A team of researchers from the University of Massachusetts Amherst accidentally managed to obtain, in the laboratory, the first permanent magnetized liquid in the world.
According to a new study published in the latest issue of the journal Science, the drops in this liquid move in unison and can be associated in different forms, while being manipulated from the outside by the means of a magnet.
“We usually imagine magnets as being in a solid aggregation state,” said Thomas Russell, a professor of polymer science and engineering at the University of Massachusetts Amherst. But now we know that “we can get magnets in the liquid state, which can take different shapes and we can decide the shapes to take”, he added, noting that the drops in this magnetic liquid can form spheres, cylinders or flat disk shapes. “We can make them look like a sea urchin if we want,” he added.
Russell and his team accidentally got this liquid magnet while experimenting with a 3D printer. They have tried to print liquids in order to obtain new solid materials but which have the properties of fluids, for different energy applications.
One day, the postdoctoral student and coordinator of this study, Xubo Liu, noticed that drops of material from the 3D printer, which consisted of magnetized iron oxide particles, were spinning in unison on magnetic support. Later the team noticed that the entire construct, not just those particles, had become magnetic.
Using a 3D printer, specially adapted for liquids, the team managed to generate drops of the order of millimeters in water, oil and iron oxides. “These droplets retain their shape because of some of the iron oxide particles in the composition form bonds with surfactants (also called surfactants – substances that reduce the surface tension of the liquid). Surfactants form a film around the water, and some iron oxide particles enter the composition of this film, while the rest stay inside,” as Russell explains.
Then, the team placed these drops near a magnetic coil to magnetize them. After the magnetic coil was removed, the droplets demonstrated an unprecedented behavior in the liquid substances – they retained their magnetic properties. Magnetic liquids were known to physicists. They are called ferrofluids and are fluids made of ferromagnetic, ferimagnetic or paramagnetic colloidal particles, suspended in a carrier fluid. However, the characteristic of ferrofluids is that they remain magnetized only in the presence of a magnetic field.
When the droplets were close to the magnetic field, the iron oxide particles aligned in unison, pointing in the same direction. Once the magnetic field was stopped, the iron oxide particles clung to the surfactant in the tightly formed film, unable to move and thus kept their alignment. The iron oxide particles that remained floating inside the liquid also took over this alignment.
Scientists still do not understand the mechanism by which these particles are kept in a magnetized state. Once they have this explanation, the applications of this discovery can be multiple, both in the field of energy, robotics, and space programs.