FABRICATION AND PURIFICATION OF SELF-MOTILE NOBLE METAL-SEMICONDUCTOR ACTIVE COLLOIDAL DEVICES

Open Access
Author:
McDermott, Joseph James
Graduate Program:
Chemical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 28, 2001
Committee Members:
  • Darrell Velegol, Dissertation Advisor
  • Darrell Velegol, Committee Chair
  • Michael John Janik, Committee Member
  • Themis Matsoukas, Committee Member
  • Ayusman Sen, Committee Member
Keywords:
  • electrophoresis
  • colloidal assembly
  • micromotors
Abstract:
Colloidal assembly is a field of scientific research that can be found at the intersection of many fields and disciplines. As a result, chemists, physicists, materials scientists, and chemical engineers are all active in assembly research. However, most assemblies currently being fabricated are of model systems (such as assemblies of inert polymer microparticles) and are assembled using material-specific techniques that produce only lab scale quantities of product. In this work, the chemical engineering aspects of colloidal assembly are explored. The primary question being: how can we design, build, and purify a functional colloidal assembly, using techniques that are generalized and scalable, envisioning the entire colloidal assembly process as one might picture a chemical plant. The two most important steps in this process, both the assembly of the product from component particles and the separation and purification of the product, are considered. The functional colloidal assembly produced here is a three-component colloidal ‘trimer’ consisting of three micron-sized particles attached in a specific order, i.e., gold – cadmium sulfide – silver, but without a specific orientation. The assembly process used to form these trimers is developed and characterized in this work. It is a diffusion-limited, selective, controlled aggregation process called ‘Quenched Electrostatic Assembly’. When placed into a solution of hydrogen peroxide, these trimers act as photoresponsive catalytic motors. Through selective decomposition of the peroxide and other photoelectrochemical reactions, the motor induces a localized ionic concentration gradient which moves the motor and other particles around it through electro- or diffusiophoresis. Other systems explored using similar principles are gold-silver heterodoublet motors, calcium carbonate diffusion-induced micropumps and motors, and flows in microchannels due to dissolution and passivation of disturbed geologic samples. Because colloidal assembly is such a broad field, this work encompasses many different fields: interparticle forces, diffusion and aggregation kinetics, catalysis, photoelectrochemistry, geology, and solution electrodynamics, along with many types of colloidal functionalization and analysis.