Researchers for the first time create magnets from liquids

Ferrofluid Magnet
Ferrofluid on a reflective glass plate under the influence of a strong magnetic field. (Credits - Wikimedia Commons)

Magnets have made our lives easier and better in several ways starting from the magnetic needle on a compass to magnetic data storage devices and MRI scanning machines. All of these technologies are based on magnets which are made from solid materials. 
Now a team of researchers from Berkeley Lab have used a modified 3D printer to manufacture a magnetic device from liquids. The study has been published in the Science journal. This could have a large number of applications from artificial cells which deliver targeted cancer therapies to flexible liquid robots that are able to change their shape according to the surroundings. 
Tom Russell, a visiting faculty researcher at Berkeley Lab and a polymer science professor at the University of Massachusetts, Amherst led the research. He said that the material is both liquid and magnetic, a feat which has been achieved for the first time. It creates new possibilities in the area of magnetic soft matter. 
Russell for the past seven years has focused on making a new type of materials, 3D printable all-liquid structures. Russell and Xubo Liu, the first author of the current study came up with an idea to create liquid structures from ferrofluids which are solutions of iron oxide particles that become very strongly magnetic in the presence of another magnet. They thought of possibilities to turn it to a permanent magnet but still retaining the properties of a liquid. They used a 3D printing method which they had developed with Joe Forth, a former postdoc researcher in Berkeley Lab to print droplets of 1 millimetre from ferrofluid solution containing iron-oxide-nanoparticles of 20 nanometres diameter. 
Paul Ashby and Brett Helms, co-authors of the study said that nanoparticles formed a solid-like shell at the interface between two liquids through a method known as “interfacial jamming” that makes the nanoparticles to crowd at the surface of the droplet. Researchers placed droplets by the magnetic coil in the solution for making them magnetic. The coil pulled the nanoparticles toward it. However, on the removal of the magnetic coil, the droplets gravitated toward each other in unison forming an elegant swirl. Researchers could not believe that the droplets had become permanent magnets as before this it was believed that only solids make permanent magnets.

With the help of magnetometry measurements, researchers found out that on placing a magnetic field by droplet, all the north-south poles of the nanoparticles from the 70 billion iron-oxide nanoparticles floating around to the 1 billion nanoparticles on the surface of the droplet responded exactly as a solid magnet. 
The iron-oxide nanoparticles jamming tightly at the surface of the droplet was key to this finding. With only 8 nm separation between each of the nanoparticles, they created a solid surface around a single liquid droplet. When the jammed nanoparticles were magnetized, the magnetic orientation was transferred to the particles in the core making the entire droplet a permanent magnet. Scientists also found that on dividing the droplets to smaller, thinner ones the magnetic properties were preserved. 
Russell added that they could change their shape according to the surroundings from a sphere to a cylinder without losing the magnetic properties. They could also be switched between a magnetic and non-magnetic mode. An external magnet can control their movements remotely when the magnetic mode is turned on. Liu and Russell aim to develop more complex 3D magnetic liquid structures such as mini robots or liquid printed artificial cell. 
Journal Reference: Science


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