(Nanowerk News) The Cornell-led collaboration harnessed chemical reactions to make micro-scale origami machines self-folding – freeing them from the fluids in which they normally function, so they can operate in dry environments and at room temperature.
Such an approach could one day lead to the creation of a new fleet of small autonomous devices that can quickly respond to their chemical environment.
The group’s paper, “Gas-Phase Microactuation Using Kinetically Controlled Surface Conditions of Ultrathin Catalytic Sheets,” was published in Proceedings of the National Academy of Sciences (“Microactuation of the gas phase using kinetically controlled ultrathin catalytic sheet surface conditions”). The lead author of this paper is Nanqi Bao, Ph.D. ’22, and former postdoctoral researcher Qingkun Liu, Ph.D. ’22.
The project was led by senior author Nicholas Abbott, a Tisch University Professor in the Robert F. Smith School of Chemical and Biomolecular Engineering at Cornell Engineering, along with Itai Cohen, professor of physics, and Paul McEuen, John A. Newman Professor of Physical Sciences, both at College of Arts and Sciences; and David Muller, Samuel B. Eckert Professor of Engineering at Cornell Engineering.
“There are quite good technologies for the transduction of electrical energy to mechanical energy, such as electric motors, and McEuen and Cohen’s group have demonstrated a strategy for doing it on the micro scale, with their robots,” said Abbott. “But if you’re looking for direct chemical to mechanical transduction, there really are very few options.”
Previous attempts have relied on chemical reactions that can only occur under extreme conditions, such as at high temperatures of a few 100 degrees Celsius, and the reactions are often very slow – sometimes as long as 10 minutes – making this approach impractical for everyday technological applications.
However, Abbott’s group found a kind of loophole while reviewing data from the catalysis experiments: a small part of a chemical reaction pathway contains slow and fast steps.
“If you look at the response of a chemical actuator, it’s not because it’s going from one immediate state to another. It actually goes through a journey into a twisted state, a curvature, which is more extreme than either of the two final states,” said Abbott. “If you understand the basic reaction steps in the catalytic pathway, you can go in and surgically remove the fast steps. You can operate your chemical actuator around that fast pace, and just ignore the rest.
The researchers needed the right material platform to take advantage of those fast kinetic moments, so they turned to McEuen and Cohen, who had worked with Muller to develop ultra-thin platinum sheets covered with titanium.
The group is also collaborating with theorists, led by professor Manos Mavrikakis at the University of Wisconsin, Madison, who are using electronic structure calculations to dissect the chemical reactions that occur when hydrogen – which is adsorbed into materials – is exposed to oxygen.
The researchers were then able to exploit the crucial moment that oxygen rapidly releases hydrogen, causing the atomically thin material to deform and buckle, like a hinge.
The system runs at 600 milliseconds per cycle and can operate at 20 degrees Celsius – that is, room temperature – in a dry environment.
“The results are fairly generalizable,” Abbott said. “There are many catalytic reactions that have been developed based on all kinds of species. So carbon monoxide, nitrogen oxides, ammonia: all of them are candidates for use as chemically driven actuator fuels.”
The team anticipates applying this technique to other catalytic metals, such as palladium and palladium gold alloys. Ultimately this work could lead to autonomous material systems where onboard controlling and computing circuits are handled by material responses – for example, autonomous chemical systems that regulate flow based on chemical composition.
“We are excited because this work paved the way for micro-scale origami machines that work in gaseous environments,” said Cohen.