Electro-osmotic streaming on application of traveling-wave electric fields.

We describe ac electro-osmotic flow of an aqueous electrolyte on application of a traveling-wave electric field. Depending on the frequency of the applied traveling wave, the interaction of the electric double layer charge and the tangential electric field leads to fluid flow in the direction of the traveling wave. We have derived two theoretical models that describe this flow as a function of the amplitude of the applied electric potential, the signal frequency, and the material properties of the system. The first is based on a capacitative model and is limited to frequencies much lower than the double layer relaxation frequency. The second is an analytical solution of the electrokinetic equations and is also valid at higher frequencies. We provide experimental evidence that streaming takes place on application of a traveling wave of potential by tracing the movements of fluorescent latex beads over a spiral electrode structure. Streaming takes place at applied potentials low enough for the method to be easily integrated into lab-on-a-chip devices.