Effect of poly-dispersed nanostructures on concentration polarization phenomena in ion exchange membranes

Abstract

We investigated the effect of poly-dispersed nanostructures on concentration polarization (CP) phenomena in ion exchange membranes through fabrication of poly-dispersed interconnecting channels (Pd-ICs) integrated microfluidic chip and characterized the CP phenomena which happens near the interconnecting channel and main microchannel interface. Current-voltage (I-V) characteristics and depletion (enrichment) layer formation behavior within Pd-IC system are examined. We found that “Electric field focusing” affects the I-V characteristics of Pd-IC system, and Pd-IC system follows the “Limiting current occurrence” criterion. The visualization results show that the depletion layer thickness at the anodic side decreases with an increasing dispersity and also for increasing bulk concentration. We attribute this phenomena to the high electroosmotic flow in the sub-microchannel and “Electroosmosis of the second kind” at the electrolyte-membrane (Pd-IC) interface. The perm-selectivity of interconnecting channels also play an important role. At the cathodic side, we observed that fluorescent dye depleted at the microchannel and sub-microchannel interface due to the ejecting flow and current balance at the corner wedge of sub-microchannels. We hope these working mechanisms of Pd-IC system to be beneficial to model pseudo-ion exchange membrane and to develop high efficiency ion exchange membranes.