New 3D Printing Techniques Create Free-Standing Structures Made Of Liquid Metal

Researchers have developed three-dimensional (3-D) printing techniques to create free-standing structures made of liquid metal at room temperature.

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.

While 3D printing of plastic objects has become almost commonplace, creating 3D structures out of metal is still a rarity. NASA has demonstrated a technique using “selective laser melting“ to produce intricate metal parts such as rocket engine components, but this requires the use of a high energy laser.

“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.

Unlike processes that pattern metal "in plane," – or on one level – the team has developed multiple techniques that allow the creation of liquid metal structures that reach up or down, which is valuable in the connection of electrical components in three dimensions.

A thin (about 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. Because the structures have a liquid center retained by only a thin film, the shape tends to be fragile while free-standing.

"They won't fall apart on their own weight (which is what makes this cool), but if you touched them or shook them with enough vigor, they would break," says Dickey.

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. Video of the process is available here.

To print metal structures involves stacking droplets of liquid metal on top of each other or  injection of the liquid metal into a polymer template

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.

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.”

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

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Write by: RC - Wednesday, July 10, 2013