doi:10.1038/nindia.2015.15 Published online 30 January 2015
Using sophisticated imaging techniques, researchers have discovered how single organic crystals of hexachlorobenzene bend and structurally deform when subjected to an external force1. They found that the layers inside the crystals slide over each other through the breaking and reforming of bonds between atoms.
This knowledge of molecular motion in single crystals is potentially useful for fabricating functional crystals that can harness external energy and convert it into motion, raising the possibility of making molecular motors.
Previous studies had observed that single organic crystals could hop, bend, curl and twist when exposed to external stimuli such as light, heat and external pressure. But scientists do not fully understand atomic-scale structural deformations that alter the elastic and optical properties of such crystals.
The researchers bent a single crystal of hexachlorobenezene by applying external pressure. They used sophisticated imaging and analytical techniques to find that the bent portion of the crystal’s surface became striated, forming distinct layers. As the crystal bent, macroscopic domains within the layers evolved, grew and segregated.
Applying three-point pressure on the face of the crystal resulted in the formation of ridged layers, which glided on top of each other. This was due to the weak interactions between chlorine atoms in the crystal; the bonds between these atoms broke and then reformed after gliding. This gliding happened in a self-healing process, so that the overall structural integrity of the crystal was retained. “Such bendable organic crystals could potentially be used to fabricate high-performance smart materials,” says co-researcher C. Malla Reddy.
1. Panda, M. K. et al. Spatially resolved analysis of short-range structure perturbations in a plastically bent molecular crystal. Nat. Chem. 7, 65–72 (2015)