Electrokinetic processes for microfluidic devices

This thesis is devoted to the development of electrokinetic process for use with microfluidic devices. The study is limited to low Reynolds number, electrokinetic liquid flows in microchannels with hydraulic diameters ranging from 25mum to 200mum. These parameters are typical of the targeted applications of interest, analytical microfluidic chips. A microfluidic mixing strategy was developed which exploits stream-wise diffusion of a sequentially interlaced fluid stream. A numerical model is developed, implemented and applied to demonstrate the microfluidic mixing technique and predict its performance. Based on the numerical results, prototype microfluidic chips are fabricated using soft-lithography methods. Fluorescence microscopy is employed to analyze, quantify and demonstrate the effectiveness of this mixing strategy, as well as to determine an optimal frequency range for operation. A novel strategy for three-dimensional hydrodynamic focusing in a planar microfluidic geometry is developed and tested numerically. Both the microfluidic mixing and focusing technologies developed here have unique advantages over current methods.