By Gary Thomas
Ferrofluid: An overview
Theory behind Ferrofluid
Useful Properties and
Applications of Ferrofluid
Sources and Further Reading
Ferrofluid: An overview
Ferrofluid sounds like a concept straight from a bad science-fiction
film – a black, shape-shifting metallic liquid, that moves and forms
spikes using magnetic fields. But ferrofluid is not the product of
studio trickery; it is real and one of the most exciting materials to
emerge in modern times.
NASA first developed ferrofluids in the 1960’s whilst researching
methods of using liquids in space, but in the 21st century
ferrofluid has found new levels of fame. In recent years, ferrofluid
has also become somewhat of a YouTube sensation, due to the fantastical
shapes that it can create simply using a magnetic field. A great
example of this is shown below. However, ferrofluid is not just an
internet curio – its inherent pliability opens up a whole range of
applications which are discussed in more detail later.
Theory behind Ferrofluid
The term ‘ferrofluid’ is a portmanteau of ferromagnetic and fluid
and is used to describe a fluid that is strongly magnetized by a
magnetic field. This occurs because the fluid is composed of tiny
magnetic particles, up to 100 times smaller than the wavelength of
visible light. The most common minerals used in making these magnetic
particles are iron oxides such as magnetite (Fe3O4)
and hematite (Fe2O3), though other ferromagnetic
or ferrimagnetic substances can be used. The particles are usually less
than 10nm across.
These tiny particles are suspended in a liquid carrier fluid, which
can be water or an organic solvent. Thus, ferrofluids can be termed
colloidal liquids, as they contain evenly dispersed microscopic
particles in another substance.
Once a magnetic field is applied to a ferrofluid, the nanoparticles
are attracted and pull the entire liquid towards the magnetic field.
However, if exposed to a strong magnetic force, some of the
nanoparticles can be ripped out from the carrier fluid, forming an
incredibly fine dust.
To stop the clumping of the nanoparticles via van der Waals forces,
a surfactant (usually a hydrocarbon) coating is applied to the surface
of each of the metallic particles, which overcomes the weak
The particles suspended in a ferrofluid conform to Brownian motion,
which means particle movement is generally random and the liquid will
not settle under standard conditions.
Properties and Applications of Ferrofluid
Aside from being used to create stunning sculptures, ferrofluid also
has exciting real world applications. A major benefit of ferrofluid is
that the liquid can be forced to flow via the positioning and strength
of the magnetic field and so the ferrofluid can be positioned very
exactly. Ferrofluids also have the capability of reducing friction,
making them useful in a variety of electronic and transportation
For example, ferrofluids can be used in hydraulic suspension
pistons, with the strength of the magnetic field allowing the
suspension to be hard or soft depending on what is necessary.
It can also be used as a liquid seal in many electronic devices. For
example, in computer hard-drives ferrofluid can be used to form a seal
around the rotating shaft. Furthermore, it can be used in loudspeakers
to improve performance.
Ferrofluids could be used to keep us safe too: new body armour is
being developed by MIT which utilises ferrofluid in hollow fibres. This
body armour could act as a artificial splint in the heat of battle.
Ferrofluids also have medical applications and it is hoped that
these will increase in the future. Two examples of on-going research
related to ferrofluids are:
- Carrying medications to exact locations within the body
- Use as a contrasting agent for MRI scans
Currently, research on using ferrofluids to create an artificial
heart with no mechanical parts is being undertaken by Suprock
Technologies. By surrounding the heart with magnets, the ferrofluid
fixed to frame of the heart will expand and contract when needed,
imitating the pumping of the real thing. If developed correctly this
system may be a better option than current heart assist devices because
they do not have moving parts, meaning there will be less stress on the
heart and they will also be cheaper.
Further disparate fields in which ferrofluids can be used are:
- Heat transfer
- Analytical instrumentation
We are only just discovering the full potential of ferrofluids and
we are now opening up a world of opportunity that will hopefully
continue to grow rapidly in the next decade.
Sources and Further
Army seeks nanotech suits, New Scientist, 14/03/02
of Making, University College London
mirror could clear the skies for astronomers, New Scientist,
heart uses ferrofluid to pump blood, New Scientist, 13/06/12
Materials Research Science and Engineering Center, University of