Migration of ions near charged surface.

Detailed understanding of ionic behavior in the region near a charged surface is important for the enhancement of water filtration mechanisms. In this study, a highly charged membrane is hypothesized to form an ion depletion zone (IDZ) without an external power supply. The formation of IDZ was experimentally investigated using membranes with varying surface zeta potential (SZP) values to confirm the hypothesis. The surface zeta potential of the charged membrane was controlled by layer-by-layer deposition method. Our results indicate that indicated that the fluorescent intensity near the charged surface becomes weaker with an increased absolute magnitude of SZP. Ionic surfactants enhance the formation of IDZ by increasing SZP magnitude, and by forming a secondary filtration layer. These findings provide information that is helpful in understanding the ionic behavior near the highly charged surface. In addition, the information provided by the findings would be helpful in fabricating a small-scale water filtration device.