These are great: ferrofluids are stable suspensions of ferromagnetic particles. Typically, the liquid is something organic and nonvolatile, and the magnetic particles are iron oxides (such as Fe2O3 or Fe3O4).
Why so neat? Look here. Magnets, moved around near a ferrofluid, can create beautiful patterns that are a direct effect of the field lines.
Image courtesy Flickr User Steve Jurvetson.
It's tricky stuff to make: generating liquid colloids is hard enough, but making one that's stable for any appreciable length of time is even harder. Over time, the particles tend to settle and aggregate. You can buy them, but they're a little expensive (100mL for $30, which is really quite a bit of the stuff). And why buy something when you can spend a great deal of time making something that works a fraction as well?!
The tricky part about making ferrofluids is making a colloid (rather than just some magnetic particles in liquid, which happily settle to the bottom). Two ways to help achieve this colloidal bliss this are: a) using small particles (at a certain point, thermal motion beats gravity) and b) chemically combating aggregation.
To get the small particles, you can either grow particles quickly, hopefully precipitating them before they grow too large, or just harvest laser toner, which apparently often contains a good chunk of magnetite (did you have any idea?)
To achieve the second part, you can use surfactants. As this Journal of Chemical Education Demo explains, detergents can form "reverse micelles," with their polar ends facing in and nonpolar ends facing out. This happens in organic solvents (where the nonpolar tails interact more strongly with the solvent than the polar heads; in water, the opposite is true). Apparently, a coat of detergent surrounds the metal oxide, allowing it to interact more strongly with the detergent (and providing a monolayer coat that helps prevent aggregation of the metal oxide surfaces).
Here, the circles represent the polar ends and the lines represent the nonpolar tails of a amphiphilic molecule such as sodium dodecanoate
Obviously, I've been playing with them. I didn't realize regular toner had ferromagnetic particles in it. I tried making some suspensions of toner in vegetable oil and WD-40 (which is pretty close to kerosene, if I remember correctly - anyway, it's just a nonviscous nonpolar liquid for our purposes). I have managed to get little lumps on the surface of the liquid, but no spikes. Give it a try and share your results!
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YES! Oh, man, this stuff is so much fun . . . I went to the Exploratorium last year and they had an exhibit with ferrofluid there, which might have been one of the coolest things in the place (a very high standard indeed).
Yep, little bits of iron in toner. Cereal too.
Maybe you could drag a magnet through some sand and get iron particles that way? I think Thedore Gray got some of his iron that way.
Anyway, I am so trying this this weekend. And I have plenty of oil and detergent around to boot!
Excellent article on magnetism. I forwarded a copy to my dad who just loves this kind of stuff - nice find and well written.
Ah, thanks for that lovely photo of the ferrofluid. Somebody should make little chocolate candies shaped like that and sell them to scientists. That picture looks good enough to eat!
I work with ferrites all the time, and they're pretty cool. One way to get a suspension is to use a high molecular weight polymer in conjunction with a low MW polymer dissolved in organic solvent (like isopropanol - rubbing alcohol) along with your surfactant (the detergent). The small chain polymers will coat the surface of the particles and tangle with the large chains, which will act as a "fluffy barrier" to keep the particles apart, preventing them from agglomerating due to surface charges and magnetic attraction(they can't get close enough to coalesce) and will also increase the viscosity of the liquid, making it harder for the particles to move around and "bump into each other". Small particles will help if you can keep them separated before you put them in the suspension, but otherwise they just have more surface area to cause electrostatic attraction, so you have to strike a balance there (very small particles tend to agglomerate easily and fall out of suspension). The best part of all this is if you use a solid polymer (that would be the high MW kind) that you dissolve, when you're done playing and everything dries out, you'll have made your own floopy plastic refrigerator magnet :) I'll let you figure out what powder/polymer ratios work best! Enjoy!
you can make this stuff easy, follow the steps.
http://chemistry.about.com/od/demonstrationsexperiments/ss/liquidmagnet…
enjoy.
que suave