Modified-Electrodes for Redox-Magnetohydrodynamic (MHD) Pumping for Microfluidic Applications

Author

Christena Kayl Nash, University of Arkansas, FayettevilleFollow

Date of Graduation

8-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Fritsch, Ingrid

Committee Member

Durham, Bill

Second Committee Member

Paul, David W.

Third Committee Member

Wilkins, Charles L.

Keywords

Conducting Polymers; Electrochemistry; Lab-on-a-chip; Magnetohydrodynamics; Microfluidics

Abstract

A new microfluidic pumping and stirring technique was demonstrated for lab-on-a-chip applications. Microfluidics was accomplished via redox-MHD, which takes advantage of a body force (F_B) that is generated when there is a net movement of ions in solution (j) in the presence of a perpendicular magnetic field (B), according to the equation F_B = j×B. In this work the movement of ions in solution was generated using electrodes modified with the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) rather than a redox species in solution, which can interfere with analyte detection and with biological species. The monomer solution and electrochemical method used for electrodeposition has a profound effect on the morphology and the electrochemical behavior of the film. These conditions were investigated to improve the properties of the PEDOT film for redox-MHD applications, such as coulombic capacity, current response, and electrochemical stability. PEDOT-modified microband electrodes were shown to be effective for microfluidic pumping applications, exhibiting a fairly flat flow across a 5600 μm gap. PEDOT-modified concentric ring-disk electrodes demonstrated a rotational fluid flow with nonuniform velocity between the disk and ring electrodes. This created a spiraling fluid flow that could be useful for stirring applications. PEDOT-modified electrodes were shown to be capable of initially high currents, and therefore velocities (up to 980 μm s^-1 at microband electrodes during an applied potential experiment), until the film was exhausted, limiting the time scale of pumping. This limitation was solved by taking advantage of the reversible nature of PEDOT. The bias of the PEDOT-modified electrodes was switched by applying a sinusoidal potential waveform while a synchronized potential waveform was driving an electromagnet under the chip, creating an AC magnetic field. This generated continuous fluid flow in a single direction. AC redox-MHD pumping was demonstrated at PEDOT-modified microband electrodes (115 μm s^-1) and at concentric ring-disk electrodes (<268 μm s^-1) for pumping and stirring applications respectively.

Citation

Nash, C. K. (2014). Modified-Electrodes for Redox-Magnetohydrodynamic (MHD) Pumping for Microfluidic Applications. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/2172