Particle Electrokinetics in Non-Newtonian Microfluidics

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Microfluidic devices have been increasingly used over the past two decades for numerous chemical, biomedical and environmental applications. Many applications require precise placement and transport of particles (ranging from macromolecules to viruses and cells, from colloids to beads, etc.) in microchannels. The application of an electric field is the method of choice to control particle motions in microfluidic systems because of the ease, precision, autonomy of operation and integration with other components for analysis. The electric field can induce motion of a charged particle (electrophoresis) or the motion of the surrounding fluid (electroosmosis). This so-called electrokinetic particle motion has been extensively studied in simple liquids. However, it has not been studied extensively in complex fluids such as polymer solutions, colloidal solutions, biological fluids, which are examples of non-Newtonian fluids that exhibit unusual properties in flow. The goal of this project is to develop a fundamental knowledge of electrokinetic particle motion in polymer solutions through microchannels. The research will delinate effects of fluid elasticity and shear-thinning effects on electrophoretic motion in the direction of the channel axis and lateral migration of particles toward the channel walls in order to find ways to control particle motions. The experiments will be extended to large electric fields that have not yet been considered for non-Newtonian fluid systems. The research will be intimately weaved into undergraduate and graduate curricula at Clemson University and will form the basis for activities developed for high school students in South Carolina. Undergraduate and high school students, especially those from underrepresented groups, will be actively involved in the project through various programs available in the department, university, and state.This project will be the first comprehensive study of electrokinetic particle motion in non-Newtonian fluids through microchannels. A systematic experimental investigation of both the axial motion and lateral migration of particles will be performed in the flow of polymer solutions through straight rectangular microchannels under (1) pure DC electric field, (2) DC electric field imposed with a pressure gradient, and (3) pure AC electric field with a magnitude of up to 1 MV/m (one order of magnitude higher than in typical electrokinetic microfluidics) in each case. Five types of common polymer solutions with distinct rheological properties will be tested and compared against Newtonian fluids. The experiments will investigate effects of fluid elasticity and shear thinning, individually and in combination, on the linear and nonlinear electrophoretic particle motions as well as the accompanying lateral particle migration. The experimental data of particle mobility and migration will be compared with the predictions of theoretical formulae and numerical simulations, if available.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.