Simulation and experimental validation of electroosmotic flow in a microfluidic channel

In this paper steady electroosmotic and pressure driven flows in geometries of interest to biomacromolecular detection are considered. For both types of flow, experimental data are obtained by imaging fluorescent dye propagation. Numerical simulations are carried out using finite volume methods. Test structures are made of Polydimethylsiloxane (PDMS) mold using the negative of the desired structure fabricated by SU-8 thick negative photoresist. Steady electroosmotic flow is governed by the Laplace equation under certain idealized conditions such as when the Helmholtz-Smoluchowski relation is satisfied at the inlet and outlet boundaries, and when the zeta potential is uniform across the domain. In many of these cases, electroosmotic fluid flow can be further idealized as two-dimensional when two parallel plates confine the flow. Such conditions are frequently encountered in many microfluidic devices. In this paper, numerical solutions of such an idealized two-dimensional electroosmotic flow are obtained and compared to experimental data. Equations describing the transient dye propagation are then solved in a straight channel followed by a downstream circular well. Effects of channel size, electric field and possible pressure driven flow components are also explored. The effects of flow three-dimensionality are also examined.