A new metamaterial transforms into new forms and acquires new properties

A new type of architectured metamaterial has the ability to change shape in an adjustable way.

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

Greer, Professor Ruben F. and Donna Mettler of Materials Science, Mechanics and Medical Engineering at Caltech's Engineering and Applied Science Division, creates materials from micro-scale building blocks and nanoscale organized in sophisticated architectures that can be periodic, as a network, or non-periodic in a custom way, giving them unusual physical properties.

Most materials designed to change shape require a persistent external stimulus to change shape and remain so: for example, they may be a shape when it is wet and a different shape when dry, such as a swelling sponge when it absorbs water.

On the other hand, the new nanomaterial deforms during an electrochemically controlled silicon-lithium alloy reaction, which means that it can be precisely controlled to reach any "intermediate" state, remains in these configurations, even when the suppression of the stimulus, and is easily reversed. Apply a little current and the resulting chemical reaction slightly changes the shape. Apply a lot of current and the shape changes considerably. Remove the electrical control and the configuration is kept as if you are attaching a balloon. A description of the new type of material was published online by the journal Nature September 11th.

Defects and imperfections exist in all materials and can often determine the properties of a material. In this case, the team chose to take advantage of this fact and create defects to give the material the desired properties.

"The most intriguing part of this work is for me the critical role of defects in architectural materials that are both responsive and dynamic," says Xiaoxing Xia, a Caltech graduate student and lead author of the book. Nature paper.

For the Nature On paper, the team designed a silicon-coated network with straight microscopic beams curving in curves under electrochemical stimulation, thus acquiring unique mechanical and vibratory properties. The Greer team created these materials using an ultra-high resolution 3D printing process called two-photon lithography. Using this new manufacturing method, they were able to incorporate defects in the architectural material system, based on a predefined design. During a test of the system, the team made a sheet of material that, under electrical control, reveals a Caltech icon.

"It still shows that materials are like people, it's the imperfections that make them interesting." I've always had a special liking for flaws, and this time, Xiaoxing has managed to discover it first. the effect of different types of defects on these metamaterials, and then use them to program a particular model that would emerge in response to an electrochemical stimulus, "says Greer.

A material with such a finely controllable shape-fit capability has potential for future energy storage systems because it allows for the creation of adaptive energy storage systems that allow batteries, for example, to be significantly lighter, safer and have a significantly longer service life. , Said Greer. Some battery materials increase when they store energy, which causes mechanical degradation due to stress caused by repeated expansion and contraction. Architectural materials like this can be designed to support such structural transformations.

"Electrochemically active metamaterials offer a new avenue for the development of next-generation smart batteries with increased capacity and new features." At Georgia Tech, we are developing computer tools to predict coupled coupled electro-chemo-mechanical behavior, " explains Claudio V. Di Leo, assistant professor of aerospace engineering at the Georgia Institute of Technology.

the Nature The document is entitled "Electrochemically Reconfigurable Architectural Materials".