Tangential electrokinetic characterization of hollow fiber membranes: Effects of external solution on cell electric conductance and streaming current Anthony Efligenir a , Patrick Fievet a,n , Sébastien Déon a , Patrick Sauvade b a Institut UTINAM, UMR CNRS 6213, Université de Franche-Comté,16 route de Gray, Besançon Cedex 25030, France b SUEZ environnement – AQUASOURCE, 20 Avenue Didier Daurat, 31029 Toulouse, France article info Article history: Received 3 June 2015 Received in revised form 31 August 2015 Accepted 1 September 2015 Available online 12 September 2015 Keywords: Electrokinetic characterization Hollow fibers Streaming current/potential Zeta potential abstract The methodology of tangential electrokinetic measurements with hollow fiber (HF) membranes was investigated. Two cell configurations were used, one configuration in which HF were immersed in the measuring solution and another one in which HF were embedded in a gel. The experiments were con- ducted with hydrophilic polysulfone HF of different lumen cross sections but of the same cross section of porous body in order to evaluate the contributions of porous fiber body and its lumen to both streaming current and cell electric conductance. The good linearity of streaming current/potential data vs. pressure difference gives evidence that expressions of the streaming current/potential derived in laminar flow are still valid for turbulent flux conditions (at least for experimental conditions used in the present study). Significant differences in both electric conductances and streaming current coefficients were obtained between the two cell configurations. The differences in the electric conductances show that the solution around fibers makes contribution to the cell electric conductance (as demonstrated previously). The observed differences in the streaming current coefficients could be due to either the contribution of the external surface of fibers to the measured streaming current or a non-negligible Starling recirculation flow. For tests conducted with HF embedded in the gel, linear variations of streaming current coefficient and cell electric conductance on channel cross section were obtained, as originally demonstrated by Yaroshchuk and Luxbacher for channels with porouswalls (A.E. Yaroshchuk, T. Luxbacher, Interpretation of electrokinetic measurements with porous films: role of electric conductance and streaming current within porous structure, Langmuir, vol. 26, 2010, pp. 10882–10889). Surprisingly, it is found that the (negative) zeta potential of pore surface is higher (in absolute value) than that of the lumen surface. The contribution of the fiber body to both streaming current and cell electric conductance turns out to be considerable. It is shown that neglecting this additional path (i.e. the fiber body) for streaming current leads to an overestimation (in absolute value) of the zeta potential by a factor of 1.7–5.7 depending on the fiber. This is a clear indication that the contribution of the fiber body to the streaming current cannot be neglected in the case of standard HF ultra-filtration membranes otherwise the interpretation of their electrokinetic properties could be distorted. With such materials, it is therefore recommended not to convert the measurement of the streaming current into zeta potential of lumen surface. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Assessing the zeta potential of membranes is particularly at- tractive because this parameter is very sensitive to any change in surface charge properties. It can therefore serve as a probe in studies dealing with rejection mechanisms of charged solutes [1– 3], membrane fouling [4–6], membrane ageing and cleaning [7–9], membrane functionalization [10,11], etc. In the case of fine-porous and asymmetric/composite membranes used in pressure-driven processes, the zeta potential is determined from the measurement of the tangential streaming potential and/or streaming current. In the case of flat membranes, the tangential mode consists in ap- plying a pressure gradient along a slit channel formed by two identical membranes facing each other and measuring the re- sulting electric potential difference or electric current with a pair of reversible electrodes located on both sides of the channel, near the ends. Yaroshchuk and Luxbacher [12] have shown that in tangential electrokinetic measurements with porous substrates soaked with electrolyte solution, the pores could make contribu- tion not only to the cell electric conductance (as first suggested by Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science http://dx.doi.org/10.1016/j.memsci.2015.09.002 0376-7388/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. Fax: þ33 81 66 62 88. E-mail address: patrick.fievet@univ-fcomte.fr (P. Fievet). Journal of Membrane Science 496 (2015) 293–300