The Cornell-led collaboration utilized chemical reactions to make micro-scale origami machines self-folding – freeing them from the fluids they normally work with, 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.
group paper, “Microactuation of Gas Phase Using Kinetically Controlled Surface Conditions of Ultrathin Catalytic Sheets,” published May 1 in the Proceedings of the National Academy of Sciences. 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 a micro-scale, with their robots,” Abbott said. “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 the chemical actuator, it’s not moving from one straight state to another. It’s actually going through a journey to a state of bend, of curvature, which is more extreme than either end of it states,” Abbott said. “If you understand the basic reaction steps in the catalytic pathway, you can go in and surgically remove those fast steps. You can operate your chemical actuators around those fast steps, 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 quite generalizable,” Abbott said. “There are many catalytic reactions that have been developed based on all kinds of species. So carbon monoxide, nitrogen oxides, ammonia: they’re all 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 very excited because this work paved the way for micro-scale origami machines that work in gaseous environments,” Cohen said.
Co-authors include postdoctoral researcher Michael Reynolds, MS ’17, Ph.D. ’21; doctoral student Wei Wang; Michael Cao ’14; and researchers at the University of Wisconsin, Madison.
This research was supported by the Cornell Center for Materials Research, which is supported by the National Science Foundation’s MRSEC program, the Army Research Office, NSF, the Air Force Office of Scientific Research and the Kavli Institute at Cornell for Nanoscale Science.
The researchers leveraged the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure, supported by NSF; and National Energy Research Scientific Computing Center (NERSC) resources, supported by the US Department of Energy’s Office of Science.
The project is part of the Nanoscale Science and Microsystems Engineering (NEXT Nano) program, which is designed to propel nanoscale science and microsystems engineering to the next level of design, function and integration.