Modeling particle-fluid interactions in microfluidic systems under the action of an electric field

Microfluidics refers to systems composed of fluid conduits and chambers with characteristic dimensions ranging from tens to hundreds of microns. Microfluidic devices have an advantage over macroscopic devices in small sample and reagent consumption, automated and rapid processing, and low cost. Electrokinetic forces are often used to drive flows in the microfluidic conduits (electroosmosis), propel and separate charged molecules and particles in solution (electrophoresis), and drive, collect, and separate uncharged, polarizable particles with non-uniform electric fields (dielectrophoresis).; This dissertation focuses on continuum modeling and simulations of the migration of cylindrical particles under the action of the external electric fields. Specifically, the electrophoresic motion of charged, cylindrical particles submerged in ionic solution and translating in long tubes and through pores was studied theoretically both when the electric double layer is thin and thick. The effect of the particles' translocation on the ionic current was elucidated. The simulations demonstrate that in some cases the presence of the particle may cause a blockade in the ionic current while in some other circumstances it may enhance the ionic transport. The theoretical results are compared, and qualitatively agree with experimental data and molecular dynamics simulations of double and single stranded DNA molecules translocating through synthetic nanopores. The results of the work are applicable to particle counting, sorting, biosensing, and DNA sequencing.; This dissertation also addresses dielectrophoretic migration and nano-positioning. The forces acting on and the velocities of particles submerged in perfectly dielectric media were studied analytically. The motion of nanorods such as carbon nanotubes migrating in electric field was computed and compared with experimental observations. The models presented here can be used to test various operating conditions and assist in the design and optimization of microfluidic devices.