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All magnets, no matter how big or small, have a north pole and a south pole. Opposite poles are attracted to each other, while the same poles repel each other.
Through magnetometry measurements, the scientists found that when they placed a magnetic field by a droplet, all of the nanoparticles’ north-south poles, from the 70 billion iron-oxide nanoparticles floating around in the droplet to the 1 billion nanoparticles on the droplet’s surface, responded in unison, just like a solid magnet.
Key to this finding were the iron-oxide nanoparticles jamming tightly together at the droplet’s surface. With just 8 nanometers between each of the billion nanoparticles, together they created a solid surface around each liquid droplet.
Somehow, when the jammed nanoparticles on the surface are magnetized, they transfer this magnetic orientation to the particles swimming around in the core, and the entire droplet becomes permanently magnetic—just like a solid, Russell and Liu explained.
The researchers also found that the droplet’s magnetic properties were preserved even if they divided a droplet into smaller, thinner droplets about the size of a human hair, added Russell.
Among the magnetic droplets’ many amazing qualities, what stands out even more, Russell noted, is that they change shape to adapt to their surroundings. They morph from a sphere to a cylinder to a pancake, or a tube as thin as a strand of hair, or even to the shape of an octopus—all without losing their magnetic properties.
The droplets can also be tuned to switch between a magnetic mode and a nonmagnetic mode. And when their magnetic mode is switched on, their movements can be remotely controlled as directed by an external magnet, Russell added.
Liu and Russell plan to continue research at Berkeley Lab and other national labs to develop even more complex 3D-printed magnetic liquid structures, such as a liquid-printed artificial cell, or miniature robotics that move like a tiny propeller for noninvasive yet targeted delivery of drug therapies to diseased cells.
“What began as a curious observation ended up opening a new area of science,” said Liu. “It’s something all young researchers dream of, and I was lucky to have the chance to work with a great group of scientists supported by Berkeley Lab’s world-class user facilities to make it a reality,” said Liu.
Also contributing to the study were researchers from UC Santa Cruz, UC Berkeley, the WPI–Advanced Institute for Materials Research (WPI-AIMR) at Tohoku University, and Beijing University of Chemical Technology.
The magnetometry measurements were taken with assistance from Berkeley Lab Materials Sciences Division co-authors Peter Fischer, senior staff scientist; Frances Hellman, senior faculty scientist and professor of physics at UC Berkeley; Robert Streubel, postdoctoral fellow; Noah Kent, graduate student researcher and doctoral student at UC Santa Cruz; and Alejandro Ceballos, Berkeley Lab graduate student researcher and doctoral student at UC Berkeley.
Other co-authors are staff scientists Paul Ashby and Brett Helms, and postdoctoral researchers Yu Chai and Paul Kim, with Berkeley Lab’s Molecular Foundry; Yufeng Jiang, graduate student researcher in Berkeley Lab’s Materials Sciences Division; and Shaowei Shi and Dong Wang of Beijing University of Chemical Technology.
This work was supported by the DOE Office of Science and included research at the Molecular Foundry, a DOE Office of Science User Facility that specializes in nanoscale science.
Scientists at Berkeley Lab have made a new material that is both liquid and magnetic, opening the door to a new area of science in magnetic soft matter. Their findings could lead to a revolutionary class of printable liquid devices for a variety of applications from artificial cells that deliver targeted cancer therapies to flexible liquid robots that can change their shape to adapt to their surroundings. (Video credit: Marilyn Chung/Berkeley Lab; footage of droplets courtesy of Xubo Liu and Tom Russell/Berkeley Lab)
