Surface Conduction in a Microchannel.

Ionic current through a microchannel has drawn significant attention not only for fundamental electrokinetic research but also for the development of novel micro/nanofluidic applications. Among various ion transport mechanisms, surface conduction, which is a predominant mechanism in micro/nanofluidic devices, has been theoretically characterized based on two-dimensional analysis. However, its infinite axis assumption has become a barrier for direct application in practical micro/nanochannel networks. In this work, we conducted rigorous experiments to include all of the three-dimensional length scales. There, L/ A, the perimeter to area ratio of the microchannel cross-section, came up as a single parameter to quantitatively interpret the surface conductive ion transportation. Overlimiting conductance of microchannel devices increased with larger perimeter, which is equivalent to specific surface area, even with the same cross sectional area. Finally, a micro/nanofluidic diode with a different L/ A value on its forward and reverse channel was demonstrated as a simple application. The analysis presented could provide a practical guideline to design a micro/nanofluidic application.