Magnetic fields are everywhere. Every electric circuit creates one. They are utilized in such diverse applications as real time brain imaging (fMRI), and in developing future means of transport (MAGLEV trains). The earth itself, with its north and south poles, emits a magnetic field which protects us from dangerous solar radiation – and radiation from further afield. The `magnetospheres` interaction with this radiation is revealed, at least indirectly, in the beauty of the aurora borealis.
Thankfully, we don`t have to trek to the poles to visualize the shape of magnetic fields. The unique behavior of ferrofluids, as they trace the field lines of readily available magnets in 3 dimensions, give us an insight into how different the world would look if we could see the magnetic fields which surround us on a daily basis.
The key property of ferrofluids stem from the tiny particles of a compound dispersed in a liquid, all sharing one thing in common – ferromagnetism, or the tendency to respond strongly to magnetic fields. How tiny? A human hair is 75,000 nanometres across, with ferromagnetic particles typically from 1 to 10 nanometres. A common ferromagnetic metal is iron (Fe), and the most commonly utilized compound to create ferrofluids is a particular combination of Oxygen and Iron atoms – Magnetite (Fe3O4). For home experiments, iron compound-containing laser printer toner powder (mixed with oil) will do the trick.
When mixed, the ferromagnetic particles stay dispersed throughout the liquid through continuous random collisions with the liquid molecules (`Brownian` motion). Dispersal is assisted by coating the ferromagnetic particles in surfactant (i.e citric acid) which increases the affinity of the particles for liquid molecule collision and blocks particles clumping together. However, each component – ferromagnetic particles and liquid – retain their own separate properties. These the key characteristics of a `colloidal` solution, and allow the shape of the ferrofluid to immediately respond to a magnet placed directly below, forming spikes throughout the fluid proportional to the strength of the magnetic field – and looking pretty bizarre while doing so!
The development of ferrofluids was part of the `space age` of the 1960s. NASA scientists were seeking to develop mechanisms to pump fuel in a weightless environment. Dr Steve Pappell created the first `magnetic fuel` in 1965, though the use of solid fuel meant the idea was put on the back burner. Since then, magnetic fluids have found many applications, including in industry. However, some of the most fascinating are the tentative applications to human health – improving drug delivery through magnetic targeting, selectively heating and destroying tumors through `magnetic hyperthermia` , and even helping to cure blindness by sealing the retinal tear created by retinal detachments.
`Magneto`-like superpowers might not be fictional for long! Happy Chemistry Week!