Experiment #14: Polymers
The Ghostbusters made slime famous with "I've been slimed" line from Bill Murray and the scenes of ectoplasm (slime) used throughout the movie.
|Slime has a wide range of behaviors. It can of course be slimey and runny like mucus. But it can also be fairly stiff like a rubber ball and bounce.
|Slime is made of two components. One is a polymer that dissolves in water. The other is a salt that crosslinks the polymer chains together. The two strands of polymers here are made of a chain of carbon atoms. This slime has every other carbon with an oxygen atom which is connected to a hydrogen. The polymer name is polyvinyl alcohol. The OH's are why it's called "alcohol." Vinyl is the building block. It consists of 2 carbons and 3 hydrogens and readily connects to itself to form chains. Here the right carbon connects to OH. In other polymers the OH is replaced by something else.
The salt used for crosslinking these polymer chains together is borax (sodium borate). Borate has one boron atom surrounded by four oxygen atoms, each with a hydrogen. Borate's hydrogen atoms are attracted to the oxygen atoms in the polymers (dotted lines). Likewise, borate's oxygen atoms are attracted to the hydrogen atoms in the polymers. This holds the chains of polymers together, which gives it more stiffness. The more borate molecules the more stiff the slime will be.
Equipment needed to do experiment
You will use the 250 mL beaker, the 100mL graduated cylinder, and the small plastic cup that came with your kit.
You will use the Borax powder. You will also use Polyvinyl alcohol. You may have two tubes of polyvinyl alcohol. This will let you do the experiment twice.
The polyvinyl alcohol powder you have will need to be dissolved in water and that takes some heating and a lot of stirring.
Some background information
I did this experiment three times in order to get it where I think you will have success. My first time was a failure. I followed the instructions from a book that gave measurements in teaspoons and tablespoons. It also said that hot tap water was all you needed to dissolve the polyvinyl alcohol. When this didn't work, I found another source on making slime which appeared more scientific. I followed those instructions and it worked fine.
Basically the instructions were to make up a 4% solution of polyvinyl alcohol and a 4% solution of borax. In medicine and chemistry a 4% solution is normally interpreted to mean 4 grams of the solid dissolved in every 100 milliliters of water.
|So I weighed out 4.0 grams of polyvinyl alcohol and placed it in 100 mL of water. I did the same thing with the borax.
For this experiment, I weighed the tube filled with polyvinyl alcohol. It measured 10.8 grams.
I then found the weight of the empty polyvinyl test tube. It was 6.0 grams (see below). Therefore, by subtracting the weight of the empty tube from the full tube of 10.8 grams, I found that you had 4.8 grams of polyvinyl alcohol in your kit.
But we could not put this in 100 mL of water, because it would not be a 4% solution. We needed more water because we have more than 4.0 grams; we had 4.8 grams. So here's the math. The fraction 4 grams over 100 mL is 4% solution. If we divide 4 by 100, we get 0.04. We need 4.8 to be divided by some volume that is also equal to 0.04. So we make an equation.
4 grams = 4.8 grams
To solve for ? volume, we can do some cross multiplying.
4 grams x ? volume = 4.8 grams x 100 mL
Then divide both sides by 4 grams.
4 grams x ? volume = 4.8 grams
x 100 mL
The 4 grams cancel on the left and we end up with:
? volume = 120 mL
So we need to dissolve the 4.8 grams of polyvinyl alcohol in 120 mL of water in order to have the same concentration as 4 grams in 100 mL of water (4% solution).
The Borax tube with borax weighed 12.4 grams. The empty tube was the same as the empty polyvinyl alcohol tube (6.0 grams). So that means the borax tube must be holding 6.4 grams of borax. To make a 4% solution we need to dissolve the 6.4 grams in enough water to be equal to 4%. We use the same formula as before.
4 grams = 6.4 grams
4 grams x ? volume = 6.4 grams x 100 mL
Then divide both sides by 4 grams.
4 grams x ? volume = 6.4 grams
x 100 mL
The 4 grams cancel on the left and we end up with:
? volume = 160 mL
So we need to dissolve the whole tube of borax into 160 mL of water in order to get 4%. Our graduated cylinder only goes to 100mL, so we will first measure out 100mL followed by 60mL.
INSTRUCTIONS FOR DISSOLVING THE POLYVINYL ALCOHOL
|Fill your 100mL graduated cylinder to close to the 100mL mark with tap water.
|Pour the 100mL of the water into the 250mL beaker.
|Get some more water and make it close to 20 mL. Add this to the 100mL of water already in the beaker.
|Pour the whole contents of the polyvinyl alcohol tube into the 120 mL of water slowly. Keep stirring.
If you were like me, the polyvinyl alcohol doesn't dissolve very easily. This is where I learned about the different purity levels of polyvinyl alcohol.
Apparently, polyvinyl alcohol is made from another polymer, polyvinyl acetate. See the two red oxygens, the two gray carbons, and three white hydrogens? That's acetate. When polyvinyl alcohol is made, these acetates are supposed to come off and be replaced by alcohol groups (one oxygen and one hydrogen). Often not all of these acetates come off. This can make the polyvinyl alcohol polymer not as water soluble as it would be if all acetates had come off.
The container that I got the polyvinyl alcohol from did not indicate the purity. So it's possible that it contained some residual polyvinyl acetate, which made it less water soluble. So that means we have to heat it.
To begin I turned the electric stove temperature to the second lowest temperature. If using a gas stove, turn it as low as you can. A microwave oven is another option (see below).
|Here it is sitting on the smooth stove top of the electric stove. Place a thermometer in it to check the temperature.
|An alternative is the microwave oven. But you only want to heat it for about 15 seconds at a time. You can leave the stirrer in it, but don't leave the thermometer in the beaker, it has metal on it!
|From either using the microwave or the stove top, get the temperature to between 160 degrees Fahrenheit and 180 degrees Fahrenheit. Keep stirring with the stirring rod.
|If using a electric stove top, turn down the temperature to low once the liquid is above 160 degrees.
Keep stirring and heating until most of it is dissolved. It will take several minutes. You won't get every bit of it too dissolve, but try to get as much as you can to dissolve.
Turn off the heat.
|Once it cools enough to pick up, set it on a plate or saucer to further cool down. It should get below 120 degrees before using. While it's cooling we can make up the borax solution.
|Let your tap water get hot and fill up the 100mL graduated cylinder with 100mL of hot tap water. Pour that into the plastic cup shown a the top of this Web page.
|Remember, we need a total of 160mL of water to make the borax we have a 4% solution. So measure 60 more milliliters of hot water and pour it into the plastic cup.
|Now you can add the borax (hydrated sodium borate) to the 160mL of hot tap water. The 6.4 grams of borax and 160mL of water should be 4% solution because dividing 6.4 grams by 160mL equals 0.04
|You can use the microspatula to stir the borax to help it dissolve. The stirring rod is still in the dissolved polyvinyl alcohol.
So here's our 4% polyvinyl alcohol solution on the left and the 4% borax solution on the right.
Take a picture of at this point before you mix the two ingredients.
|If you want, you can add one drop of food coloring to the polyvinyl alcohol solution. In my first two experiments I didn't. The second one, which was successful, produced a clear slime that looked like mucus. It's the first picture on this Web page.
|Notice that we have about 100mL left, even though we started with 120mL. Some of the water must have evaporated in all the heating.
|Here's a moment of decision. According to the literature, slime can be made by adding borax solution that is from 1/20 to 1/2 the volume of the polyvinyl solution. Since we have 100mL of polyvinyl solution, 1/20 of that is 5mL and 1/2 of that is 50mL. 5mL of the borax solution would make it slimey and runny; 50mL should make it stiff like a rubber ball. For me, I tried about half way in between, which is 25mL of borax solution. You can try a different amount of borax solution. Just record how much you used.
|So I measured out 25mL of the borax solution in the graduated cylinder and poured it in as I stirred vigorously. This is where a helper is handy. Someone can do the pouring as the other stirs vigorously and holds on to the beaker. The liquid will start getting thicker in a couple of seconds. Stir until it won't let you stir.
|In a few seconds, the polyvinyl polymers are crosslinked by the borate molecules (remember the illustration at the beginning?) This turns the liquid into a strange gel.
At first it seemed like a clump of Jello. I was a little disappointed.
It started flowing, behaving much different than Jello.
Drooling and stretching while feeling cold and slimey.
It slowly engulfs whatever it encounters.
What if it also had the power to take control over the brain...?
(Take some pictures of your slime, even if it didn't work. Also include a picture where I can see your face. No, you don't have to be slimed.)
Elmer's Glue-All contains two polymers, polyvinyl alcohol and polyvinyl acetate. The borax cross-links these together to make something like Silly Putty. The beauty of this approach is that it's fast. No time needed to dissolve the polyvinyl alcohol powder; however, this isn't the one I want you to make for this lab. I just mention it for something you may do in the future.
The school children that come to our college on Science day make "Silly Putty." This "slime" is not translucent like the type we made here with polyvinyl alcohol and borax.
Email the tap water temperature, plus the picture taken before you mixed the polymer and the borax and some pictures after you mixed them, plus at least one with your face visible.