Printing electronic circuits from liquid metal

Scientists have invented a new method to use inkjet printing technology to mass produce electronic circuits made of liquid metal alloys for soft robots and flexible electronics.

The new manufacturing approach, called mechanically sintered gallium-indium nanoparticles, focuses on harnessing inkjet printing to create devices made of liquid alloys.

"Conductors made from liquid metal can stretch and deform without breaking," said Rebecca Kramer from Purdue University.

"This process now allows us to print flexible and stretchable conductors onto anything, including elastic materials and fabrics," Kramer said.

A printable ink is made by dispersing the liquid metal in a non-metallic solvent using ultrasound, which breaks up the bulk liquid metal into nanoparticles.

This nanoparticle-filled ink is compatible with inkjet printing.

"Liquid metal in its native form is not inkjet-able. So what we do is create liquid metal nanoparticles that are small enough to pass through an inkjet nozzle," Kramer said.

"Sonicating liquid metal in a carrier solvent, such as ethanol, both creates the nanoparticles and disperses them in the solvent. Then we can print the ink onto any substrate."

"The ethanol evaporates away so we are just left with liquid metal nanoparticles on a surface," she explained.

After printing, the nanoparticles must be rejoined by applying light pressure, which renders the material conductive.

This step is necessary because the liquid metal nanoparticles are initially coated with oxidised gallium, which acts as a skin that prevents electrical conductivity.

"But it's a fragile skin, so when you apply pressure it breaks the skin and everything coalesces into one uniform film," Kramer said.

The process could make it possible to rapidly mass produce large quantities of the film.

"We want to create stretchable electronics that might be compatible with soft machines, such as robots that need to squeeze through small spaces, or wearable technologies that aren't restrictive of motion," Kramer said.

The paper is scheduled to be published in the journal Advanced Materials.