(166a) Electrokinetic Locomotion by Reaction Induced Charge Auto-Electrophoresis

The controlled motion of synthetic nanoscale motors may represent a major step towards the development of practical nanomachines, artificial cells, and autonomous microsystems. We are investigating locomotion of bimetallic synthetic nanomotors that, analogous to their biological counterparts, harvest chemical energy from their local environment and convert it to useful work. Bimetallic nanorods can autonomously propel themselves at a hundred body lengths per second through aqueous solutions by using hydrogen peroxide as a fuel. We can control the motion of nanomotors using magnetic fields and chemical species to control the motion of Pt-Ni-Au nanorods.

Several arguments have been proposed to describe the physics underlying their locomotion, but there is no detailed theory on the propulsion mechanism. We are simulating the physics of rod-shaped nanoparticles with asymmetric surface fluxes. Our models show that locomotion is driven by electric body forces in the fluid that arise due to finite space charge and internally generated electric fields surrounding the rod. The electric fields and charge density are generated by dipolar cation fluxes, such as those generated by heterogeneous electrochemical reactions with broken symmetry. We present a set of governing equations, a scaling analysis, numerical simulations, and experiments that describe the physics underlying the autonomous motion of electrocatalytic bimetallic nanomotors due to a mechanism we call Reaction Induced Charge Auto-Electrophoresis (RICA).