(Nanowerk News)Researchers have developed a metallic gel that is highly electrically conductive and can be used to print three-dimensional (3D) solid objects at room temperature. They published their findings in Affairs (“Metallic gel for conductive 3D and 4D printing”).
“3D printing has revolutionized manufacturing, but we were aware of no previous technology that would allow you to 3D print metal objects at room temperature in one step,” said Michael Dickey, co-author of the paper on the work and Camille & Henry Dreyfus Professor of Chemical and Biomolecular Engineering at North Carolina State University. “This opens the door to manufacture a wide range of electronic components and devices.”
To make the metallic gel, the researchers started with a solution of micron-scale copper particles suspended in water. The researchers then added a small amount of indium-gallium alloy, which is a liquid metal at room temperature. The resulting mixture is then stirred together.
As the mixture is stirred, the molten metal and copper particles essentially stick to each other, forming a gel “network” of metal in the aqueous solution.
“This gel-like consistency is important, because it means you have a fairly even distribution of the copper particles throughout the material,” says Dickey. “This does two things. First, it means a network of particles connected to form electrical paths. And secondly, it means copper particles don’t come out of solution and clog the printer.”
The resulting gel can be printed using a conventional 3D printing nozzle and it retains its shape when printed. And, when allowed to dry at room temperature, the resulting 3D object becomes denser while retaining its shape.
However, if the user decides to apply heat to the printed object while it is drying, some interesting things can happen.
The researchers found that the alignment of the particles affects how the material dries. For example, if you are printing a cylindrical object, the sides will shrink more than the top and bottom as they dry. If something dries at room temperature, the process is slow enough that it doesn’t make any structural changes to the object. However, if you apply heat – for example, placing it under a heating lamp at 80 degrees Celsius – the rapid drying can cause structural deformation. Because these deformations are predictable, it means that you can make printed objects deform after printing by controlling the pattern of the printed object and the amount of heat the object is exposed to during drying.
“Ultimately, this kind of four-dimensional printing – traditional three-dimensional, plus time – is one more tool with which to create structures of desired dimensions,” says Dickey. “But what we find most interesting about this material is its conductivity.
“Because the printed objects consist of 97.5% metal, they are very conductive. It’s definitely not as conductive as conventional copper wire, but it’s impossible to 3D print copper wire at room temperature. And what we’ve developed is far more conductive than anything that can be printed. We are very happy with the apps here.
“We are open to working with industry partners to explore potential applications, and are always happy to speak with potential collaborators about future research directions,” said Dickey.