First developed by NASA for the space program, magnetic fluids have found their way into many aspects of the modern world. From being used in music videos to loudspeakers and MRI scans, magnetic fluids are all around us today.
Here we explore what they are, how they work and show you how to make one for yourself at home.
What is a magnetic liquid?
"Colloidal systems consisting of single-domain magnetic nanoparticles dispersed in a carrier liquid and are convenient model systems to explore fundamental properties of magnetic nanoparticle systems."
These fluids tend to remain in a liquid state even while being controlled, moved, or kinetically interacted upon by a magnetic field.
"Traditional methods of preparing magnetic fluids involve long-term tumbling of the magnetic material with steel balls for several weeks in a carrier medium containing the dispersing agent.
In these grinding methods, oleic acid was commonly used to stabilize dispersions in kerosene and other hydrocarbon dispersion media." - 911 Metallurgist.
These fluids do not exist in nature and were first created between the mid-1960s and 1970s. Early preparation of these strange materials was fairly expensive and cost around $85 per ml.
This high cost initially held back the material's application in material and mineral science. But later research by the U.S. Bureau of Mines using magnetite in a kerosine suspension reduced the around $1 per liter.
One example is called a ferrofluid, or ferromagnetic fluid. This magnetic fluid becomes strongly magnetized in the presence of a magnetic field and was first developed by NASA in the early-1960s.
It was developed to find a way of moving liquid rocket fuel to a pump inlet in a low-gravity or weightless environment.
Magnetic fluids, like ferrofluids, tend to consist of nanoscale particles each of which will usually be coated in a surfactant to prevent them from clumping together. Ferrofluids usually lose any induced magnetism when removed from an external magnetic field.
For this reason, they are classified as "superparamagnets."
However, in 2019 a team of researchers from the University of Massachusetts and Beijing University of Chemical Technology succeeded in creating a magnetic fluid that can remain permanently magnetized. This breakthrough has defied the established belief that only dense solids with a fixed shape were capable of this property.
How do ferrofluids work?
Ferrofluids, as we have seen, contains tiny particles of iron oxide. When a magnet is drawn close to the liquid, these particles are attracted to it.
This typically causes the fluid to create amazing looking needles or spikes. The reason for this is because of a complex interaction of various forces.
The iron oxide particles are drawn to the magnetic field, as well as the magnetic field itself is attracted to the fluid.
The particles and oil work together as one thanks to the presence of a surfactant. One end of the surfactant locks on tight to the iron oxide particles, while the other also holds onto the oil.
This prevents the iron oxide particles from clumping together and being separated from the oil carrier -- as you would see happening if you simply mixed oil and iron-oxide particles.
Because of this, the ferrofluid as a whole is steered into concentrated columns.
At the same time, gravity tries to pull the columns back down while the surface tension of the oil causes each column to pull in on itself creating the fluid's characteristic needles.
Can you touch ferrofluid?
You most certainly can but it is not recommended. Ferrofluids are considered a major skin irritant.
Once you contact the ferrofluid with your finger, the liquid quickly begins to travel up the ridges of your finger and around your nail.
This not only looks unsightly, but it can and will irritate your skin. It may also leave a long-lasting discoloration on your skin.
15 takeaway facts about magnetic fluids
So, without further ado, here are 15 takeaway facts about the wonder materials that are magnetic fluids. This list is far from exhaustive and is in no particular order.
1. Magnetic fluids, namely ferrofluids, were developed in the 1960s by Steve Papell of NASA to help move rocket fuel around in micro-gravity.
2. When these fluids are subjected to a magnetic field, they tend to form characteristic spikes or needles.
3. Most magnetic fluids do not remain magnetized in the absence of an external magnetic field.
4. Ferrofluids have a strong staining capacity and can stain skin, glass, and even ceramic surfaces.
5. A true ferrofluid remains stable over a long period of time. This is because the solid particles within them do not agglomerate or separate out due to gravity.
6. Ferrofluids are actually currently being investigated to treat tumors. The idea is to inject them into the tumor and tear them apart using magnetic fields.
7. It is hoped that magnetic fluids could help develop smart liquids in the future. Such liquids could change state between solid and liquid on command.
8. Some ferrofluids have been used in car suspension systems. By varying an electrical current through them, the fluid adjusts suspension stiffness in response to driving conditions.
9. Magnetic fluids are becoming more popular as an artistic medium. Some art and science museums have special exhibits dedicated to these awesome liquids.
10. You may have also noticed ferrofluids in more than a few music videos too. For example, Pendulum used ferrofluid for the music video for the track, Watercolour.
11. A typical ferrofluid consists of 5% magnetic solids, 10% surfactant, and 85% carrier fluid.
12. Surfactants are vital to ferrofluids as they lower the surface tension between the liquid and solid components. Typically oleic acid, tetramethylammonium hydroxide, citric acid, or soy lecithin are used for this purpose.
13. NASA has also experimented with flowing ferrofluids in a closed loop with electromagnets as an altitude control system.
14. Magnetic fluids, like ferrofluids, are used in various technologies today. Applications include within loudspeakers, computer hard drives, rotating shaft motors, and as a contrasting agent for MRIs.
15. Ferrofluids should not be confused with magnetorheological fluids (MR). The later consists of micrometer-scale particles that will settle out over time under gravity.