A stretchy, impervious liquid metal

Flexible liquid metal elastic seal being held between two gloved thumbs
The flexible, liquid metal hermetic seal. Credit: Michael Dickey, NC State University

A team of Chinese and US researchers has used liquid metals to make an elastic.

The material is not only soft and stretchy, but refuses to let gases pass through.

“This is an important step because there has long been a trade-off between elasticity and being impervious to gases,” says Professor Michael Dickey, a researcher at North Carolina State University in the US, and co-corresponding author on a paper describing the substance, published in Science.

“Basically, things that were good at keeping gases out tended to be hard and stiff. And things that offered elasticity allowed gases to seep through. We’ve come up with something that offers the desired elasticity while keeping gases out.”

Such a substance could be a valuable way to preserve and pack technologies that are sensitive to oxygen – like flexible solar panels or batteries.

The material is made from an alloy of the metals gallium and indium (called EGaIn). Both metals are solid at room temperature (only just, in gallium’s case) but when mixed, they’re eutectic: their melting point drops and they become a liquid.

The researchers encased a thin film of this alloy in a stretchy polymer, studded with tiny glass beads to stop the metal from pooling.

They tested their new material against both evaporating liquid and oxygen in a sealed container.

“We found there was no measurable loss of either liquid or oxygen for the new material,” says Professor Tao Deng, co-corresponding author and a researchers at Shanghai Jiao Tong University, China.

They also showed that it worked with a flexible lithium-ion battery, and a stretchable heat transfer system (a device used to manage the heat in electronics).

The researchers hope their material will one day be a useful way to protect high-value electronics. Because of the metals it uses, it’s unlikely to ever be the cheapest thing on the market.

“The liquid metals themselves are fairly expensive,” says Deng. (Gallium is currently over US$600 per kilogram, and indium is about US$500 per kilogram. Steel is US$1399 a tonne.)

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“However, we’re optimistic that we can optimize the technique – for example, making the EGaIn film thinner –to reduce the cost.

“At the moment, a single package would cost a few dollars, but we did not attempt to optimize for cost so there is a path forward to drive cost down.”

Dickey says they’re now “looking for industry partners to explore potential applications for this work”.

“Flexible batteries for use with soft electronics is one obvious application, but other devices that either use liquids or are sensitive to oxygen will benefit from this technology,” says Dickey.

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