Mechanically interlocked architecture aids an ultra-stiff and ultra-hard elastically bendable cocrystal.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31420538.
- Also identified by DOI 10.1038/s41467-019-11657-0 and PMC identifier 6697680.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Molecular crystals are not known to be as stiff as metals, composites and ceramics. Here we report an exceptional mechanical stiffness and high hardness in a known elastically bendable organic cocrystal [caffeine (CAF), 4-chloro-3-nitrobenzoic acid (CNB) and methanol (1:1:1)] which is comparable to certain low-density metals. Spatially resolved atomic level studies reveal that the mechanically interlocked weak hydrogen bond networks which are separated by dispersive interactions give rise to these mechanical properties. Upon bending, the crystals significantly conserve the overall energy by efficient redistribution of stress while perturbations in hydrogen bonds are compensated by strengthened π-stacking. Furthermore we report a remarkable stiffening and hardening in the elastically bent crystal. Hence, mechanically interlocked architectures provide an unexplored route to reach new mechanical limits and adaptability in organic crystals. This proof of concept inspires the design of light-weight, stiff crystalline organics with potential to rival certain inorganics, which currently seem inconceivable.