Comparison of three electrokinetic methods to determine the zeta potential of solid surfaces

The aim of this work was to compare informations obtained on surface electric charge of solids using three different methods based on electrokinetic phenomena study. These methods were microelectrophoresis, which only applies to particles, electro-osmosis, useful on flat plate specimens, and streaming potential, which applies either to particles and macroscopic samples. Two model materials were used, glass and poly (methylmethacrylate), in contact with 10-2 mol.l-1 potassium nitrate, from pH 2 to 9. For each material, under the form of particles or plates, the three methods gave similar profiles of the pH-dependant zeta potential curves and very close isoelectric points, so that global informations obtained were the same. However, numerical values of zeta potential differed from one method to another. Results suggest that these deviations are related to the location of the shearing plane within the electrical double-layer