The Purdue University researchers shows how inkjet-printing technology can be used to produce electronic circuits made of liquid-metal alloys for “soft robots” and flexible electronics.
Elastic technologies could make possible a new class of pliable robots and stretchable garments that people might wear to interact with computers or for therapeutic purposes. 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. Conductors made from liquid metal can stretch and deform without breaking.
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. The liquid metal nanoparticles are small enough to pass through an inkjet nozzle. 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.
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 oxidized gallium, which acts as a skin that prevents electrical conductivity. But it’s a fragile skin, so when we apply pressure it breaks the skin and everything coalesces into one uniform film. We can do this either by stamping or by dragging something across the surface, such as the sharp edge of a silicon tip.
The process could make it possible to rapidly mass-produce large quantities of the film. This study will facilitate new applications across a broad array of fields such as soft robotics, conformable electronics, wireless communications, micro/nanofluidics, wearable/implantable devices, and energy storage and transport systems.
A research paper about the method will appear on April 18 in the journal Advanced Materials. The paper generally introduces the method, called mechanically sintered gallium-indium nanoparticles, and describes research leading up to the project.
Future research will explore how the interaction between the ink and the surface being printed on might be conducive to the production of specific types of devices. The researchers also will study and model how individual particles rupture when pressure is applied, providing information that could allow the manufacture of ultrathin traces and new types of sensors.
