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 basics

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.

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.

Slime Polymerization

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.

Basic Slime Recipe


Materials (per individual or group)

Procedure

  1. With the 10 mL graduated cylinder, measure 5 mL of 4% sodium borate decahydrate (borax) into the plastic bag.

  2. With the 50 mL graduated cylinder, measure 40 mL of 4% polyvinyl alcohol (PVA) into the same plastic bag.

  3. Add 2 to 3 drops of food coloring to the plastic bag (optional).

  4. 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.

  5. 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.

Magnetic Slime

Oozy, gooey, sticky, and fun, the creation of magnetic slime is a good way to get your students interested in polymers and magnetism. In this lab activity students will create a poly(vinyl alcohol) polymer that has iron(II, III) oxide incorporated into its matrix. Because of the incorporated iron(II, III) oxide, the slime is attracted to neodymium magnets.

Magnetism

Magnetism is the ability of a material to attract iron and produce a magnetic field. The word magnet comes from the Greek word, magnes, meaning “the stone of Magnesia.” In the region known as Magnesia, the Greeks found a magnetic iron ore called lodestone that attracted other iron-containing materials. Magnetism does occur naturally, as the Greeks discovered, but it also can be created or “induced” in certain materials, especially iron, nickel, and cobalt. In many instances, this magnetic property is weak or temporary. Whether natural or induced, permanent or temporary, each magnet produces a magnetic field. A magnetic field is an area where magnetic lines of force can be felt or measured. These lines of force seem to “flow” through and around the magnet, out from the north pole, then back in through the south pole of the magnet.

Magnetic Lines of Force

Scientists use the orientation of magnetic domains to help explain the behavior of magnets. A magnetic domain is a molecule of a substance that acts as a tiny magnet and exhibits a tiny magnetic field. In non-magnetic objects, the domains are oriented randomly. As a result, the magnetic fields cancel each other out. In magnetic objects, however, most or all of the domains are oriented in the same direction; they are aligned so that their magnetic fields combine to create a net magnetic field.

Unmagnetized Material (left) and Magnetized Material (right)

Materials for magnetic slime (per group)

Procedure

  1. Place a neodymium magnet in a small plastic bag. This will keep it clean while you perform your experiments.

  2. Place 15 mL of water in 1 of the 2 plastic cups.

  3. Add 0.2 g of borax to the water. Stir the solution with a spoon until all of the borax has dissolved.

  4. In a separate cup, place 40 mL of PVA.

  5. Add 5 g of Iron(II, III) oxide to the PVA. Stir the mixture with a clean spoon until the Iron(II, III) oxide is dispersed evenly.

  6. Pour the borax solution into the PVA mixture.

  7. Stir the mixture with a spoon. The solution should come together quickly in a gel, forming slime.

  8. Pick up the slime and mix it with your hands, then place it in a large weigh boat.

  9. Bring the magnet in the plastic bag towards the slime but do not touch it. Determine how far from the slime the bag is when the slime starts being pulled toward the magnet.

  10. Remove any slime from the exterior of the plastic bag and from your hands by washing them with soap and water.

  11. Open the plastic bag and add another magnet.

  12. Bring the magnets in the plastic bag toward the slime but do not touch the slime. Determine how far from the slime the bag is when the slime starts being pulled towards the magnets.

  13. Repeat steps 10–12.

Extension activities

  • 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.

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