Dynamics of Electrocatalytic Nanomotors and Powered Random Walkers

Restricted (Penn State Only)
Author:
Nourhani, Amir
Graduate Program:
Chemical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 19, 2011
Committee Members:
  • Ali Borhan, Dissertation Advisor
  • Vincent Henry Crespi, Dissertation Advisor
  • Ali Borhan, Committee Chair
  • Vincent Henry Crespi, Committee Chair
  • James Spiro Vrentas, Committee Member
  • Kristen Ann Fichthorn, Committee Member
  • Thomas E Mallouk, Committee Member
Keywords:
  • nanomotor
  • nanorotor
  • random walker
  • electrocatalytic
  • effective diffusion
Abstract:
A variety of synthetic catalytic nanomotors have been fabricated in recent years, one aim being to mimic microscopic biological motors. We propose and analyze a model for deterministic dynamics of hydrogen peroxide powered bimetallic motors, which have been shown to operate by electrokinetic self-propulsion. Using perturbation analysis and the method of matched asymptotic expansions, we find the particle velocity to leading order in Debye length and first order in reaction-induced ion flux for spherical and spheroidal particles. The results are consistent with experiments and numerical calculations. The velocity depends linearly on interfacial potential at the particle surface and hydrogen ion production intensity, as well as inversely on the fluid viscosity, background ion concentration in the electrolyte and hydronium diffusion coefficient. In the regime of low Reynolds flow, both the deterministic and the stochastic dynamics of the nanomotor contribute to the dynamics of the particle. The coupling between these two types of dynamics results in quasi-circular trajectories. We analyzed the proposed mechanisms of motion for some nanorotors and proposed some design principles for making faster rotors. We also showed that the coupling of deterministic dynamics and stochastic orientational dynamics of nanorotors leads to an effective translational diffusion which can be as significant as the translational diffusion of unpowered nanorod.