Electrical impedance spectroscopy characterisation of conducting membranesII. Experimental

An electrical impedance spectroscopy (EIS) method and apparatus that elimin ates the need for electrodes in the feed and permeate solutions was evaluat ed as a means of characterising physical and performance properties of poly sulphone ultrafiltration membranes in situ. The membranes were sputter-coat ed on one side with platinum before assembly in the apparatus. Alternating electrical current used for impedance measurements was injected directly in to the coat via dry electrical contacts with the edges of the membrane. As the frequency of the EIS measurement was increased the current increasingly dispersed into the solution via the interfacial region (double layer) and/ or fouling layers that the coat formed with the solution. These spatial dis persions manifested as characteristic dispersions with frequency of the imp edance of the system. Water flux measurements. field emission scanning elec tron microscopy and atomic force microscopy were also used to quantify the important membrane performance parameters of porosity and surface roughness . These estimates were in good agreement with the impedance model for the i n situ membrane system that was fitted to the measured impedance dispersion s. The study shows that EIS measurements potentially can quantify membrane performance parameters in situ better than those techniques that require di sruption of the membrane separation process. The method also has the potent ial for monitoring the deposition of particulate that can lead to fouling. (C) 2002 Published by Elsevier Science B.V.