A breakthrough in the development of liquid electronics could pave the way to producing soft, flexible electronic devices. Researchers at Carnegie Mellon and North Carolina State University have created a fluidic transistor using an indium gallium alloy, an alloy that, like mercury, is liquid at room temperature but, unlike mercury, is nontoxic.Liquid at room temperature, an indium gallium alloy can be used to create stretchable circuit wiring and electrical switches. Source: Carnegie Mellon

The solution exploits a property of liquids that causes them to break into droplets when flow rate decreases — a Rayleigh instability. A common example of this instability is observable in water streaming from a faucet. If the faucet closes slowly, the stream will break into droplets. The researchers found a way to use this characteristic to create an electrical switch using two droplets of metal.

By creating a voltage drop in one direction, the droplets move closer together. When the drop occurs in the opposite direction, the single droplet breaks in two. Quickly alternating the current creates a kind of transistor.

Mechanical engineers Carmel Majidi and James Wissman, of Carnegie Mellon’s Soft Materials Lab, and chemical engineer Michael Dickey from NC State, found that passing a current through the metal within a sodium hydroxide bath had the desired effect. The team refers to their result as a liquid metal transistor.

The team calls it a liquid metal transistor because it has the same kind of circuit properties found in a conventional circuit transistor. "We have these two droplets that are analogous to source and drain electrodes in a field-effect transistor, and we can use this shape programmable effect to open and close the circuit," says Majidi. "You could eventually use this effect to create these physically reconfigurable circuits."

Future applications for the soft, deformable devices that this discovery makes possible range from tiny computers that monitor diseases within a body to flying robots. A programmable material could be instructed to change shape to suit changes in an environment.

The research is published in Advanced Science.