Interdisciplinary Applied Mathematics

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Q A = Q c = Q ac + Q bc    (7.43)

due to the mass conservation requirements.

In summary:

• Locally imposed electroosmotic forces in the Stokes flow regime enable linear flowrate control in the branches of a microchannel network system. This linear response can be utilized in the design of various elec-troosmotically actuated micropump/valve systems and flow switches. For example, the cross-flow junction geometry presented above can be used for dispensing a precise amount of fluid from one channel to another in the absence of valves or pumps with moving components.

Array of Circular and Square Posts: Measurements of electroosmotic flow in arrays of circular and square posts have been obtained by Cummings in the absence of externally imposed pressure gradients, by maintaining zero elevation difference between the upstream and downstream reservoirs (Cummings, 2001). The microfluidic system consisted of uniformly distributed

FIGURE 7.19. Electrokinetic speed contours in an array of circular posts at 45° with respect to the applied electric field of 2 V/mm. (Courtesy of E. Cummings.)

post arrays that are isotropically etched in glass with a thermally bounded glass cover    slip.    The    circular    posts    have    diameter    93    p,m    and    the    square

post dimensions are 104 p,m, with center-to-center separation of 200 p,m. Phosphate-buffered saline solution of 1 mM, resulting in buffer pH = 7.7 is used. An external electric field was applied in various angles to the post arrays, and the electric field value was kept low to avoid particle dielectrophoresis. MicroPIV measurements of the velocity field were performed, and the results were presented in the form of a simulated interferogram (Cummings, 2001).

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