In-situ Monitoring of Polyelectrolytes Adsorption Kinetics by Electrochemical Impedance Spectroscopy: Application in Fabricating Nanofiltration Membranes Via Layer-by-layer Deposition

We herein report a novel approach based on electrochemical impedance spectroscopy (EIS) for in-situ monitoring of the adsorption kinetics in preparing polyelectrolyte multilayer nanofiltration membranes using layer-by-layer (LbL) deposition. Unlike existing methods for monitoring adsorption kinetics, this new approach is non-destructive and applicable to various substrates (as it does not use the substrate as a sensor). The model nanofiltration membrane used in this study is prepared by alternate depositions of Poly(diallyldimethylammonium chloride) and Poly(sodium 4-styrenesulfonate) on a polyacrylonitrile ultrafiltration membrane as the support. In each deposition step, the EIS measurements yield two important parameters, including the interfacial layer solution resistance and the film resistance, for probing the extent of polyelectrolyte deposition and membrane performance. The extent of polyelectrolyte deposition as probed by the EIS measurements is well corroborated by independent measurements of the membrane surface potential and the nanofiltration performance including water permeability and Na2SO4 rejection. This EIS-based approach enables the optimization of membrane fabrication using LbL deposition by conveniently identifying the minimum deposition time required to attain surface saturation.