Light-controlled Polymers can switch between Sturdy and Soft

MIT chemists have designed a polymer that can reversibly switch from a large structure (orange spheres) to the smaller blue shapes, in response to light. Image: Demin Liu/Molgraphics

MIT researchers have designed a polymer material that can change its structure in response to light, converting from a rigid substance to a softer one that can heal itself when damaged.

“You can switch the material states back and forth, and in each of those states, the material acts as though it was a completely different material, even though it’s made of all the same components,” says Jeremiah Johnson, an associate professor of chemistry at MIT, a member of MIT’s Koch Institute for Integrative Cancer Research and the Program in Polymers and Soft Matter, and the leader of the research team.

The material consists of polymers attached to a light-sensitive molecule that can be used to alter the bonds formed within the material. Such materials could be used to coat objects such as cars or satellites, giving them the ability to heal after being damaged, though such applications are still far in the future, Johnson says.

The lead author of the paper, which appears in the July 18 issue of Nature, is MIT graduate student Yuwei Gu. Other authors are MIT graduate student Eric Alt, MIT assistant professor of chemistry Adam Willard, and Heng Wang and Xiaopeng Li of the University of South Florida.

Controlled structure

Many of the properties of polymers, such as their stiffness and their ability to expand, are controlled by their topology — how the components of the material are arranged. Usually, once a material is formed, its topology cannot be changed reversibly. For example, a rubber ball remains elastic and cannot be made brittle without changing its chemical composition.

In this paper, the researchers wanted to create a material that could reversibly switch between two different topological states, which has not been done before.

Johnson and his colleagues realized that a type of material they designed a few years ago, known as polymer metal-organic cages, or polyMOCs, was a promising candidate for this approach. PolyMOCs consist of metal-containing, cage-like structures joined together by flexible polymer linkers. The researchers created these materials by mixing polymers attached to groups called ligands, which can bind to a metal atom.

Read more: Light-controlled Polymers can switch between Sturdy and Soft

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