Weaving is the oldest and most enduring method of making fabrics. This practical art has found another purpose: Making nanomaterials.
An international collaboration led by scientists at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California Berkeley, has woven the first three-dimensional covalent organic frameworks (COFs) from helical organic threads. The woven COFs were more flexible and resilient compared to previous COFs.
"We have taken the art of weaving into the atomic and molecular level, giving us a powerful new way of manipulating matter with incredible precision in order to achieve unique and valuable mechanical properties," says Omar Yaghi, a chemist who holds joint appointments with Berkeley Lab's Materials Sciences Division and UC Berkeley's Chemistry Department, and is the co-director of the Kavli Energy NanoScience Institute.
COFs and MOFs
Invented by Yaghi, COFs and their cousin materials, metal organic frameworks (MOFs), are porous three-dimensional crystals with huge internal surface areas that can absorb and store enormous quantities of targeted molecules. COFs for example, are highly prized for the potential to capture and store carbon dioxide then convert it into valuable chemical products. Both frameworks consist of molecules that are stitched into large and extended netlike frameworks whose structures are held together by strong chemical bonds.
"Weaving in chemistry has been long sought after and is unknown in biology," Yaghi says. Not only has his team has found a way to weave organic threads together, but they did it in a way that enables them to design and make complex two- and three-dimensional organic extended structures.
In this most recently study, Yaghi and his collaborators used a copper as a template for bringing threads of the organic compound "phenanthroline" into a woven pattern to produce a framework they dubbed COF-505. The researchers discovered that, in COF-505, the copper ions could be removed and added without changing the underlying structure, and at the same time, the elasticity can be reversibly changed.
The result almost looks like a molecular version of the Vikings chain-armor. The material is very flexible, says Peter Oleynikov, researcher at the Department of Materials and Environmental Chemistry at Stockholm University.
Importance of Weaving
Yaghi believes that his team's research will influence the future of "making materials with exceptional mechanical properties and dynamics." Woven structures could be made as nanoparticules or polymers, which means they can be fabricated into thin films and electronic devices.
"That our system can switch between two states of elasticity reversibly by a simple operation, the first such demonstration in an extended chemical structure, means that cycling between these states can be done repeatedly without degrading or altering the structure," Yaghi says. "Based on these results, it is easy to imagine the creation of molecular cloths that combine unusual resiliency, strength, flexibility and chemical variability in one material."
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