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ABSTRACT
A new electrokinetic setup was developed for assessing the active layer ζ-potential of tubular membranes based on tangential streaming potential and electrical resistance measurements. Although the flow was not wholly laminar (because of the large hydraulic diameter of channels), the electrokinetics theory could be used to convert the streaming potential data into ζ-potentials because the electrical double layer lay within a laminar sublayer near the channel walls. Electrical resistance data allowed for the account of the conduction phenomenon through the membrane porous body. The new device was tested over a range of pH with a tubular ceramic membrane composed of three channels with a titania active layer. The isoelectric point was found to be in good agreement with that determined from salt retention data. The ζ-potential value determined at pH = 3.5 using the present device was compared with that obtained on a flat membrane made of the same material using the traditional microslit electrokinetic setup. A good agreement between the two measurements was observed. It was shown that neglecting the electric conduction phenomenon through the membrane porous body leads to a low underestimation of the ζ-potential (less than ~20%). This is related to the large size of channels. The contribution of the membrane porous body was found to be independent of the pH of solution. This suggests that the support layer of the membrane would make a decisive contribution to the electric conductivity of membrane porous body.
