Magnetic fluids or ferrofluids, "relatives" of solid magnets, consist of particles of iron oxide in suspension. However, their magnetic properties are activated exclusively under the influence of other magnets - that is, only for a certain time.
Researchers at Lawrence Berkeley National Laboratory (USA) have succeeded in creating fluids in which magnetic properties are permanently maintained, which opens up new perspectives in the field of electronics and robotics.
The scientists began by 3D printing 1 mm ferrofluid droplets, each containing billions of 20 nanometer diameter iron oxide nanoparticles. After they were suspended in another liquid solution, the researchers found that the droplets retained their shape as the nanoparticles clustered around their edges.
Then the scientists directed a magnetic coil at them - and unlike conventional ferrofluids, this magnetism remained even after the coil was turned off. Moreover, the drops began to spin synchronously around each other.
After examining the droplet magnetometry data, the team found an explanation for this. All the iron oxide nanoparticles in each drop reacted to the magnetic field simultaneously, and since many of them clustered on the surface, they were able to form a stable magnetic shell. These outer particles also extended their magnetic properties to the nanoparticles in the core of each droplet.
The researchers suggest that the ferrofluid they created could be used to create artificial cells or magnetically controlled robots that deliver drugs to the inside of the body.