Soft materials are highly permeable to gases, making it difficult to create stretchable hermetic seals. An often overlooked aspect of stretchable electronics and technology is the choice of materials to hermetically protect them.

An international team of researchers developed a technique that uses liquid metal to create an elastic material impermeable to gases and liquids.

The new method uses a eutectic alloy of gallium and indium (EGaIn). Eutectic refers to an alloy with a lower melting point than its constituent elements. The EGaIn in this case is liquid at room temperature. The scientists produced a thin layer of EGaIn and then covered it with an elastic polymer.

Glass microspheres were placed on the inner surface of the polymer to prevent the liquid coating of EGaIn from accumulating. The result is an elastic bag or enclosure lined with liquid metal that is impermeable to gases and liquids.

By measuring how much liquid was allowed to evaporate and how much oxygen was allowed to escape from a sealed container of the new material, the researchers were able to determine how effective the material was.

Tao Deng, co-corresponding author and Zhi Yuan Chair Professor at Shanghai Jiao Tong University, said: “We found that there was no measurable loss of fluid or oxygen for the new material.”

“The liquid metals themselves are quite expensive. However, we are optimistic that we can optimize the technique – for example by making the EGaIn film thinner – to reduce costs. At the moment a single package would cost a few dollars, but we have not tried to optimize costs, so there is a way forward to reduce costs.”

Researchers reported that the material could be used in packaging for high-performance technologies that require gas protection, such as flexible batteries.

Michael Dickey, co-corresponding author of a paper on the work and the Camille & Henry Dreyfus Professor of Chemical and Biomolecular Engineering at North Carolina State University, said: “This is an important step because there has long been a trade-off between elasticity and gas impermeability.”

“Things that were good at keeping gases out were usually hard and stiff. And things that offered elasticity allowed gases to seep through. We made something that provides the desired elasticity while also keeping gases out.”

The researchers are currently exploring testing options to determine whether the material is an even more effective barrier than they have been able to demonstrate so far.

Magazine reference:

  1. Qingchen Shen, Modi Jiang, et al. Liquid metal-based soft, hermetic, and wirelessly communicable seals for stretchable systems. Science. DOI: 10.1126/science.ade7341