Magnetic Slime

This little project feels like something out of a sci-fi, which perhaps is why I love it so much. Add some magnetite powder to your next batch of slime, get a strong rare earth magnet, and your kids (or you) will have a blast making zombie worms and magnet eating monsters- straight out of the movies!

Safety: Do not ingest any part of this project. Do not use any of the materials around small children or children who put things in their mouth. Too much iron is poisonous and it should not be ingested in this form. Rare earth magnets are very strong and can pinch fingers, be careful when using them. Magnets should never be left around small children who could ingest them. Do not use magnets near electronics or credit cards. The magnet in the video has a pulling force of 48 lbs. This was more than sufficient. If you are doing this with kids, do not use a more powerful magnet and only use one magnet at a time to avoid pinched fingers.

Materials

Procedure

  1. In a bowl or cup, dissolve the 1/8 tsp borax in 1/4 cup hot water. Set aside.
  2. To a different bowl, add 1/4 cup glue, 1/4 cup water, and 3 tbs iron oxide powder. Mix well. (Note: The powder will stain skin, so try not touch the iron oxide with your hands at this point, wait until the borax solution is mixed it. If you do get it on your hands, dish soap washes most of it off.)
  3. Slowly add the borax solution to the glue mixture and mix well.
  4. Take the slime out and knead with your hands till it is smooth. If it feels sticky, dip it in the extra liquid in the bowl and knead again.
  5. Start playing with the slime and magnet!

The Science Behind Slime

The glue contains a long molecule called polyvinyl alcohol (PVA). It is a polymer, which is a molecule that contains repeats of a subunit molecule (for example, “A” is a subunit and “AAAAAAAAAAAAAAA” is a polymer of A). Borax (sodium tetraborate) is a small molecule that can stick to parts of the PVA through hydrogen bonds. This means one side of the borate molecule can stick to one strand of PVA, while the other side of the borate can also stick to a different strand of PVA, creating a bridge between the two PVA strands. This is called crosslinking.

Having many crosslinking sites usually makes a polymer more rigid, but the interesting thing about borate/PVA crosslinking is that the bond is transient, meaning it can easily break and reform somewhere else. This causes the slime to act kind of like a liquid and kind of like a solid. If given time, the PVA can ‘flow’ as gravity pulls and breaks the borate/PVA crosslinks. It acts like a slime instead of a true liquid because as the PVA molecules pass by more borate, they can momentarily bond to borate and another strand of PVA, slowing down the flow. If you pull the slime fast, you break all those bonds quickly, allowing the slime to act like a solid momentarily.

The Science Behind Magnetic Slime

The iron oxide powder in the link above is magnetite, which is a natural mineral made of iron and oxygen. Like many iron-containing compounds, it is attracted to a magnet.

The iron oxide particles in the powder will become suspended in your slime matrix. As the particles are attracted to the magnet, they will pull the slime matrix with them, causing a whole section of the slime to move with it. This makes for some really cool effects!


If you’re looking for a project to use some of the leftover ion oxide powder, try our DIY Magnetic Shapes!

The Best Black Slime Recipe Ever

For the most perfect black slime recipe ever, look no further! Say goodbye to grit and residue with this amazing deep dark goop!

Materials

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Procedure

  1. In one bowl, dissolve 1/2 tsp of borax into 1/2 cup of hot water.
  2. In the other bowl, mix 1/4 cup of glue with 1/4 cup water.
  3. A tsp at a time, mix 4-6 tsp of activated charcoal into the glue/water mixture. It won’t mix in at first, but just keep stirring, it will eventually mix in! Just a minute or so of stirring. Stop adding when it’s black enough for you. Mix until thoroughly combined.
  4. Add 12 tsp borax solution to the glue mixture a teaspoon at a time while stirring. This slow addition of the borax ensures a super smooth slime without the need for lots of kneading. You will know when to stop adding when all of the black glue mixture is in the ball of slime and there is none left in a puddle at the bottom of the bowl.
  5. Pick up the glob and fold and squish a few times. You’re done! After you’re finished playing with it, store it in an air tight container. If it feels gooey after a few days, add a little more borax solution till you get the consistency you like. We think this gradual goo-ing might be due to the activated charcoal absorbing some of the borax (see below for what borax does!).

Discussion

The glue contains a long molecule called polyvinyl alcohol (PVA). It is a polymer, which is a molecule that contains repeats of a subunit molecule (for example, “A” is a subunit and “AAAAAAAAAAAAAAA” is a polymer of A). Borax (sodium tetraborate) is a small molecule that can stick to parts of the PVA through hydrogen bonds. One side of the borate molecule can stick to one strand of PVA, while the other side of the borate can also stick to a different strand of PVA, creating a bridge between the two PVA strands. This is called crosslinking.

Having many crosslinking sites usually makes a polymer more rigid, but the interesting thing about borate/PVA crosslinking is that the bond is transient, meaning it can easily break and reform somewhere else. This causes the slime to act kind of like a liquid and kind of like a solid. If given time, the PVA can ‘flow’ as gravity pulls and breaks the borate/PVA crosslinks. It acts like a slime instead of a true liquid because as the PVA molecules pass by more borate, they can momentarily bond to borate and another strand of PVA, slowing down the flow. If you pull the slime fast, you break all those bonds quickly, allowing the slime to act like a solid momentarily.

This dark black slime is perfect for Halloween. Throw some googly eyes, plastic spiders, or confetti in there for hours of fun!