A microparticle image velocimetry (MPIV) system has been used to measure streamwise and spanwise velocity fields along a 100 ¡Ñ200 ¡Ñ20 mm microchannel with a hydraulic diameter of 133.3 at 10¡ØRe¡Ø421.4. The measuring technique uses 1 diameter orange fluorescent polystyrene flow tracing particles, a pulsed Nd: YAG double resonant tube laser with a micro electroscope, and a high resolution CCD camera to record particle-image fields. Local velocity profiles as flow proceeds downstream were measured at particular positions to examine the entrance effect and hydrodynamically fully developed length as well as velocity slip at wall for liquid flow in a microchannel. Velocity slip exists with a considerable value over the entire range of Re under study. Moreover, the friction factors were calculated and compared with those of previous study. Good agreement was found which also assesses the accuracy of the present results.

In this study, sharp/gradual converging-diverging microchannels with contraction/ expansion ratio of 4:1/1:4 was designed to generate elongational flow with uniform velocity in the centerline. The £f-DNA stained with YOYO-1 was observed in the flow. MPIV was built to measure the velocity distribution and local strain rate was estimated by MPIV measurements. The deformation and conformation of individual DNA molecules in the flow was visualized with confocal laser scanning microscopy (CLSM). The goal of the present work was to develop a method for stretching DNA molecules, in order to perform analysis of coil-stretch transition of DNA. By measuring dynamic properties and relaxation time of DNA molecules stretched by pressure driven at various flow rate and viscosity, we have shown how one could investigate the influence of hydrodynamic interactions in the case of stretching of DNA molecules.

Experiments were conducted on the investigation of the electroosmotic flow with five different electric field strength, four kinds of buffer solution concentration, six different pH values, and three kinds of microchannel geometry. Joule heating effects were also taken into consideration. Experiments were performed using a microparticle image velocimetry (MPIV) for full field velocity distributions and micro laser-induced fluorescent (£gLIF) for full field temperature distributions. It is found that the presence of Joule heating and flow area change could have a great impact on the microfluidic transportation, e.g. dispersion. Furthermore, data were presented and the relation between zeta potential and pH value were discussed in detail. It is found that, as pH > 7.5, all silanol sites are deprotonated.

Experiments were investigated on passive mixing enhancements in different geometric microchannels with roughened surfaces and flow was driven by electroosmotic flow (0.027 ≤ Re ≤ 0.081). Experiments were perform using micro particle image velocimetry (MPIV) technology for velocity measurements and relative analysis. Iodine and DI water mixing experiments were captured by common optical microscope for flow visualization, and rhodamine B and buffers mixing experiments were measured by micro laser-induced fluorescence (µLIF) technology for concentration field measurements and analysis. The experimental results showed that the Twr and Tcdr micromixers can generate chaotic flow and enhance the mixing performance in the short channel length. Finally, the mixing length was developed in terms of within accuracy between the experimental data and prediction data.