Teachers' Domain; Physical Science/Engineering; Mystery Mud: Exploring Changes in States of Matter

How does this feel to you. This piece of ice cold. Ha ha that's good. These middle school students are visiting Professor Patrick Boyle's Laboratory at the Massachusetts Institute of Technology. They're here to learn about what happens when the matter changes state. So what in your everyday life have you seen that changes from most solar to liquid. I've seen water change from a solid state to a liquid state ice. OK that's a good one. Earth metal gets too hot it can turn into liquid. How hot do you think it has to get would have to get like thousands of degrees. Yeah pretty bad. Yeah that's a good answer yeah you have to have both. So it's pretty extreme if that's something that you're going to do in your kitchen. Right. Most materials in everyday life from water to plastic to metal will change their state of matter from a liquid to a solid or solid to a liquid. Only if cooled or heated. Well when we think about something a little different that I don't think you've ever seen before and this is something that I work

with recorded Mystery Mine. OK it's in this jar and I'm going to shove Fessor Doyle now shows the students as. Well kind of fluid that doesn't need a change in temperature to change its state from a liquid to a solid. When I pour it it's a lot like ketchup. Yeah let's get it to go up out. Let's go. People like you that like contempt. Yeah exactly. This is entirely safe so why don't you guys just hold it. You can even touch it. It's. Lost. It's gone. That's really feels like a really really wet clay. So would you say that it's more like the ice or more like the water more like water lines in water right. It's more like a liquid. Right. OK let's do a little it's. A myth and let's bring It's near this really big magnet. Oh thank god it's me. Really. Yeah let us you know you guys can come around and touch it. It's much more likely I just

think that yeah it's not. That's much more far right. Looks like he's. But when you press it down it's hard to. Fuse really cool tell you the consistency suddenly change. If you. Only get soft. That's exactly how. It comes to life for it. Now you could bring it into your hands and you see people at the lake with the candles and closer to the center mass audience you know. What's making it yet. What do you guys think. Either there's like mental illness or man that's in this. Well it is definitely being a trap. So it has to you know I think it has to do with magnetism. The right to fun. Is not having to do with us heating it up with the ice. Why does the magnetism make it hard. Oh OK. Mystery mud is really a magnetic fluid and the reason that we saw this magnetic fluid change from a liquid to a solid like state we put it near this magnet is that there are these very very small iron

particles. But they're mixed into the solution. OK so these individual little iron particles are a hundred times smaller than the thickness of your hair. So these are very very small. You can think about these little particles as my hand sort of the particles now and when we're away from the magnetic field these particles are just moving around very randomly. I think everything exactly they don't have strong interactions. In this computer simulation the magnetic fluid is in a liquid like state and the iron particles. Are moving freely and randomly. And when we put it near a magnet they actually start to attract one another. And what we see actually when we zoom in and look at what's happening at the particle level is that they start actually chaining up with one another so the little particles are forming this looks like a column or stack structure. And these columns are

relatively fixed in space. So when we look at the particles they're no longer moving a whole lot like they were in the liquid state. They still vibrate a little bit but they're pretty much fixed into position. And if we take it away from the magnetic field these particles start moving all around again. This video of the magnetic fluid recorded through a microscope we see actual iron particles forming cluster. Containing hundreds of microscopic columns. When we look without a microscope we can see spikes made up of thousands and thousands of little cloud. And we can feel the change that takes place when we bring the fluid near a magnet. So that's why. When you start pushing on it it feels more solid like it's because these little particles are aligning and fixed in this solar structure. But it's weird because you think you're just going through the liquid just like sticks to the man but when you get it harder it would make these little sticky up things.

It's actually pretty complex. They want to chain up in this direction which you see the spikes coming out. But actually spikes next to one another republish other a little bit. And that's what actually gives it this very nice structure that you see right. Right. So this stuff is pretty cool. It's a fluid that we bring near a magnet and it becomes a solid. It changes its state without even using temperature. Exactly right. Right. So let's think about the materials now that we see all around the city's other solid materials like the rock. OK Nick rock. Now we know that it will change from a solid to a liquid by heating it which is different than the magnetic fluid. What is similar about the magnetic fluid and the volcanic rock is how these materials act at the particle level. When any material is in a liquid state. Particles move freely and when it is in a solid state they are fixed in place.

The advantage of the magnetic fluid is that particle motion can be controlled quickly and without the need for extreme heat or cold. So there. Is stuff which we're working on for research. But part of research is thinking about what do you what could you do with this. Maybe you have a switch that you can turn. Turn on the magnetic field and you suddenly have something that's a solid. Could you invent something. That this might be useful for if it was just the hardness. Exactly. Like in those little like. Like a bad cell like move up here down. Yeah that's what happens like that and I think it'll be just the firmness of maybe what kind of an invention would you come up with that uses magnetic fluid.