Ferrofluid

by Stephanie Chasteen on December 20, 2007

ferrofluidI just realized I haven’t yet written about ferrofluid… I was mentioning it to a few folks last night over dinner (no, dinner with me isn’t as geeky as I’d generally like) and they hadn’t heard of it.

Ferrofluid is a thick oil with tiny suspended particles of iron (magnetite) in it. That means that it behaves like a magnetic fluid — it’s attracted to magnetic fields. You can make this fluid jump with a bar magnet. The picture on the left shows a ferrofluid that is on a surface above a bar magnet. The “hedgehog” shape shows the lines of the magnetic field.

Remember when you were in middle school and you sprinkled iron filings on a piece of paper above a bar magnet? You could see the “magnetic field lines” as the filings lined up on either side of the bar magnet, and made spiky things on the ends. Here’s an image of that, to the right.magnet0873.png Well, this is the same sort of thing. The hedgehog spikes just show the same thing as the iron filings, but in three dimensions.
It’s hard to make ferrofluid, though. I know, I’ve tried. You can take corn oil and put iron filings in it, and that’s kind of fun, but the iron filings just sit in the bottom of the jar. Stick a magnet to it and the filings still look spiky, they don’t flow smoothly. I’ve tried taking magnetic toner powder (used for printing magnetic ink on checks) and suspending that in motor oil, but it’s not magnetic enough. The first problem is the oil — it has to be something very thin (30W motor oil is supposed to be thin enough) so that it can flow, but not so thin (like mineral oil) that the magnetite settles out. Also, big particles, like filings, tend to settle out because they’re heavy. So they make tiny (often nano-sized) particles so that their weight can be held up by the oil. But, when you make particles that tiny, they have a tendency to clump together. So you need some sort of “surfactant” — a coating on the particles that keeps them apart. (Soap is a “surfactant” because it keeps grease molecules apart). Plus, you need the surface tension on the fluid to counterbalance the magnetic attraction in just the right amount so the fluid holds together but it responds nicely to the magnetic fields. You can imagine, for instance, if this had a low surface tension (like water) the stuff would just stream onto the magnet and not hold together enough to make these shapes.
So, it’s hard to make good ferrofluid. But once you do, it’s a lot of fun. You can make it defy gravity by bringing a magnet down towards it from above, until it jumps up to the magnet. (Word to the wise, put the magnet inside a test tube or something, or else you’ll *never* get the ferrofluid off). You can make beautiful patterns, as in “Ebb Protrude Flow”, in this YouTube video.

[youtube=http://www.youtube.com/watch?v=GPvo4fJSTRQ]

Or this one also beautiful

In practice, ferrofluid is used to dampen high-end speaker systems (I don’t know much about that), and also in space, where you can’t make hydraulics work like they do on earth because there’s no gravity. Instead, the hydraulics can be driven and precisely controlled using magnetic fields.

{ 30 comments }

s_fassnacht December 25, 2007 at 7:18 am

Hello,
I recently read your blog on Ferrofluids and figured you might be able to help me out a bit. For my AP Chemistry II class i have to do a research project and have the discovered the interesting quality’s of Ferrofluids. However, the only way i can come up with to present my project is placing drops of Ferrofluid between two glass plates and subject them to strong electromagnetic forces so it kinda spins about, while I talk about the science behind it. If you have any ideas of something more creative or something that could improve my presentation would be excellent.

Also, what would you recommend as the best Carrier for the Ferrofluid and the best Surfactant.

Also, if you have never heard of the glass plate thing here is the link in which i discovered it: http://wohba.com/2005/10/magnetic-liquid-weirdness.html. Do you believe that there would be any way to suspend the Ferrofluid in mid-air while it does its acrobatics to be more eye appealing?

s_fassnacht December 25, 2007 at 3:27 pm

A thought just occurred to me, I have read that the Ferrofluid is nearly a solid, is there any way to make it completely solid. If so, how could you go about it.

sciencegeekgirl December 26, 2007 at 1:53 pm

Hi s_fassnacht,

Some great questions. Here’s what I know — I’ll put each in a separate comment.

1. “Placing drops of Ferrofluid between two glass plates”…
What you’re talking about is called “constraining” the ferrofluid… you’re making it into something flat (two-dimensional) and not letting it go up or down. The behavior of ferrofluid when “dimensionally constrained” like this is quite fascinating. It’s also pretty different from ferrofluid that just flows around in three dimensions. We had an exhibit at the Exploratorium that constrained ferrofluid like this, but I don’t think we ever figured out just why it behaved as it does. YOu can see some amazing videos of constrained ferrofluid at http://youtube.com/watch?v=A5OhZ9wT568

sciencegeekgirl December 26, 2007 at 2:02 pm

“If you have any ideas of something more creative or something that could improve my presentation would be excellent.”

I think the behavior of ferrofluid on its own is fascinating. People are amazed by this stuff.

“Do you believe that there would be any way to suspend the Ferrofluid in mid-air while it does its acrobatics to be more eye appealing?”

Not mid-air, but close. I did a short webcast with ferrofluid (see the last video at http://www.exo.net/~drsteph/webcasts.html), and what I did was to get a clear plexiglass surface. Any plastic will do, but you want something that the ferrofluid beads up well on instead of sticking to too much. *Don’t* use glass — when playing with strong magnets it’s too easy to break glass.

Neodymium magnets are the best to use for these demonstrations as they’re very strong. However, they can be VERY dangerous as they are strong enough to pinch your skin and really hurt you. If you ever have more than one neodymium magnet, hold them far apart from each other so they don’t inadvertently stick to each other. When they snap together they can REALLY hurt you! They can also shatter. If you do want to stick them together, bring them slowly towards each other so they stick carefully. You may even want to wear gloves.

I put some neodymium magnets into a plastic test tube (again, don’t use glass!), like you can see in the picture on my website. Then I brought those magnets over the ferrofluid, which leapt up onto the test tube. The crowd was pretty excited.

Of course, you then have ferrofluid stuck to a test tube. It’s tricky to get the magnets out without getting the ferrofluid on them. I had attached a string to my magnets so that I could pull them up out of the test tube, and that mostly worked, but I did get some ferrofluid creeping up the test tube with them and it got on the magnet.

I also made a kinetic sculpture using bolts and nuts. I made a symmetric pile of a few bolts and nuts on the plexiglass sheet, and put some strong magnets underneath it. I then poured ferrofluid on top of it, which streamed to the sculpture, attracted by the magnetic field. It got spiky and I could even twirl the spikes. Neat.

All of this only works with the commercial grade ferrofluid — you gotta buy it, the homemade stuff doesn’t cut it.

sciencegeekgirl December 26, 2007 at 2:04 pm

“Also, what would you recommend as the best Carrier for the Ferrofluid and the best Surfactant.”

If you already have commercial grade store-bought ferrofluid, you don’t have to worry about it. It’s already got a surfactant in it, and the greasy oily stuff is the carrier.

If you want to make your own, the best procedure we’ve found was made by my colleague: http://www.exo.net/~jillj/activities/ferrofluid.pdf

sciencegeekgirl December 26, 2007 at 2:05 pm

“I have read that the Ferrofluid is nearly a solid, is there any way to make it completely solid. If so, how could you go about it.”

I think what you are referring to is the fact that ferrofluid “turns solid” in the presence of a magnetic field. You see how it gets the little spikes on it and it seems to become solid when you put a magnet near it? That’s what they mean when they say it turns solid in a magnetic field. So, really, the only way to get that solid-like behavior is to put it near a magnet. The stronger the magnet, the more clear the effect.

Hope this helps!

s_fassnacht December 26, 2007 at 2:17 pm

Ya thanks it did. But with the magnet there is it a solid? And if it is how fragile is it?

Also, for my project i need something to prove. Thats why im asking about it being a solid or not. I was thinking, maybe, if it isn’t a solid if there a way to make it actually “hard”. If you have any other ideas for something that could be proved with ferrofluid.

sciencegeekgirl December 26, 2007 at 3:15 pm

Hi there,
What is the definition of a solid? Perhaps if you start with that, you can consider the ways that ferrofluid is and isn’t a solid. Or, is ferrofluid truly a “fluid”? In what ways is and isn’t it a fluid? Maybe if you start there, you will come up with some nice things you can “prove”. (Of course, we usually don’t say “prove” in science… you can prove things in math, but in science we can demonstrate certain principles but not generally prove that they are true).

s_fassnacht December 28, 2007 at 4:03 pm

Ok.. that sounds good.. How could u test if something ir truly a fluid?

sciencegeekgirl December 28, 2007 at 4:06 pm

Well, what *is* the definition of a fluid and of a solid? I think you need to start there. Then brainstorm a few ways to see if ferrofluid fits that definition. Throw out a few ideas and I’ll be happy to give feedback!

s_fassnacht December 30, 2007 at 12:24 pm

Well, from what i can tell a liquid is something that flows and from what i have read ferrofluid doesnt flow with out the carrier or the surfacant. And with it being a solid the magnetic particles are solid and since i have never actually seen ferrofluid i dont know if the spikes it creates are solid or if u touched one, i dont know what it would do.

Is there a way to see if it is a liquid besides just observation?

sciencegeekgirl January 2, 2008 at 1:14 pm

What exactly do you mean by “a liquid is something that flows?” What does it mean to flow? Is that the best definition that your science text book (or WIkipedia) gave you? You need to be as precise as possible in your definitions of something if you want to test whether or not it’s true.

Will you be getting some ferrofluid to test out? It’s hard for you to demonstrate something if you don’t have the stuff. I’ll tell you that if you make those “spikes” with the ferrofluid by bringing a magnet near it, and then turn the whole thing upside-down, the “spikes” will stay — they won’t drip away. But if you touch it with your finger, you can squish them down.

Do you think the force of gravity pulling on the ferrofluid (when you turn it upside down) is greater than the force of your finger (squishing it down) or the other way around? What does that tell you?

s_fassnacht January 9, 2008 at 7:57 am

With the suggested procedure to make the ferrofluid. Does it need the carrier fluid and the surfacant added or is it already in?

sciencegeekgirl January 9, 2008 at 8:16 am

If you’re using commercial ferrofluid, it already contains carrier fluid and surfactant.

If you’re making your own, you only need a surfactant if you’re using nano-sized particles, because those particles tend to clump together. That is the case with the ferrofluid recipe I gave at http://www.exo.net/~jillj/activities/ferrofluid.pdf, but it tells you exactly how to make it and what to use as a surfactant and carrier fluid.

Or you can just stick iron filings into motor oil or mineral oil and it acts “sort of” like ferrofluid (but not really, the particles are too big).

Agebtelty December 18, 2008 at 7:30 pm

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mnorgovudkka December 28, 2008 at 8:03 pm

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Lavacoa January 5, 2009 at 11:27 am

I’m interested in making Ferrofluid, but I’m having a hard time finding nano-sized iron particles. Do you know where I might be able to find a supplier?

sciencegeekgirl January 5, 2009 at 11:58 am

Hi Lavacoa,

It’s tricky but there are a few things you can try. See the PDF at http://www.exo.net/~drsteph/activities/ferrofluid_chasteen.pdf for a few suggestions. For commercial nano-sized iron particles, and step by step instructions on how to make ferrofluid with them, see http://www.exo.net/~jillj/activities/ferrofluid.pdf.

Bazooka November 19, 2009 at 11:27 am

hey lavacoa!
http://www.chemicalstore.com/navigation/detail.asp?id=FE3O4M1#
hey geek!
i’m trying to plan an art installation based on ferrofluid, but the quantities i’d need make it so that making my own is the only viable option. does the “recipe” on exo.net make fluid of a high enough quality for this bit of silliness?
i want to hook a pulse generator up to an electromagnet and have that piece suspended in the middle of a plexiglas sphere about three or four feet in diameter. what i’d like to do is get or make a pulse generator that will allow me to input variable bpm, so that the spheres can be set up on either side of a dj both and wiggle to the tempo of the music. any problems, in principle, that i’m not seeing? also, is there any way other particles could be suspended with the magnetite, or would that throw off the density to much for the substance to behave magnetically? i wanna suspend alkali earth minerals in the spheres as well, to make the whole mess ultraviolet reactive.

sciencegeekgirl November 19, 2009 at 3:10 pm

Hi Bazooka,

it’s been a while since I made that ferrofluid recipe on exo.net, but my recollection is that it’s not as good as the commercial stuff by a long shot, but it’s much better than just “iron filings in oil.” It’s the best that I know of without buying hte expensive stuff. The difference is that with the exo.net stuff you won’t see the strong spikes that you do in the photo in the post — it’s not as responsive, and the magnetic reaction isn’t strong enough to overcome surface tension to the same degree. So you get slightly rounded blobs instead of nice clean spikes. You will still see it wiggle in response to the music, but it won’t be in such crisp spikes.
If you suspend something else with the magnetite you’ll get a less strong response for sure, and there’s the possibility of getting clumping. But like any good experimentalist, all you can do is try….
There are probably other things you could use than ferrofluid if all you’re trying to do is to get the ball to *swing* instead of to get the spikes going. Filings in oil, for example.
Stephanie

Ferrofluid June 8, 2011 at 2:12 am

CZ Ferrofluid desk toys come in 6 versions the nano drop, spYke, Motion, Klock, Squared, and nano Tree. They make an interesting gift for your boss, co-worker, or yourself

J Chu October 21, 2011 at 3:23 am

Wow. This site is dead useful. I came across this post while doing research on FFs. Thank you so much for taking the time to answer questions and write intelligent posts.

arsis February 5, 2013 at 11:41 am

hy everyone
im trying to make a ferrofluid using laser jet toner powder and canola oil, but its not working right
i only get a big blob instead of spikes
can anyone please suggest what i should do
and also a sustitue for oliec acid as surfactant

john March 16, 2015 at 9:40 pm

sciencegeekgirl, do you have updated URLs for the ferrofluid recipe? Those links are all broken now. Thank you!

Yurka July 2, 2015 at 5:34 am

https://youtu.be/KDbIFkSEAmM

I make it without printer toner.

Sophie Horrocks September 9, 2015 at 10:35 pm

Hi, I realise that this post is very old – however I am (like someone above) trying to figure out if you can hold the shape of the ferrofluid spikes without the magnet being there. I have seen this being done by people using dry ice, however is there any other way to do this? And if you could do this, would the solid state still react to a magnetic field, i.e. would the whole solid state move towards/against a magnet, or would the solid return to a liquid form?
Would love to have your help on this, many thanks

meyona January 20, 2016 at 11:31 pm

i dont get it how do different oils affect the ferrofluid

janae January 27, 2016 at 12:29 pm

Hi, I wanted to use ferro fluids for our science fair…but is there an easy way to make it? Because the ink toner is expensive and I saw some comments about using iron fillings and vegetable oil don’t work….Is there another easy way? 🙂

PRATYUSH KUMAR March 26, 2016 at 5:52 am

Hello

I have few doubts about ferrofluid. It would be great if you guys can help me clearing my doubts about it.

1. Suppose, I have a container with 5 ml ferrofluid in it, which is attached closely to a magnet. If I place (attach) that magnet-ferrofluid container on my shoulders and start running, will the ferrofluid spill out of the container or the magnet wont let it spill out rather it would make the animation more fast?

2. How does closeness of magnet effects the ferrofluid?

Imon Konar July 29, 2016 at 6:26 pm

Hello!

I have a question for you. Why does the ferrofluid follows the sharp edges of a magnetic bolt?

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