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Nanoparticles in liquids are mostly electrically charged due to the dissociation of the molecules at the liquid–solid interface or the adsorption of surface-active agents. The zeta potential is a characteristic of this electric interfacial charge that plays an important role in aggregative stability of nanodispersions. The determination of zeta potential can be used to establish the region of stability for nanodispersions and for investigating or monitoring surface adsorption of nanoparticles and various chemicals from the liquid phase. A general model of the interfacial electric double layer with regard to defining zeta potential is presented in this chapter omitting many details, followed by two groups of measuring methods for characterizing this property: electrophoresis and electroacoustics. Zeta potential is not a directly measurable quantity, but one that is established by the use of an appropriate theory. Finally, sample preparation for zeta-potential measurement is discussed. Zeta potential is not a property of suspended particles alone; it depends on both particle and medium properties and how they interact at the interface. Any variation of the liquid chemical and ionic composition affects this interfacial equilibrium and, consequently, the zeta potential. Therefore, sample preparation and measurement procedures can both affect the measurement result. Incorrect conclusions often result from inappropriate sample preparation and measurement procedures or the inappropriate application of theoretical models for calculating zeta potential from measurement data. |
