To make a polymer.
- Masking tape
- 2 1-pint (500-mL) jars
- 4-ounce (120-mL) bottle of white multipurpose school glue
- Tap water
- 2 mixing spoons
- 1 teaspoon (5 mL) borax powder (found near laundry detergents in the supermarket)
- 1-cup (250-mL) measuring cup
- 2 3-ounce (90-mL) paper cups
- 2-quart (2-L) bowl
- 12-inch (30-cm) -square piece of waxed paper timer
CAUTION: As with any chemistry experiment, follow warnings on the containers of the materials used. Do not eat the glob produced.
- Use the masking tape and marker to label the jars "Borax" and "Glue."
- Pour the glue into the Glue jar.
- Fill the empty glue bottle with water and pour the water into the Glue jar. Stir the glue and water to mix them together thoroughly.
- Put the borax and 1 cup (250 mL) of water into the Borax jar. Stir, using a different spoon, until the borax dissolves.
- Fill the paper cups, one with the glue-and-water mixture and the other with the borax-and-water mixture.
- Pour the contents of each paper cup into the bowl, using either spoon to stir the mixture until it thickens.
- Take the thickened substance called glob that forms out of the bowl and place it on the waxed paper for 1 to 2 minutes. Then remove the glob from the paper and knead it with your hands for about 1 minute.
- Try these experiments with the glob and record your observations of how the glob responds in a data table:
- Roll the glob into a ball and bounce it on a smooth surface.
- Hold it in your hands and quickly pull the ends in opposite directions.
- Hold it in your hands and very slowly pull the ends in opposite directions.
You have made a soft, pliable (easily bent) material that spreads out when not confined, bounces slightly when dropped, breaks apart if pulled quickly, and stretches if pulled slowly.
In this experiment, a chemical reaction occurs when the reactants—borax, glue, and water—combine to form a cross-linked polymer called a glob. Cross-links are chemical bridges between two molecules. A polymer is a large, chainlike molecule made by combining many small single molecules called monomers. In this experiment, the borax forms bridges (cross-links) between the polymer chains in the glue much as the rungs of a ladder link the two sides together. The cross-linked polymer produced is much more viscous (thick; having a high resistance to flow) than the glue.
The glob has some properties of a solid—for example, it breaks when pressure is applied—and some properties of a liquid—for example, it flows. Sir Isaac Newton (1642–1727), an English scientist, described fluids (liquid or gas) as materials that flow under pressure. Since the glob flows, it is a fluid. But unlike the fluids described by Newton, the glob has some properties of a solid, so it is called a non-Newtonian fluid.
For Further Investigation
The cross-links make the glob less fluid than glue. Would more cross-links make the glob solid? A project question might be, How would the concentration of the reactants affect the fluid property of the glob?