Abstract: The controlled motion of synthetic nanoscale motors may represent a major step towards the development of practical nanomachines, artificial cells, and autonomous microsystems.  At ASU, 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 physical 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)

We observe collective dynamic behavior of nanomotors similar to biological chemotaxis.  Simulations and experimental results suggest that artificial chemotaxis exists for systems that demonstrate concentration dependent velocity and rotational diffusivity.  We observe both positive and negative chemotaxis of nanomotors depending on the chemistry used.  This work suggests that artificial collective behaviors can be engineered into nanoscale systems and that temporal sensing may not be required for biological chemotaxis.

Biography: Dr. Jonathan D. Posner is an assistant professor at Arizona State University in the faculties of Mechanical Engineering and Chemical Engineering as well as adjunct faculty in the Consortium for Science, Policy, & Outcomes (CSPO). He is the director of the ASU Micro/Nanofluidics Lab and the PI of eight ongoing projects. Dr. Posner earned his Ph.D. (2001) degree in Mechanical Engineering at the University of California, Irvine. He spent 18 months as a fellow at the von Karman Institute for Fluid Mechanics in Rhode Saint Genèse, Belgium and two years as a postdoctoral fellow at the Stanford University.  His interests include electrokinetics, self-assembly of colloids, and the physics of nanoparticles at interfaces. At CSPO, Posner has interest in the social implications of technology, role of science in policy and regulation, as well as ethics education.  Dr. Posner was honored with a 2008 NSF CAREER award for his work on the physics of self-assembly of nanoparticles at fluid-solid and fluid-fluid interfaces. He has also been recognized for his Excellence in Experimental Research by the von Karman Institute for Fluid Dynamics.

Host: Rouslan Krechetnikov