Scientists have been studying the properties of metamaterials for a few years now due to their ability to manipulate light and sound waves, essentially turning them into "invisibility cloaks." These materials change their shape upon exposure to certain stimuli. However, these materials only react to the stimuli in a way that they shift only between two states, much like the on and off of a light switch.
Recently, a research team from Caltech has detailed their study about metamaterials in an issue of Nature. The team has created reconfigurable materials from silicon and lithium, and grounded on electrochemistry, these materials are able to shift to "mid states" along a continuum.
A nanoarchitected metamaterial deforming to create the Caltech icon. Image from Caltech
The material changes shape when triggered by an electric current. The researchers claim that the key to its shapeshifting properties is an electrochemically-driven alloying reaction in a three dimensional lattice of lithium coated with silicon. As current is applied, the lithium and silicon would form an alloy. The amount of change is proportionally dependent on the amount of electric current-as the current increases, the more drastic the change in shape is. They took note of the fact that all lattice structures contain imperfections, so they intentionally built in some imperfections into the material in order to bring out certain properties.
The researchers used the process of two-photon lithography, an ultraresolution method of 3D printing to create the silicon-coated lattice structure. The material's microscale straight beams would bend after being subjected to electrochemical stimulation, making them take on unique mechanical and vibrational properties and in turn, change their shape.
This kind of material could potentially be applied in adaptive energy storage systems then possibly allowing batteries and the like to be lighter, safer to transport and handle, and have longer lives. This is compared to currently existing batteries that expand when storing energy, posing mechanical stress and degradation.
Lead author and Caltech graduate student, Xiaoxing Xia, and Caltech materials scientist, Julia Greer, likened their work to people saying that it is the imperfections that make the materials interesting.
"The most intriguing part of this work to me is the critical role of defects in such dynamically responsive architected materials," Xia said.
"This just further shows that materials are just like people, it's the imperfections that make them interesting," added Greer. "I have always had a particular liking for defects, and this time Xiaoxing managed to first uncover the effect of different types of defects on these metamaterials and then use them to program a particular pattern that would emerge in response to electrochemical stimulus."
