POWERED MOTION AT MICRO/NANOSCALES AND CONTROLLED INTERACTIONS BETWEEN CATALYTIC MOTORS

Open Access
Author:
Wang, Yang
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 28, 2009
Committee Members:
  • Thomas E Mallouk, Dissertation Advisor
  • Thomas E Mallouk, Committee Chair
  • Ayusman Sen, Committee Member
  • Mark Maroncelli, Committee Member
  • Darrell Velegol, Committee Member
Keywords:
  • nanofabrication
  • electroanalysis
  • colloidal science
  • microfluids
  • microscopy
Abstract:
Nano- and microscale motors have been studied intensively over the past decade and are of much current interest because of their potential applications in the electronic and biomedical fields. While research on molecular motors and artificial muscles has resulted in a number of breakthroughs, one of the most promising recent directions has been the discovery of free-moving catalytic motor systems. Catalytic motors have the potential to operate with a variety of possible fuel-catalyst combinations. In this thesis we report mechanistic studies of catalytic motors that use hydrogen peroxide and other fuels, as well as the observation of pairwise motor interactions in fuel-containing solutions. In the mechanistic study, we developed a mixed potential model for the hydrogen peroxide bimetallic nanorod system. This analysis can correctly predict the relative speed and direction of different metal pairings. We applied the same method to the hydrazine fuel system and catalytic micropumps, and those experiments supported a similar electrokinetic mechanism for those systems also. Control experiments with catalytic nanorods that had low electronic conductivity also supported the electrokinetic mechanism. To expand the application of catalytic nanomotor systems and to further understand scaling effects we fabricated bimetallic catalytic motors by lithographic methods. These experiments showed that catalytic motors still function in the 10µm size range and that electrokinetic propulsion is still dominant over inertial mechanisms. Some differences in behavior were observed that may be attributed to artifacts of the fabrication process, such as poor electrical contact between components of the bimetallic motors and poisoning of catalytic surfaces. Lithographically fabricated chiral bimetallic designs led to successful fabrication of rotary motors, which are interesting for the observation of pairwise motor interactions and collective phenomena.. One of the interesting extensions of catalytic rotor research is the possible interactions and dynamic assemblies brought about by microscale rotating objects, which should operate on different principles compared to centimeter-scale rotary motor systems. We designed and fabricated fast-spinning catalytic rotors based on bimetallic nanorod designs, and our observations have shown various types of interactions between spinning rotors in close proximity, which may be due to a number of different effect. We then constructed a magnetic rotational system involving ferromagnetic nanorods and compared them with the catalytic micro-rotors. Interactions between rotors were again observed, and the potential exists for the formation of dynamic ordered matrices.