Ferrofluid
It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended in a carrier fluid (usually an organic solvent or water).
In addition Rosensweig evolved a new branch of fluid mechanics termed ferrohydrodynamics which sparked further theoretical research on intriguing physical phenomena in ferrofluids.
The researchers also found that the droplet's magnetic properties were preserved even if the shape was physically changed or it was divided.
[8] Ferrofluids are composed of very small nanoscale particles (diameter usually 10 nanometers or less) of magnetite, hematite or some other compound containing iron, and a liquid (usually oil).
This means that the solid particles do not agglomerate or phase separate even in extremely strong magnetic fields.
However, the surfactant tends to break down over time (a few years), and eventually the nano-particles will agglomerate, and they will separate out and no longer contribute to the fluid's magnetic response.
The term magnetorheological fluid (MRF) refers to liquids similar to ferrofluids (FF) that solidify in the presence of a magnetic field.
When a paramagnetic fluid is subjected to a strong vertical magnetic field, the surface forms a regular pattern of peaks and valleys.
The instability is driven by the magnetic field; it can be explained by considering which shape of the fluid minimizes the total energy of the system.
Ferrofluids can be used to image magnetic domain structures on the surface of ferromagnetic materials using a technique developed by Francis Bitter.
[15] Starting in 1973, ferrofluids have been used in loudspeakers to remove heat from the voice coil, and to passively damp the movement of the cone.
Today, some 300 million sound-generating transducers per year are produced with ferrofluid inside, including speakers installed in laptops, cell phones, headphones and earbuds.
[19] Ferrofluids conjugated with antibodies or common capture agents such as Streptavidin (SA) or rat anti-mouse Ig (RAM) are used in immunomagnetic separation, a subset of cell sorting.
An electromagnet acts on the shape of the ferrofluid in response to the volume or the audio frequency of the music, allowing it to selectively react to a song’s treble or bass.
[21][22] A magneto-optic device and magnetic-field flux viewer dynamic lens can be created by using a superparamagnetic thin-film encapsulated and sealed between two optic flat glasses.
When they reach a critical thinness, the needles begin emitting jets that might be used in the future as a thruster mechanism to propel small satellites such as CubeSats.
Special magnetic nanofluids with tunable thermal conductivity to viscosity ratio can be used as multifunctional ‘smart materials’ that can remove heat and also arrest vibrations (damper).
[37] Research is under way to create an adaptive optics shape-shifting magnetic mirror from ferrofluid for Earth-based astronomical telescopes.
Optical filters tunable for different wavelengths by varying the magnetic field can be built using ferrofluid emulsion.
When external vibrations cause the ferrofluid to slosh around in the container, there is a change in magnetic flux fields with respect to the coil of wire.
Through Faraday's law of electromagnetic induction, voltage is induced in the coil of wire due to change in magnetic flux.
