The Science of Slime, by John Cowens
A slippery sort of activity your middle school students will love.
What is "slime" anyway? Well, if you look it up in the dictionary, you'll find several definitions. But for classroom purposes, it's a gooey polymer consisting of over 97 percent water – plus polyvinyl alcohol, which easily dissolves in water, causing its units to link and form "chains." This gives the solution a thick, syrupy appearance.
When borax (sodium tetraborate) is added to the polyvinyl alcohol solution, the chains of polyvinyl alcohol cross-link to form a viscous, elastic gel. Since the cross-linking is weak, the chains continually form and break under the weight of the gel or with handling. The mixture of polyvinyl alcohol, borax and water results in a rubbery, slimy colloid, which feels cool because it absorbs the heat from your hand.
Making green slime is one science activity kids will never forget – and that's guaranteed.
Unlike many types of plastic, this type dissolves in water. Hospitals use it to make laundry bags for storing clothing, linen, rags and other materials that might be germ-infested. The whole bag is thrown into a washing machine without ever being opened.
Following this investigation, students should be able to predict what will happen when 1) polyvinyl alcohol and borax are combined; 2) record observations made during the experiment; 3) explain the properties of slime and compare it to gelatin; and 4) discuss conclusions based on observations.
In most chemical supply catalogs, polyvinyl alcohol and borax are sold as dry powders. The borax is available in supermarkets; just look for the laundry soap called "Borax." The polyvinyl alcohol can be purchased from Science Kit & Boreal Laboratories at sciencekit.com.
The brewing process
Both chemicals need to be dissolved in water. The polyvinyl alcohol takes more of an effort, so if you have a crock pot, set it on low, sprinkle in the polyvinyl powder, stir and cover. For 20 students, use 40 g of polyvinyl alcohol for each liter of water. Stir every 30 minutes until the powder is completely dissolved. This should be done the day before.
When the powder is completely dissolved, there will be no evidence of particles in the water. But, the particles are clear, so check for them under a bright light. Pour the solution into a labeled storage bottle and save for later use.
To mix the sodium tetraborate (borax), use 5 g of borax per 100 ml of water. Dissolve the borax in warm distilled water, allow the solution to cool and transfer it to a labeled bottle.
If you don't want to go through this cheap brewing process, look through chemical catalogs for polyvinyl alcohol and sodium tetraborate in liquid form. High school and middle school science departments should have many such catalogs.
In addition to the two solutions, you'll need the following materials before the class can start the activity: 20 clear plastic cups (6 or 8 ounces); 20 popsicle sticks; a small bottle of food coloring (red, blue or green); paper and pencil. If you're dissolving the powder chemicals, you'll also need a crock pot and a stirring spoon.
Slime is born
Students begin by measuring 50 ml of polyvinyl alcohol and placing it in each cup. They then stir, stir, stir with a popsicle stick. Next, ask them to measure 5 ml of borax, put it in each cup with the polyvinyl and stir vigorously. End result: slime. And remember – if that's not slimy enough for the kids, they can always add more of the borax solution.
For colorful slime, simply add two drops of food coloring to the mixture and stir. Before the kids do that, however, warn them about the dangers of getting food coloring on their clothes. It may not wash out.
If you want to save the slime, cover the cup with cellophane. If you don't want to save it, just toss it out.
Examine the properties of the cross-linked polymer (a.k.a. slime) – or, in other words, play with it!
Discuss the students' predictions, observations and conclusions about the experiment.
Have the students record their observations about the experiment on paper.
Remove the slime from the plastic cup and observe its properties with the class. Does it stretch? Bounce? Hold its shape? Record all observations after each experiment.
Have the students decide how the slime is similar to and different from gelatin.
Have them draw conclusions regarding gelatin and properties they have observed in the slime.
White "flubber" or "pseudo plastic" is liquid white glue and sodium tetraborate (Borax laundry detergent).
A simple recipe
No time to gather and set up all the materials? Here's an alternative that will cut down on your preparation time considerably. The secret is to mix the ingredients at the start of the school day and investigate the slime in the afternoon.
You'll need two medium-sized bowls, a large bottle of liquid white glue, measuring spoons and cups. In one bowl, mix 1 1/2 cups of warm water and 2 cups of white glue. In the other bowl, mix 1 1/3 cup of warm water and 4 tsp. of Borax laundry detergent. Mix the contents of the second bowl with the contents of the first bowl.
In order for polymerization to occur, keep in mind that the chemicals need from two to three hours before the "plastic" can form. Drain off any water, break off a chunk and play with this new polymer.
John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.