In a study of “some of the smallest moving elements ever observed,” researchers at Georgia Tech and the University of Toledo have confirmed the existence of synchronized, molecular “gears” in a self-assembling material. Like an array of micro machines, the gears rotate together when pressure is applied to the material, then resume their original position when pressure is released.
Since the Air Force Office of Scientific Research and Department of Energy both funded the molecular gear study, let’s see how that material could play into a new energy future of portable, microscale energy harvesting and storage devices.
Nanoscale Gears In A Superlattice
The self-assembling material, called a superlattice, really does behave like a nanoscale machine. It is composed of 500-atom nanoparticles made up of silver and organic molecules. Hydrogen bonds between the components form the hinges.
The nanoparticles self-assemble into a lattice-like structure and when pressure is applied, they shift around the hydrogen bonds to form a rotating movement. The movement itself is made possible by the open, crystalline structure of the nanoparticles.
Lead researcher Uzi Landman of Georgia Tech describes it this way:
The hydrogen bond likes to have directionality in its orientation,” Landman explained. “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.
Harvesting Energy From A Superlattice
This is probably starting to ring some bells, if you’ve been following the field of piezoelectronics. Piezoelectronics refers to the ability of some crystalline, bone, or ceramic materials to generate energy when pressure is applied to them.
If you’ve used a cigarette lighter or backyard grill starter, you’ve already used a piezoelectric device.
However, mainstreaming the piezoelectric effect into broader areas of use presents a challenge, partly due to the field’s reliance on lead, a known toxin. That’s why the lead-free material under development at Georgia Tech could have significant implications.
One significant growth area for piezoelectric devices is in remote sensing. For example, you could install a set of piezoelectric sensors in a bridge to monitor the structure for early signs of deterioration, without the complication and expense of installing a power or transmission system. The on again, off again pattern of traffic on the bridge would provide the energy input to power the device.
As an aside, there’s also a related field called piezo-phototronics, which refers to the ability of some materials to generate light when pressure is applied.
Steps Away From a Piezoelectric Future
Though the new Georgia Tech/U. Toledo research is foundational, it has immediate significance in terms of a more complete understanding of the nano-mechanics that underlay the piezoelectric effect.
That, in turn, should lead to the development of a new generation of tailored, high-efficiency piezoelectric materials.
Meanwhile, the piezoelectric effect has already been working its way into daily life.
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