- Post Doctoral
MIT Unit Affiliation:
- Mechanical Engineering
Post Doc Sponsor / Advisor:
Date PhD Completed:
Top 3 Areas of Expertise:
Expected End Date of Post Doctoral Position:
- Numerical modeling of electroporation in bacteria to theoretically explore the relationship between a bacterium's polarizability and its susceptibility to genetic transformation by electroporation
- Separation of transition metal oxide nanoparticles according to material composition using free-flow isoelectric focusing in a microchannel
- Numerical simulation of nonlinear electrophoresis of ideally polarizable particles
The past decade has seen the rapid development of synthetic particles capable of propelling themselves at the micro- and nanometer scale through aqueous media. Several groundbreaking experiments have shown these so-called “nanomotors” to be capable of performing several useful microscale tasks. However, alongside this progress, the need has arisen to understand the physical mechanisms governing their motion, as well as the limitations on their capabilities. Explanations of the propulsion mechanisms driving synthetic nanomotors are critical not only for providing insight into novel physical phenomena, but also to guide and inform the design and implementation of nanomotors and nanomachines.
Bimetallic rods, 2 microns in length, were first shown to move autonomously using hydrogen peroxide fuel in 2004. Since then, a number of theories have been proposed to explain how these particles convert chemical energy in the hydrogen peroxide to kinetic energy of motion. The leading theory states that the rod functions as a shortcircuited electrochemical cell, with electrochemical reactions occurring asymmetrically on its surface. These reactions are thought to generate an electric field, which propels the particle via electrophoresis. However, until now, this mechanism has not received a rigorous theoretical treatment as it applies to bimetallic rods, hindering the development of these particles for practical applications.
The goals of this dissertation are (i) to understand physically the motion of self-propelling metallic particles with electrochemical surface reactions, and (ii) to characterize the limitations on the propulsion mechanism. To accomplish these goals, I construct a complete numerical model for the motors using the finite-element method. The model includes the coupled Poisson-Nernst-Planck-Stokes equations with Frumkin-corrected Butler-Volmer boundary conditions to represent the surface reactions. I devote special attention to the transport phenomena occurring in the interfacial layer near the particle/solution interface, which play a key role in the locomotion.
The model enables one to understand how the rods’ motion depends on the properties of their environment, such as hydrogen peroxide concentration, solution electrical conductivity, and solution viscosity. The numerical simulations are complemented with a scaling analysis based on the governing equations, which makes definite, verifiable predictions of these dependences. One of the most important trends that has been observed experimentally is the significant decrease in speed induced by adding sub-millimolar concentrations of inert electrolyte. It is important to understand the physical reasons for the electrolyte-induced speed decrease, in order to know whether it is fundamental to this propulsion mechanism, or if there is some feasible means to circumvent it.
Successful completion of this research will result in an improved understanding of the capabilities, as well as the risks and limits of applicability, of the bimetallic nanomotors for applications in nanotechnology and nanomedicine. Potential applications of the rods include the targeted delivery of drugs in the human body, sensing of chemical impurities in drinking water, and as engines to drive fabrication of microscale structures.
Top 5 Awards and honors (name of award, date received):
5 Recent Papers:
Figliuzzi, B.M., Chan, W.H.R., Moran, J.L., Buie, C.R. (2014) Nonlinear electrophoresis of ideally polarizable particles. Physics of Fluids, Vol. 26, No. 10, 102002.
Moran, J.L., Posner, J.D. (2014) Role of Solution Conductivity in Reaction Induced Charge Auto-Electrophoresis. Physics of Fluids, Vol. 26, No. 4, 042001.
Moran, J.L., Posner, J.D. (2011) Electrokinetic Locomotion due to Reaction Induced Charge Auto-Electrophoresis. Journal of Fluid Mechanics, Vol. 680, 31-66.
Wheat, P.M., Marine, N.A., Moran, J.L., Posner, J.D. (2010) Rapid Fabrication of Bimetallic Spherical Motors. Langmuir, Vol. 26, No. 16, 13052-13055.
Moran, J.L., Wheat, P.M., Posner, J.D. (2010) Locomotion of electrocatalytic nanomotors due to reaction induced charge autoelectrophoresis. Physical Review E, Vol. 81, No. 6, 065302.