Using Electrochemical Impedance Spectroscopy to Probe Permselectivity in Polyamide Membranes

We use electrochemical impedance spectroscopy (EIS) to study the permselectivity of model polyamide membrane selective layers, prepared via molecular layer-by-layer deposition of trimesoyl chloride and m-phenylene diamine. The thickness of the polyamide layer was systematically varied by controlling the number of molecular layers deposited. An equivalent circuit was established to model the impedance response of thin polyamide films in electrolyte solutions. The resistive and capacitive behavior of the polyamide films were quantified as a function of the thickness of the polyamide layer as well as the nature of the electrolyte (monovalent vs divalent salts). We also employed a more traditional electrochemical cell to probe the permselectivity of commercial polyamide membranes for comparison. We will discuss similarities and differences between the two geometries (silicon support vs porous support) as well as the membrane chemistry.