Interdisciplinary Applied Mathematics

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FIGURE 6.39. Atomistic (SMILE) and continuum (GASP) predictions for the specific impulse along the micronozzle axis at different stagnation pressures. (Courtesy of M. Ivanov.)


X, m


(Pa)



— filter 1


— filter 2 — filter 4


— filter 1


— filter 2 — filter 4


Part II: Liquid Flows

7

Electrokinetic Flows


Rapid developments in microfabrication technologies have enabled a variety of microfluidic systems consisting of valves, pumps, and mixers to be utilized effectively for medical, pharmaceutical, defense, and environmental monitoring applications. Examples of such applications are drug delivery, DNA analysis/sequencing systems, and biological/chemical agent detection sensors on microchips. These microfluidic systems require seamless integration of sample collection, separation, biological and chemical detection units with fluid pumping, flow control elements, and the necessary electronics on a single microchip. The reliability and compliance of these components are important for successful design and operation of the entire microfluidic system. In particular, subsystems like microvalves and micropumps with moving components are complicated to design and fabricate, and they are prone to mechanical failure due to fatigue and fabrication defects.


In this chapter, we review and explore ideas of microflow control elements using electrokinetic flow control schemes, which do not require any moving components. We cover electroosmotic and electrophoretic transport in detail. We also present dielectrophoresis, which enables separation and detection of similar size particles based on their polarizability. Theoretical treatments of these electrokinetic transport mechanisms are kept at an introductory level for brevity. For further information, the reader is referred to classical textbooks (Probstein, 1994; Hunter, 1981; Melvin, 1987; Righetti, 1983; Shaw, 1980; Westermeier, 1990; Pohl, 1978). Other reviews of electrokinetically driven liquid microflows can be found in (Stone et al., 2004; Gad-El-Hak, 2001; Nguyen and Wereley, 2003; Morgan and Green, 2003). Also, in Chapter 12 we focus on electroosmotic flows in nanochannels.

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