Catalytically propelled micro‐/nanomotors: how fast can they move?

Abstract

Synthetic micro-/nanomotors represent one of the most exciting challenges facing nanotechnology and hold considerable promise for diverse future applications. This review discusses different strategies to improve the speed of the catalytic nanomotors, summarizing and comparing the maximum absolute and relative speeds obtained with different catalytically propelled micro-/nanomotors. Remarkably ultrafast nanowires and microtube engines, with speeds of 60 and 375 body lengths s(-1), respectively, have been developed recently. Achieving such amazingly high speed and power has been accomplished through rational optimization of key factors governing the propulsion behavior, including composition of the motor and fuel, the motor morphology and various external stimuli. We hope that our discussion will serve as a guide to the rational design of even faster and more powerful catalytically propelled fuel-efficient micro-/nanomotors, with speed limits that are limited only by our imagination.

Efficient bubble propulsion of polymer-based microengines in real-life environments

“…Such favorable morphology and composition lead to a remarkably efficient propulsion behavior and hence to record-breaking speeds. 21,22 Hence, such microengines can tolerate a diminished speed in raw viscous real-life media while still display a highly efficient propulsion. Further improvements would require better understanding of the fundamental uid ow physics that propel catalytic micro/nanomotors, and of the exact effect of the motor design, composition and surface morphology, on the propulsion efficiency in different media.…”

“…1a). 10,21 Such polymer-based microengines have been shown recently to display a record-breaking speed of over 1400 body lengths per s. 21,22 The preparation conditions, particularly the electropolymerization parameters, have been shown to have a profound effect on the morphology and propulsion behavior of polymer-based microengines. 21 Such motor morphology and performance are thus greatly inuenced by the nature and concentration of the monomer and of the supporting electrolyte, as well as by the surfactant present.…”

Synthetic micro/nanomotors in drug delivery

“…46 This force is reected by a remarkable speed that can exceed 1000 bodylengths s À1 . 47 Motion control is another important requirement for targeted drug delivery. The directionality of catalytic micro/ nanoscale motors can be readily controlled (commonly via magnetic guidance) and their speed can be regulated using different stimuli.…”

Hierarchical nanoporous microtubes for high-speed catalytic microengines

“…21,22 Various approaches have been employed to boost the catalytic reaction rate and in turn increase the motor's speed. 23,24 Tailoring the motors' geometry is considered to be an especially effective method. For instance, the incorporation of carbon nanotubes within the Pt segments, 25 enhancing the surface roughness of Pt 26 and the assembly of Pt nanoparticles in microtubes 27 have been used to enhance the speeds of self-propelled motors.…”