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Flexible crystals reveal secrets of elasticity

Australian scientists have gained new insights into the fundamental behavior of flexible materials, allowing for the design of new building materials and technology.

The work has been in Nature Materials.

A team involving researchers at The University of Queensland and QUT has identified the origin of the restoring force that lets elastic crystals return to their original shape.

Professor Jack Clegg from UQ's School of Chemistry and Molecular Biosciences said the team bent flexible crystals—including one developed at UQ which can be tied in a knot—to calculate how intermolecular interactions changed under compressive and expansive strain.

"Elasticity is a property that underpins a myriad of existing technologies including optical fibers, airplane components and load-bearing bridges," Professor Clegg said.

"We looked at how and where the energy was stored as the crystals contracted and went back to their original shape and size."

The experiments showed the potential energy that allowed the crystal to spontaneously straighten out was stored in the interactions between the molecules.

"Under strain, the molecules reversibly rotate and reorganize in a way that stores energy differently on the inside and the outside of the bend," Professor Clegg said.

"We were able to show that enough energy was stored in our bent flexible crystals to lift something 30 times the weight of the crystal a meter into the air.

"The new understanding of this common phenomenon could lead to new hybrid materials for applications from components of spacecraft to new building materials or electronic devices."

Professor John McMurtrie from QUT said the method developed by the research team could be used to explore elasticity in other flexible crystalline materials.

"This is an exciting prospect given that there are millions of different types of crystals already known and many more yet to be discovered," Professor McMurtrie said.

"Elasticity is ubiquitous and is fundamental to life and technology, allowing animals to move and sky-scrapers to stand up.

"Humans have used elastic materials for millennia for an almost infinite number of applications, but the molecular origin of the restoring remained elusive until now."