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New metamaterial changes in new forms and takes on new properties



  New metamaterial changes into new forms, takes on new properties
A nanoarchitected metamaterial that deforms to create the Caltech icon. Credit: Julia Greer / Caltech

A newly developed type of architected metamaterial has the ability to change shape in a tunable way.

While most reconfigurable materials can switch between two distinct states, how a switch is turned on or off, the shape of the new material can be fine-tuned, adjusting its physical properties as desired. The material, which has potential applications in the next generation of energy storage and bioimplantable micro devices, was developed by a joint Caltech-Georgia Tech-ETH Zurich team in Julia R. Greer's lab.

Greer, Ruben F. and Donna Mettler Professor of Materials Science, Mechanical Engineering and Medical Technology at Caltech's Department of Technology and Applied Science, create materials from micro- and nanoscale building blocks arranged in sophisticated architectures that can be periodic, like a grid , or non-periodic in a customized way, giving them unusual physical properties.

Most materials designed to change shape require a sustained external stimulus to change from one mold to another and remain so: for example, they can be one mold when wet and another mold when dry ̵

1; like a fungus that swells when it absorbs water. In contrast, the new nanomaterial is deformed by an electrochemically driven silicon-lithium alloy reaction, which means that it can be finely controlled to achieve all intermediate states, remain in these configurations even after removal of the stimulus, and is easily reversed. Apply a little current, and a resultant chemical reaction changes the shape to a controlled, small degree. Apply a lot of current, and the shape changes significantly. Remove the electrical control and keep the configuration – just like tying a balloon. A description of the new type of material was published online by the journal Nature on September 11.

Defects and defects are present in all materials and can often determine the properties of the material. In this case, the team chose to take advantage of this fact and build in defects to complete the material with the properties they wanted.

"The most exciting part of this work for me is the critical role of defects in such a dynamically responsive architected material," says Xiaoxing Xia, a research student at Caltech and lead author of the paper Nature .

For the paper Nature the team designed a silicon-coated grid with micro-scale straight beams that bend in curves under electrochemical stimulation, with unique mechanical and vibrational properties. Greer's team created these materials with an ultra-high resolution 3-D printing process called two-photon lithography. Using this new manufacturing method, they were able to build defects into the architected material system, based on a predetermined design. In a test of the system, the team produced a sheet of material that, under electrical control, reveals a Caltech icon.

"This further shows that materials are just like humans, it is the deficiencies that make them interesting. I have always had a special taste for defects, and this time Xiaoxing first managed to reveal the effect of different types of defects on these metamaterials and then use them to program a certain pattern that would emerge in response to electrochemical stimulation, "says Greer. [19659005] A material with such a finely controllable ability to change shape has potential in future energy storage systems because it provides a way to create customizable energy storage systems that would allow batteries, for example, to be significantly lighter, safer and to have substantially longer lives, says Greer. Some battery materials expand when storing energy, which creates a mechanical breakdown due to voltage from repeated expansion and contraction. Architected materials such as this can be designed to handle such structural transformations.

"Electrochemically active metamaterials provide a new path for the development of the next generation of smart batteries with both increased capacity and new features. At Georgia Tech, we develop computational tools to predict this complex coupled electrochemical behavior," says Claudio V. Di Leo, assistant professor of aerospace engineering at the Georgia Institute of Technology.

Paper [Nature9459015] is entitled "Electrochemically Reconfigurable Architected Material."


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More information:
Xiaoxing Xia et al., Electrochemically Reconfigurable Architected Materials, Nature (2019). DOI: 10.1038 / s41586-019-1538-z

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California Institute of Technology




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New metamaterial changes in new forms, takes on new properties (2019, September 11)
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