An improved method for calculating zeta-potentials from measurements of the electrokinetic sonic amplitude

The surface electric properties of the commercially available silica, Monos pher 1000 (Fa. Merck), have been studied by conductivity and ESA (electroki netic sonic amplitude) experiments. It could be shown that accounting for t he contribution of the stagnant layer to surface conductivity is indispensa ble in the interpretation of electrokinetic data at low ionic strength. A g eneral method has been put forward which allows to take into account the to tal, experimentally accessible surface conductivity in the evaluation of ES A data of moderately concentrated suspensions. This includes additional con ductivity measurements which serve for the independent estimation of the to tal relative surface conductivity. The resulting zeta-potentials are clearl y higher than those obtained after neglecting the contribution of the stagn ant layer to surface conductivity. In addition, the ionic mobilities of pot assium and magnesium in the hydrodynamically stagnant layer have been inves tigated in some detail. It has been found that the ionic mobility of potass ium is of the same order of magnitude as in the bulk solution while the mob ility of magnesium is significantly reduced. (C) 2000 Academic Press.