Interdisciplinary Applied Mathematics

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The possibility of local and temporal zeta potential variations has opened a new direction for extensive flow control and mixing enhancement applications. Erickson and Li have simulated microfluidic mixing induced by electroosmotic flow with local zeta potential variations, resulting in enhanced mixing efficiency (Erickson and Li, 2002). Qian and Bau (2002) have developed a theoretical model that induces chaotic mixing by electroosmotic stirring. For details on chaotic advection and mixing, see Chapter 9, where we also present some details about the chaotic electroosmotic stirrer (Qian and Bau, 2002).


Electroosmotic Flow Control


Electroosmotic forces can be selectively applied for flow control in complex microgeometries either by utilization of local electric fields or by modification of surface zeta potential (Z). In this section, we will primarily study flow control in flow junctions using multiple electric fields by keeping the zeta potential unaltered.


The simulations are performed for a dielectric material of Z = —25.4 mV and half-channel-height of h = 3 /am, corresponding to XD/h = 0.01. The magnitude of the externally imposed electric field ||Eo|| corresponds to 950 V/cm, resulting in a Helmholtz-Smoluchowski velocity of wHs = 1.6 mm/s. We assumed that the buffer solution is water and the ion concentration density is    no =    0.1    mM.    The    Reynolds    number based    on    the    average


channel velocity and half-channel height is Re = 0.005. These simulation parameters are selected according to the data given in (Hunter, 1981). Here we must    note    that    for    Re =    0.005,    we    practically    have    Stokes flow    with








t = 1.5s

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