N.C. State-Researchers Build 3D Structures Out of Liquid Metal

by NC State, Raleigh, North Carolina, USA

Researchers from North Carolina State University have developed three-dimensional (3-D) printing technology and techniques to create free-standing structures made of liquid metal at room temperature.

Researchers have developed three-dimensional structures out of liquid metal. Image: (Image courtesy of Professor Michael Dickey, NC State)

Researchers have developed three-dimensional structures out of liquid metal. (Image courtesy of Dr. Michael Dickey, NC State)

Researchers have developed three-dimensional structures out of liquid metal.

“It’s difficult to create structures out of liquids, because liquids want to bead up. But we’ve found that a liquid metal alloy of gallium and indium reacts to the oxygen in the air at room temperature to form a ‘skin’ that allows the liquid metal structures to retain their shapes,” says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and co-author of a paper describing the work.

The researchers developed multiple techniques for creating these structures, which can be used to connect electronic components in three dimensions. White it is relatively straightforward to pattern the metal “in plane” – meaning all on the same level – these liquid metal structures can also form shapes that reach up or down.

One technique involves stacking droplets of liquid metal on top of each other, much like a stack of oranges at the supermarket. The droplets adhere to one another, but retain their shape – they do not merge into a single, larger droplet.

Another technique injects liquid metal into a polymer template, so that the metal takes on a specific shape. The template is then dissolved, leaving the bare, liquid metal in the desired shape. The researchers also developed techniques for creating liquid metal wires, which retain their shape even when held perpendicular to the substrate.

The structures are stabilized by a thin oxide ‘skin’ that forms on the liquid metal. The approaches shown here represent new ways to direct write metals in 3D.  In addition, the resulting components can, in principle, self-heal.

Dickey’s team is currently exploring how to further develop these techniques, as well as how to use them in various electronics applications and in conjunction with established 3-D printing technologies.

“I’d also like to note that the work by an undergraduate, Collin Ladd, was indispensable to this project,” Dickey says. “He helped develop the concept, and literally created some of this technology out of spare parts he found himself.”

Our appreciation to Dr. Michael Dickey, Matt Shipman and North Carolina State University for permission to publish news about this ground-breaking research in 3D Printing.

Technical Paper
The paper, “3-D Printing of Free Standing Liquid Metal Microstructures,” is published online in Advanced Materials. Ladd, a recent NC State graduate, is lead author. Co-authors are Dickey; former NC State Ph.D. student Dr. Ju-Hee So; and Dr. John Muth, a professor of electrical and computer engineering at NC State.

The work was supported by a National Science Foundation CAREER award and the National Science Foundation’s ASSIST Engineering Research Center at NC State.

The study abstract follows “3-D Printing of Free Standing Liquid Metal Microstructures”  Authors: Collin Ladd, Ju-Hee So, John Muth and Michael D. Dickey, North Carolina State University

Abstract: This paper describes a method to direct-write liquid metal microcomponents at room temperature. 3-D printing is gaining popularity for rapid prototyping and patterning. Most 3-D printers extrude molten polymer that quickly cools and solidifies. The ability to pattern liquids into arbitrary shapes both in and out of plane is usually limited by interfacial tension.

A classic example is the break-up of cylinders of liquid into droplets when the aspect ratio of the cylinder exceeds the Rayleigh stability limit of [pi]. Here, we show it is possible to direct-write a low viscosity liquid metal at room temperature into a variety of stable free-standing 3-D microstructures (cylinders with aspect ratios significantly beyond the Rayleigh stability limit, 3-D arrays of droplets, out of plane arches, wires).

A thin (~ 1 nm thick), passivating oxide skin forms rapidly on the surface of the liquid metal and stabilizes the microstructures despite the low viscosity and large surface energy of the liquid. The ability to directly print metals with liquid-like properties is important for soft, stretchable, and shape reconfigurable analogs to wires, electrical interconnects, electrodes, antennas, meta-materials, and optical materials.

Published: Online July 4 in Advanced Materials, DOI: 10.1002/adma.201301400

About NC State
Since the day of its creation – March 7, 1887 – NC State has been moving forward.

It moved forward in 1889, when the first class of 72 students enrolled. A clear mission propelled the land-grant college: to open the doors of higher education to all of North Carolina, and to transform the state by developing and dispersing an understanding of agricultural and mechanical sciences.

And NC State still moves forward today. With more than 34,000 students and nearly 8,000 faculty and staff, North Carolina State University is a comprehensive university known for its leadership in education and research, and globally recognized for its science, technology, engineering and mathematics leadership.

NC State students, faculty and staff are focused. As one of the leading land-grant institutions in the nation, NC State is committed to playing an active and vital role in improving the quality of life for the citizens of North Carolina, the nation and the world.

How? Researchers across the university and Centennial Campus are deeply engaged in making new, application-driven discoveries. As a major research university, NC State has the people —from undergraduate and graduate students to faculty — and the responsibility to advance knowledge, transfer technology, and discover and develop innovations that solve some of the world’s most pressing problems.

NC State’s research expenditures are approaching more than $325 million annually, with almost 70 percent of faculty engaged in sponsored research and 2,500 graduate students supported by research grants. NC State is ranked third among all public universities (without medical schools) in industry-sponsored research expenditures.

 

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