Breakthrough in Shape-Changing Materials

Applying heat and light stimulates material self-assembly.

(Video courtesy of Washington State University.)

A team of engineers and materials scientists have developed a smart material capable of changing shape when exposed to heat and light. Classified as a multifunctional smart material with the additional ability to self-assemble, this is the first material capable of combining several “smart” abilities.

Previously developed smart materials performed one function at a time and were difficult to make and reprocess. The new material overcomes these challenges and its creators believe additional functions can be added to bring even more versatility.

How Shape Memory Works

To develop the new material, the research team used long-chain molecules called liquid crystalline networks (LCNs). Exhibiting behavior between that of a solid and liquid, LCNs have unique properties that allow them to be reprocessed. The material molecules are not as rigid as solid molecules and more orderly than liquid molecules.

LCN molecular behavior can be compared to that of Jell-O since the molecules face the same direction but maintain a level of mobility. 

Comparison of solid, liquid crystal and liquid molecule arrangements. (Image courtesy of Case Western Reserve University.)

Comparison of solid, liquid crystal and liquid molecule arrangements. (Image courtesy of Case Western Reserve University.)

The team focused on LCNs due to how they change shape when exposed to heat. To improve responses and reprocessing of the material, the team added groups of atoms that reacted to polarized light and implemented dynamic chemical bonds. Their results showed three-way shape shifting ability: folding, unfolding and healing when damaged.

“We knew these different technologies worked independently and tried to combine them in a way that would be compatible,” said Michael Kessler, professor in the Washington State University school of mechanical and materials engineering.

Dynamic chemical bonds are based on covalent bonds; when a particular change is added to the molecule, for example, adding heat or light, this shifts the total equilibrium of the overall molecule.

The molecule is then forced to change into a shape that is different and complex in order to reach equilibrium. For instance, a razor blade scratch in the material fixes itself when exposed to ultraviolet light. The material’s movements can also be preprogrammed with custom-made properties.

Applications for Shape-Changing Materials

Possible applications for these shape changers include actuators, drug delivery systems and self-assembling devices. The smart materials could also be used to unfold solar panels on a satellite without the need for battery-powered mechanical devices. Skipping the added step of intermediary equipment can bring versatility and reduce costs of such processes.

For more on shape-changing materials, check out this shape-memory polymer that responds to body temperature and lifts 1,000 times its weight.