Kids, do you want to make a solid-liquid combination that can morph into weird shapes right before your eyes? All that you will need is some corn syrup, a thin, flat-bottomed dish (a Petri dish is perfect, but even plasticware will work), iron filings, and a strong bar magnet. Here is what you do with them. Pour a thin layer (very thin, less than 1/8") of the corn syrup into the dish. Add a small amount of iron filings to the syrup and stir. Put your strong magnet under the dish and move it around. What happens? Experiment with different ratios of iron filings to corn syrup by gradually adding more filings each time. Which ratio gives the best results? The best iron:syrup ratios will make a tiny but spectacular hedgehog of silvery spikes.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
What's happening? The spikes form because the iron filings are drawn toward the magnet, dragging the syrup along with them. Individual spikes take shape as the iron filings pack together along the invisible lines of magnetic force coming from the magnet.
This is only a demonstration of a real high-tech magnetic fluid called a ferrofluid. What is the difference between the two? Size. Ferrofluids contain iron particles that are much smaller than these iron filings. In most ferrofluids the iron particles are really nanoparticles, at only 10 nanometers across. Look at a meterstick to see how small a millimeter (mm) is compared to a meter. One mm is a thousandth of a meter. A micrometer (mm) is a thousandth of a single mm, and a nanometer (nm) is a thousandth of that. In other words, one nm is a billionth of a meter! Chemists and materials scientists know well how to make particles this small.
Ferrofluids were first developed by NASA scientists in the 1960s as a way to control liquid fuel in low gravity. They added magnetic particles to the fuel and then manipulated it with magnets. In DVD players, magnets and ferrofluids work together as shock absorbers to control the vibrations that could make the player skip. The same technique is even used in audio speakers to improve sound quality by absorbing unwanted vibrations. Ferrofluids suspended between electronic parts by magnets create airtight liquid seals in computer hard drives and X-ray machines to keep out dust. And scientists are even looking at medical applications for ferrofluids, such as using magnets to perhaps guide tiny drops of the fluid mixed with cancer-fighting agents directly to a tumor.
There is no such thing as a liquid magnet, but solid magnetic particles that are really tiny can be suspended in a liquid that then behaves with magnetic properties. So, ferrofluids have the fluid properties of a liquid and the magnetic properties of a solid. When you are done with your experiment, dispose of the mixture in the trash (not in a sink). Iron filings can be purchased from a science supply store (including on-line versions). You can even "harvest" them from playground or beach sand using a strong magnet! (Warning though, this can be rather tedious to get a lot).
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
April 2004
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References: Check the "Fun Stuff!" link at www.strangematterexhibit.com and scroll down to the section on ferrofluids under "The Transformer". Strange Matter is a traveling exhibition developed by the Ontario Science Centre and presented by the Materials Research Society with the support of the National Science Foundation.
