Scientists from the Department of Energy‘s Office of Science, working at the Lawrence Berkeley National Laboratory, have created the first ever liquid magnet. This substance retains its magnetism even when it changes its shape. According to the researchers, this makes the material attractive for the creation of flexible liquid robots that can change their shape at will to adapt to their surroundings.
“We’ve made a new material that is both liquid and magnetic. No one has ever observed this before,” said Tom Russell, professor of polymer science and engineering at the University of Massachusetts, Amherst and a visiting faculty scientist at the Berkeley National Laboratory.
“This opens the door to a new area of science in magnetic soft matter.”
Russell and Xubo Liu, the first author of the study and a doctoral student at the Beijing University of Chemical Technology, came up with the idea of creating liquid structures using ferrofluids, or nanoparticles that became strongly magnetic when they were in the presence of a magnetic substance.
Russell and Liu’s hypothesis rested on the possibility of turning ferrofluids permanently magnetic. This hypothetical material would behave much like a solid magnet while maintaining the properties of a liquid substance.
To test whether or not their hypothesis is, in fact, doable, Russell and Liu used 3D printing technology developed in the Berkeley National Lab to print 1 mL droplets of a ferrofluid solution. This solution contains iron-oxide nanoparticles that are just 20 nm in diameter, or the average size of an antibody protein.
With the help of other colleagues from the Berkeley National Lab and using knowledge obtained from surface chemistry and sophisticated atomic force microscopy techniques, Russel and Liu discovered that the nanoparticles created a liquid “shell” at the interface between the two liquids. This rare phenomenon is known as “interfacial jamming.” The nanoparticles crowded onto the surface of the droplet “like the walls coming together in a small room jampacked with people,” Russell explained.
To make this liquid magnetic, the researchers placed the substance by a magnetic coil in solution. As they predicted, the magnetic coil pulled the iron-oxide nanoparticles. However, when they removed the magnetic coil, they were surprised to find that the droplets became permanently magnetic.
The droplets began to gravitate toward each other, almost like dancing as Liu explained, in a perfect unison. They formed an elegant swirl. Before this study, the scientific consensus was that only solid objects could be permanently magnetized. (Related: New magnet technology called HyMag could pave the way for affordable, eco-friendly electric- and hybrid-powered vehicles.)
Russell noted that one of the great things about the liquid magnet is its ability to adapt to its own surroundings, much like other liquids. They were able to morph the magnet into a sphere, a cylinder, a pancake and even into a tube as thin as a strand of hair. The researchers note that it can even be morphed into the shape of an octopus and it still won’t lose any of its magnetic properties. Furthermore, the movements of the magnetic liquid can be directed with the use of an external magnet and it doesn’t lose any of its magnetism when divided into even smaller liquids.
Russell and Liu’s pioneering discovery can change scientific understanding of magnetic materials. Its future practical applications could be endless. They anticipate that their reconfigurable liquid magnets may one day be used to control magnetically operated liquid robots that can also change their shape in order to adapt to their surroundings.
They plan to continue their research at the Berkeley National Lab, hoping to develop even more complex magnetic liquid structures such as liquid-printed artificial cells or even miniature robotics that can be used for the targeted and non-invasive delivery of drug therapies to diseased cells.
“What began as a curious observation ended up opening a new area of science,” said Liu.