Physica A 373 (2007) 21–28 Influence of the stick-slip transition on the electrokinetic behavior of nanoporous material Christophe Cheikh, Ger Koper DelftChemTech, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands Received 11 May 2006 Available online 25 September 2006 Abstract Electrokinetic phenomena exhibiting discontinuities are described in terms of a stick-slip transition. The flux-force equations are partially linear and in the linear regimes the coefficients satisfy Onsager’s reciprocal relations. From an interpretation of existing data on ion exchange membranes we find a linear dependence of the slip length with t potential. We conclude that slippage offers an alternative explanation for the so-called anomalous surface condu often found in electrokinetic phenomena. This would imply an enhancement of electrokinetic effects in nanopore r 2006 Elsevier B.V. All rights reserved. Keywords: Stick-slip transition; Nanoporous material; Anomalous surface conduction; Electrokinetic phenomena 1. Introduction In contact with an electrolyte solution, a surface may become charged either by ionization or by ads of ions from solution. This surface charge is balanced by an equal and oppositely charged diffuse electric double layer that extends from the wall into the fluid and in which the counterions form the majority. Counterions can also be bound to the surface forming a so-called Stern or Helmholtz layer. Under the influence ofa hydrostatic pressure gradient, the liquid willflow pastthe surface thereby dragging along the diffuse ions. The resulting accumulation of charges downstream causes an ionic countercurrent th absence of charge transfer in the external circuit, leads to the so-called streaming potential . The ions the electric field are dragging along solvent molecules which manifests itself as an increased apparen In industry, electrokineticeffectsare primarily of importancein small channels,such as found in membranes or porous plugs, and are therefore often exploited in technical applications [1,2] such as water purification [3], desalination [4], and food processing [5,6]. A detailed analysis of the electrokinetic effects in pores has been put forward by Levine et al. [7]and its quantification would, in addition to pore radius and Debye length, only need the effective surface charge which is related to the surface potential [8].According to Zukoski and Saville [9–11], this single surface parameter in itself is insufficient to describe the observed phenomena and they suggested the presence o ARTICLE IN PRESS www.elsevier.com/locate/physa 0378-4371/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physa.2006.08.068 Corresponding author. Tel.: +31 715317237. E-mail address: g.j.m.koper@tudelft.nl (G. Koper).