Fundamentals and applications of fluid- structure interactions in compliant microchannels

Thesis (Ph.D.)--Boston UniversityThe development of soft lithography techniques for fabricating microfluidic channels has enabled the study of microscale flows. These studies have become an essential component of experimental research in biology, fluid dynamics, engineering and related fields. A systematic understanding of microscale flows requires that the characteristics of the flow fields be determined accurately. However, as microchannels are scaled down, the size of most experimental probes becomes comparable to or even bigger than the micro-flows themselves, making the measurement of the distribution of flow fields problematic. In this work, we take advantage of the fact that most microfluidic channels are made up of soft materials and can deform during flow. We develop a non-invasive optical measurement technique to correlate the channel deformation with the pressure field inside the microchannel; we then apply this technique to studies of biological flows and flows on superhydrophobic surfaces. [TRUNCATED

Porous Superhydrophobic Membranes: Hydrodynamic Anomaly in Oscillating Flows

We have fabricated and characterized a novel superhydrophobic system, a mesh-like porous superhydrophobic membrane with solid area fraction $\Phi_s$, which can maintain intimate contact with outside air and water reservoirs simultaneously. Oscillatory hydrodynamic measurements on porous superhydrophobic membranes as a function of $\Phi_s$ reveal surprising effects. The hydrodynamic mass oscillating in-phase with the membranes stays constant for $0.9\le\Phi_s\le1$, but drops precipitously for $\Phi_s < 0.9$. The viscous friction shows a similar drop after a slow initial decrease proportional to $\Phi_s$. We attribute these effects to the percolation of a stable Knudsen layer of air at the interface.Comment: 5 pages, 3 figure