Magnets as we know them are always solid, but the closest thing we have to a magnetic liquid is a class of liquids called ferrofluids. Made up of iron-oxide particles suspended in liquids, these materials are only magnetic temporarily, when exposed to other magnets. But now, researchers at Lawrence Berkeley National Laboratory have managed to create the first permanently magnetic liquids, which could open up new avenues for electronics and robotics.
Ferrofluids have been around since the 1960s, and since then they've shown up in speakers, eye-catching clocks, surfaces that can change their stickiness or slipperiness on demand, and may soon be used to propel small satellites. But in all these cases, the liquid only shows magnetism when a magnetic field is applied. The Berkeley Lab's new liquid is the first to be permanently so.
"We've made a new material that is both liquid and magnetic," says Tom Russell, lead researcher on the study. "No one has ever observed this before. We wondered, 'If a ferrofluid can become temporarily magnetic, what could we do to make it permanently magnetic, and behave like a solid magnet but still look and feel like a liquid'?"
The team started by 3D printing 1-mm droplets of a ferrofluid, each of which contained billions of iron-oxide nanoparticles just 20 nanometers wide. These were suspended in another liquid solution. On closer inspection, the researchers found that the droplets retained their shape because the nanoparticles were crowding around the edges.
Next, the team passed a magnetic coil over the droplets, which fired up their magnetism. But unlike usual ferrofluids, this magnetism remained even after the coil was removed. The droplets began swirling around each other in unison.
By studying the magnetometry of the droplets, the team figured out why this was. Each iron-oxide nanoparticle in each droplet was responding to the magnetic field at once, and because so many were jammed together at the surface, they essentially were forming a solid magnetic shell. These outer particles were also passing their magnetic orientation onto the nanoparticles in the core of each droplet.
As you'd hope from a magnetic liquid, the stuff retains its magnetic properties in basically any shape. The researchers showed that they could divide droplets into smaller ones, or morph them into spheres, cylinders, pancakes, tubes and even an octopus shape, while still being magnetic. On top of that, the droplets can be tuned so their magnetism can be switched on and off at will.
Altogether, these properties could make the droplets very useful in robots or electronic devices. The team suggests that they could be used to make liquid-printed artificial cells, or magnet-controlled robots that deliver drugs inside the body.
The research was published in the journal Science and the magnetic liquids can be seen in action in the video below.
Source: Berkeley Lab
