(340a) On-Demand Control of the Limiting Current in Nano-Slot Devices By Varying the Diffusion Layer Length

The passage of an electric current through a permselective medium (membranes or nanochannel) under an applied electric field is characterized by the formation of ionic concentration gradients, which result in regions of depleted and enriched ionic concentration at opposite ends of the medium. In the low-voltage region, the current-voltage behavior is approximately Ohmic until the diffusion-limited current saturates when both ion concentrations are completely depleted at the surface. Here, we study the effect of controlling the limiting current, which roughly scales as the inverse of the diffusion length, in a microchannel-permselective medium system via varying of the diffusion layer length. The latter is varied by changing the distance of the reservoir or that of an on-demand convective mixing element from the nanoslot interface. We fabricated and tested nanoslot devices made of Nafion connecting two opposite microchambers made of PDMS. The device response was studied by visualizing concentration-polarization, colloid dynamics and measuring current-voltage. Enhancement of the limiting current by on-demand control of the diffusion length is of importance in on-chip electro-dialysis, desalination and preconcentration of analytes.