Development of a microfluidic device for simultaneous mixing and pumping

Abstract

This dissertation presents numeral simulations and experiments for simultaneously mixing and pumping small liquid using asymmetric microelectrodes. To this end, four arrangements of electrode pairs were considered with diagonal/herringbone shapes. For the diagonal shape of the electrodes, a repeated pattern and a staggered pattern were studied. For the herringbone shape, a diverging flow case and a converging flow case were examined. Numerical simulations were made of three- dimensional geometries, using the linear theory with regard to AC electroosmosis. The pumping ability was assessed using the mean flow velocity, and the mixing degree was quantified by a mixing efficiency parameter. The mixing efficiencies for three cases were increased at a cost of the pumping performances, compared to the reference case in which mixing occurs only by diffusion. However, for the converging flow case with the herringbone electrodes, even though the mixing degree was slightly inferior to those of other three cases, the pumping and mixing were increased at the same time, compared to the reference. This desirable behavior is attributed to higher slip velocity in the middle region of the channel. To validate the numerical predictions, the microfluidic devices were made through MEMS. The flow rate was obtained by using micro PIV, increasing the applied frequency. The electrolyte was potassium chloride solution. The flow patterns above electrodes were visualized to see lateral flow for mixing. The experimental results showed good agreements with the numerical predictions. Additionally, an advanced image processing for PIV was developed to increase the measurement accuracy.