Permanent Magnetic Fluids

Abstract

A team of researchers at the University of Massachusetts Amherst has accidentally obtained the first magnetized permanent liquid in the world, the droplets of this liquid moving in unison and able to associate in different forms while being manipulated exterior by means of a magnet, according to a new study published in the latest issue of the journal Science, reports Agerpres. We usually imagine magnets as being in a solid-state of aggregation, "says Thomas Russell, professor of polymers and engineering at the University of Massachusetts Amherst. But we now know that "we can get liquid magnets that can take different forms - and we can decide the forms they take," he added, specifying that droplets in this magnetic fluid can form spheres, cylinders, or the shape of a flat disc of the pancake dough. "We can make them look like a sea hedge if we want," he said. Russell and his team obtained this liquid magnet by chance while experimenting with a 3D printer. They have tried to print liquids in order to obtain new solid materials, but having the properties of fluids, for various applications in the field of energy. One day, the postdoctoral student and coordinator of this study, Xubo Liu, noticed that droplets of the resulting 3D material, made up of magnetized iron oxide particles, rode unison on magnetic support. Subsequently, his team noticed that the entire construct, not just those particles, had become magnetic. Using a specially customized 3D printer for liquids, the team managed to generate millimeters drops of water, oil and iron oxides. These drops retain their shape because of some of the iron oxide particles in the composition form bonds with the surfactants (also called tensides - 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 the film, while the rest remain inside, as Russell explains. Then the team placed these droplets near a magnetic coil to magnetize them. After removing the magnetic coil, droplets have shown unprecedented behavior to liquid substances so far-they have retained their magnetic properties. Magnetic fluids were known to physicists. They are called ferrofluids and are fluids consisting of ferromagnetic, ferromagnetic or paramagnetic colloidal particles suspended in a carrier liquid. 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 unison, indicating the same direction. Once the magnetic field has been stopped, the iron oxide particles have joined the surfactant in the film in tight formation, without being able to move and thus keep their alignment. The iron oxide particles that have remained floating inside the liquid have also taken this alignment. Scientists still do not understand the mechanism by which these particles remain magnetized. Once they have this explanation, the applications of this discovery can be multiple, both in the field of energy, robotics and space programs.