the bagged slime into the freezer and observe how the properties of the polymer change with temperature.