Determination of the porosity to thickness ratio A(k)/Delta x for UF and MF membranes by diffusion experiments

The structural parameter A(k)/Delta x, which represents the ratio of membra ne porosity to membrane thickness, was determined by means of diffusion exp eriments using aqueous solutions of neutral solutes (formamid, urea) and st rong electrolytes (HCl, KCl....). The membranes under investigation were co mmercial ultrafiltration (UF) polyethersulfone (PES), polyvinylidenefluorid e (PVDF) and acrylic membranes of various molecular weight cut-offs. The me thod used to measure A(k)/Delta x involves diffusion experiments at the pse udo-stationary state between two half cells. Experiments are non-time-consu ming, and exploitation of results does not require any pore model. Results show that neutral solutes, as well as salts or diluted strong acid, can be used for the determination of A(k)/Delta x. Discrepancies between A(k)/Delt a x values obtained by diffusion and water permeability measurements are ex plained by the pore tortuosity and the interconnection of the pores. (C) 20 00 Elsevier Science B.V. All rights reserved.