Performance and scaling of an electro-osmotic mixer

We report on the design, fabrication and detailed characterization of a microfluidic mixer, designed to mix two streams of electrolytic fluid rapidly and efficiently using electrokinetic forces. The effectiveness of the mixer as a function of the applied electric field, frequency and flow rate was characterized by the intensity distribution measured downstream from the mixing zone. The effectiveness is found to behave in a smooth and predictable manner over a wide range of operating conditions when the electric field is scaled by the mean flow velocity and the electro-osmotic mobility, and the frequency is scaled by the characteristic mixing chamber size and the mean flow velocity. It is confirmed that the Reynolds number effects are not important (the Re is O(1) at all times). It is also found that increased frequencies decrease effectiveness, but that at low frequencies, electrode saturation and bubble formation inhibit operation.