Author ORCID Identifier:
Date of Graduation
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Chemistry (PhD)
Degree Level
Graduate
Department
Chemistry & Biochemistry
Advisor/Mentor
Fritsch, Ingrid
Committee Member
Dong, Bin
Second Committee Member
Wilkins, Charles
Third Committee Member
Stenken, Julie
Fourth Committee Member
Edwards, Martin
Fifth Committee Member
Kaman, Tulin
Keywords
Redox Magnetohydrodynamics (R-MHD); Microfluidic Chemical Separations; Finite Element Modeling (FEM); Lab-on-a-chip (LOC) Systems
Abstract
Rapid separation of small volume liquid mixtures is essential in fields such as medicine, pharmaceuticals, chemistry, and biology. Different techniques, such as ultra-high performance liquid chromatography (U-HPLC) and capillary electrochromatography (CEC), which are based on phase equilibria, and capillary electrophoresis (CE), which is based on differences in electrophoretic migration rates of analytes, have been widely used for efficient chemical separations. However, they typically require high pressure, high voltage, and bulky external pumping systems. In contrast, magnetohydrodynamic (MHD) pumping offers a compact alternative to conventional high pressure or voltage systems, driving fluid motion through the magnetic component of Lorentz force resulting from the interaction between the ionic current the possibility of enabling indefinitely long separation paths in microscale devices, while allowing precise control of fluid velocity and direction through adjustment of key operating parameters, including the applied current and magnetic field. This dissertation investigates the feasibility of redox magnetohydrodynamics (R-MHD), a coupling of MHD and electrochemical redox reactions, for on-chip chemical separations modeling by finite element method (FEM) was used to examine velocity and concentration profiles in the system where the fluid flow and molecular species transport, driven both by diffusion and R-MHD, depend strongly on fluid properties, device geometry, and phase interactions. The simulations examined the impact of electrode configurations, applied current, electrode gap-to-chamber height ratio, electrolyte composition, and flow velocity on sample plug dispersion, utilizing various electrode configurations and chamber designs. The FEM predictions showed strong agreement with experimental results, with over 90% agreement in velocity profiles, confirming the model’s accuracy. Overall, this work shows that R-MHD provides precise control of microscale flow and supports on-chip chemical separations. Larger wGap/h ratios preserved sample plug shape, and the larger ring geometry produced lower plate heights, indicating improved efficiency. Spatial–temporal detection and chromatogram construction confirmed how electrode design and operating conditions influence dispersion and resolution. These results demonstrate the promise of optimized R-MHD systems as compact, tunable, pump-free separation platforms. Finally, loop-based partitioning liquid chromatography was successfully implemented in an R-MHD channel, demonstrating the on-chip separation of two molecular species with defined diffusion coefficients in both the stationary and mobile phases, and distinct partition coefficients for each component. This study represents one of the first combined experimental and modeling efforts to enable chemical separations through magnetohydrodynamic pumping, providing a foundation for further optimization. The findings of this work provide valuable guidance for optimizing the design and operation of lab-on-a-chip (LOC) microfluidic systems that enable efficient chemical separations through redox-driven MHD pumping integrated with loop-based partitioning chromatography.
Citation
Hesan, S. (2025). Comprehensive Studies of Microfluidic Flow Driven by Redox-Magnetohydrodynamics (R-MHD) in Devices with Different Electrode Configurations and Chamber Designs with Applications to Chemical Separations. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6070
