How Does Slime Work?- Science Explainer
Whether you think slime is amazing or disgusting, it’s one of our most popular STEAM experiments! But what’s going on under the slimy, science-y bonnet that makes it so interesting (and so gross).
Slime is a favourite among STEAMWORKS club leaders and kids at our activity workshops and FabLabs. Using nothing but household materials we can produce new a new polymer that’s not quite liquid and not quite solid either.
We all know what it looks like, but how does it work? This little blog tells you how slime gets so slimy using a little chemistry lesson!
The slime basics
Slime is a very special kind of liquid. First is it’s high ‘viscosity’. Viscosity is a measure of how quickly liquids flows. Water has a pretty low viscosity and flows quickly. Slime, however, has a much higher viscosity and runs much slower.
Slime is also a non-Newtonian fluid. Sir Issac Newton, 17th century scientist behind such physics blockbusters as gravity and the laws of motion, also studied liquids’ viscosity and how it changes at different pressures and temperatures. Because slime breaks most of the rules he set, we call it non-Newtonian.
Non-Newtonian fluids like slime react differently under different pressures, becoming thicker when hit quickly or runnier when held gently. That’s why other non-Newtonian fluids, like cornstarch mixed in water, can even be walked on!
Another way slime is special is it’s molecular structure. Slime is a polymer, meaning it’s made of lengthy chains of tiny particles called monomers which give it it’s strange properties.
The slime we make is made of PVA glue, bicarbonate of soda and a contact lens solution containing boric acid. We won’t give away all the slime making secrets here though! Check out our blog on how to make super simple slime:
Chemistry behind slime
Behind the scenes of this very fun and simple FabLab activity is a complex chemical reaction. It goes through multiple steps before you get to the oozy end product.
Our slime recipe combines two ingredients (reactants) which are polyvinyl alcohol (PVA) and borate ions. These two react together to produce the “products”, in this case a very long polymer chain that we know as slime.
Ions are very reactive, unstable particles which want to combine with something around them to become stable again. In slime making, we use borate ions which you usually get from a chemical called borax. Because borax is slightly toxic though, we use a mix of bicarbonate of soda and boric acid instead to make the ions we need.
There are actually a few more steps than this with many, many more ions. But today, we’ll stick with just borate ions to save time!
Bicarb (or sodium bicarbonate to chemists) can be used to make boric acid react and produce borate ions. Now, with borate ions and PVA glue free to mingle and react, and thousands of bonds are formed between them to make a long chain.
Slime is wet because water from the contact lens solution gets trapped in the chain structure.
At the same time, the large number of bonds between the glue and the borate ions means it’s strong enough to be picked up in your hands, bounced like a ball and to be pulled into stretchy shapes.
The reaction uses lots of energy to make so many bonds between the PVA glue and the borate ions. By taking and trapping so much energy from it’s surroundings the temperature in your mixing bowl it actually gets a little bit colder. This is called an endothermic reaction.
So, next time you’re making slime, concentrate and see if you can notice the slime getting cooler as you mix!
Slime troubleshooting
Now you know what’s going on under the microscope, you can figure out what to do if you run into any problems.
If your slime is too runny and passes through your fingers if you try to pick it up, not enough bonds have formed. To fix it you need more borate ions, so mix in more bicarb to thicken your slime.
Is it too thick? Add small amounts of contact lens solution or even more PVA until you get it just right.
