A Cornell-led collaboration harnessed chemical reactions to make microscale origami machines self-fold 鈥 freeing them from the liquids in which they usually function, so they can operate in dry environments and at room temperature.
The approach could one day lead to the creation of a new fleet of tiny autonomous devices that can rapidly respond to their chemical environment.
The group鈥檚 paper, 鈥,鈥 published May 1 in Proceedings of the National Academy of 麻豆视频. The paper鈥檚 co-lead authors are Nanqi Bao, Ph.D. 鈥22, and former postdoctoral researcher Qingkun Liu, Ph.D. 鈥22.
The project was led by senior author , a Tisch University Professor in the Robert F. Smith School of Chemical and Biomolecular Engineering in Cornell Engineering, along with , professor of physics, and , the John A. Newman Professor of Physical Science, both in the 麻豆视频 and 麻豆视频; and , the Samuel B. Eckert Professor of Engineering in Cornell Engineering.
鈥淭here are quite good technologies for electrical to mechanical energy transduction, such as the electric motor, and the McEuen and Cohen groups have shown a strategy for doing that on the microscale, with their robots,鈥 Abbott said. 鈥淏ut if you look for direct chemical to mechanical transductions, actually there are very few options.鈥
Prior efforts depended on chemical reactions that could only occur in extreme conditions, such as at high temperatures of several 100 degrees Celsius, and the reactions were often tediously slow 鈥 sometimes as long as 10 minutes 鈥 making the approach impractical for everyday technological applications.
However, Abbott鈥檚 group found a loophole of sorts while reviewing data from a catalysis experiment: a small section of the chemical reaction pathway contained both slow and fast steps.
鈥淚f you look at the response of the chemical actuator, it鈥檚 not that it goes from one state directly to the other state. It actually goes through an excursion into a bent state, a curvature, which is more extreme than either of the two end states,鈥 Abbott said. 鈥淚f you understand the elementary reaction steps in a catalytic pathway, you can go in and sort of surgically extract out the rapid steps. You can operate your chemical actuator around those rapid steps, and just ignore the rest of it.鈥
The researchers needed the right material platform to leverage that rapid kinetic moment, so they turned to McEuen and Cohen, who had worked with Muller to develop ultrathin platinum sheets capped with titanium.
The group also collaborated with theorists, led by professor Manos Mavrikakis at the University of Wisconsin, Madison, who used electronic structure calculations to dissect the chemical reaction that occurs when hydrogen 鈥 adsorbed to the material 鈥 is exposed to oxygen.
The researchers were then able to exploit the crucial moment that the oxygen quickly strips the hydrogen, causing the atomically thin material to deform and bend, like a hinge.
The system actuates at 600 milliseconds per cycle and can operate at 20 degrees Celsius 鈥 i.e., room temperature 鈥 in dry environments.
鈥淭he result is quite generalizable,鈥 Abbott said. 鈥淭here are a lot of catalytic reactions which have been developed based on all sorts of species. So carbon monoxide, nitrogen oxides, ammonia: they鈥檙e all candidates to use as fuels for chemically driven actuators.鈥
The team anticipates applying the technique to other catalytic metals, such as palladium and palladium gold alloys. Eventually this work could lead to autonomous material systems in which the controlling circuitry and onboard computation are handled by the material鈥檚 response 鈥 for example, an autonomous chemical system that regulates flows based on chemical composition.
鈥淲e are really excited because this work paves the way to microscale origami machines that work in gaseous environments,鈥 Cohen said.
Co-authors include postdoctoral researcher Michael Reynolds, M.S. 鈥17, Ph.D. 鈥21; doctoral student Wei Wang; Michael Cao 鈥14; and researchers at the University of Wisconsin, Madison.
The research was supported by the , which is supported by the National Science Foundation鈥檚 MRSEC program, the Army Research Office, the NSF, the Air Force Office of Scientific Research and the Kavli Institute at Cornell for Nanoscale Science.
The researchers made use of the , a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the NSF; and National Energy Research Scientific Computing Center (NERSC) resources, which is supported by the U.S. Department of Energy鈥檚 Office of Science.
The project is part of the (NEXT Nano) program, which is designed to push nanoscale science and microsystems engineering to the next level of design, function and integration.
Read the story in the .
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