What is the difference between the zeta potential and the surface potential?
The zeta potential is located at the solid-liquid interface in close proximity to the solid surface. The zeta potential is thus related to but not identical with the surface potential. For functionalized surfaces the surface potential is approximated by an extrapolation of the ionic strength dependence of the zeta potential towards zero salinity.
The interest in the zeta potential for solid surface analysis has increased in the past thirty years with the demand for monitoring surface treatment to tune surface functionalities by maintaining the bulk material properties, and with the introduction of commercial instruments. The theory of the zeta potential dates back to the beginning of the last century and to the correlation of the electrokinetic phenomena (electrophoretic mobility, sedimentation potential, electro-osmotic flow, streaming potential and streaming current) with the electrokinetic potential (which was later called the zeta potential ζ). For the explanation of the observed phenomena and the existence of the zeta potential the model of the electrochemical double layer (EDL) was developed. The EDL model describes all electrokinetic effects and is still in use today. The model assists in answering the question about the difference between the zeta potential and the (solid) surface potential.
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