This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too! (Click here if you’re looking for the more recent version that also includes Chemical Engineering.)
When you think of slime, do you imagine slugs, snails, and puppy kisses? Or does the science fiction film The Blob come to mind? Any way you picture it, slime is definitely slippery, slithery, and just plain icky — and a perfect forum for learning real science. But which ingredients work in making a truly slimy concoction, and why do they work? Let’s take a closer look…
- Sodium tetraborate (also called “Borax” – it’s a laundry whitener) – about 2 tablespoons
- Clear glue or white glue (clear works better if you can find it) – about 1/2 cup
- Yellow highlighter
- Pliers or sharp razor (with adult help). (PREPARE: Use this to get the end off your highlighter before class starts so you can extract the ink-soaked felt inside. Leave the felt inside highlighter with the end loosely on (so it doesn’t dry out))
- Resuable Instant Hand Warmer that contains sodium acetate (Brand Name: EZ Hand Warmer) – you’ll need two of these
- Glass half full of COLD water (PREPARE: put this in the fridge overnight)
- Mixing bowl full of ice (PREPARE: leave in freezer)
- Disposable aluminum pie place or foil-wrapped paper plate
- Disposable cups for solutions (4-6)
- Popsicle sticks for mixing (4-6)
- Rubber gloves for your hands
- Optional: If you want to see your experiments glow in the dark, you’ll need a fluorescent UV black light (about $10 from the pet store – look in cleaning supplies under “Urine-Off” for a fluorescent UV light). UV flashlights and UV LEDs will not work.
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If you’ve ever mixed together cornstarch and water, you know that you can get it to be both a liquid and a solid at the same time. (If you haven’t you should definitely try it! Use a 2:1 ratio of cornstarch:water.) The long molecular chains (polymers) are all tangled up when you scrunch them together (and the thing feels solid), but the polymers are so slick that as soon as you release the tension, they slide free (and drips between your fingers like a liquid).
Scientists call this a non-Newtonian fluid. You can also fill an empty water bottle or a plastic test tube half-full with this stuff and cap it. Notice that when you shake it hard, the slime turns into a solid and doesn’t slosh around the tube. When you rotate the tube slowly, it acts like a liquid.
Long, spaghetti-like chains of molecules (called polymers) don’t clump together until you cross-link the molecule strands (polymers) together into something that looks more like a fishnet. This is how we’re going to make slime.
What’s Going On?
Imagine a plate of spaghetti. The noodles slide around and don’t clump together, just like the long chains of molecules (called polymers) that make up slime. They slide around without getting tangled up. The pasta by itself (fresh from the boiling water) doesn’t hold together until you put the sauce on. Slime works the same way. Long, spaghetti-like chains of molecules don’t clump together until you add the sauce – something to cross-link the molecule strands together.
The borax mixture holds the glue mixture together in a gloppy, gelatinous mass. In more scientific terms, the sodium tetraborate cross-links the long polymer chains in the glue to form the slime.
Why does the slime glow? Note that a black light emits high-energy UV light. You can’t see this part of the spectrum (just as you can’t see infrared light, found in the beam emitted from the remote control to the TV), which is why “black lights” were named that. Stuff glows because fluorescent objects absorb the UV light and then spit light back out almost instantaneously. Some of the energy gets lost during that process, which changes the wavelength of the light, which makes this light visible and causes the material to appear to glow.
Questions to Ask
- What happens when you freeze your slime? Is there a color change?
- How long does it take to thaw your slime in the microwave?
- Do you see the little bubbles in your slime?
- How many states of matter do you have in your slime now?
- Does this work with any laundry detergent, or just borax?
- What happens if you omit the water in the 50-50- glue-water mixture, and just use straight glue? (Hint – use the glow juice with the borax to keep the glowing feature.)
- Does your slime pick up newsprint from a newspaper?
- What other kinds of glue work well with this slime?