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Elastic Material That Is Impervious to Gases and Liquids

This is a slightly modified version of an article written by Matt Shipman, Research Lead in University Communications.

An international team that includes Professor Michael Dickey and past and present members of his research group has developed a technique that uses liquid metal to create an elastic material that is impervious to both gases and liquids. Applications for the material include use as packaging for high-value technologies that require protection from gases, such as flexible batteries and as stretchable heat transfer systems that involve volatile fluids, including water and organic fluids.

“This is an important step because there has long been a trade-off between elasticity and being impervious to gases,” says Prof. Dickey, co-corresponding author of a paper on the work and the Camille & Henry Dreyfus Professor of Chemical and Biomolecular Engineering. “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.”

The new technique makes use of a eutectic alloy of gallium and indium (EGaIn). Eutectic means that the alloy has a melting point that is lower than its constituent parts. In this case, the EGaIn is liquid at room temperature. The researchers created a thin film of EGaIn, and encased it in an elastic polymer. The interior surface of the polymer was studded with microscale glass beads, which prevented the liquid film of EGaIn from pooling. The end result is essentially an elastic bag or sheath lined with liquid metal, which does not allow gases or liquids in or out.

The researchers tested the effectiveness of the new material by assessing the extent to which it allowed liquid contents to evaporate, as well as the extent to which it allowed oxygen to leak out of a sealed container made of the material.

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

The researchers are also conscious of costs associated with manufacturing the new material.

“The liquid metals themselves are fairly expensive,” Deng says. “However, we’re optimistic that we can optimize the technique – for example, making the EGaIn film thinner – in order 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.”

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

“Basically, we reached the limit of the testing equipment that we had available,” Dickey says.

“We’re also 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.”

The paper, “Liquid Metal-Based Soft and Hermetic Seals for Stretchable Systems,” is published in the journal Science. Co-first authors of the paper are Qingchen Shen, a former visiting scholar with Prof. Dickey’s research group who is at Shanghai Jiao Tong University; Man Hou Vong, a Ph.D. student in the Dickey group; and Modi Jiang, Ruitong Wang and Kexian Song of Shanghai Jiao Tong University. Co-corresponding authors of the paper are Dickey; Deng; Wen Shang of Shanghai Jiao Tong University; and Jun Wang of A123 Systems. Co-authors include Ph.D. student Febby Krisnadi and former visiting scholar Woojin Jung, both from the Dickey research group; and Ruyu Kan, Feiyu Zheng, Benwei Fu, Peng Tao, Chengyi Song and Guoming Weng of Shanghai Jiao Tong University, and Bo Peng of A123 systems.

The work was done with support from the National Science Foundation, under grant CMMI- 2032415; the National Natural Science Foundation of China, under grants 51873105 and 51973109; the Innovation Program of the Shanghai Municipal Education Commission, under grant 2019-01-07-00-02-E00069; the Zhi-Yuan Endowed fund from Shanghai Jiao Tong University; and Shanghai Jiao Tong University Overseas Study Grants. The work received additional support from the National Science Foundation through the ASSIST Engineering Research Center at NC State, under grant number EEC-1160483.