Microfluidic Components Research
While pursuing the various application-driven as well as fundamental studies described in the other categories, we often come across unexpected or unexplained phenomena, or we realize that a certain microscale component is missing. For example, we have studied the influence of gravity on multistream laminar flows, a side study to our laminar flow fuel cell project. Furthermore, we continue to develop new fluidic valves, actuated either in pneumatic or electrostatic fashion, in our pursuit of various integrated microfluidic networks for microanalysis systems, as well as drug discovery and crystallization chips. The ever increasing complexity of these VLSI microfluidic chips also has led to various multiplexing strategies for pneumatic valve operation and sensor array readout to reduce their overall complexity. These are the current areas of our research:
Gravity-induced re-orientation of laminar flow interfaces
Gravity-induced re-orientation of laminar flow interfaces
Collaboration: (None)
Funding: University of Illinois, National Science Foundation (NSF).
The parallel, laminar flow of two liquid streams is encountered commonly in microfluidic systems. This flow geometry provides a well-defined and controllable interface for the chemical reactions and mass transport processes that are critical to many applications of microfluidics, including chemical sensing, spatially controlled patterning of microchannel walls or cells within microchannels, liquid-liquid extractions, the study of protein crystallization and folding, and microfluidic, membraneless fuel cells. In this project, we study the re-orientation of this interface that occurs when two liquid streams of different density flow along a microchannel in parallel (see Figure 3). In each of the applications mentioned above, re-orientation of the stream interface would result in a severe reduction in performance, or even a complete loss of functionality. Our study of this phenomenon elucidated the roles played by viscous, gravitational and inertial forces in the re-orientation of the interface between two miscible fluids of similar viscosity, flowing at equal rates within microchannels of aspect ratios of 1:1 and 1:2. Qualitatively, we found that inertial forces have a negligible effect on re-orientation behavior, and that high viscous forces increase the time required for re-orientation. Using dimensional analysis and experimental measurements of the length and orientation of the interface, we generated a correlation that quantifies the effects of these forces. While the applicability of this correlation is limited to the specific conditions of our investigation, the process by which it was obtained provides a basis for the development of general design rules for the optimization of new microchemical systems that exploit the parallel, laminar flow of multiple liquid streams of differing density to provide spatial control of chemical reactions and mass transport processes in microfluidic systems.
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| Figure 3: Re-orientation of the interface between two liquid streams of different density when flowing along a microchannel. |
- Reorientation of the interface between two liquids of different densities flowing laminarly through a microchannel. S.K. Yoon, M. Mitchell, E.R. Choban, Paul J.A. Kenis, Lab on a Chip, 2005, 5, 1259-1263.