| When an electric field is applied to a microchannel-nanochannel junction for a nanochannel with overlapping electric double layers (EDL), a microvortex instability is produced at the interface. By incorporating nanochannels within microfluidic systems, functional lab-on-a-chip devices have been created for sample preparation, separation, and detection. Understanding ion transport and hydrodynamics in these systems is critical to fluid manipulation. The present numerical study models steady-state electrokinetically-driven flow in a hybrid microchannel-nanochannel system containing a cylindrical nanochannel with overlapping double layers connected to reservoirs on either side. The transport of potassium and chlorine ions was simulated in this system for a range of applied voltages. Ion concentration and fluid flow were studied at the microchannel-nanochannel interface, using large reservoirs to capture the role of ion depletion and microvortices. Microvortex instability was observed near the channel inlet. The vortices were shown to grow with increasing voltage. It was found that at a critical voltage, the vortex separated into multiple vortices, coinciding with a large drop of ionic current in the channel. |
