Journal of Membrane Science 226 (2003) 227–236 Determining the ζ -potential of plane membranes from tangential streaming potential measurements: effect of the membrane body conductance P. Fievet ∗ , M. Sba¨ı, A. Szymczyk, A. Vidonne Laboratoire de Chimie des Matériaux et Interfaces, 16 Route de Gray, 25030 Besançon Cedex, France Received 28 April 2003; received in revised form 5 September 2003; accepted 11 September 2003 Abstract The ζ-potential is an important and reliable indicator of the surface charge of membranes and its knowledge is essential for the design and operation of membrane processes. The streaming potential remains the most widely used technique for determining the ζ-potential of membranes. In the case of asymmetric or composite membranes, the ζ-potential is now frequently determined from tangential flow streaming potential measurements. However, the interpretation of data in terms of ζ-potential is usually carried out by doing the implicit assumption of non-conducting substrates. In this paper, we investigate the electrokinetic properties of a ceramic membrane close to the NF range, the porous structure of which affects the streaming potential because streaming and conduction currents involved in the streaming potential process do not flow through identical paths (the streaming current flows only through the slit channel formed by the two membrane samples facing each other whereas a non-negligible part of the conduction current is likely to flow through the membrane pores filled with electrolyte solution). In this case, the so-called Fairbrother and Mastin (F–M) procedure accounting for the surface conductance to correct the Helmholtz–Smoluchowski (H–S) relation is not suitable and leads to an erroneous ζ-potential. The correct ζ-potential value is determined from an extrapolation method for which a set of measurements with various channel heights is required. A very good agreement is obtained with ζ-potential values deduced from consecutive streaming potential and total conductance measurements. The contribution of the membrane body to the total conductivity of the membrane/channel/membrane system appears to be independent of the pH of solution, probably due to the fact that the electric conduction takes place through the membrane porous body inside a thick layer dominated by the support layer which then enforces its conductivity. © 2003 Elsevier B.V. All rights reserved. Keywords: Zeta potential; Tangential streaming potential; Electric conductivity; Membrane body conductance 1. Introduction Most membranes acquire an electric surface charge when brought into contact with an aqueous solution. It is now well recognised that charge or electrical poten- tial properties of membranes have a very substantial ∗ Corresponding author. Fax: +33-3-81-66-20-33. E-mail address: patrick.fievet@univ-fcomte.fr (P. Fievet). influence on their filtration performances. That is the reason for which there is much interest in character- ising these properties. The electric potential at the solid surface cannot be measured directly; however, the electrical potential at the hydrodynamic plane of shear, called the zeta (ζ) potential, can be determined from streaming potential measurement. Streaming potential occurs when there is a relative motion between a fluid containing charged 0376-7388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2003.09.007