Numerical Modelling of Electrokinetic Flow in Microchannels: Streaming Potential and Electroosmosis

• Author / Creator

  Riad, Adham

• Investigating the flow-behavior in microfluidic systems has become of interest due to the need for precise control of the mass and momentum transport in microfluidic devices. In multiphase flows, precise control of the flow behavior is much more challenging as it depends on multiple parameters. The following thesis focuses on two aspects of microfluidics discussed in two chapters: the flow reversal phenomenon in streaming potential flows and the magnetic fields generated by electroosmotic and streaming potential flows. In the first chapter, the proposed microfluidic system consists of an aqueous solution between a moving plate and a stationary wall, where the moving plate represents a charged oil-water interface. A numerical model was developed to predict the streaming potential flow created due to the shear-driven motion of the charged upper wall along with its associated electric double layer (EDL) effect. Additionally, analytical expressions were derived by solving the nonlinear Poisson-Boltzmann equation along with the simplified Navier- Stokes equation in order to describe the effect of the EDL on the shear-driven flow of the aqueous electrolyte solution. Results show that the interfacial charge of the moving interface greatly impacts the velocity profile of the flow and can reverse its overall direction. The numerical results were validated by the analytical expressions, where both models predicted that flow can reverse its overall direction when the surface potential of the oil-water interface exceeds 120mV.
  For the second chapter, models were constructed for the transient electrokinetics, for both the electroosmotic flow and for the shear driven streaming potential flow, in a charged nanocapillary channel. Additionally, the transient effects of ionic currents and the magnetic field generated both inside and outside the microchannel were evaluated, and the results compared with known analytical solutions for verification purposes. In order to correctly simulate the above models, the following partial differential equations are solved together for the electrolyte continuum to capture the physics of the problem: a) the Navier-Stokes equation for the fluid flow b) Poisson-Nernst-Planck equations for the electric potential distribution and ion transport and c) Ampere-Maxwell’s law for the associated magnetic field. The obtained results showed that the magnetic field detected outside of the nanochannels can be used as a secondary electromagnetic signal for biomolecules as a part of a sequencing technique.

• Subjects / Keywords

  • Electroosmosis
  • Ionic currents
  • Electrokinetics
  • Magnetic fields
  • Microfluidic devices
  • Streaming potential

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-rydj-mz34

• License

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