The science of slime: What is it and why are we so obsessed?

Homemade slime is sticky, gooey and all the rage, but what is it?

Slime magic starts when you add something called sodium borate to water. In laundry detergent these are already mixed, but some slime makers do it themselves.

“When you add that compound – sodium borate – in to water, it makes an anion which is a negatively charged compound,” explained Raychelle Burks, an assistant professor of chemistry at Saint Edward’s University in Austin Texas.

Burks says that negative compound takes on a special shape.

“I like to describe it as if you looked at your hand you could turn it into a bit of a claw so you could grab stuff… that’s what this ion does.”

Next, this grabby ion meets the glue and starts…well, grabbing. Glue is made up of something called polymers. These are just strings of molecules bonded together. Burks says you can think of a polymer like a like a long, rubbery spaghetti noodle.

“When glue is just glue it’s a just a bunch of loose spaghetti noodles just sliding past each other,” she said.
“Once you add in the borax, you’ve added in a bunch of claws, and what that does is one claw grabs one sticky glue polymer, another claw grabs another one…now two polymer strands are actually connected through kind of a claw bridge.”

Burks says those polymers can no longer slide around. They become stuck. This happens all across the glue giving it a thicker, less runny texture. That’s how slime forms.

And did you know slime, quicksand and ketchup all have something in common? They are what’s called non-Newtonian fluids.

That means these fluids sometimes act like solids and sometimes act like liquids, depending on the force you apply to it.

For instance, if you threw water against a wall, it would just splash everywhere. Water is a Newtonian fluid. If you threw slime against a wall, it would smack, like a solid. However, if you slowly poured slime into a bowl, it would flow more like a liquid.

“So just how we treat it give us kind of different properties that we are seeing,” Burks noted.

Maybe that’s why slime is so fun to play with — it’s surprising compared to other liquids.

“It doesn’t do what we expect it to, because we expect things to be either a liquid or a solid. We usually don’t expect things to kind of exist in this middle realm.”

So make slime and experiment. See how different forces affect whether it behaves more like a solid or a liquid. Just remember to have an adult help you with this project. Oh, and keep slime out of your face and wash your hands when done. Have fun!