Dielectric analysis of concentration polarization structure at anion-exchange membrane/solution interface under dc bias voltage application

Abstract

Abstract Dielectric measurement was carried out on anion-exchange membrane AMV immersed in distilled water and in sucrose solution under applicatio of dc bias voltage. The frequency dependence of the capacitance C and the conductance G observed for the whole system was clearly characterized by a double dielectric relaxation. The dielectric relaxation at lower frequencies around 3 kHz is caused by a concentration polarization boundary layer generated alongside the membrane. The relaxation at higher frequencies around 200–700 kHz is attributed to interfacial polarization due to a series combination of the two aqueous phases adjacent to the membrane. The feature of the double relaxation is very similar to that observed previously for the cation-exchange membrane CMV. The data on double dielectric relaxations were analyzed using an analytical method recently developed to calculate the structure parameters of the boundary layer, the capacitances, and the conductances of the two adjoining aqueous phases. The thickness of the concentration polarization boundary layer obtained by the analysis is about 0.3 mm for the system composed of the AMV membrane and distilled water and about 1.6 mm for the system composed of the AMV membrane and sucrose solution. These values are consistent with those obtained by other methods of observation. In view of the results for sucrose solutions, it is inferred that the thickness of the concentration polarization layer is affected by the viscosity of the aqueous phase.