posted on 2016-10-18, 00:00authored byBumjin Jang, Wei Wang, Samuel Wiget, Andrew
J. Petruska, Xiangzhong Chen, Chengzhi Hu, Ayoung Hong, David Folio, Antoine Ferreira, Salvador Pané, Bradley J. Nelson
We
report Au/Ru core–shell nanowire motors. These nanowires
are fabricated using our previously developed electrodeposition-based
technique, and their catalytic locomotion in the presence of H2O2 is investigated. Unlike conventional bimetallic
nanowires that are self-electroosmotically propelled, our open-ended
Au/Ru core–shell nanowires show both a noticeable decrease
in rotational diffusivity and increase in motor speed with increasing
nanowire length. Numerical modeling based on self-electroosmosis attributes
decreases in rotational diffusivity to the formation of toroidal vortices
at the nanowire tail, but fails to explain the speed increase with
length. To reconcile this inconsistency, we propose a combined mechanism
of self-diffusiophoresis and electroosmosis based on the oxygen gradient
produced by catalytic shells. This mechanism successfully explains
not only the speed increase of Au/Ru core–shell nanomotors
with increasing length, but also the large variation in speed among
Au/Ru, Au/Rh, and Rh/Au core–shell nanomotors. The possible
contribution of diffusiophoresis to an otherwise well-established
electroosmotic mechanism sheds light on future designs of nanomotors,
at the same time highlighting the complex nature of nanoscale propulsion.