engleski

The relationship between the inner surface potential and the electrokinetic potential from an experimental and theoretical point of view

The contact of small solid particles and macroscopic flat planes with aqueous electro- lyte solutions results in the accumulation of ions at the interface and the formation of the elec-trical interfacial layer. Analysis of well-defined monocrystal surfaces, which are building blocks of a single particle, leads to a better understanding of surface reactions and mutual in-teractions of adjacent crystal planes on average surface properties of particles. We analyze in-ner surface potential (obtained by Single Crystal Electrode) and zeta-potential data (obtained by streaming potential measurements) that have been obtained on identical samples. Among the systems for which comparable surface and zeta/DLVO potentials are available, measured inner surface potential data for sapphire (0001), hematite (0001) and rutile (110) show the ex-pected behavior based on the face specific surface chemistry model, while the slopes for rutile (110) and quartz (0001) do not. Isoelectric points for sapphire (0001), hematite (0001), and rutile (100) are in conflict with the standard model that implies consistent behavior of surface potential and diffuse layer potential. For the two former systems previous results from the lit-erature suggest that the charge of interfacial water can explain the discrepancy. The water lay-er could also play a role for quartz (0001), but in this case the discrepancy would simply not be noticed, since both point of zero potential and isoelectric point are low. Along with the data on silver halides, it can be concluded that six-ring water structures on solids may generate the electrokinetic behavior that is typical of inert surfaces like Teflon.

electrical interfacial layer ; haematite ; interfacial water ; quartz ; rutile ; sapphire ; silica ; single-crystal electrodes ; streaming potential

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