Shapeshifting Material Transforms Under Light and Heat

The new material can even be tuned to specific temperatures and wavelengths of light.

Subtle photochemical and thermal reactions power some of the most efficient mechanical systems in nature — like, say, a flower opening to the sun. That same self-sufficient elegance is coming to the future of robotics and other high-tech devices, thanks to new research out of the University of Colorado, Boulder.

A group of chemical and biological engineers there have fabricated a plastic that can transform repeatedly from one complex, predefined shape to another, based on changes in temperature or exposure to certain wavelengths of light. The material is made from the same liquid crystal elastomers (LCEs) that are common to many of today’s flatscreen video displays. The research was published this month in the journal Science Advances.

It’s sort of a futuristic expansion on the tech behind those novelty drinking straws or kids’ winter gloves that change color in the heat — except in that it actually has some utility.

Matthew McBride, a post-doctoral researcher at CU Boulder and the study’s lead author tells Inverse says the shapeshifting material claims a multitude of uses.

“Soft robotics gets thrown around a lot,” he says. “Biomedical devices, I’ve even heard of interest in the oil and gas industry — essentially any application where you would need to remotely actuate something.”

If you’re not there to change something yourself, in other words — and you aren’t especially confident that you’ll always have the electricity to automate it either — then something like this new polymer would come in handy.

You might notice that the green grid-like prototype above has been designed to fold and unfold, miura-style, a kind of highly reversible ‘shape-memory origami’ that’s proven popular in the design of solar arrays for satellites and other space probes.

Bowman, mentioned in a statement to CU Boulder Today that the new material might also be applicable in the world of additive manufacturing, another term for 3D printing — a clue as to how it substance works.

Acrylate polymers are a kind of plastic material that are common as glues, adhesives, and as 3D-printer ink because of how its elastic properties and the ways it can deform and then set itself into a rigid form. The CU Boulder material was tuned to certain temperatures and light wavelengths by inserting molecules in the structure that are known to undergo thiol-Michael addition reactions in the matrix of liquid crystal elastomer molecules. It’s sometimes called “click-chemistry” because of the satisfying and dramatic pivots it produces in the geometry at a molecular level. Light and heat essentially generate the free radical electrons required to trigger the click.

“These molecules generate radicals which then react with these dynamic bonds and cause them to reshuffle,” according to McBride. “When the bonds aren’t reshuffling it’s just a polymer network, so it’s a static, kinda permanent, 3D network.”

The red starred regions in the diagrams above represent the dynamic bonds that reorient the liquid crystal elastomer material into tighter and looser formations with the addition of light or heat. The small photos on graphing paper show thin strips of the LCE material as it stretches or shrinks via this process. More details can be found in [the journal article itself at Science Advances:

CU Boulder / Science Advances 

For the miura-style, green material, the team chose 80 degrees Celsius as the clearing temperature that would ‘relax’ the material back into a flat shape, because cooler temperature-points threatened to get too close to the so-called Glass transition where soft plastics move to more brittle and hard plastics. The light wavelengths were programmed into the material by first folding it and then irradiating it with 320 to 500 nanometer wavelength light — so between violet, blue and green light along the visible spectrum — using a mercury bulb light source.

The material has proven remarkably resilient thus far, but the team is very candid about the amount of work needed to get it from here to actual real-world applications

“I have this one piece that I’ve been using for demonstrations, for like over a year now,” McBride says, “that one’s probably gone like 50 times or so and it seems to be still kicking a long.”

“But, certainly, if you actually were to make a practical device, you would need to test it thousands to even millions of times.”