Evaluation of three methods for the characterisation of the membrane–solution interface: streaming potential, membrane potential and electrolyte conductivity inside pores

Filtration and separation performances of microfiltration, ultrafiltration and nanofiltration membranes can be greatly affected by the charge (or electrical potential) on their surface. These surface properties can be characterised in terms of potential in the Outer Helmholtz Plane (Ψd). A theoretical analysis of electrical and electrokinetic phenomena (electrolyte conductivity inside pores λpore, membrane potential Em and streaming potential SP) occurring in charged capillaries was developed in the framework of the linear thermodynamics of irreversible processes with the aim of studying the variation of SP, Em and λpore as a function of Ψd for various pore sizes and electrolyte concentrations. From these results, the accuracy on the determination of Ψd from experimental measurements of λpore, Em and SP could be estimated and a ‘method limitation’ diagram was constructed using the constraints of pore size and surface charge.