At first glance, you might mistake this silvery puddle for the T-1000 of the Terminator series. But don’t speed dial the Governator just yet: this miracle moving liquid is called a ferrofluid.
The word “ferrofluid” is in part derived from the term “ferromagnetic,” which describes materials that are strongly attracted to magnets. A good example of a ferromagnetic substance is iron (think Wooly Willie, which uses iron filings). In a ferrofluid, ferromagnetic nano particles of hematite, magnetite or other iron compounds are suspended in a solvent, creating a colloidal mixture that resists magnetic clumping. What this means is that when a magnetic field is applied by placing a magnet nearby, the liquid responds by arranging itself in a dazzling display of spikes. When the magnet is removed, the fluid returns to its former, runny self.
Why the Chia pet arrangement? Why doesn’t a ferrofluid turn into a series of peaks and valleys or a swirling vortex? The answer is in the shape of the invisible magnetic field, which can be (rudimentarily) imagined as a series of hairs that jut out of the north pole of the magnet being used and gently bend, either continuing onward into space for the hairs close to the very end or wrapping back around to the south pole. Ferromagnets, like iron filings or those in ferrofluids, naturally want to align themselves with these “hairs,” or magnetic field lines.
Ferrofluids are commonly used in applications that take advantage of the heat transfer and magnetic properties of metals, combined with the flexibility in shape and movement of fluids. One example is in loudspeakers: ferrofluids are simultaneously used to transfer heat from the voice coil while damping vibration of the cone. Other applications include medical diagnosis, external hard drives and optics.
The least useful and most entertaining aspect of ferrofluids is in the art created by magnetizing funny-shaped pieces of metal. Check out the video below to see what I mean.