| This thesis studies the electrokinetic transport phenomena in microfluidic devices. The scope of this thesis work is best broken down into two parts. The first part concentrates on the theoretical and experimental study of Joule heating effects on the transports of heat, electricity, momentum and mass species in capillary-based electrophoretic separations. It is found that Joule heating effects cause temperature gradients in both cross-stream and stream-wise directions. As a result, the electric field and thus the electrical body become non-uniform in flow equations so that pressure gradients are induced passively to satisfy the mass continuity. This disturbance to the otherwise plug-like electroosmotic flow field increases the sample dispersion and hence reduces the separation efficiency. The second part of this thesis work concerns the electrophoretic motion and the electrokinetic manipulation (for example, focusing, dispensing and separation) of particles and cells in microfluidic chips. Theoretical predictions of the particle electrophoretic mobility that are available in the literature are experimentally validated in both cylindrical and rectangular microchannels by visualizing the single particle motion. We also examine intensively the accelerated particle electrophoretic motion and separation in converging-diverging microchannels along with the focused electrophoretic motion of particles and cells in cross-microchannels. In addition, an electrokinetic method is proposed to dispense efficiently single particles in a double-cross microchannel. The totally electrokinetic manipulation of particles is believed to facilitate developing integrated lab-on-a-chip devices for studies of single cells. |
