Many of you may have seen commercials on television that show what looks like black oil taking on a life of its own, spiking up and dancing around. Perhaps you have seen videos on YouTube that look like magically dancing black fluid spiraling up and down, and wondered what it was. These were most likely ferrofluids, exposed to magnetic fields to make them “perform”.
Ferrofluid can be defined as a uniform mixture of magnetic particles, soap-like molecules and carrier fluid that will behave as a single unit in a magnetic field. In reality, the sharp spikes that appear are actually still fluid and are not solid points. The fluid behaves as one unit when the conditions are right, and magic apparently happens!!
Ferrofluid also exhibits an apparent change in density when exposed to a magnetic field. One of the favorite tricks for science demonstrations is the “floating penny” in which a ferrofluid will lift small items, such as non-magnetic coins, on their surfaces when in a reasonably strong magnetic field.
This behavior is illustrated to the left, and may be shown during the ferrofluid demonstration. This property actually has a practical application in industry, with a system known as “Magnetic Density Separation” used in recycling of non-magnetic materials.