Ferrofluids have been around since the 1960s, and since then they have appeared on speakers, eye-catching timepieces that can change the viscous or slidable surface as needed, and may soon be used to push small satellite. In all of these cases, however, the liquid exhibits magnetic properties only when a magnetic field is applied. The new liquid at Berkeley Labs is the first permanent magnetic fluid.
“We have created a new material that has both fluidity and magnetic properties,” said Tom Russell, lead researcher at the study. “No one has ever observed this before. We want to know, 'If ferrofluids can temporarily become magnetic, what can we do to make them permanent magnets and behave like a solid magnet, but still look like Like a liquid??
The team began using 3D printed 1 mm ferrofluid droplets, each containing billions of 20 nm wide iron oxide nanoparticles. They are suspended in another liquid solution. After careful inspection, the researchers found that the droplets retained their shape because the nanoparticles "squeeze together" at the edges.
Next, the team passed a magnetic coil over the water droplets, inspiring their magnetic force. However, unlike conventional ferrofluids, this magnetism still exists after the coil is removed. The droplets begin to rotate uniformly around each other. The team identified the cause by studying the magnetic measurements of the droplets. Each of the iron oxide nanoparticles in each droplet immediately responds to the magnetic field, and because many are squeezed together at the surface, they substantially form a solid magnetic shell. These outer particles also transfer their magnetic orientation to the nanoparticles in the core of each droplet.
Researchers have shown that they can divide droplets into smaller droplets or turn them into spheres, cylinders, pancakes, tubes or even octopus while still being magnetic. Most importantly, the droplets can be adjusted so that their magnetic properties can be turned on and off at will.
All in all, these features make droplets very useful in robots or electronic devices. The team recommends using them for making liquid-printed artificial cells or for magnetron-controlled robots that deliver drugs in the body.
The study was published in the journal Science.