The exclusion-diffusion potential in charged porous membranes

• Published in: Journal of electroanalytical chemistry and interfacial electrochemistry 1986-02, Vol.198 (2), p.213-231
• Main Authors: Westermann-Clark, G.B., Christoforou, C.C.
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Membranes; Porous materials
• ISSN: 0022-0728
• DOI: 10.1016/0022-0728(86)90001-X

In previous work in which the electrical potential Δ ed was measured across charged porous membranes in contact with electrolyte solutions with different concentrations, the Meyer-Sievers model occasionally agreed with the more detailed space-charge model and occasionally there were discrepancies. To explain the sources and implications of these discrepancies, theoretical predictions from the Meyer-Sievers and space-charge models for Δ ed in charged porous membranes are compared. The Meyer-Sievers model uses the Henderson and Donnan potential expressions for the exclusion and diffusion portions, respectively, of Δ ed. The space-charge model uses the Poisson-Boltzmann equation for the electrostatic condition of the pore fluid, and the Nernst-Planck and Navier-Stokes equations for transport through pores. The two models give similar results for low pore wall surface charge densities, but for large surface charge densities the Meyer-Sievers results differ considerably from those of the space-charge model. The discrepancies between the two models are attributable to the failure of the Meyer-Sievens model to include the radical variation of ionic concentrations within pores. These results can have a significant influence on the prediction and interpretation of electrolyte transport rates through charged porous membranes.