An advanced imaging technique developed at Cornell has revealed the first two-dimensional, mechanically interlocked polymer - confirming a breakthrough in both material design and electron microscopy.
Atomic structure of a two-dimensional, mechanically interlocked polymer obtained using tilted-corrected bright field microscopy.
Resembling the interlocking links in chainmail, the nanoscale material was developed by researchers at Northwestern University and features remarkable flexibility and strength, making it a promising material for applications such as light-weight body armor and ballistic fabrics.
Publishing Jan. 16 in the journal Science, the study achieves several milestones. The material demonstrates 100 trillion mechanical bonds per 1 square centimeter, the highest density of mechanical bonds ever achieved, according to the researchers. The polymer's high degree of crystallinity and interlocking structure were confirmed at Cornell, where tilt-corrected bright field imaging was used to atomically image a crystalline material for the first time.
"The results were remarkable - sharp and high-contrast - clearly revealing the structure," said Schuyler Zixiao Shi, a doctoral student who conducted the imaging in the lab of David Muller, the Samuel B. Eckert Professor in the School of Applied and Engineering Physics and the co-director of the Kavli Institute at Cornell.
Shi and Muller co-authored the study, which was led by William Dichtel, professor of chemistry at Northwestern.
In 2021, Cornell electron microscopists set a world record by imaging complex metal oxides with atomic precision using a technique called electron ptychography. However, imaging polymers poses an additional challenge - they are highly sensitive to electron beams, and their structures can easily degrade under high-energy electron exposure.
To overcome this challenge, teams led by Muller and Lena Kourkoutis, the late associate professor of applied and engineering physics, developed an imaging technique called tilted-corrected bright field. This method makes it possible to image beam-sensitive materials, such as polymers and biological samples, with a resolution comparable to electron ptychography.
The technique's lead developer, Yu Yue, Ph.D. '23, paved the way for the innovation. Building on this foundation, Shi demonstrated the method's exceptional capability by achieving atomic-resolution imaging of the new polymer, revealing its intricate chainmail-like structure for the first time.
"Unlike electron ptychography, this method requires significantly fewer computing resources while achieving comparable resolution when the signal on electron detectors is weak," Shi said. "With tilted-corrected bright field, researchers were able to visualize the zigzag polymer chains knitting together into a flexible 2D chainmail structure that bends locally while maintaining its strength."
Shi added that in addition to its standalone capabilities, tilted-corrected bright field can serve as a real-time diagnostic tool for ptychography, providing valuable information and reducing computational time for ptychographic reconstructions.
Schuyler Zixiao Shi and Diane Tessaglia-Hymes, communications specialist for Cornell Engineering, contributed to this article.
