Researchers have created gear-like molecular-scale machines that rotate as one when pressure is applied to them; the device was made with "self-assembled silver-based structures."
Superlattice structures are assembled from silver nanoparticle structures and organic protecting molecules, a Georgia Tech news release reported.
These particles form into layers, with hydrogen bonds acting as hinges, which allows the devices to rotate.
This type of device could be used in "molecular-scale switching, sensing and even energy absorption," the news release reported. This complex superlattice structure may be the largest solid ever mapped using both "X-ray and computational techniques."
"As we squeeze on this material, it gets softer and softer and suddenly experiences a dramatic change," said Uzi Landman, a Regents' and F.E. Callaway professor in the School of Physics at the Georgia Institute of Technology, said in the news release. "When we look at the orientation of the microscopic structure of the crystal in the region of this transition, we see that something very unusual happens. The structures start to rotate with respect to one another, creating a molecular machine with some of the smallest moving elements ever observed."
The gears can rotate as much as 23 degrees and then return to their original position when released. The structures are composed of 44 silver atoms which are protected by 30 ligand molecules of an organic material.
"It's not the individual atoms that form the superlattice," explained Landman. "You actually make the larger structure from clusters that are already crystallized. You can make an ordered array from those."
"The self-assembly process is guided by the desire to form hydrogen bonds," he said. "These bonds are directional and cannot vary significantly, which restricts the orientation that the molecules can have."
These hydrogen bonds affect how the superlattice was formed as well as how it moves under pressure.
"The hydrogen bond likes to have directionality in its orientation," Landman said. "When you press on the superlattice, it wants to maintain the hydrogen bonds. In the process of trying to maintain the hydrogen bonds, all the organic ligands bend the silver cores in one layer one way, and those in the next layer bend and rotate the other way."
This type of rotation could allow the superlattice structure act as an energy-absorbing structure which converts "force to mechanical motion." Compressing the structure could also lead to "molecular-scale sensors and switches," the news release reported.
"We now have complete control over a unique material that by its composition has a diversity of molecules," Landman said. "It has metal, it has organic materials and it has a stiff metallic core surrounded by a soft material."
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