Advanced electrokinetic characterization of layer-by-layer assembled polyelectrolyte membranes: Consideration and use of the electrokinetic leakage phenomenon

The sensitivity of zeta potential to the sign of the surface charge of membranes makes it an interesting parameter for the characterization of layer-by-layer (Lbl) modified polyelectrolytes membranes. However, during tangential electrokinetic measurements, a non-negligible parasitic phenomenon referred to as "electrokinetic leakage" may occur. If not taken into account, this phenomenon can lead to dramatic quantitative and qualitative errors, especially when it comes to characterize the surface charge of layer-by-layer assembled polyelectrolyte mem-branes. In this work, we show that it can lead to substantial errors when interpreting experimental data, including misinterpreting the sign of the membrane surface charge density. An advanced protocol based on the measurement of the streaming current by varying the spacing between the two samples needed for the mea-surements allows to (i) correct the raw data for the electrokinetic leakage phenomenon and thus to correctly and accurately determine the zeta potential of the membrane surface and (ii) to detect whether polyelectrolytes are deposited only on the membrane surface or whether they can also penetrate into the membrane pores. The approach followed and the conclusions drawn in this study can be straightforwardly applied to any kind of membrane functionalization.