Materials that change their properties in response to different environmental triggers promise all kinds of versatility for all kinds of applications, and an international team of scientists has just come up with a particularly inventive one. With an ability to stiffen up under a certain type of light and go soft in the dark, the new material shows particular promise for the world of 3D printing, where it could be used as a temporary support for complex structures that melts away when the job is done.

The new material is the handiwork of scientists from Australia's Queensland University of Technology (QUT), Belgium's Ghent University and Germany's Karlsruhe Institute of Technology, and consists of a polymer structure that can change its structure in response to light, and then revert back again.

Key to its changeable properties are the inexpensive chemical compounds the team has worked into the material. Among these are coupling molecules called triazolinediones and an ingredient common in moth repellent called napthalene.

Together, these enable the material to stay solid and firm so long as it is exposed to green LED light. But when the researchers switch the light off and the material is left in the dark for a little while, these chemical bonds begin to break up and cause it to become a soft, runny mess. Switching the light back on then sees it harden up once again.

Further, dimming the light rather than shutting it off enabled them to tweak the material's mechanical properties to somewhere in between. These capabilities are unique when it comes to materials, the researchers say, and run counter to today's common understanding of chemistry.

"Typically, you use different wavelengths of light or additional heat or harsh chemicals to break up the polymer molecule chains that form a network structure," the researchers say. "However, in this case, we used green LED light to stabilize the network. The trigger to break up the network, make it collapse and flow away is actually the mildest one of all: darkness. Switch the light back on and the material re-hardens and retains its strength and stability."

The team calls its new structure a "light-stabilized dynamic material," and hopes that it can give rise to a new class of materials that respond to light in novel and useful ways. It is eyeing applications in 3D printing, where creating structures such bridges or staircases with overhanging features is inherently tricky, as 3D printing typically works by building one layer on top of another from the ground up.

"What you need to 3D print something like a bridge is a support scaffold, a second ink that provides that scaffold during printing of the design, but which you can later remove when it is no longer needed," says Professor Christopher Barner-Kowollik, a macromolecular chemist at QUT. "With a light-stabilized dynamic ink used as a scaffold you could 3D print under light, then switch the light off to let the scaffold ink flow away."

The research was published in the Journal of the American Chemical Society, while the video below shows the material's transformative abilities in action.

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