Microfluidics: Fluid flow, transport, control, characterization and applications

Microfluidic flows are studied experimentally and compared to simulations. Applications of flow control and flow networks are demonstrated. Microfluidic devices are fabricated by soft lithography. Flows are visualized by microscopy and analyzed by image processing.; Steady electroosmotic and pressure driven flows in geometries of interest to biomacromolecular detection are considered. For both types of flow, experimental data are obtained by imaging fluorescent dye propagation. Numerical simulations are carried out using finite volume methods. In many of these cases, electroosmotic fluid flow can be idealized as two-dimensional when two parallel plates confine the flow. Effects of channel size, electric field and possible pressure driven flow components are also explored. The effects of flow three-dimensionality are also examined. General good agreement between experimental and simulation results validates the flow visualization techniques.; A numerical and experimental study of the injection into a microchannel of a fluid with a spatially modulated composition is presented. The investigation employs test structures constructed in polydimethylsiloxane by standard replica molding. Fluid-flow simulations are compared to flow results obtained by fluorescence microscopy experiments. Results show that for a given channel dimension the desired modulation of the solution composition is only possible below a threshold frequency. The value of the threshold frequency is dependent on channel size as well as flow rate. Experimental results are in accord with numerical simulations and theoretical considerations.; The flow modulation scheme is adapted by employing a hydrostatic pressure driven flow and applied towards cell dynamic osmotic loading studies. This microfluidic dynamic osmotic loading scheme provides a wider frequency range over the previous flow chamber technique, and exhibits minimal wall shear stress to the immobilized cells in the main channel.; A microchannel with a patterned network was used in a preliminary study of two-phase flow related to fuel cells. Such microfluidic emulation may offer many advantages in investigating two-phase flows, such as easy fabrication by soft lithography and flow visualization by microscopy. The dimensions of the patterned microchannels closely approximate the pore size and porosity of the gas diffusion backing used in PEM fuel cells.