Experimental Verification of Overlimiting Current by Surface Conduction and Electro-Osmotic Flow in Microchannels

• Main Authors: Nam, Sungmin (Author), Cho, Inhee (Author), Heo, Joonseong (Author), Lim, Geunbae (Author), Bazant, Martin Z. (Contributor), Moon, Dustin Jaesuk (Author), Sung, Gun Yong (Author), Kim, Sung Jae (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Chemical Engineering (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2015-03-24T16:04:59Z.
• Subjects: Article
• Online Access: Get fulltext

 Direct evidence is provided for the transition from surface conduction (SC) to electro-osmotic flow (EOF) above a critical channel depth (d) of a nanofluidic device. The dependence of the overlimiting conductance (OLC) on d is consistent with theoretical predictions, scaling as d[superscript −1] for SC and d[superscript 4 over 5] for EOF with a minimum around d=8  μm. The propagation of transient deionization shocks is also visualized, revealing complex patterns of EOF vortices and unstable convection with increasing d. This unified picture of surface-driven OLC can guide further advances in electrokinetic theory, as well as engineering applications of ion concentration polarization in microfluidics and porous media.