Jul 29.07.2019, 3 - Revolutionary material could lead to XNUMXD printable magnetic fluid devices for the manufacture of flexible electronics or to artificial cells that deliver targeted drug therapies to diseased cells.

Scientists at Berkeley Lab have created a new material that is both liquid and magnetic, opening the door to a new field of science in magnetic soft matter. Their findings could lead to a revolutionary class of printable fluid devices for a wide variety of applications, from artificial cells that deliver targeted cancer therapies to flexible fluid robots that can change shape to adapt to their surroundings. (Video: Marilyn Chung / Berkeley Lab; images of droplets courtesy of Xubo Liu and Tom Russell / Berkeley Lab)

Centuries-old inventors and today's scientists have found sophisticated ways to improve our lives with magnets - from the magnetic needle on a compass to magnetic data storage devices to MRI body scanners.

All of these technologies are based on magnets made of solid materials. But what if you could make a magnetic device out of liquids? Using a modified 3D printer, a team of scientists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) did just that. Their findings, published July 19 in the journal Science, could lead to a revolutionary class of printable fluid devices for a wide variety of applications - from artificial cells that deliver targeted cancer therapies to flexible fluid robots that can change shape, to adapt to their surroundings.

“We made a new material that is both liquid and magnetic. Nobody has seen it before, ”said Tom Russell, visiting scientist at Berkeley Lab and professor of polymer science and engineering at the University of Massachusetts at Amherst, who led the study. "This opens the door to a new area of ​​magnetic soft matter science."

For the past seven years, Russell, who leads a program called Adaptive Interface Assemblies for Structuring Liquids in Berkeley Lab's Materials Science division and who led the current study, has focused on developing a new class of materials - 3D printable all-liquid. Structures.

Arrangement of 1 millimeter magnetic droplets: Fluorescent green droplets are paramagnetic without nanoparticles settling at the liquid interface. red are paramagnetic with non-magnetic nanoparticles trapped at the interface; Brown droplets are ferromagnetic with magnetic nanoparticles attached to the interface. (Source: Xubo Liu et al./Berkeley Lab)

Russell and Xubo Liu, the lead author of the study, came up with the idea of ​​creating liquid structures from ferrofluids, which are solutions of iron oxide particles that become strongly magnetic in the presence of another magnet. “We asked ourselves:“ If a ferrofluid can temporarily become magnetic, what can we do to make it permanently magnetic, but still look and feel like a liquid? "Said Russell.

To find out, Russell and Liu used an 3D printing technique, developed with former postdoctoral researcher Joe Forth in the Berkeley Lab materials science department, to print 1-millimeter droplets from a ferrofluid solution, the iron oxide nanoparticles with a diameter of only 20 nanometers (size of an antibody protein).

Scientists Paul Ashby and Brett Helms of Berkeley Labs Molecular Foundry have demonstrated, with the help of surface chemistry and sophisticated atomic force microscopy techniques, that nanoparticles form a solid-like shell at the interface between the two liquids through a phenomenon called "interfacial disorder." The nanoparticles that accumulate on the surface of the droplet look like the walls surrounding a small room filled with people.

To make them magnetic, the scientists placed the droplets in a solution inside a magnetic coil. As expected, the magnetic coil attracted the iron oxide nanoparticles.

But when they removed the solenoid, something quite unexpected happened.

Permanently magnetized iron oxide nanoparticles fuse perfectly. (Source: Xubo Liu et al./Berkeley Lab)

Like synchronized floats, the droplets moved in perfect harmony and formed an elegant vortex "like little dancing droplets," said Liu, a graduate student in the Berkeley Lab Materials Sciences Division and a PhD student at the Beijing University of Chemical Technology.

Somehow these droplets had become permanently magnetic. "We almost couldn't believe it," said Russell. "Before our study, people always assumed that permanent magnets could only be made from solids."

Endless checks, - it is still a magnet

All magnets, no matter how big or small, have a north pole and a south pole. Opposite poles attract while the same poles repel each other.

Using magnetometric measurements, the scientists found that all the north-south poles of the nanoparticles, when placing a magnetic field through a droplet, range from the 70 billions of iron oxide nanoparticles floating in the droplets to as many as 1 billion nanoparticles on the surface of the droplet , answered in unison, just like a fixed magnet.

Decisive for this finding were the iron oxide nanoparticles, which settle on the surface of the droplet. With only 8 nanometers between the billions of nanoparticles, they together formed a solid surface around each droplet of liquid.

Somehow the jammed nanoparticles on the surface, when magnetized, transfer that magnetic orientation to the particles floating around in the core, and the entire droplet becomes permanently magnetic - just like a solid, explained Russell and Liu.

The researchers also found that the magnetic properties of the droplet were maintained even when they divided a droplet into smaller, thinner droplets the size of a human hair, Russell added.

To make the iron oxide nanoparticles permanently magnetic, the scientists placed the droplets in a solution in a magnetic coil. As expected, the magnetic coil attracted the iron oxide nanoparticles. (Source: Xubo Liu et al. / Berkeley Lab

Russell noted that among the many amazing properties of magnetic droplets, they change shape to adapt to their surroundings. They transform from a ball into a cylinder, into a pancake, into a hair-thin tube or even into the shape of an octopus - and all of this without losing their magnetic properties.

The droplets can also be adjusted to switch between a magnetic and a non-magnetic mode. And when her magnetic mode is on, her movements can be remotely controlled by an external magnet, Russell added.

Liu and Russell plan to continue research at the Berkeley Lab and other national labs to develop even more complex 3D-printed magnetic fluid structures, such as a liquid-printed artificial cell or miniature robotics that acts like a tiny propeller for non-invasive but targeted propulsion Delivery of fluids from direct drug therapies for diseased cells.

"What started as a strange observation opened a new field of science," said Liu. "This is what all young researchers dream of, and I've been fortunate to work with a large group of scientists, backed by Berkeley Labs from world-class user facilities, to make this a reality," said Liu.

Researchers from UC Santa Cruz, UC Berkeley, the WPI (Advanced Institute for Materials Research) (WPI-AIMR) at Tohoku University and the Beijing University of Chemical Technology also participated in the study.

The magnetometry measurements were carried out with the support of the co-author of the Berkeley Lab Materials Sciences Division, Peter Fischer, Senior Staff Scientist. Frances Hellman, senior faculty scientist and professor of physics at UC Berkeley; Robert Streubel, postdoctoral fellow; Noah Kent, PhD student and PhD student at UC Santa Cruz; and Alejandro Ceballos, doctoral student and researcher at the Berkeley Lab at UC Berkeley.

Other co-authors include scientists Paul Ashby and Brett Helms, and postdoctoral researchers Yu Chai and Paul Kim of Berkeley Labs Molecular Foundry. Yufeng Jiang, PhD candidate in the Materials Science Department of Berkeley Lab; and Shaowei Shi and Dong Wang from the Beijing University of Chemical Technology.

This work was supported by the DOE Office of Science and involved research at the Molecular Foundry, a nanoscale science-based user facility of the DOE Office of Science.

The Lawrence Berkeley National Laboratory and its scientists were founded on 1931's belief that the greatest scientific challenges are best handled by teams. Currently awarded 13 Nobel Prizes. Today, Berkeley Lab researchers are developing sustainable energy and environmental solutions, developing useful new materials, expanding the boundaries of the computer domain, and exploring the secrets of life, matter, and the universe. Scientists from around the world rely on the lab facilities for their own discovery science. The Berkeley Lab is a national multi-program lab managed by the University of California for the Office of Science of the US Department of Energy.

The DOE Office of Science is the largest advocate of basic science science in the US and is committed to addressing some of the most pressing challenges of our time.

Source: Text and Image - Lawrence Berkeley National Laboratory - Berkeley Lab Translation: Institute for Rare Earths and Metals - July 2019

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