The parallels between ionic transport, electrophoresis and electro-osmosis are briefly discussed. It is pointed out that the interpretation of the electrophoretic mobility cannot be based on charge and friction constant alone. The flow and the distortion of the ionic atmosphere (electric double layer) cause in nearly all circumstances a large retardation.
The zeta potential is defined as the potential at the surface between the freely mobile liquid and the liquid firmly adhering to the particle surface. It is a useful notion when the particle surface is well defined, much less useful in the case of polyelectrolytes or highly swollen structures. Electrolytes compress ionic atmospheres and double layers and thereby cause a decrease of the electrokinetic mobility and the zeta potential.
The electrokinetic mobility can be used to obtain information on the charge of particles and from that to estimate electrostatic repulsion or attraction. Here again the effect is determined by charge and electrolyte content, not by charge or zeta potential alone. Direct applications of electrokinetic phenomena are drying by electro-osmosis, electrodeposition on electrodes, accumulation on a membrane or filter, orientation of fibres and plates, separations based on differences in mobility.