Active Micromixers Based on Polarization Instability and Acoustic Streaming

This paper reports two pressure-driven high-throughput active micromixers. Mixing enhancement was achieved with applied external electrical and acoustic fields. In the first active mixer, nanoporous charge-selective Nafion membrane was used to achieve strong mixing vortices. These vortices are caused by electroconvection in the concentration polarization zone above the membrane. The required applied voltage is found to be propotional to the square root of the flow rate. In the second active mixer, surface acoustic wave lauched from an interdigitated electrode deposited on a piezoelectric substrate causes acoustic streaming and improves the mixing efficiency significantly. Surface wave with a frequency of 13 MHz was launched perpendicular to the flow. The mixing efficiency was observed to be proportional to the square of the applied voltage. Compared to conventional parallel electrodes, a focusing design of the interdigitated electrode leads to a better mixing efficiency.