Ferrofluid monsters

Imagine you put a lot of magnetic particles inside an oily substance, so that they get “stuck”, but they can flow. Then you got a ferrofluid. These fluids have very strange behaviour. Look at the almost alive forms in these videos…

Why do they behave like that? The magnetic particles get attracted by the magnetic field, and they “drag” the oil. Of course, a special kind of mixing is necessary here, but we won’t go into that. But, why the spikes? Because of the surface tension. As in any liquid, ferrofluids want to minimise their free-surface area, so the optimum shape is this array of conical shapes.

They do have practical applications. For example, in your hard drive, they are a good lubricant to the magnetic shafts. They are normally used as seals, since they will attach to any magnetized surface very tightly.

But, despite their name, ferrofluids are not ferromagnetic! The magnetic particles inside are not interacting, so it does not acquire a net magnetization in absence of external fields. I am developing myself some theory regarding possible “truly” ferromagnetic fluids, if they might exist… you know how theorists work, we have the idea, and then we pray the experimentalists to find it out…

With thanks to Rodolfo

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6 thoughts on “Ferrofluid monsters

  1. damn I tought this was the answer to my prayers…Long ago I saw that some german engineers created a kind of damping which could be modified on the move just by changing magnetic fields. So when I saw this I said thank god until I reached that last paragraph “… ferrofluids are not ferromagnetic…”

    any idea of how they can work theorist :D ??

  2. Yes, the technical term is “superparamagnetism”… but I think it requires explanation…

    All atoms are small magnets (we call them spins) and, normally, they polarize when you apply an external magnetic field. This behaviour is called paramagnetism. The material gets a magnetization, but it dies when you remove the magnetic field.

    A ferromagnet is different. Neighbouring spins like to point in the same direction. So, you start with all spins pointing randomly. Now you apply an external magnetic field. The spins all point in the same direction as the field. Now you remove the field and… voilà! the spins are kind of “attached” to each other, and they don’t lose the magnetization.

    A ferrofluid is made of tiny particles, each of which is ferromagnetic. But when you remove the external magnetic field the “attachment” is not strong enough, so they lose the magnetization. This behaviour is called superparamagnetism

    I know this was long… I hope it was clear! :)

  3. Well, I had heard about them, but I didn’t know of their artistic possibilities until a week back… See? There was a time, long back, when it was very normal for artists to know some science… :)

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